Covalently Linked 2D-Co3O4/GO Heterostructures: Catalytic and Electrochemical Properties

Covalently cross-linked 2D heterostructures may represent a ground-breaking approach to creating materials with multifunctionalities. To date, however, this field still remains relatively unexplored. In the present work, Co3O4/GO covalently linked heterostructures (Co3O4/GO-CL) were produced using 2D-Co3O4 functionalized with (3-aminopropyl)triethoxysilane (APTES) to react with the carboxyl groups of graphene oxide (GO). The surface and interface properties of the final material were assessed through electrochemical and catalytic studies. We found that the covalent bonds lead to a self-standing and ordered final structure, not observed for the noncovalent material (Co3O4/GO-nCL), also produced for comparison. The catalytic activity of Co3O4/GO-CL over the degradation of Rhodamine 6G showed great performance and the possibility of recycling the catalyst. Electrochemical evaluation stated higher specific capacitance for the covalently bonded material (468 F g-1 against 110 F g-1). Overall, results showed that the covalent bonds may be improving charge-transfer and interfacial area features, thus leading to enhanced catalytic and electrochemical performances.

Unveiling the charge storage mechanisms of Co-based perovskite fluoride in a mild aqueous electrolyte

This study is an in-depth exploration of the charge storage mechanisms of KCoF3 in 1 M Na2SO4 mild aqueous electrolytes via an array of ex situ/in situ physicochemical/electrochemical methods, especially the electrochemical quartz crystal microbalance (EQCM) technique, showing a combination of conversion, insertion/extraction and adsorption mechanisms. Specifically, during the first charge phase, Co(OH)2 is formed/oxidized into amorphous CoOOH and Co3O4, and then CoOOH undergoes partial proton extraction to yield CoO2, which is simultaneously accompanied by the transformation of Co3O4 into CoOOH and (hydrated) CoO2. During the first discharge process, the partial insertion of H+ into (hydrated) CoO2 leads to the formation of CoOOH and Co3O4, with the conversion of Co3O4 into CoOOH and both Co3O4 and CoOOH undergoing further transformations into (hydrated) Co(OH)2via the insertion of H+. This work offers valuable references for the development of aqueous energy storage.

Moisture-Stable CsSnBr2Cl Halide Perovskite: Electrochemical Insights in Aqueous Environments

In this investigation, moisture-stable CsSnBr2Cl nanoparticles were synthesized by incorporating Cl into CsSnBr3 halide perovskite using the hot injection method. Various analyses including XRD, XPS, UV-vis absorbance, photoluminescence, and Mott-Schottky have confirmed that the structural properties, chemical states, optical properties, and electronic band structure of CsSnBr2Cl nanoparticles remain intact even after 75 days of water immersion, thereby conclusively demonstrating their moisture stability. In a three-electrode system, the comparative electrochemical performance of pristine CsSnBr3 nanoparticles and moisture-stable Cl-incorporated CsSnBr2Cl nanoparticles was evaluated in various aqueous electrolytes, including HCl, Na2SO4, and KOH. The results indicate that the CsSnBr2Cl electrode material exhibits superior electrochemical properties, such as a larger integrated cyclic voltammetry (CV) area, a wider potential window, longer charge-discharge times, and lower impedance parameters compared to the pristine CsSnBr3 nanoparticles. The electrochemical performance of CsSnBr2Cl nanoparticles was evaluated for potential applications in batteries, supercapacitors, fuel cells, and water splitting, with a focus on reaction kinetics, charge storage mechanisms, and impedance parameters. The electrochemical properties of the nanoparticles were assessed using a three-electrode configuration across various 0.5 M aqueous electrolytes (HCl, Na2SO4, and KOH). In HCl, the nanoparticles demonstrated impressive charge storage capability, achieving a capacitance of 474 F g-1 at 1 A g-1, affirming their suitability for energy storage devices. In Na2SO4(aq.), the nanoparticles exhibited excellent stability for supercapacitors, operating up to 1.6 V without significant oxygen evolution. Notably, in KOH, they demonstrated potential as effective water-splitting electrodes. The practical applicability of the nanoparticles was evaluated using a symmetric two-electrode configuration with HCl and Na2SO4 electrolytes. The capacitance values were 117 F g-1 in HCl and 70 F g-1 in Na2SO4 at 1 A g-1. Notably, after 5000 GCD cycles in HCl(aq.), the nanoparticles retained 93% of their capacitance and maintained 91% Coulombic efficiency. They also demonstrated stable operation across a temperature range of 3 to 60 °C, achieving an energy density of 5.83 W h kg-1 at a power density of 600 W kg-1. This study emphasizes the considerable potential of CsSnBr2Cl nanoparticles in advancing electrochemical energy storage technologies and sets a solid foundation for future research and development in metal halide perovskites.

An Engineering Porous Spherical Carbon Cathode for High-Energy Sodium-Ion Capacitor

Sodium-ion hybrid capacitors (SICs) are emerging as promising devices that can balance energy and power output. However, the lack of a high-capacity cathode that can match the anode has limited its further application. In this work, we develop an efficient method to prepare spherical porous carbons (SPCs) with great specific surface area and narrow pore size distribution from coal-based humic acid via spray drying and a subsequent chemical activation process. Thanks to this unique porous structure, the SPC cathode has a superb capacity of 223 F g-1 at 0.05 A g-1, as well as splendid rate performance and cycling stability. SICs constructed by an SPC cathode and hard carbon anode can exhibit a high energy density of 179.8 Wh kg-1 at 155 W kg-1 and achieved 89.4% capacity retention after 10 000 cycles at 0.5 A g-1. This outcome presents a viable approach to attaining high-capacity cathodes for constructing outstanding performance hybrid capacitors.

Advancements in Asymmetric Supercapacitors: From Historical Milestones to Challenges and Future Directions

Numerous challenges, like the uninterrupted supply of electricity, stable and reliable power, and energy storage during non-operational hours, arise across various industries due to the absence of advanced energy storage technologies. With the continual technological advancements in portable electronics, green energy, and transportation, there are inherent limitations in their innovative production. Thus, ongoing research is focused on pursuing sustainable energy storage technologies. An emerging solution lies in the development of asymmetric supercapacitors (ASCs), which offer the potential to extend their operational voltage limit beyond the thermodynamic breakdown voltage range of electrolytes. This is achieved by employing two distinct electrode materials, presenting an effective solution to the energy storage limitations faced by ASCs. The current review concentrates on the progression of working materials to develop authentic pseudocapacitive energy storage systems (ESS). Also, evaluates their ability to exceed energy storage constraints. It provides insights into fundamental energy storage mechanisms, performance evaluation methodologies, and recent advancements in electrode material strategies. The review approaches developing high-performance electrode materials and achieving efficient ASC types. It delves into critical aspects for enhancing the energy density of ASCs, presenting debates and prospects, thereby offering a comprehensive understanding and design principles for next-generation ASCs in diverse applications.

New Engineering Science Insights into the Electrode Materials Pairing of Electrochemical Energy Storage Devices

Pairing the positive and negative electrodes with their individual dynamic characteristics at a realistic cell level is essential to the practical optimal design of electrochemical energy storage devices. However, the complex relationship between the performance data measured for individual electrodes and the two-electrode cells used in practice often makes an optimal pairing experimentally challenging. Taking advantage of the developed tunable graphene-based electrodes with controllable structure, experiments with machine learning are successfully united to generate a large pool of capacitance data for graphene-based electrode materials with varied slit pore sizes, thicknesses, and charging rates and numerically pair them into different combinations for two-electrode cells. The results show that the optimal pairing parameters of positive and negative electrodes vary considerably with the operation rate of the cells and are even influenced by the thickness of inactive components. The best-performing individual electrode does not necessarily result in optimal cell-level performance. The machine learning-assisted pairing approach presents much higher efficiency compared with the traditional trial-and-error approach for the optimal design of supercapacitors. The new engineering science insights observed in this work enable the adoption of artificial intelligence techniques to efficiently translate well-developed high-performance individual electrode materials into real energy storage devices.

Hybrid and Asymmetric Supercapacitors: Achieving Balanced Stored Charge across Electrode Materials

An electrochemical capacitor configuration extends its operational potential window by leveraging diverse charge storage mechanisms on the positive and negative electrodes. Beyond harnessing capacitive, pseudocapacitive, or Faradaic energy storage mechanisms and enhancing electrochemical performance at high rates, achieving a balance of stored charge across electrodes poses a significant challenge over a wide range of charge-discharge currents or sweep rates. Consequently, fabricating hybrid and asymmetric supercapacitors demands precise electrochemical evaluations of electrode materials and the development of a reliable methodology. This work provides an overview of fundamental aspects related to charge-storage mechanisms and electrochemical methods, aiming to discern the contribution of each process. Subsequently, the electrochemical properties, including the working potential windows, rate capability profiles, and stabilities, of various families of electrode materials are explored. It is then demonstrated, how charge balancing between electrodes falters across a broad range of charge-discharge currents or sweep rates. Finally, a methodology for achieving charge balance in hybrid and asymmetric supercapacitors is proposed, outlining multiple conditions dependent on loaded mass and charge-discharge current. Two step-by-step tutorials and model examples for applying this methodology are also provided. The proposed methodology is anticipated to stimulate continued dialogue among researchers, fostering advancements in achieving stable and high-performance supercapacitor devices.

Ni Single Atom Decorated Porous Hollow Carbon Nanosphere-Based Electrodes for High Performance Symmetric Solid-State Supercapacitors

Ni single atom containing hollow carbon nanospheres with nitrogen doping has been synthesized by carbonization of Ni(NO3)2/phloroglucinol-formaldehyde polymer/silica composite. The samples have been characterized by powder X-ray diffraction, nitrogen adsorption/desorption, electron microscopic, Raman and X-ray photoelectron spectroscopic studies. The microstructure and surface area vary with the amount of Ni(NO3)2 employed in the syntheses and the carbonization environment. An optimized amount of nickel and argon as the carbonization gas afford Ni-1.0@N@HCN-Ar which possesses overall superior features. The uniformly dispersed Ni single atoms within the hollow porous carbon framework fully utilize all the electroactive sites thereby improving the supercapacitive performance. The specific capacitance of Ni-1.0@N@HCN-Ar reaches 777 F g-1 at 1 A g-1 with a Coulombic efficiency of 98.4 % and excellent recyclability. The energy and power density of Ni-1.0@N@HCN-Ar are found to be high; at 1 A g-1 its energy density is 155.4 Wh kg-1 with a power density of 600.3 W kg-1. At a high current density of 10 A g-1 the material shows a high energy density of 118.4 Wh kg-1 with excellent power density of 6003.4 W kg-1. A symmetric solid-state supercapacitor assembled with this material, Ni-1.0@N@HCN-Ar//Ni-1.0@N@HCN-Ar using H2SO4/PVA gel electrolyte shows a superior energy density value of 30 Wh kg-1 at a power density of 1200 W kg-1.

Chitosan Oligosaccharide Laser Lithograph: A Facile Route to Porous Graphene Electrodes for Flexible On-Chip Microsupercapacitors

In this study, a convenient chitosan oligosaccharide laser lithograph (COSLL) technology was developed to fabricate laser-induced graphene (LIG) electrodes and flexible on-chip microsupercapacitors (MSCs). With a simple one-step CO2 laser, the pyrolysis of a chitosan oligosaccharide (COS) and in situ welding of the generated LIGs to engineering plastic substrates are achieved simultaneously. The resulting LIG products display a hierarchical porous architecture, excellent electrical conductivity (6.3 Ω sq-1), and superhydrophilic properties, making them ideal electrode materials for MSCs. The pyrolysis-welding coupled mechanism is deeply discussed through cross-sectional analyses and finite element simulations. The MSCs prepared by COSLL exhibit considerable areal capacitance of over 4 mF cm-2, which is comparable to that of the polyimide-LIG-based counterpart. COSLL is also compatible with complementary metal-oxide-semiconductor (CMOS) and micro-electro-mechanical system (MEMS) processes, enabling the fabrication of LIG/Au MSCs with comparable areal capacitance and lower internal resistance. Furthermore, the as-prepared MSCs demonstrate excellent mechanical robustness, long-cycle capability, and ease of series-parallel integration, benefiting their practical application in various scenarios. With the use of eco-friendly biomass carbon source and convenient process flowchart, the COSLL emerges as an attractive method for the fabrication of flexible LIG on-chip MSCs and various other advanced LIG devices.

MXene-Derived TiO2/Starbon Nanocomposite as a Remarkable Electrode Material for Coin-Cell Symmetric Supercapacitor

In this study, the synthesis of a MXene (Ti3C2Tx)-derived TiO2/starbon (M-TiO2/Starbon-800 °C) nanocomposite using a facile calcination method is explored. High-temperature exposure transforms layered Ti3C2Tx into rod-like TiO2 and starbon into amorphous carbon. The resulting M-TiO2/Starbon-800 °C nanocomposite exhibits a significantly larger surface area and pore volume compared to its individual components, leading to superior electrochemical performance. In a three-electrode configuration, the nanocomposite achieved a specific capacitance (Csp) of 1352 Fg⁻¹ at 1 Ag⁻¹, while retaining more than 99% of its Csp after 50 000 charge/discharge cycles. Furthermore, when incorporated into a two-electrode symmetric coin cell, it demonstrates a Csp of 115 Fg⁻¹ along with exceptional long cycle life. Moreover, the device shows an energy density (ED) of 51 Whkg-1 and a power density (PD) of 7912 Wkg-1 at 5 Ag-1. The enhanced charge storage is attributed to the formation of a porous structure with a high specific surface area resulting from the interaction between M-TiO2 nanorods and starbon, which facilitates efficient ion penetration.

A Molecular Adsorption Concept for Increasing Energy Density of Hybrid Supercapacitors

In this report, we demonstrate that high-capacity hybrid supercapacitors can be realized by utilizing iron azaphthalocyanine (FeAzPc-4N) adsorbed activated carbons (ACs) as an electrode due to the combination of the electric double layer of activated carbon surfaces and redox reactions of FeAzPc-4N molecules. By increasing the mixing ratio of FeAzPc-4N with ACs, a maximum capacity of 907 F/gAC is achieved, also enabling rapid charging and discharging at 20 A/g. The revelation of the capacitor electrode's durability through 20 000 cycles of charging and discharging is realized, and the capacitor cell had sufficient output power to illuminate LEDs. This concept illustrates the potential for enhancing capacitor performance by immobilizing redox-active species.

High-performance electrode materials of heteroatom-doped lignin-based carbon materials for supercapacitor applications

Supercapacitors are the preferred option for supporting renewable energy sources owing to many benefits, including fast charging, long life, high energy and power density, and saving energy. While electrode materials with environmentally friendly preparation, high performance, and low cost are important research directions of supercapacitors. At present, the growing global population and the increasingly pressing issue of environmental pollution have drawn the focus of numerous researchers worldwide to the development and utilization of renewable biomass resources. Lignin, a renewable aromatic polymer, has reserves second only to cellulose in nature. Ten million tonnes of industrial lignin are produced in pulp and paper mills annually, most of which are disposed of as waste or burned for fuel, seriously depleting natural resources and polluting the environment. One practical strategy to accomplish sustainable development is to employ lignin resources to create high-value materials. Based on the high carbon content and rich functional groups of lignin, the lignin-based carbon materials generated after carbonization treatment display specific electrochemical properties as electrode materials. Nevertheless, low electrochemical activity of untreated lignin precludes it from achieving its full potential for application in energy storage. Heteroatom doping is a common modification method that aims to improve the electrochemical performance of the electrode materials by optimizing the structure of the lignin, improving its pore structure and increasing the number of active sites on its surface. This paper aims to establish theoretical foundations for design, preparation, and optimizing the performance of heteroatom-doped lignin-based carbon materials, as well as for developing high-value-added lignin materials. The most reported the mechanism of supercapacitors, the doping process involving various types of heteroatoms, and the analysis of how heteroatoms affect the performance of lignin-based carbon materials are also detailed in this review.

Compositionally Tunable Mn-V-Fe Phosphoselenide Nanorods with Minimal Ion-Diffusion Barrier as High Energy Density Battery Electrode Materials

The design and synthesis of novel heterostructured electrode materials are crucial to enable the fabrication of efficient supercapacitor devices. In this regard, transition metal phosphochalcogenides (S, Se) are promising candidates owing to their exotic electronic properties. Herein, a facile two-step hydrothermal protocol was used to synthesize binary and ternary metal phospho-selenide electrodes (Mn-Fe-P-Se, V-Fe-P-Se, Mn-V-P-Se, and Mn-Fe-V-P-Se). The chemical composition, morphology, and structure of the as-fabricated materials were fully investigated. The three-electrode electrochemical evaluation at 1.0 A g-1 demonstrated that the ternary metal electrode (MFVP-Se) exhibits a high capacity of 1968.63 C g-1. To assess the practical value of the rationally designed Mn-Fe-V-P-Se electrode material, Mn-Fe-V-P-Se was used as a positive electrode coupled with activated carbon (AC) as a negative electrode to assemble a hybrid supercapacitor device. This Mn-Fe-V-P-Se//AC device delivers a power density of 1999.96 W kg-1 with a high energy density of 149.88 Wh kg-1 coupled with no capacity loss after 5000 charging/discharging cycles. Additionally, density functional theory calculations revealed that our electrode exhibits suitable adsorption energy for OH- ions with a minimal diffusion barrier for ions.

Preparation of Few-Layered MoS2 by One-Pot Hydrothermal Method for High Supercapacitor Performance

Molybdenum disulfide (MoS2), a typical layered material, has important applications in various fields, such as optoelectronics, catalysis, electronic devices, sensors, and supercapacitors. Extensive research has been carried out on few-layered MoS2 in the field of electrochemistry due to its large specific surface area, abundant active sites and short electron transport path. However, the preparation of few-layered MoS2 is a significant challenge. This work presents a simple one-pot hydrothermal method for synthesizing few-layered MoS2. Furthermore, it investigates the exfoliation effect of different amounts of sodium borohydride (NaBH4) as a stripping agent on the layer number of MoS2. Na+ ions, as alkali metal ions, can intercalate between layers to achieve the purpose of exfoliating MoS2. Additionally, NaBH4 exhibits reducibility, which can effectively promote the formation of the metallic phase of MoS2. Few-layered MoS2, as an electrode for supercapacitor, possesses a wide potential window of 0.9 V, and a high specific capacitance of 150 F g-1 at 1 A g-1. This work provides a facile method to prepare few-layered two-dimensional materials for high electrochemical performance.

Quantum capacitance induced by electron orbital reconstruction of g-C3N4/Co3O4 heterojunction: Improving electrochemical performance

Utilizing diverse material combinations in heterogeneous structures has become an effective approach for regulating interface characteristics and electronic structures. The g-C3N4/Co3O4 heterostructures were fabricated by uniformly modifying Co3O4 nanoparticles onto discrete clusters of g-C3N4 nanosheets. Then, they were subsequently employed as positive electrode materials for assembling hybrid supercapacitors. According to the first-principles calculation, Co3O4 and g-C3N4 formed Co-N ionic bonds, establishing interfacial space symmetry-broken heterojunction and direct exchange and superexchange between ions at the interface and sub-interface. This resulted in a high-density spin-orbit hybrid heterogeneous polarization interface, significantly improving the quantum capacitance of heterojunction materials. Experimental results showed that the heterojunction had a specific capacitance of 2662 F g-1 at 1 A g-1. When the power density was 750 W kg-1, the energy density reached 128 Wh kg-1. Even when the power density was 16850 W kg-1, it could show an energy density of 62.5 Wh kg-1. The g-C3N4/Co3O4 heterojunction could realize high energy density charge storage as the cathode material of supercapacitors. The construction of heterogeneous polarization interfaces for high-energy quantum capacitors provides a new and effective method for the energy storage field.

A Binary Ionogel Electrolyte for the Realization of an All Solid-State Electrical Double-Layer Capacitor Performing at Low Temperature

Over the last years, solid-state electrolytes made of an ionic liquid (IL) confined in a solid (inorganic or polymer) matrix, also known as ionogels, have been proposed to solve the leakage problems occurring at high temperatures in classical electrical double-layer capacitors (EDLCs) with an organic electrolyte, and thereof improve the safety. However, making ionogel-based EDLCs perform with reasonable power at low temperature is still a major challenge due to the high melting point of the confined IL. To overcome these limitations, the present contribution discloses ionogel films prepared in a totally oxygen/moisture-free atmosphere by encapsulating 70 wt % of an equimolar mixture of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide and 1-ethyl-3-methylimidazolium tetrafluoroborate - [EMIm][BF4]0.5[FSI]0.5 - into a poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) network. The further called "binary ionogel" films demonstrated a high flexibility and a good ionic conductivity of 5.8 mS cm-1 at 20 °C. Contrary to the ionogels prepared from either [EMIm][FSI] or [EMIm][BF4], displaying melting at Tm=-16 °C and -7 °C, respectively, the crystallization of confined [EMIm][BF4]0.5[FSI]0.5 is quenched in the binary ionogel, which shows only a glass transition at -101 °C. This quenching enables an increased ionicity and ionic diffusion at the interface with the PVdF host network, leading the binary ionogel membrane to display higher ionic conductivity below -20 °C than the parent binary [EMIm][BF4]0.5[FSI]0.5 liquid. Laminate EDLCs were built with a 100 μm thick binary ionogel separator and electrodes made from a hierarchical micro-/mesoporous MgO-templated carbon containing a reasonable proportion of mesopores to enhance the mass transport of ions, especially at low temperature where the ionic diffusion noticeably decreases. The EDLCs operated up to 3.0 V with ideal EDL characteristics from -40 °C to room temperature. Their output specific energy under a discharge power of 1 kW kg-1 is ca. 4 times larger than with a cell implementing the same carbon electrodes together with the binary [EMIm][BF4]0.5[FSI]0.5 liquid. Hence, this binary ionogel electrolyte concept paves the road for developing safe and flexible solid-state energy storage devices operating at subambient temperatures in extreme environments.

All Plant-Based Compact Supercapacitor in Living Plants

Biomass-based energy storage devices (BESDs) have drawn much attention to substitute traditional electronic devices based on petroleum or synthetic chemical materials for the advantages of biodegradability, biocompatibility, and low cost. However, most of the BESDs are almost made of reconstructed plant materials and exogenous chemical additives which constrain the autonomous and widespread advantages of living plants. Herein, an all-plant-based compact supercapacitor (APCSC) without any nonhomologous additives is reported. This type of supercapacitor formed within living plants acts as a form of electronic plant (e-plant) by using its tissue fluid electrolyte, which surprisingly presents a satisfying electrical capacitance of 182.5 mF cm-2, higher than those of biomass-based micro-supercapacitors reported previously. In addition, all constituents of the device come from the same plant, effectively avoid biologically incompatible with other extraneous substances, and almost do no harm to the growth of plant. This e-plant can not only be constructed in aloe, but also be built in most of succulents, such as cactus in desert, offering timely electricity supply to people in extreme conditions. It is believed that this work will enrich the applications of electronic plants, and shed light on smart botany, forestry, and agriculture.

Fabrication of CNT-N@Manganese Oxide Hybrid Nanomaterials through a Versatile One-Pot Eco-Friendly Route toward Engineered Textile Supercapacitors

The expansion of the Internet of Things market and the proliferation of wearable technologies have generated a significant demand for textile-based energy storage systems. This work reports the engineered design of hybrid electrode nanomaterials of N-doped carbon nanotubes (CNT-N) functionalized with two types of manganese oxides (MOs)-birnessite (MnO2) and hausmannite (Mn3O4)-and their application in solid-state textile-based hybrid supercapacitors (SCs). A versatile citric acid-mediated eco-friendly one-pot aqueous precipitation process is proposed for the fabrication of the hybrids. Remarkably, different types of MOs were obtained by simply changing the reaction temperature from room temperature to 100 °C, without any post-thermal treatment. Asymmetric textile SCs were developed using cotton fabrics coated with CNT-N and the hybrids as textile electrodes, and poly(vinyl) alcohol/orthophosphoric acid as the solid-gel electrolyte. The asymmetric devices presented enhanced energy storage performance relative to the symmetric device based on CNT-N and excellent cycling stability (>96%) after 8000 charge/discharge cycles owing to synergistic effects between CNT-N and the MOs, which endowed nonfaradaic and pseudocapacitive features to the SCs. The asymmetric SC based on CNT-N@MnO2 featured 47% higher energy density and comparable power density to the symmetric CNT-N-based device (8.70 W h cm-2 at 309.01 μW cm-2 vs. 5.93 W h cm-2 at 346.58 μW cm-2). The engineered hybrid CNT-N@MO nanomaterials and the eco-friendly citric acid-assisted one-pot precipitation route open promising prospects not only for energy storage, but also for (photo)(electro)catalysis, wastewater treatment, and (bio)sensing.

In Situ Fabrication of Hierarchical CuO@CoNi-LDH Composite Structures for High-Performance Supercapacitors

Layered double hydroxide (LDH) materials, despite their high theoretical capacity, exhibit significant performance degradation with increasing load due to their low conductivity. Simultaneously achieving both high capacity and high rate performance is challenging. Herein, we fabricated vertically aligned CuO nanowires in situ on the copper foam (CF) substrate by alkali-etching combined with the annealing process. Using this as a skeleton, electrochemical deposition technology was used to grow the amorphous α-phase CoNi-LDH nanosheets on its surface. Thanks to the high specific surface area of the CuO skeleton, ultrahigh loading (̃16.36 mg cm-2) was obtained in the fabricated CF/CuO@CoNi-LDH electrode with the cactus-like hierarchical structure, which enhanced the charge transfer and ion diffusion dynamics. The CF/CuO@CoNi-LDH electrode achieved a good combination of high areal capacitance (33.5 F cm-2) and high rate performance (61% capacitance retention as the current density increases 50 times). The assembled asymmetric supercapacitor device demonstrated a maximum potential window of 0-1.6 V and an energy density of 1.7 mWh cm-2 at a power density of 4 mW cm-2. This work provides a feasible strategy for the design and fabrication of high-mass-loading LDH composites for electrochemical energy storage applications.

Recent Advances in Biopolymer-Based Hydrogel Electrolytes for Flexible Supercapacitors

Growing concern regarding the impact of fossil fuels has led to demands for the development of green and renewable materials for advanced electrochemical energy storage devices. Biopolymers with unique hierarchical structures and physicochemical properties, serving as an appealing platform for the advancement of sustainable energy, have found widespread application in the gel electrolytes of supercapacitors. In this Review, we outline the structure and characteristics of various biopolymers, discuss the proposed mechanisms and assess the evaluation metrics of gel electrolytes in supercapacitor devices, and further analyze the roles of biopolymer materials in this context. The state-of-the-art electrochemical performance of biopolymer-based hydrogel electrolytes for supercapacitors and their multiple functionalities are summarized, while underscoring the current technical challenges and potential solutions. This Review is intended to offer a thorough overview of recent developments in biopolymer-based hydrogel electrolytes, highlighting research concerning green and sustainable energy storage devices and potential avenues for further development.

Heterogeneous Structures Consisting of Rod-like ZnO Interspersed with Ce2S3 Nanoparticles for Photo-Sensitive Supercapacitors with Enhanced Capacitive Performance

Photosensitive supercapacitors incorporate light-sensitive materials on capacitive electrodes, enabling solar energy conversion and storage in one device. In this study, heterogeneous structures of rod-shaped ZnO decorated with Ce2S3 nanoparticles on nickel foam (ZnO@Ce2S3/NF) are synthesized using a two-step hydrothermal method as photosensitive supercapacitor electrodes for capacitance enhancement under visible light. The formation of ZnO@Ce2S3 heterogeneous structures is confirmed using various structural characterization techniques. The area-specific capacitance of the ZnO@Ce2S3/NF composite electrode increased from 1738.1 to 1844.0 mF cm-2 after illumination under a current density of 5 mA cm-2, which is 2.4 and 2.8 times higher than that of ZnO and Ce2S3 electrodes under similar conditions, respectively, indicating the remarkable light-induced capacitance enhancement performance. The ZnO@Ce2S3/NF electrode also exhibits a higher photocurrent and photovoltage than the two single electrodes, demonstrating its excellent photosensitivity. The improved capacitance performance and photosensitivity under illumination are attributed to the well-constructed energy-level structure, which stimulates the flow of photogenerated electrons from the outer circuit and the involvement of photogenerated holes in the resulting surface-controlled capacitance. In addition, the assembled ZnO@Ce2S3/NF-based hybrid supercapacitor exhibits a great energy density of 145.0 mWh cm-2 under illumination. This study provides a novel strategy for the development of high-performance solar energy conversion/storage devices.

Hydrogen-Assisted Thermal Treatment of Electrode Materials for Electrochemical Double-Layer Capacitors

The capacitance of electrode materials used in electrochemical double-layer capacitors (EDLCs) is currently limited by several factors, including inaccessible isolated micropores in high-surface area carbons, the finite density of states resulting in a quantum capacitance in series to Helmholtz double-layer capacitance, and the presence of surface impurities, such as functional groups and adsorbed species. To unlock the full potential of EDLC active materials and corresponding electrodes, several post-production treatments are commonly proposed to improve their capacitance and, thus, the energy density of the corresponding devices. In this work, we report a systematic study of the effect of a prototypical treatment, namely H2-assisted thermal treatment, on the chemical, structural, and thermal properties of activated carbon and corresponding electrodes. By combining multiple characterization techniques, we clarify the actual origins of the improvement of the performance (e.g., > +35% energy density for the investigated power densities in the 0.5-45 kW kg-1 range) of the EDLCs based on treated electrodes compared to the case based on the pristine electrodes. Contrary to previous works supporting a questionable graphitization of the activated carbon at temperatures <1000 °C, we found that a "surface graphitization" of the activated carbon, detected by spectroscopic analysis, is mainly associated with the desorption of surface contaminants. The elimination of surface impurities, including adsorbed species, improves the surface capacitance of the activated carbon (CsurfAC) by +37.1 and +36.3% at specific currents of 1 and 10 A g-1, respectively. Despite the presence of slight densification of the activated carbon upon the thermal treatment, the latter still improves the cell gravimetric capacitance normalized on the mass of the activated carbon only (CgAC), e.g., + 28% at 1 A g-1. Besides, our holistic approach identifies the change in the active material and binder contents as a concomitant cause of the increase of cell gravimetric capacitance (Cg), accounting for the mass of all of the electrode materials measured for treated electrodes compared to pristine ones. Overall, this study provides new insights into the relationship between the modifications of the electrode materials induced by H2-assisted thermal treatments and the performance of the resulting EDLCs.

Designed Synthesis and Electrochemical Performance Regulation of the Hierarchical Hollow Structure Cu2S/Cu7S4/NC Anode for Hybrid Supercapacitors

Copper-based compounds have attracted increasing attention as electrode materials for rechargeable devices, but their poor conductivity and insufficient stability inhibit their further development. Herein, an effective method has been proposed to improve the electrochemical properties of the copper-based electrodes by coating carbon materials and generating unique micro/nanostructures. The prepared Cu2S/Cu7S4/NC with hierarchical hollow structure possesses excellent electrochemical performance, attributing to the composition and structure optimization. The superior charge storage performance has been assessed by theoretical and experimental research. Specifically, the Cu2S/Cu7S4/NC exhibits remarkably higher electrical conductivity and lower adsorption-free energy for O* and OH* than those of Cu2O. Moreover, the Cu2S/Cu7S4/NC delivers a high specific capacitance of 1261.3 F·g-1 at the current density of 1 A·g-1 and also has great rate performance at higher current densities, which are much better than those of the Cu2O nanocubes. In addition, the assembled hybrid supercapacitor using Cu2S/Cu7S4/NC as the anode exhibits great energy density, power density, and cycling stability. This study has proposed a novel and feasible method for the synthesis of high-performance copper-based electrodes and their electrochemical performance regulation, which is of great significance for the advancement of high-quality electrode materials and rechargeable devices.

Multiscale Structural Design of 2D Nanomaterials-based Flexible Electrodes for Wearable Energy Storage Applications

2D nanomaterials play a critical role in realizing high-performance flexible electrodes for wearable energy storge devices, owing to their merits of large surface area, high conductivity and high strength. The electrode is a complex system and the performance is determined by multiple and interrelated factors including the intrinsic properties of materials and the structures at different scales from macroscale to atomic scale. Multiscale design strategies have been developed to engineer the structures to exploit full potential and mitigate drawbacks of 2D materials. Analyzing the design strategies and understanding the working mechanisms are essential to facilitate the integration and harvest the synergistic effects. This review summarizes the multiscale design strategies from macroscale down to micro/nano-scale structures and atomic-scale structures for developing 2D nanomaterials-based flexible electrodes. It starts with brief introduction of 2D nanomaterials, followed by analysis of structural design strategies at different scales focusing on the elucidation of structure-property relationship, and ends with the presentation of challenges and future prospects. This review highlights the importance of integrating multiscale design strategies. Finding from this review may deepen the understanding of electrode performance and provide valuable guidelines for designing 2D nanomaterials-based flexible electrodes.

Ultrathin Dielectric Triggered Charge Injection Dynamics for High-Performance Metal Organic Framework/MXene Supercapacitors

A MOF-MXene-BN three-component heterostructure exhibits impressive pseudocapacitive behavior with fast charge injection facilitated by an ultrathin dielectric h-BN. To address the MOF's low electronic conductivity, a 2D NiCo-MOF is grown on MXene nanosheets, enhancing conductivity and providing abundant redox-active sites. BN (boron nitride) serves a dual purpose, preventing restacking and facilitating charge injection toward NiCo-MOF. Synergistic contributions of 2D materials and a heterostructure with favorable charge injection dynamics among MOF, MXene, and BN contribute to enhanced electrochemical performance. Charge transfer mechanisms are elucidated using distribution of relaxation time technique to analyze complex EIS data and to differentiate electrode kinetics based on their respective relaxation time constants. An asymmetric supercapacitor, MOF-MXene-BN//activated carbon, achieves a specific capacity of 798 C/g, an energy density of 81 Wh/kg at 365 W/kg, and 81% capacitance retention over 5,000 cycles.

Direct Graphene Deposition via a Modified Laser-Assisted Method for Interdigitated Microflexible Supercapacitors

The transcendence toward smarter technologies and the rapid expansion of the Internet of Things requires miniaturized energy storage systems, which may also be shape-conformable, such as microflexible supercapacitors. Their fabrication must be compatible with emerging manufacturing platforms with regard to scalability and sustainability. Here, we modify a laser-based method we recently developed for simultaneously synthesizing and transferring graphene onto a selected substrate. The modification of the method lies in the tuning of two key parameters, namely, the inclination of the laser beam and the distance between the precursor material and the acceptor substrate. A proper combination of these parameters enables the displacement of the trace of the transmitted laser beam from the deposited graphene film area. This mitigates the negative effects that arise from the laser-induced ablation of graphene on heat-sensitive substrates and significantly improves the electrical conductivity of the graphene films. The optimized graphene exhibits very high C/O (36) and sp2/sp3 (13) ratios. Post-transport irradiation was used to transform the continuous graphene films to interdigitated electrodes. The capacitance of the microflexible supercapacitor was measured to be among the highest reported ones in relation to interdigitated supercapacitors with electrodes based on laser-grown graphene. The device shows good cycling stability, retaining 91% of its capacitance after 10,000 cycles, showing no substantial degradation after applying bending conditions. This promising laser-based approach emerges as a viable alternative for the fabrication of microflexible interdigitated supercapacitors for paper electronics and smart textiles.

Carbon Threads Supercapacitors for Washable e-Textile Applications: Configurations and Electrochemical Performance

Technological solutions for emerging e-textiles are being sought to enable e-wear technology to be self-sustaining and lightweight. A rippling 1D carbon fiber capacitor design was made with commercial carbon threads as electrodes using simulated sweat solution as the electrolyte. This is particularly relevant for potential sports textile applications in which sweat could serve as an electrochemical energy source. An electrospun cellulose acetate fiber membrane and a commercially available felt were used as separators capable of soaking the electrolyte. These were tested in braided and woven electrode configurations, respectively. Functionalizing the carbon wires with polypyrrole (PPy) enhanced the surface area and significantly increased the specific capacity by approximately an order of magnitude (0.62 F/g). Cyclic voltammetry and charge-discharge tests confirmed the washability and durability of the devices for at least 1000 cycles.

Ultraconformable Integrated Wireless Charging Micro-Supercapacitor Skin

Conformable and wireless charging energy storage devices play important roles in enabling the fast development of wearable, non-contact soft electronics. However, current wireless charging power sources are still restricted by limited flexural angles and fragile connection of components, resulting in the failure expression of performance and constraining their further applications in health monitoring wearables and moveable artificial limbs. Herein, we present an ultracompatible skin-like integrated wireless charging micro-supercapacitor, which building blocks (including electrolyte, electrode and substrate) are all evaporated by liquid precursor. Owing to the infiltration and permeation of the liquid, each part of the integrated device attached firmly with each other, forming a compact and all-in-one configuration. In addition, benefitting from the controllable volume of electrode solution precursor, the electrode thickness is easily regulated varying from 11.7 to 112.5 μm. This prepared thin IWC-MSC skin can fit well with curving human body, and could be wireless charged to store electricity into high capacitive micro-supercapacitors (11.39 F cm-3) of the integrated device. We believe this work will shed light on the construction of skin-attachable electronics and irregular sensing microrobots.

Enhancing Sodium-Ion Transport by Hollow Nanotube Structure Design of a V5S8@C Anode for Sodium-Ion Batteries

V5S8 has received extensive attention in the field of sodium-ion batteries (SIBs) due to its two-dimensional (2D) layered structure, and weak van der Waals forces between V-S accelerate the transport of sodium ions. However, the long-term cycling of V5S8 still suffers from volume expansion and low conductivity. Herein, a hollow nanotube V5S8@C (H-V5S8@C) with improved conductivity was synthesized by a solvothermal method to alleviate cracking caused by volume expansion. Benefiting from the large specific surface area of the hollow nanotube structure and uniform carbon coating, H-V5S8@C exhibits a more active site and enhanced conductivity. Meanwhile, the heterojunction formed by a few residual MoS2 and the outer layer of V5S8 stabilizes the structure and reduces the ion migration barrier with fast Na+ transport. Specifically, the H-V5S8@C anode provides an enhanced rate performance of 270.1 mAh g-1 at 15 A g-1 and high cycling stability of 291.7 mAh g-1 with a retention rate of 90.98% after 300 cycles at 5 A g-1. This work provides a feasible approach for the structural design of 2D layered materials, which can promote the practical application of fast-charging sodium-ion batteries.

1D/3D Heterogeneous Assembling Body of Cobalt Nitrides for Highly Efficient Overall Hydrazine Splitting and Supercapacitors

Herein, the construction of a heterostructured 1D/3D CoN-Co2 N@NF (nickel foam) electrode used for thermodynamically favorable hydrazine oxidation reaction (HzOR), as an alternative to sluggish anodic oxygen evolution reaction (OER) in water splitting for hydrogen production, is reported. The electrode exhibits remarkable catalytic activities, with an onset potential of -0.11 V in HzOR and -71 mV for a current density of 10 mA cm-2 in hydrogen evolution reaction (HER). Consequently, an extraordinary low cell voltage of 53 mV is required to achieve 10 mA cm-2 for overall hydrazine splitting in a two-electrode system, demonstrating significant energy-saving advantages over conventional water splitting. The HzOR proceeds through the 4e- reaction pathway to release N2 while the 1e- pathway to emit NH3 is uncompetitive, as evidenced by differential electrochemical mass spectrometric measurements. The X-ray absorption spectroscopy, in situ Raman spectroscopy, and theoretical calculations identify cobalt nitrides rather than corresponding oxides/(oxy)hydroxides as catalytic species for HzOR and illustrate advantages of heterostructured CoN-Co2 N in optimizing adsorption energies of intermediates/reagents and promoting catalytic activities toward both HzOR and HER. The CoN-Co2 N@NF is also an excellent supercapacitive material, exhibiting an increased specific capacity (938 F g-1 at 1 A g-1 ) with excellent cycling stability (95.8%, 5000 cycles).

Enhanced Sodium Ion Batteries' Performance: Optimal Strategies on Electrolytes for Different Carbon-based Anodes

Carbon-based materials have emerged as promising anodes for sodium-ion batteries (SIBs) due to the merits of cost-effectiveness and renewability. However, the unsatisfactory performance has hindered the commercialization of SIBs. During the past decades, tremendous attention has been put into enhancing the electrochemical performance of carbon-based anodes from the perspective of improving the compatibility of electrolytes and electrodes. Hence, a systematic summary of strategies for optimizing electrolytes between hard carbon, graphite, and other structural carbon anodes of SIBs is provided. The formulations and properties of electrolytes with solvents, salts, and additives added are comprehensively presented, which are closely related to the formation of solid electrolyte interface (SEI) and crucial to the sodium ion storage performance. Cost analysis of commonly used electrolytes has been provided as well. This review is anticipated to provide guidance in future rational tailoring of electrolytes with carbon-based anodes for sodium-ion batteries.

Heterostructured MoO3@CoWO4 nanobelts towards high electrochemical performances via oxygen vacancies generation

Heterostructured nanomaterials tend to have a high proportion of oxygen vacancies (VO) due to the presence of heterogeneous interfaces. Herein, a new kind of heterostructured MoO3@CoWO4 nanobelts was successfully evaluated as fascinating cathode material. SEM and TEM analysis indicated that the MoO3 nanobelts were fully blanketed with CoWO4 nanodots. The generation of Vo species was confirmed by XPS and EPR data. By profiting both synergistic and Vo generation effects, MoO3@CoWO4 electrode displayed an excellent capacitance of 246 mAh·g-1 (1966 F·g-1at 0.5 A·g-1) with high-rate capability of 174 mAh·g-1 (1394 F·g-1 at 30 A·g-1) as well as superb stability of 94 % (over 15,000 cycles). Notably, all-solid-state device delivered a good energy value of 63.1 Wh·kg-1 at 375 W·kg-1. Interestingly, the supercapacitor device showed super-low self-discharge comportment of only 12.1 % during 24 h. Importantly, the generation of the VO defects could control the ions diffusion process and lead a sharp decrease in the self-discharge process.

Unveiling the Latest Advancements in Vanadium Carbide MXene based Supercapacitors and their Future Trends

Vanadium-carbide-based MXenes have bewitched the scientific community due to their distinctive characteristics, which make them potential candidates for several technological applications, such as supercapacitors (SCs), batteries, gas separation, biological sensors, and desalination. This article provides an overview of recent developments in the synthesis and applications of vanadium-carbide MXene in SCs. Vanadium carbide is one of the most difficult MXenes to synthesize, and various synthesis techniques, including electrochemical exfoliation and chemical etching, have been utilized to fabricate this material. Additionally, the review article also emphasizes the potential use of vanadium carbide MXene as SCs. Finally, the paper concludes with the challenges faced in the synthesis process and the prospects of vanadium carbide MXene-based material fabrication. Overall, this review article provides in-depth and detailed information on recent research on vanadium carbide MXene and its possible uses.

Modified 3D Graphene for Sensing and Electrochemical Capacitor Applications

Less defective, nitrogen-doped 3-dimensional graphene (N3DG) and defect-rich, nitrogen-doped 3-dimensional graphene (N3DG-D) were made by the thermal CVD (Chemical Vapor Deposition) process via varying the carbon precursors and synthesis temperature. These modified 3D graphene materials were compared with pristine 3-dimensional graphene (P3DG), which has fewer defects and no nitrogen in its structure. The different types of graphene obtained were characterized for morphological, structural, and compositional assessment through Scanning Electron Microscopy (SEM), Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) techniques. Electrodes were fabricated, and electrochemical characterizations were conducted to evaluate the suitability of the three types of graphene for heavy metal sensing (lead) and Electric Double-Layer Capacitor (EDLC) applications. Initially, the various electrodes were treated with a mixture of 2.5 mM Ruhex (Ru (NH3)6Cl3 and 25 mM KCl to confirm that all the electrodes underwent a reversible and diffusion-controlled electrochemical process. Defect-rich graphene (N3DG-D) revealed the highest current density, followed by pristine (P3DG) and less-defect graphene (N3DG). Further, the three types of graphene were subjected to a sensing test by square wave anodic stripping voltammetry (SWASV) for lead detection. The obtained preliminary results showed that the N3DG material provided a great lead-sensing capability, detecting as little as 1 µM of lead in a water solution. The suitability of the electrodes to be employed in an Electric Double-Layer Capacitor (EDLC) was also comparatively assessed. Electrochemical characterization using 1 M sodium sulfate electrolyte was conducted through cyclic voltammetry and galvanostatic charge-discharge studies. The voltammogram and the galvanostatic charge-discharge (GCD) curves of the three types of graphene confirmed their suitability to be used as EDLC. The N3DG electrode proved superior with a gravimetric capacitance of 6.1 mF/g, followed by P3DG and N3DG, exhibiting 1.74 mF/g and 0.32 mF/g, respectively, at a current density of 2 A/g.

Laser-induced transient conversion of rhodochrosite/polyimide into multifunctional MnO2/graphene electrodes for energy storage applications

Laser-induced graphene (LIG) has been extensively investigated for electrochemical energy storage due to its easy synthesis and highly conductive nature. However, the limited charge accumulation in LIG usually leads to significantly low energy densities. In this work, we report a novel strategy to directly transform natural rhodochrosite into ultrafine manganese dioxide (MnO2) nanoparticles (NPs) in the polyimide (PI) substrate for high-performance micro-supercapacitors (MSCs) and lithium-ion batteries (LIBs) through a scalable and cost-effective laser processing method. Specifically, laser treatment on rhodochrosite/polyimide precursors induces the thermal explosion, which splits rhodochrosite (10 μm) into MnO2 NPs (12-16 nm) on the carbon matrix of LIG due to the sputtering effect. Benefiting from largely exposed active sites from the ultrafine MnO2 and the synergetic effect from highly conductive LIG, the MnO2/LIG MSCs show a high specific capacitance of 544.0 F g-1 (154.3 mF cm-2; 14.16 F cm-3) at 3 A/g and 82.1% capacitance retention after 10,000 cycles at 5A/g, in contrast to pure LIG (<100 F g-1). Moreover, the MnO2/LIG-based LIBs show the highest reversible discharge capacity of ∼1097 mAh g-1 at 0.2 A/g and ∼ 866.4 mAh g-1 at 1.0 A/g. This study opens a new route for synthesizing novel LIG-based composites from natural minerals.

Understanding the Degradation Mechanisms of Conducting Polymer Supercapacitors

Conducting polymers like polyaniline (PANI) are promising pseudocapacitive electrode materials, yet experience instability in cycling performance. Since polymers often degrade into oligomers, short chain length anilines have been developed to improve the cycling stability of PANI-based supercapacitors. However, the capacitance degradation mechanisms of aniline oligomer-based materials have not been systematically investigated and are little understood. Herein, two composite electrodes based on aniline trimers (AT) and carbon nanotubes (CNTs) are studied as model systems and evaluated at both pre-cycling and post-cycling states through physicochemical and electrochemical characterizations. The favorable effect of covalent bonding between AT and CNTs is confirmed to enhance cycling stability by preventing the detachment of aniline trimer and preserving the electrode microstructure throughout the charge/discharge cycling process. In addition, higher porosity has a positive effect on electron/ion transfer and the adaptation to volumetric changes, resulting in higher conductivity and extended cycle life. This work provides insights into the mechanism of enhanced cycling stability of aniline oligomers, indicating design features for aniline oligomer electrode materials to improve their electrochemical performance.

Recent Developments on Electroactive Organic Electrolytes for Non-Aqueous Redox Flow Batteries: Current Status, Challenges, and Prospects

The ever-increasing threat of climate change and the depletion of fossil fuel resources necessitate the use of solar- and wind-based renewable energy sources. Large-scale energy storage technologies, such as redox flow batteries (RFBs), offer a continuous supply of energy. Depending on the nature of the electrolytes used, RFBs are broadly categorized into aqueous redox flow batteries (ARFBs) and non-aqueous redox flow batteries (NARFBs). ARFBs suffer from various problems, including low conductivity of electrolytes, inferior charge/discharge current densities, high-capacity fading, and lower energy densities. NARFBs offer a wider potential window and range of operating temperatures, faster electron transfer kinetics, and higher energy densities. In this review article, a critical analysis is provided on the design of organic electroactive molecules, their physiochemical/electrochemical properties, and various organic solvents used in NARFBs. Furthermore, various redox-active organic materials, such as metal-based coordination complexes, quinones, radicals, polymers, and miscellaneous electroactive species, explored for NARFBs during 2012-2023 are discussed. Finally, the current challenges and prospects of NARFBs are summarized.

Atomic Layer Deposition-A Versatile Toolbox for Designing/Engineering Electrodes for Advanced Supercapacitors

Atomic layer deposition (ALD) has become the most widely used thin-film deposition technique in various fields due to its unique advantages, such as self-terminating growth, precise thickness control, and excellent deposition quality. In the energy storage domain, ALD has shown great potential for supercapacitors (SCs) by enabling the construction and surface engineering of novel electrode materials. This review aims to present a comprehensive outlook on the development, achievements, and design of advanced electrodes involving the application of ALD for realizing high-performance SCs to date, as organized in several sections of this paper. Specifically, this review focuses on understanding the influence of ALD parameters on the electrochemical performance and discusses the ALD of nanostructured electrochemically active electrode materials on various templates for SCs. It examines the influence of ALD parameters on electrochemical performance and highlights ALD's role in passivating electrodes and creating 3D nanoarchitectures. The relationship between synthesis procedures and SC properties is analyzed to guide future research in preparing materials for various applications. Finally, it is concluded by suggesting the directions and scope of future research and development to further leverage the unique advantages of ALD for fabricating new materials and harness the unexplored opportunities in the fabrication of advanced-generation SCs.

Molecular Understanding of Charging Dynamics in Supercapacitors with Porous Electrodes and Ionic Liquids

Porous electrodes and ionic liquids could significantly enhance the energy storage of supercapacitors. However, they may reduce the charging dynamics and power density due to the nanoconfinement of porous electrodes and the high viscosity of ionic liquids. A comprehensive understanding of the charging mechanism in porous supercapacitors with ionic liquids provides a crucial theoretical foundation for their design optimization. Here, we review the progress of molecular simulations of the charging dynamics in supercapacitors consisting of porous electrodes and ionic liquids. We highlight and delve into the breakthroughs in the ion transport and charging mechanism for electrodes with subnanometer pores and realistic porous structures. We also discuss future directions for the charging dynamics of supercapacitors.

Topochemically prepared tungsten disulfide nanostructures as a novel pseudocapacitive electrode for high performance supercapacitor

The topochemical preparation of nanostructured materials (NMs) has received significant attention in recent years due to the exceptional electrochemical properties exhibited by the resulting NMs. This work focuses on the preparation of two-dimensional tungsten di-sulfide (WS2) nanostructures through the topochemical conversion of tungsten trioxide (WO3) nanostructures and also evaluates their potential applications as electrode materials for supercapacitors (SCs). The X-ray diffraction and photoelectron studies conducted in this research reveal the conversion of hexagonal WO3 into hexagonal WS2 nanosheets, accompanied by changes in oxidation states. The FE-SEM and HR-TEM studies confirm the formation of WS2 in the sheet-like morphologies with lateral dimensions of 100 × 100 nm. The electrochemical investigation, using techniques such as CV, galvanostatic CD, and EIS, confirmed the presence of intercalation pseudocapacitance in the WS2 electrode, with a higher electrode-specific-capacitance (260 F g-1) than that of WO3 electrode. The WS2 symmetric SC delivered high device capacitance (59.17 F g-1), energy density (8.21 Wh kg-1) and power density (3,750 W kg-1) with better cyclic stability over 5000 cycles. These experimental findings show that the topochemically synthesized WS2as novel supercapacitor electrodes might be useful for the advancement of future-generation energy storage devices.

Analyzing synthesis routes for BaCuPO4: implications for hydrogen evolution and supercapattery performance

In recent years, energy storage and conversion tools have evolved significantly in response to rising energy demands. Owing to their large surface area, superior electric and chemical stabilities, and thermal conductivities, barium copper phosphate (BaCuPO4) materials are promising electrode materials for electrochemical energy storage systems. In this study, the synthesis of nanostructures (NSs) using hydrothermal and chemical precipitation methods and exploring the electrochemical characteristics of BaCuPO4 in asymmetric supercapacitors provides a comparative investigation. Systematic characterization shows that nanomaterials prepared by applying the hydrothermal method have a more crystalline and large surface area than chemical precipitation. In the three cell arrangements, the hydrothermally prepared BaCuPO4 NSs delivered a high specific capacity (764.4 C g-1) compared to the chemical precipitation route (660 C g-1). Additionally, the supercapattery associated with the two electrode assemblages delivers an optimum specific capacity of 77 C g-1. The energy and power density of BaCuPO4//AC NSs were 52.13 W h kg-1 and 950 W kg-1, respectively. A durability test was also performed with BaCuPO4//AC NSs for 5000 consecutive cycles. Further, the coulombic efficiency and capacity retention of BaCuPO4//AC after 5000 cycles were 81% and 92%, respectively. Bimetallic phosphate is comparatively suggested for future perspectives towards HER to overcome the performance of single metal phosphate materials. This is the first approach, we are aware of, for investigating the electrochemical behavior of BaCuPO4, and our results suggest that it may be useful as an electrode material in electrochemical systems requiring high energy and rate capabilities.

Super-fast Charging Biohybrid Batteries through a Power-to-formate-to-bioelectricity Process by Combining Microbial Electrochemistry and CO2 Electrolysis

Extensive study on renewable energy storage has been sparked by the growing worries regarding global warming. In this study, incorporating the latest advancements in microbial electrochemistry and electrochemical CO2 reduction, a super-fast charging biohybrid battery was introduced by using pure formic acid as an energy carrier. CO2 electrolyser with a slim-catholyte layer and a solid electrolyte layer was built, which made it possible to use affordable anion exchange membranes and electrocatalysts that are readily accessible. The biohybrid battery only required a 3-minute charging to accomplish an astounding 25-hour discharging phase. In the power-to-formate-to-bioelectricity process, bioconversion played a vital role in restricting both the overall Faradaic efficiency and Energy efficiency. The CO2 electrolyser was able to operate continuously for an impressive total duration of 164 hours under Gas Stand-By model, by storing N2 gas in the extraction chamber during stand-by periods. Additionally, the electric signal generated during the discharging phase was utilized for monitoring water biotoxicity. Functional genes related to formate metabolism were identified in the bioanode and electrochemically active bacteria were discovered. On the other hand, Paracoccus was predominantly found in the used air cathode. These results advance our current knowledge of exploiting biohybrid technology.

Amorphous Co-Mo-S nanospheres fabricated via room-temperature vulcanization for asymmetric supercapacitors

Ternary metal sulfides employed in supercapacitors exhibit better electrochemical performances than their counterpart oxides due to their superior conductivity. However, the insertion/extraction of electrolyte ions can lead to a significant volume change in electrode materials, which can result in poor cycling stability. Herein, novel amorphous Co-Mo-S nanospheres were fabricated through a facile room-temperature vulcanization method. It involves the conversion of crystalline CoMoO4 by reacting it with Na2S at room temperature. In addition to the conversion of the crystalline state into an amorphous structure with more grain boundaries, which is beneficial for the transport of electron/ion and can accommodate the volume change generated by the insertion/extraction of electrolyte ions, the production of more pores led to an increased specific surface area. The electrochemical results indicate that the as-prepared amorphous Co-Mo-S nanospheres had a specific capacitance of up to 2049.7F/g@1 A/g together with good rate capability. The amorphous Co-Mo-S nanospheres can be used as the cathode of supercapacitors and assembled with an activated carbon anode into an asymmetric supercapacitor possessing a satisfactory energy density of 47.6 Wh kg-1@1012.9 W kg-1. One of the prominent features exhibited by this asymmetric device is its remarkable cyclic stability, with a capacitance retention of 107% after 10,000 cycles.

Hierarchical Porous Activated Carbon Derived from Coconut Shell for Ultrahigh-Performance Supercapacitors

In this research, we successfully produced hierarchical porous activated carbon from biowaste employing one-step KOH activation and applied as ultrahigh-performance supercapacitor electrode materials. The coconut shell-derived activated carbon (CSAC) features a hierarchical porous structure in a honeycomb-like morphology, leading to a high specific surface area (2228 m2 g-1) as well as a significant pore volume (1.07 cm3 g-1). The initial test with the CSAC electrode, conducted in a 6 M KOH loaded symmetric supercapacitor, demonstrated an ultrahigh capacitance of 367 F g-1 at a current density of 0.2 A g-1 together with 92.09% retention after 10,000 cycles at 10 A g-1. More impressively, the zinc-ion hybrid supercapacitor using CSAC as a cathode achieves a high-rate capability (153 mAh g-1 at 0.2 A g-1 and 75 mAh g-1 at 10 A g-1), high energy density (134.9 Wh kg-1 at 175 W kg-1), as well as exceptional cycling stability (93.81% capacity retention after 10,000 cycles at 10 A g-1). Such work thus illuminates a new pathway for converting biowaste-derived carbons into materials for ultrahigh-performance energy storge applications.

Microwave synthesis of antimony oxide graphene nanoparticles - a new electrode material for supercapacitors

For the first time, antimony oxide nanoparticles were produced using a microwave technique and evaluated as a supercapacitor electrode. The specific capacitance derived from the material's galvanostatic charge-discharge curve was 98 F g-1 in 1 M Li2SO4 electrolyte at 0.1 A g-1 current density. The charge storage mechanism visible in the CV curve is nearly rectangular and identical to the EDLC charge storage mechanism. Additionally, antimony species were chemically attached to graphene oxide using an antimony(iii) chloride precursor and subsequently microwave aided procedures were used to convert the antimony species to SbO-G nanocomposites. The results of energy-dispersive X-ray spectroscopy demonstrated the pure character of the produced material. In a three-electrode cell arrangement, the resulting composite was electrochemically characterized. The cyclic voltammogram results showed that among the pristine SbO, graphene, and SbO-G materials, SbO-G had a higher specific capacitance value of 37.58 F g-1, at a scan rate of 10 mV s-1. The material has also demonstrated good conductivity characteristics based on electrochemical impedance spectroscopy research. After 3500 galvanostatic charge-discharge cycles, the material had excellent cycling stability of ∼100%. All the remarkable capacitive properties demonstrated by this material indicate that it can be a viable choice in the field of energy storage devices.

Bimetal Metal-Organic Framework-Derived Ni-Mn@Carbon/Reduced Graphene Oxide as a Cathode for an Asymmetric Supercapacitor with High Energy Density

As is known, metal-organic frameworks (MOFs) are a versatile class of materials in energy storage applications including supercapacitors. However, the individual kind of metal nodes connected by organic ligands to form a topological structure still limits the potential storage capacity of MOFs. Herein, a bimetal-based Ni-Mn MOF composite is configured with a one-pot hydrothermal method to derive a composite with a synergic effect to maximize the properties. Moreover, reduced graphene oxide (rGO) sheets are added as a conductive network to anchor the MOF-derived composite of Ni-Mn@C/rGO, which is expected to increase the conductivity of the materials system. The resulting composite exhibited a high specific capacitance of 1674 F g-1 at a current density of 0.3 A g-1, suggesting excellent energy storage performance. The composite was then integrated as the cathode in an asymmetrical supercapacitor with a 3D rGO aerogel anode, resulting in energy densities of 24.1 and 17.5 W h kg-1 at power densities of 88.9 and 444.4 W kg-1, respectively. Additionally, the device demonstrated remarkable long-term stability, with 90% capacitance retention after 10 000 charge-discharge cycles at 10 A g-1.

Sustainable energy and waste management: How to transform plastic waste into carbon nanostructures for electrochemical supercapacitors

Plastic waste consumption increases exponentially every year, mainly in the last three years due to the COVID-19 pandemic. The rapid growth of plastic products has exceeded the world's capacity to deal with this type of trash. Thus, it has become a substantial environmental concern in modern society. Another dire concern is the improper disposal of used supercapacitors, leading to serious environmental impacts. Consequently, critical action to tackle this issue is to transform trash into high-valued materials, such as carbon nanomaterial supercapacitors. Considering several methodologies of recycling, pyrolysis stands out due to its simplicity and easy handling of mixed plastic waste to produce carbonaceous materials with different dimensions (0, 1, 2, and 3D). Thus, from this technology, it is possible to create new opportunities for using plastic waste and other types of waste to produce cheaper carbon-based materials for supercapacitors. This review aims to provide readers with a sustainability-driven view regarding the reutilization of plastic trash, discusses the environmental consequences of not doing so, and shows plastic waste solutions. Despite the broad scope of the topic, this review focuses on identifying the currently studied strategies to convert plastic waste into carbon-based electrodes, using less expensive and more efficient competitive protocols, besides emphasizing the diverse types (0, 1, 2, and 3D) of nanostructures. This review also proposes promising options for a sustainable cycle of plastic waste and supercapacitor.

Microwave-Assisted Rational Designed CNT-Mn3 O4 /CoWO4 Hybrid Nanocomposites for High Performance Battery-Supercapacitor Hybrid Device

Extensive research interest in hybrid battery-supercapacitor (BSH) devices have led to the development of cathode materials with excellent comprehensive electrochemical properties. In this work, carbon nanotube (CNT)-Mn3 O4 /CoWO4 triple-segment hybrid electrode is synthesized by using a two-step microwave-assisted hydrothermal route. Systematic physical characterization revealed that, with the assistance of microwave, granular Mn3 O4 and spheroid-like CoWO4 with preferred orientation, and oxygen vacancies are stacked or arranged on CNTs skeletons to construct a rational designed hybrid nanocomposite with abundant heterointerfaces and interfacial chemical bonds. Electrochemical evaluations show that the synergistic cooperation in CNT-Mn3 O4 /CoWO4 resulted in an ultra-high specific capacity (1907.5 C g-1 /529.8 mA h g-1 at 1 A g-1 ), a wide operating voltage window (1.15 V), the satisfactory rate capability (capacity maintained at 1016.5 C g-1 /282.3 mA h g-1 at 15 A g-1 ), and excellent cycling stability (117.2% initial capacity retention after 13000 cycles at 15 A g-1 ). In addition, the assembled CNT-Mn3 O4 /CoWO4 //N doped porous carbon (NC) BSH device delivered a stable working voltage of 2.05 V and superior energy density of 67.5 Wh kg-1 at power density of 1025 W kg-1 , as well as excellent stability (92.2% capacity retained at 5 A g-1 for 12600 cycles). This work provides a new and feasible tactic to develop high-performance transition metal oxide-based cathodes for advanced BSH devices.

Confinement-Controlled Water Engenders Unusually High Electrochemical Capacitance

The electrodynamics of nanoconfined water have been shown to change dramatically compared to bulk water, opening room for safe electrochemical systems. We demonstrate a nanofluidic "water-only" battery that exploits anomalously high electrolytic properties of pure water at firm confinement. The device consists of a membrane electrode assembly of carbon-based nanomaterials, forming continuously interconnected water-filled nanochannels between the separator and electrodes. The efficiency of the cell in the 1-100 nm pore size range shows a maximum energy density at 3 nm, challenging the region of the current metal-ion batteries. Our results establish the electrodynamic fundamentals of nanoconfined water and pave the way for low-cost and inherently safe energy storage solutions that are much needed in the renewable energy sector.

Hierarchical Lotus-Seedpod-Derived Porous Activated Carbon Encapsulated with NiCo2S4 for a High-Performance All-Solid-State Asymmetric Supercapacitor

Converting biowaste into carbon-based supercapacitor materials provides a new solution for high-performance and environmentally friendly energy storage applications. Herein, the hierarchical PAC/NiCo2S4 composite structure was fabricated through the combination of activation and sulfuration treatments. The PAC/NiCo2S4 electrode garnered advantages from its hierarchical structure and hollow architecture, resulting in a notable specific capacitance (1217.2 F g-1 at 1.25 A g-1) and superior cycling stability. Moreover, a novel all-solid-state asymmetric supercapacitor (ASC) was successfully constructed, utilizing PAC/NiCo2S4 as the cathode and PAC as the anode. The resultant device exhibited exceptionally high energy (49.7 Wh kg-1) and power density (4785.5 W kg-1), indicating the potential of this biomass-derived, hierarchical PAC/NiCo2S4 composite structure for employment in high-performance supercapacitors.