High-Performance Flexible Quasi-Solid-State Supercapacitors Realized by Molybdenum Dioxide@Nitrogen-Doped Carbon and Copper Cobalt Sulfide Tubular Nanostructures

Zinc-Carbon Battery Recycling for Investigating Carbon Materials for Supercapacitor Applications

In this paper, carbon materials, including graphene nanosheets and carbon nanoparticles, were prepared from spent zinc-carbon batteries by the following two simple methods: electrochemical exfoliation and ultrasonication. Here, graphene nanosheets were synthesized by electrochemical exfoliation in 0.5 M H2SO4 by using a direct current power supply with two carbon rods from spent zinc-carbon batteries. Carbon nanoparticles were prepared by fast ultrasonication in a low-cost, green solution of DI water and ethanol. Graphene nanosheets in this study have high quality, large scale, and good electrochemical ability, while carbon nanoparticles have a unique nanosize and a good specific surface area. These carbon materials were applied for electrochemical measurements for supercapacitor studies and showed excellent stability at different temperatures. Moreover, electric double-layer capacitor devices based on graphene nanosheets and carbon nanoparticles were also used in electrochemical studies with strong stability and good electrochemical capability.

Constructing a 3D Ion Transport Channel-Based CNF Composite Film with an Intercalated Structure for Superior Performance Flexible Supercapacitors

The weak stiffness, huge thickness, and low specific capacitance of commonly utilized flexible supercapacitors hinder their great electrochemical performance. Learning from a biomimetic interface strategy, we design flexible film electrodes based on functional intercalated structures with excellent electrochemical properties and mechanical flexibility. A composite film with high strength and flexibility is created using graphene (reduced graphene oxide (rGO)) as the plane layer, layered double metal hydroxide (LDH) as the support layer, and cellulose nanofiber (CNF) as the connection agent and flexible agent. The interlayer height can be adjusted by the ion concentration. The highly interconnected network enables excellent electron and ion transport channels, facilitating rapid ion diffusion and redox reactions. Moreover, the high flexibility and mechanical properties of the film achieve multiple folding and bending. The CNF-rGO-NiCoLDH film electrode exhibits high capacitance performance (3620.5 mF cm-2 at 2 mA cm-2), excellent mechanical properties, and high flexibility. Notably, flexible all-solid assembled CNF-rGO-NiCoLDH//rGO has an extremely high area energy density of 53.5 mWh cm-2 at a power density of 1071.2 mW cm-2, along with cycling stability of 89.8% retention after 10 000 charge-discharge cycles. This work provides a perspective for designing high-performance energy storage materials for flexible electronics and wearable devices.

Dual Applications of Cobalt-Oxide-Grafted Carbon Quantum Dot Nanocomposite for Two Electrode Asymmetric Supercapacitors and Photocatalytic Behavior

Carbon materials, such as graphene, carbon nanotubes, and quantum-dot-doped metal oxides, are highly attractive for energy storage and environmental applications. This is due to their large surface area and efficient optical and electrochemical activity. In this particular study, a composite material of cobalt oxide and carbon quantum dots (Co3O4-CQD) was prepared using cobalt nitrate and ascorbic acid (carbon source) through a simple one-pot hydrothermal method. The properties of the composite material, including the functional groups, composition, surface area, and surface morphology, were evaluated by using various methods such as ultraviolet, Fourier transform infrared, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller, scanning electron microscopy, and transmission electron microscopy analysis. The electrochemical performance of the Co3O4-CQD composite has been studied using a three-electrode system. The results show that at 1 A g-1, the composite delivers a higher capacitance of 1209 F g-1. The asymmetric supercapacitor (Co3O4-CQD//AC) provided 13.88 W h kg-1 energy and 684.65 W kg-1 power density with a 96% capacitance retention. The Co3O4-CQD composite also demonstrated excellent photocatalytic activity (90% in 60 min) for the degradation of methylene blue dye under UV irradiation, which is higher than that of pristine Co3O4 and CQD. This demonstrates that the Co3O4-CQD composite is a promising material for commercial energy storage and environmental applications.

Oxygen-enriched pitch-derived hierarchically porous carbon toward boosted zinc-ion storage performance

The lack of cathode materials with satisfactory Zn2+ storage capability substantially hinders the realization of high-performance aqueous zinc-ion hybrid capacitors (ZHCs). Herein, we propose a facile KMnO4 template-assisted KOH activation strategy to prepare a novel oxygen-enriched hierarchically porous carbon (HPC-1-4). This strategy efficiently converts coal tar pitch (CTP) into a well-tuned carbon material with a large specific surface area of 3019 m2 g-1 and a high oxygen content of 9.20 at%, which is conducive to providing rich active sites, rapid charge transport, and appreciable pseudocapacitance for Zn-ion storage. Thus, the as-fabricated HPC-1-4-based aqueous ZHC exhibits prominent performance, including a high gravimetric capacity (206.7 mAh g-1 at 0.25 A g-1), a remarkable energy density (153.4 Wh kg-1 at 184.2 W kg-1), and an impressive power output (15240 W kg-1 at 63.5 Wh kg-1). In-depth ex-situ characterizations indicate that the excellent electrochemical properties of ZHCs are due to the synergistic effect of the Zn2+ adsorption mechanism and reversible chemisorption. In addition, the assembled quasi-solid-state device demonstrates excellent electrochemical stability of up to 100% capacity retention over 50000 cycles, accompanied with a desirable energy density of 115.6 Wh kg-1. The facile preparation method of converting CTP into carbonaceous functional materials has advanced the development of efficient and eco-friendly energy storage technologies.

Enhanced •Cl generation by introducing electrophilic Cu(II) in Co3O4 anode for efficient total nitrogen removal with hydrogen recovery in urine treatment

Urine is a nitrogen-containing waste, but can be used as an attractive alternative substrate for H2 recovery. However, conventional urea oxidation reaction is subject to complex six-electron transfer kinetics and requires alkaline conditions. Herein, an efficient method of enhancing •Cl generation by introducing electrophilic Cu(II) into Co3O4 nanowires anode was proposed, which realized the highly efficient TN removal and H2 production in urine treatment under neutral conditions. The key mechanism is that the electrophilic effect of Cu(II) attracts electrons from the oxygen atom, which causes the oxygen atom to further attract electrons from Co(II), reducing the charge density of Co(II). Electrophilic Cu(II) accelerates the difficult conversion step of Co(II) to Co(III), which enhances the generation of •Cl. The generated •Cl efficiently converts urea to N2, while the electron transport promotes H2 production on the CuO@CF nanowires cathode. Results showed that the steady-state concentration of •Cl was increased to about 1.5 times by the Cu(II) introduction. TN removal and H2 production reached 94.7% and 642.1 μmol after 50 min, which was 1.6 times and 1.5 times that of Co3O4 system, respectively. It was also 2.3 times and 2.1 times of RuO2, and 3.3 times and 2.5 times of Pt, respectively. Moreover, TN removal was 11.0 times higher than that of without •Cl mediation, and H2 production was 4.3 times higher. More importantly, excellent TN removal and H2 production were also observed in the actual urine treatment. This work provides a practical possibility for efficient total nitrogen removal and hydrogen recovery in urine wastewater treatment.

Se-doping-induced sulfur vacancy engineering of CuCo2S4 nanosheets for enhanced electrocatalytic overall water splitting

The coordination of the electronic structure and charge transfer through heteroatomic doping and sulfur vacancies is one of the most vital strategies for enhancing the electrocatalytic performance of the oxygen and hydrogen evolution reactions (OER, HER) through water splitting. Se-doped CuCo2S4 nanosheets (CuCo2S3.68Se0.32) with abundant sulfur vacancies were synthesized via a simple hydrothermal method to achieve remarkably efficient electrocatalytic water splitting. Importantly, incorporating Se in three-dimensional nanosheet structures effectively fine-tunes the electronic structure, ensuring ample accessibility of active sites for swift charge carrier transfer and improved reaction kinetics. The optimized CuCo2S3.68Se0.32 offers substantially high electrocatalytic activity with overpotentials of 65 and 230 mV at the current density of 10 mA cm-2 for HER and OER, respectively, which is comparable to commercial catalysts. Combining Se-doping and rich sulfur vacancies facilitates fast charge transport, thus significantly boosting the electrocatalytic activity. Furthermore, utilizing CuCo2S3.68Se0.32 as both the cathode and anode, a two-electrode electrolyser exhibits remarkable performance. It achieves a low voltage of 1.52 V at 10 mA cm-2 and demonstrates exceptional durability over time. This study investigates the significance of doping and vacancies in enhancing electrocatalytic activity for water splitting.

Facial Synthesis, Stability, and Interaction of Ti3C2Tx@PC Composites for High-Performance Biocathode Microbial Electrosynthesis Systems

Developing high-performance biocathodes remain one of the most challenging aspects of the microbial electrosynthesis (MES) system and the primary factor limiting its output. Herein, a hollow porous carbon (PC) fabricated with MXenes coated over an electrode was developed for MES systems to facilitate the direct delivery of CO2 to microorganisms colonized. The result highlighted that MXene@PC (Ti3C2Tx@PC) has a surface area of 434 m2/g. The Ti3C2Tx@PC MES cycle shows that in cycle 4 and cycle 5, the values are -309.2 and -352.3. Cyclic voltammetry showed that the coated electrode current response (mA) increased from -4.5 to -20.2. The substantial redox peaks of Ti3C2Tx@PC biofilms are displayed at -741, -516, and -427 mV vs Ag/AgCl, suggesting an enhanced electron transfer owing to the Ti3C2Tx@PC complex coating. Additionally, more active sites enhanced mass transfer and microbial development, resulting in a 46% rise in butyrate compared to the uncoated control. These findings demonstrate the value of PC modification as a method for MES-based product selection.

Cation-Driven Assembly of Bilayered Vanadium Oxide and Graphene Oxide Nanoflakes to Form Two-Dimensional Heterostructure Electrodes for Li-Ion Batteries

Lithium preintercalated bilayered vanadium oxide (LVO or δ-Li_xV₂O₅·nH₂O) and graphene oxide (GO) nanoflakes were assembled using a concentrated lithium chloride solution and annealed under vacuum at 200 °C to form two-dimensional (2D) δ-Li_xV₂O₅·nH₂O and reduced GO (rGO) heterostructures. We found that the Li⁺ ions from LiCl enhanced the oxide/carbon heterointerface formation and served as stabilizing ions to improve structural and electrochemical stability. The graphitic content of the heterostructure could be easily controlled by changing the initial GO concentration prior to assembly. We found that increasing the GO content in our heterostructure composition helped inhibit the electrochemical degradation of LVO during cycling and improved the rate capability of the heterostructure. A combination of scanning electron microscopy and X-ray diffraction was used to help confirm that a 2D heterointerface formed between LVO and GO, and the final phase composition was determined using energy-dispersive X-ray spectroscopy and thermogravimetric analysis. Scanning transmission electron microscopy and electron energy-loss spectroscopy were additionally used to examine the heterostructures at high resolution, mapping the orientations of rGO and LVO layers and locally imaging their interlayer spacings. Further, electrochemical cycling of the cation-assembled LVO/rGO heterostructures in Li-ion cells with a non-aqueous electrolyte revealed that increasing the rGO content led to improved cycling stability and rate performance, despite slightly decreased charge storage capacity. The heterostructures with 0, 10, 20, and 35 wt % rGO exhibited capacities of 237, 216, 174, and 150 mAh g^-1, respectively. Moreover, the LVO/rGO-35 wt % and LVO/rGO-20 wt % heterostructures retained 75% (110 mAh g^-1) and 67% (120 mAh g^-1) of their initial capacities after increasing the specific current from 20 to 200 mA g^-1, while the LVO/rGO-10 wt % sample retained only 48% (107 mAh g^-1) of its initial capacity under the same cycling conditions. In addition, the cation-assembled LVO/rGO electrodes exhibited enhanced electrochemical stability compared to electrodes prepared through physical mixing of LVO and GO nanoflakes in the same ratios as the heterostructure electrodes, further revealing the stabilizing effect of a 2D heterointerface. The cation-driven assembly approach, explored in this work using Li⁺ cations, was found to induce and stabilize the formation of stacked 2D layers of rGO and exfoliated LVO. The reported assembly methodology can be applied for a variety of systems utilizing 2D materials with complementary properties for applications as electrodes in energy storage devices.

Rational design of heterointerface between MoO2 and N-doped carbon with tunable electromagnetic interference shielding capacity

Exploring highly efficient electromagnetic interference (EMI) shielding filler is urgently desired for next-generation wireless communication and integrated electronics. In this regard, a series of heterogeneous MoO₂/N-doped carbon (MoO₂/NC) nanorods with tunable conductivity have been successfully synthesized by regulating the pyrolysis temperature within 600, 700 and 800 °C. Profiting from the rational design of heterointerface and low-dimensional structure, the MoO₂/NC powder achieves stronger EMI shielding capacity with the incremental temperature. It is found that the MoO₂/NC-800 nanorods exhibit the optimal average EMI shielding effectiveness (SE) of 57.2 dB at a thickness of ∼0.3 mm in the X band. Meanwhile, the corresponding shielding mechanisms of MoO₂/NC nanorods are also elaborately explained. More interestingly, the increase of sintering temperature makes an obvious effect on absorption loss but has little influence on reflection loss, demonstrating that adjusting the pyrolysis temperature is an effective strategy to strengthen the electromagnetic energy dissipation.

Emerging 2D Copper-Based Materials for Energy Storage and Conversion: A Review and Perspective

2D materials have shown great potential as electrode materials that determine the performance of a range of electrochemical energy technologies. Among these, 2D copper-based materials, such as Cu-O, Cu-S, Cu-Se, Cu-N, and Cu-P, have attracted tremendous research interest, because of the combination of remarkable properties, such as low cost, excellent chemical stability, facile fabrication, and significant electrochemical properties. Herein, the recent advances in the emerging 2D copper-based materials are summarized. A brief summary of the crystal structures and synthetic methods is started, and innovative strategies for improving electrochemical performances of 2D copper-based materials are described in detail through defect engineering, heterostructure construction, and surface functionalization. Furthermore, their state-of-the-art applications in electrochemical energy storage including supercapacitors (SCs), alkali (Li, Na, and K)-ion batteries, multivalent metal (Mg and Al)-ion batteries, and hybrid Mg/Li-ion batteries are described. In addition, the electrocatalysis applications of 2D copper-based materials in metal-air batteries, water-splitting, and CO₂ reduction reaction (CO₂ RR) are also discussed. This review also discusses the charge storage mechanisms of 2D copper-based materials by various advanced characterization techniques. The review with a perspective of the current challenges and research outlook of such 2D copper-based materials for high-performance energy storage and conversion applications is concluded.

Subnanometric Cu clusters on atomically Fe-doped MoO2 for furfural upgrading to aviation biofuels

Single cluster catalysts (SCCs) are considered as versatile boosters in heterogeneous catalysis due to their modifiable single cluster sites and supports. In this work, we report subnanometric Cu clusters dispersed on Fe-doped MoO₂ support for biomass-derived furfural upgrading. Systematical characterizations suggest uniform Cu clusters (composing four Cu atoms in average) are homogeneously immobilized on the atomically Fe-doped ultrafine MoO₂ nanocrystals (Cu₄/Fe_0.3Mo_0.7O₂@C). The atomic doping of Fe into MoO₂ leads to significantly modified electronic structure and consequently charge redistribution inside the supported Cu clusters. The as-prepared Cu₄/Fe_0.3Mo_0.7O₂@C shows superior catalytic performance in the oxidative coupling of furfural with C₃~C₁₀ primary/secondary alcohols to produce C₈~C₁₅ aldehydes/ketones (aviation biofuel intermediates), outperforming the conventionally prepared counterparts. DFT calculations and control experiments are further carried out to interpret the structural and compositional merits of Cu₄/Fe_0.3Mo_0.7O₂@C in the oxidative coupling reaction, and elucidate the reaction pathway and related intermediates.

Engineering hierarchical porous ternary Co-Mn-Cu-S nanodisk arrays for ultra-high-capacity hybrid supercapacitors

Transition-metal sulfides have been recognized as one of the promising electrodes for high-performance hybrid supercapacitors (HSCs). However, the poor rate performance and short cycle life heavily impede their practical applications. Herein, an advanced electrode based on hierarchical porous cobalt-manganese-copper sulfide nanodisk arrays (Co-Mn-Cu-S HPNDAs) on Ni foam is fabricated for high-capacity HSCs, using metal-organic frameworks as the self-sacrificial template. The synergistic effects of ternary Co-Mn-Cu sulfides and the hierarchical porous structure endow the as-obtained electrode with fast redox reaction kinetics. As expected, the resultant Co-Mn-Cu-S HPNDAs electrode delivers an ultrahigh specific capacity of 536.8 mAh g^-1 (3865 F g^-1) at 2 A g^-1 with a superb rate performance of 63% capacity retention at 30 A g^-1. Remarkably, an energy density of 63.8 W h kg^-1 at a power density of 743 W kg^-1 with a long cycle life is also achieved with the quasi-solid-state Co-Mn-Cu-S HPNDAs//ZIF-8-derived carbon HSC. This work offers a new pathway to fabricate high-performance multiple transition-metal-sulfide-based electrode materials for energy storage devices.

Freeze-Tolerant Hydrogel Electrolyte with High Strength for Stable Operation of Flexible Zinc-Ion Hybrid Supercapacitors

Constructing ionic conductive hydrogels with diversified properties is crucial for portable zinc-ion hybrid supercapacitors (ZHSCs). Herein, a freeze-tolerant hydrogel electrolyte (AF PVA-CMC/Zn(CF₃ SO₃ )₂ ) is developed by forming a semi-interpenetrating anti-freezing polyvinyl alcohol-carboxymethyl cellulose (AF PVA-CMC) network filled with the ethylene glycol (EG)-containing Zn(CF₃ SO₃ )₂ aqueous solution. The semi-interpenetrating AF PVA-CMC/Zn(CF₃ SO₃ )₂ possesses enhanced mechanical properties, realizes the uniform zinc deposition, and impedes the dendrite growth. Notably, the interaction between PVA and EG suppresses the ice crystal formation and prevents freezing at -20 °C. Due to these advantages, the designed hydrogel owns high ionic conductivity of 1.73/0.75 S m^-1 at 20/-20 °C with excellent tensile/compression strength at 20 °C. Impressively, the flexible AF quasi-solid-state ZHSC employing the hydrogel electrolyte achieves a superior energy density at 20/-20 °C (87.9/60.7 Wh kg^-1 ). It maintains nearly 84.8% of the initial capacity after 10 000 cycles and a low self-discharge rate (1.77 mV h^-1 ) at 20 °C, together with great tolerance to corrosion. Moreover, this device demonstrates a stable electrochemical performance at -20 °C under deformation. The obtained results provide valuable insights for constructing durable hydrogel electrolytes in cold environments.

Using Metal Cation to Control the Microstructure of Cobalt Oxide in Energy Conversion and Storage Applications

Herein, a facile and efficient synthesis of microstructured Co₃ O₄ for both supercapacitor and water-splitting applications is reported. Metal cations (Fe³⁺ , Cu²⁺ ) serve as structure-directing agents regulating the structure of Co compounds, which are subsequently annealed to yield Co₃ O₄ . Detailed characterizations and density functional theory (DFT) calculations reveal that the in situ Cl-doping introduces oxygen defects and provides abundant electroactive sites, and narrows the bandgap, which enhances the electron excitation of the as-formed Co₃ O₄ . The as-prepared Cl-doped Co₃ O₄ hierarchical nanospheres (Cl-Co₃ O₄ -h) display a high specific capacitance of 1629 F g^-1 at 1 A g^-1 as an electrode for supercapacitors, with excellent rate capability and cyclability. The Cl-Co₃ O₄ -h//activated carbon (AC) asymmetric supercapacitor (ASC) electrode achieves a specific capacitance of 237 F g^-1 at 1 A g^-1 , with an energy density of 74 Wh kg^-1 at a power density of 807 W kg^-1 and even maintains 47 Wh kg^-1 at the higher-power density of 24.2 kW kg^-1 . An integrated electrolyzer for water-splitting with Cl-Co₃ O₄ -h as both cathode and anode can be driven by Cl-Co₃ O₄ -h//AC ASC. The electrolyzer provides a high current density of 35 mA cm^-2 at a cell voltage of 1.6 V, with good current density retention over 50 h.

Realizing Superior Redox Kinetics of Hollow Bimetallic Sulfide Nanoarchitectures by Defect-Induced Manipulation toward Flexible Solid-State Supercapacitors

As a typical battery-type material, CuCo₂ S₄ is a promising candidate for supercapacitors due to the high theoretical specific capacity. However, its practical application is plagued by inherently sluggish ion diffusion kinetics and inferior electrical transport properties. Herein, sulfur vacancies are incorporated in CuCo₂ S₄ hollow nanoarchitectures (HNs) to accelerate redox reactivity. Experimental analyses and theoretical investigations uncover that the generated sulfur vacancies increase the active electron states, reduce the adsorption barriers of electrolyte ions, and enrich reactive redox species, thus achieving enhanced electrochemical performance. Consequently, the deficient CuCo₂ S₄ with optimized vacancy concentration presents a high specific capacity of 231 mAh g^-1 at 1 A g^-1 , a ≈1.78 times increase compared to that of pristine CuCo₂ S₄ , and exhibits a superior rate capability (73.8% capacity retention at 20 A g^-1 ). Furthermore, flexible solid-state asymmetric supercapacitor devices assembled with the deficient CuCo₂ S₄ HNs and VN nanosheets deliver a high energy density of 61.4 W h kg^-1 at 750 W kg^-1 . Under different bending states, the devices display exceptional mechanical flexibility with no obvious change in CV curves at 50 mV s^-1 . These findings provide insights for regulating electrode reactivity of battery-type materials through intentional nanoarchitectonics and vacancy engineering.

Strong Magnetic-Field-Engineered Porous Template for Fabricating Hierarchical Porous Ni-Co-Zn-P Nanoplate Arrays as Battery-Type Electrodes of Advanced All-Solid-State Supercapacitors

The sluggish charge transport kinetics that exist in the energy storage process of all-solid-state supercapacitors (ASSSCs) can be improved by designing open hierarchical porous structures for binder-free electrodes. Herein, a template-directed strategy is developed to fabricate open hierarchical porous Ni-Co-Zn-P nanoplate arrays (NCZP^6T) through phosphating the electrodeposited NiCo-LDH nanosheets loaded on a template. At first, porous conductive NiZn alloy nanoplate arrays are rationally devised as the template by a strong magnetic field (SMF)-assisted electrodeposition. The Lorentz force caused by coupling the SMF with the electrical current induces a magnetohydrodynamic (MHD) flow (including the micro-MHD flow), which homogenizes the deposition coating, tunes the nucleation and growth of the NiZn alloy, and produces pores in the nanoplates. The open hierarchical porous structure offers a larger specific surface area and pore volume for accelerating charge transport and gives a synergistic effect between the inner porous conductive NiZn array template and the outer electrochemical active phosphides for high-performance hybrid ASSSCs. Accordingly, the battery-type electrode of NCZP^6T shows a much higher specific capacitance of 3.81 F cm^-2 at 1 mA cm^-2, enhanced rate capability, and remarkable cycling stability at progressively varying current densities. Finally, the NCZP^6T//FeS ASSSC delivers a high energy density of 77 μW h cm^-2 at a large power density of 12 mW cm^-2, outperforming most state-of-the-art supercapacitors.

2-Dimensional layered molybdenum disulfide nanosheets and CTAB-assisted molybdenum disulfide nanoflower for high performance supercapacitor application

In this study, the supercapacitor performance of the hydrothermal synthesized molybdenum disulfide (MoS₂) nanosheets and the cetyltrimethylammonium bromide (CTAB)-assisted MoS₂ nanoflower morphology have been investigated. The as-synthesized MoS₂ nanoflower and nanosheet morphology structures were investigated via field emission scanning electron microscopy (FESEM), and the internal microstructure was examined via high resolution-transmission electron microscopy (HR-TEM) technique. The Fourier transform infrared (FT-IR) spectra were obtained to identify the chemical interaction and the functional groups present in the material. The shifting of the binding energy, oxidation states, and elemental identification were conducted by X-ray photon spectroscopy (XPS). The MoS₂ nanoflower possesses surface defects, which produce numerous active sites. The MoS₂ nanoflower and nanosheet electrodes demonstrate the high specific capacitance (C _sp) values of 516 F g^-1 and 438 F g^-1, respectively, at a current density of 1 A g^-1. However, the MoS₂ nanoflower shows high C _sp due to the large surface area with active edges, making them store more energy in the electrode.

Two-in-one template-assisted construction of hollow phosphide nanotubes for electrochemical energy storage

In this work, the template-assisted method was used to develop novel Ni2P@PANI hollow nanotubes as a positive electrode material for supercapacitors by using prepared polyaniline (PANI) nanotubes as precursors, and...

Enhancing Li-Ion Affinity of Molybdenum Dioxide/Carbon Fabric to Achieve High Pseudocapacitance

High-energy electrodes at high mass loadings (usually >8.0 mg cm^-2 ) are desired for aqueous pseudocapacitors. Yet, how to overcome the thickness-dependent resistance increase of ion/electron transport in pseudocapacitive materials is still challenging. Herein, a high-performance electrode (denoted as AMC) adapted to high mass loading is achieved by promoting the Li-ion affinity of 3D MoO₂ /carbon fabric. The experimental results and corresponding computational results reveal that the oxygen-activated surface of AMC, combined with the wettability and conductivity superiority of 3D graphite network, significantly facilitates the Li-ion adsorption and diffusion at the electrode/electrolyte interface, even at large thicknesses. Consequently, even at a high mass loading up to 8.1 mg cm^-2 , the AMC electrode also displays an impressive specific capacity (567.5 C g^-1 at 2.5 A g^-1 ), substantially superior to most advanced pseudocapacitive electrodes. The strategy of boosting energy characteristic by enhancing the affinity of charge carriers is applicable to other pseudocapacitive electrodes.

Biologically produced sulfur as a novel adsorbent to remove Cd2+ from aqueous solutions

Biological desulfurization processes of landfill gas yield an enormous amount of biologically produced S (BPS) as a byproduct. Capability of BPS to remove Cd²⁺ from aqueous solutions was tested and its removal efficiency was compared to that of granular activated carbon (GAC). Kinetics of Cd²⁺ removal by BPS was a two-stage process with an initial rapid adsorption showing 45% of initial Cd²⁺ was removed within 5 min, followed by a slower adsorption. Cadmium adsorption onto the BPS fitted the Langmuir isotherm model and maximum adsorption capacity of the BPS (63.3 mg g^-1) was 1.8 times higher than that of GAC (36.1 mg g^-1). Thermodynamic parameters showed that Cd²⁺ adsorption by BPS was favorable and endothermic. Data from XPS proved the main adsorption mechanism to be complexation of Cd²⁺ with sulfides in the BPS. Results demonstrated that BPS can be recycled as a novel adsorbent for Cd²⁺ removal from wastewater.

A safe and robust dual-network hydrogel electrolyte coupled with multi-heteroatom doped carbon nanosheets for flexible quasi-solid-state zinc ion hybrid supercapacitors

Aqueous zinc ion hybrid supercapacitors (ZHSCs) are receiving increasing research interest because of their superiority in safety, economy, and high water compatibility. However, the corrosion problems coupled with dendrite growth in an aqueous system severely limit the potential use of zinc storage systems with long service life. To delicately address the above obstacles, a κ-carrageenan/polyacrylamide/Zn(CF₃SO₃)₂ hydrogel electrolyte (denoted as κ-CG/PAAm/Zn(CF₃SO₃)₂) with an ionically and covalently double crosslinked network was constructed, which possesses a high ionic conductivity of 2.3 S m^-1, a high tensile strength of 34.6 kPa with a superior stretchability of 599.0%, and an excellent compression strength of 75.3 kPa at 75.0% strain. The double crosslinked polymer chains realize uniform zinc deposition. In addition, the intrinsic hydrophilic groups in the κ-carrageenan (κ-CG) and polyacrylamide (PAAm) chains can well immobilize water molecules, which favor electrolyte ion transport. Moreover, nitrogen and sulphur co-doped carbon nanosheets (denoted as ACNS) characterized by the rich amorphous phase associated with lots of short-range ordered microcrystalline regions were prepared as the cathode material in this work, which exhibits a high capacity of 116.4 mA h g^-1 coupled with superior rate performance and long-term cycling stability (108.0% capacity retention over 10 000 cycles) for an aqueous Zn//ACNS ZHSC. A quasi-solid-state ZHSC based on ACNS and κ-CG/PAAm/Zn(CF₃SO₃)₂ exhibits a specific capacity of 100.5 mA h g^-1 at 0.25 A g^-1 with a high capacity retention of 50.8% at 20 A g^-1. The as-fabricated ZHSC also shows excellent cycling stability of 10 000 cycles as well as a superior energy density of 86.5 W h kg^-1 at a power density of 215.3 W kg^-1. The ZHSC can also be used as a reliable source to drive various kinds of electronics (e.g., mobile phones and electronic timers), which uncovers a feasible strategy for engineering the high-performance hydrogel electrolytes and cathode materials for ZHSC applications.

Wearable Helical Molybdenum Nitride Supercapacitors for Self-Powered Healthcare Smartsensors

To meet the increasing demand for wearable sensing devices, flexible supercapacitors (SCs) as energy storage devices play significant roles in powering sensors/biosensors for healthcare monitoring. Because of its high conductivity and remarkable specific capacitance in SCs, molybdenum nitride (MoN) has been widely used. Herein, a flexible helical structure of MoN modified on nitrogen-doped carbon cloth (CC@CN@MoN) has been prepared by a simple nitride process, delivering an ultralong cycle life of 10,000 cycles and high areal capacitance of 467.6 mF cm^-2 as SCs. Moreover, the as-fabricated flexible all-solid-state asymmetrical SCs (ASCs) of CC@CN@MoN//CC@NiCo₂O₄ demonstrated outstanding electrochemical behavior after 10,000 cycles and over 90% retention, and the value of areal capacitance could reach 90.8 mF cm^-2 at 10 mA cm^-2. Integrated with solar energy, ASCs could be used as a self-powered energy system for strain sensors in detecting human movement, and finger movements could be further real-time monitored remotely via a smartphone. Prospectively, wearable helical MoN solid-state SCs for self-powered strain smartsensors would inspire the development of structured materials in the application of energy storage, portable self-powering, and strain or chemical/biochemical smartsensors.

Hierarchical urchin-like amorphous carbon with Co-adding anchored on nickel foam: A free-standing electrode for advanced asymmetrical supercapacitors and adsorbed Pb (II)

The booming development of carbon materials is of great value for diverse applications, owing to their superior electron conductivity, unique structures, and excellent cycle lifetime. This study presents two hierarchically structured amorphous carbon materials for asymmetric supercapacitor (ASC) device: i) the MOFs-derived urchin-like amorphous carbon anchored on nickel foam (UAC@NF) as positive electrode; ii) high temperature activated graphite carbon felt (GF500) as negative electrode. This ASC device achieves a higher energy density of 0.036 mWh cm^-3 at a power density of 0.984 mW cm^-3 and demonstrates better cycling performance with 91.4% capacitance retention after 10,000 cycles, compared with the other carbon-based supercapacitor. In addition, the UAC@NF after 10,000 cycles displays much better adsorption performance for Pb (II) compared with the unused UAC@NF. We have demonstrated the relationship between carbon materials' structure and performance by combining experiment and theoretical calculation. Predominantly, our work can provide a new direction for the common development of amorphous carbon materials in the field of energy and environment.

Fabrication of Robust, Highly Conductive, and Elastic Hybrid Carbon Foam Platform for High-Performance Compressible Asymmetry Supercapacitors

Highly conductive and elastic three-dimensional (3D) porous carbon materials are ideal platforms to fabricate electrodes for high-performance compressible supercapacitors. Herein, a robust, highly conductive, and elastic carbon foam (CF) hybrid material is reported, which is fabricated by integrating cellulose nanofiber/multiwalled carbon nanotube (CNF/MWCNT) aerogel sheets with a melamine sponge (MS), followed by carbonization. The carbonized CNF/MWCNT aerogel sheets contribute to the high conductivity and specific surface area of the CF, and the 3D network-like skeleton derived from the carbonization of the MS enhances the elasticity and stability of the CF. More importantly, the CF possesses good scalability, allowing the introduction of electroactive materials such as polypyrrole (PPy) and Fe₃O₄ to fabricate high-performance compressible PPy-CF and Fe₃O₄-CF electrodes. Moreover, an assembled PPy-CF//Fe₃O₄-CF device shows reversible charging-discharging at a voltage of 1.6 V and demonstrates a high specific capacitance (172.5 F/g) and an outstanding energy density (59.9 W h/kg). The device exhibits capacitance retention rates reaching 98.3% and stable energy storage characteristics even under different degrees of compressive deformation. This study offers a scalable strategy for fabricating high-performance compressible supercapacitors, thereby providing a new means of satisfying the energy storage needs of portable electronic devices that are prone to deformation.

Rational Design and Engineering of One-Dimensional Hollow Nanostructures for Efficient Electrochemical Energy Storage

The unique structural characteristics of one-dimensional (1D) hollow nanostructures result in intriguing physicochemical properties and wide applications, especially for electrochemical energy storage applications. In this Minireview, we give an overview of recent developments in the rational design and engineering of various kinds of 1D hollow nanostructures with well-designed architectures, structural/compositional complexity, controllable morphologies, and enhanced electrochemical properties for different kinds of electrochemical energy storage applications (i.e. lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, lithium-selenium sulfur batteries, lithium metal anodes, metal-air batteries, supercapacitors). We conclude with prospects on some critical challenges and possible future research directions in this field. It is anticipated that further innovative studies on the structural and compositional design of functional 1D nanostructured electrodes for energy storage applications will be stimulated.

Hybrid cobalt-manganese oxides prepared by ordered steps with a ternary nanosheet structure and its high performance as a binder-free electrode for energy storage

Binder-free electrodes for supercapacitors have attracted much attention as no additive is required in their preparation processes. Herein, a hybrid metal oxide composed of graphene oxide (Co₃O₄/MnO₂/GO) was successfully prepared. Briefly, electrochemical deposition and sintering were applied to grow Co₃O₄ nanosheets on nickel foam. Subsequently, MnO₂ nanosheets were deposited on Co₃O₄ nanosheets via the thermal decomposition of a KMnO₄ aqueous solution. Finally, graphene oxide was added to improve the performance of the composite. Particularly, the as-obtained Co₃O₄/MnO₂/GO sample grown on nickel foam possessed a ternary nanosheet structure, and when applied as a binder-free electrode in a supercapacitor, it exhibited an excellent electrochemical performance. Firstly, the electrode exhibited an ultrahigh capacitance value of 2928 F g^-1 at 1 A g^-1 in a three-electrode system. Besides, the electrode showed a promising rate performance of 853 F g^-1 at a high current density of 20 A g^-1. Moreover, the electrode displayed a relatively high energy density of 97.92 W h kg^-1 at a power density of 125 W kg^-1 and long cycle life of 93% retention after 5000 cycles at 10 A g^-1 in a two-electrode system. Thus, all the electrochemical tests suggest that the Co₃O₄/MnO₂/GO binder-free electrode is a potential candidate for energy storage.

High energy density hybrid supercapacitor based on cobalt-doped nickel sulfide flower-like hierarchitectures deposited with nitrogen-doped carbon dots

The exploration of advanced electrode materials with outstanding electrochemical properties is of considerable importance for hybrid supercapacitors but challenging. In this paper, an effective two-step solvothermal route is demonstrated to synthesize nitrogen-doped carbon dots (NCDs) decorated cobalt-doped nickel sulfide (Co-NiS) flower-like hierarchitectures. Because of the modification with NCDs and doping by cobalt atoms, the resulting Co-NiS/NCDs hierarchitectures exhibit an ultrahigh specific capacity up to 1240 C g-1 (2480 F g-1) at 1 A g-1 and a remarkable rate capability of 790.8 C g-1 (1581.6 F g-1) even at 20 A g-1 when used as advanced electrodes for supercapacitors. More significantly, coupling with ap-phenylenediamine (PPD) modified reduced graphene oxide (rGO) anode, a hybrid supercapacitor device is successfully constructed, which possesses an impressive energy density of 71.6 W h kg-1 at 712.0 W kg-1 and a decent cyclic stability with 78.3% retention after 12 000 cycles at 5 A g-1. The dual improvement strategy may provide insight to rational engineering of novel electrode materials with multi-components for high-performance hybrid supercapacitors.

Enhanced faradic activity by construction of p-n junction within reduced graphene oxide@cobalt nickel sulfide@nickle cobalt layered double hydroxide composite electrode for charge storage in hybrid supercapacitor

The intrinsic faradic reactivity is the uppermost factor determining the charge storage capability of battery material, the construction of p-n junction composing of different faradic components is a rational tactics to enhance the faradic activity. Herein, a reduced graphene oxide@cobalt nickle sulfide@nickle cobalt layered double hydroxide composite (rGO@CoNi₂S₄@NiCo LDH) with p-n junction structure is designed by deposition of n-type nickle cobalt layered double hydroxide (NiCo LDH) around p-type reduced graphene oxide@cobalt nickle sulfide (rGO@CoNi₂S₄), the charge redistribution across the p-n junction enables enhanced faradic activities of both components and further the overall charge storage capacity of the resultant rGO@CoNi₂S₄@NiCo LDH battery electrode. As expected, the rGO@CoNi₂S₄@NiCo LDH electrode can deliver high specific capacity (C_s, 1310 ± 26 C g^-1 at 1 A g^-1) and good cycleability (77% C_s maintaining ratio undergoes 5000 charge-discharge cycles). Furthermore, the hybrid supercapacitor (HSC) based on the rGO@CoNi₂S₄@NiCo LDH p-n junction battery electrode exports high energy density (E_cell, 57.4 Wh kg^-1 at 323 W kg^-1) and good durability, showing the prospect of faradic p-n junction composite in battery typed energy storage.

Positive effects of a halloysite-supported Cu/Co catalyst fabricated by a urea-driven deposition precipitation method on the CO-SCR reaction and SO2 poisoning

Cu/Co catalysts were prepared on halloysite nanotube supports by a urea-driven deposition–precipitation method for CO oxidation and the selective catalytic reduction of NO (CO-SCR).

In situ synthesis of nitrogen site activated cobalt sulfide@N, S dual-doped carbon composite for a high-performance asymmetric supercapacitor

Cobalt sulfides with high theoretical capacity are considered as potential electrodes for supercapacitors (SCs). However, the insufficient reactive sites and low electrical conductivity of bulky cobalt sulfides restrict their applications. Here, we proposed an efficient approach for in situ formation of nitrogen site activated cobalt sulfide@N, S dual-doped carbon composite (CS@NSC) by vulcanizing the cobalt-glutamine complex (CG) precursor in a tube furnace. The effects of the molecular structure and calcination temperature of CG precursors on the morphology, structure and electrochemical performance of CS@NSC were studied. The designed CS@NSC-2 exhibited a specific capacity of 593 C g^-1 at the current density of 1 A g^-1 and good cyclic stability with 88.7% retention after 2000 cycles. Moreover, an asymmetric supercapacitor (ASC) was fabricated by CS@NSC-2 (positive electrode) and activated carbon (AC) (negative electrode), which delivered ultra-high energy density of 67.8 Wh kg^-1 at a power density of 400 W kg^-1 and possessed 83.1% capacitance retention after 5000 cycles. The eco-friendly method was also suitable for synthesizing nickel sulfide. This work may provide an innovative horizon for the in situ formation of active sites in electrode materials.

True Meaning of Pseudocapacitors and Their Performance Metrics: Asymmetric versus Hybrid Supercapacitors

The development of pseudocapacitive materials for energy-oriented applications has stimulated considerable interest in recent years due to their high energy-storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery-like to the pseudocapacitive-like behavior. As a result, it becomes challenging to distinguish "pseudocapacitive" and "battery" materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery-type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid-state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state-of-the-art progress in the engineering of active materials is summarized, which will guide for the development of real-pseudocapacitive energy storage systems.

High specific capacitance of manganese-based colloidal system with rare earth modification

Ever-increasing global energy consumption has increased aggregate demand on electrochemical energy storage devices with high energy density. Over the past few decades, manganese oxides have attracted wide attention due to their abundant reserves, low cost, environmental friendliness, and high theoretical capacity. However, most reported manganese-based materials have exhibited capacity far below the theoretical capacity, which was only on the basis of Mn3+/Mn4+ couple. The rich chemistry of manganese enables it to exist in various valence states, such as Mn0, Mn2+, Mn3+, Mn4+, and Mn7+, providing great opportunity for discovering new manganese-based electrode systems. Herein, we formed a Mn2+/Mn4+ couple from a manganese-based colloidal system with rare earth (RE) modification, which was formed in-situ on nickel (Ni) foam in KOH electrolyte under an electric field assistance. The Mn-based colloidal electrode, with Mn:Ce mass ratio of 1:0.5, achieved a high specific capacitance of 2985 F g-1 at 3 A g-1, which was higher than the theoretical capacity of 2193 F g-1 on the basis of the Mn3+/Mn4+ couple. After the addition of Ce3+, the prepared sample exhibited improved rate capability performance. Our manganese-based colloidal electrode with RE modification delivered a high specific capacitance of 1223 F g-1 at 20 A g-1, with 54.5% retention of 2243 F g-1 at 3 A g-1 at Mn:Ce mass ratio of 1:0.05. Colloidal electrode systems involving Mn-based colloids are a novel way to engineer the electrochemical performance of inorganic materials.

Freestanding Needle Flower Structure CuCo2S4 on Carbon Cloth for Flexible High Energy Supercapacitors With the Gel Electrolyte

A facile hydrothermal approach was adopted to the direct synthesis of bimetallic sulfide (CuCo₂S₄) on carbon cloth (CC) without binders for the supercapacitor's electrodes. A possible formation mechanism was proposed. The prepared bimetallic electrode exhibited a high specific capacitance (Csp) of 1,312 F·g⁻¹ at 1 A·g⁻¹, and an excellent capacitance retention of 94% at 5 A·g⁻¹ over 5,000 cycles. In addition, the asymmetric supercapacitor (CuCo₂S₄/CC//AC/CC) exhibited energy density (42.9 wh·kg⁻¹ at 0.8 kW·kg⁻¹) and outstanding cycle performance (80% initial capacity retention after 5,000 cycles at 10 A·g⁻¹). It should be noted that the electrochemical performance of a supercapacitor device is quite stable at different bending angles. Two charged devices in series can light 28 red-colored LEDs (2.0 V) for 5 min. All of this serves to indicate the potentially high application value of CuCo₂S₄.

Rational design of flower-like cobalt–manganese-sulfide nanosheets for high performance supercapacitor electrode materials

The design and development of composite materials with novel structures is one of the effective ways to enhance the electrochemical properties of supercapacitors.

Phosphorus Regulated Cobalt Oxide@Nitrogen-Doped Carbon Nanowires for Flexible Quasi-Solid-State Supercapacitors

Battery-type materials are promising candidates for achieving high specific capacity for supercapacitors. However, their slow reaction kinetics hinders the improvement in electrochemical performance. Herein, a hybrid structure of P-doped Co₃ O₄ (P-Co₃ O₄ ) ultrafine nanoparticles in situ encapsulated into P, N co-doped carbon (P, N-C) nanowires by a pyrolysis-oxidation-phosphorization of 1D metal-organic frameworks derived from Co-layered double hydroxide as self-template and reactant is reported. This hybrid structure prevents active material agglomeration and maintains a 1D oriented arrangement, which exhibits a large accessible surface area and hierarchically porous feature, enabling sufficient permeation and transfer of electrolyte ions. Theoretical calculations demonstrate that the P dopants in P-Co₃ O₄ @P, N-C could reduce the adsorption energy of OH^- and regulate the electrical properties. Accordingly, the P-Co₃ O₄ @P, N-C delivers a high specific capacity of 669 mC cm^-2 at 1 mA cm^-2 and an ultralong cycle life with only 4.8% loss over 5000 cycles at 30 mA cm^-2 . During the fabrication of P-Co₃ O₄ @P, N-C, Co@P, N-C is simultaneously developed, which can be integrated with P-Co₃ O₄ @P, N-C for the assembly of asymmetric supercapacitors. These devices achieve a high energy density of 47.6 W h kg^-1 at 750 W kg^-1 and impressive flexibility, exhibiting a great potential in practical applications.

Microfluidic-Architected Nanoarrays/Porous Core-Shell Fibers toward Robust Micro-Energy-Storage

Methods enabling the controllable fabrication of orderly structural and active nanomaterials, along with high-speed ionic pathways for charge migration and storage are highly fundamental in fiber-shaped micro-supercapacitors (MSCs). However, due to fiber-electrodes with compact internal microstructure and less porosity, MSCs usually display a low energy density. Here, an innovative microfluidic strategy is proposed to design ordered porous and anisotropic core-shell fibers based on nickel oxide arrays/graphene nanomaterials. Owing to the homogeneous microchannels reaction, the graphene core maintains a uniformly anisotropic porous structure, and the nickel oxide shell keeps steadily vertically aligned nanosheets. The MSC presents an ultrahigh energy density (120.3 µWh cm-2) and large specific capacitance (605.9 mF cm-2). This higher performance originates from the microfluidic-architected core-shell fiber with abundant ionic channels (plentiful micro-/mesopores), large specific-surface-area (425.6 m2 g-1), higher electrical conductivity (176.6 S cm-1), and sufficient redox activity, facilitating ions with quicker diffusion and greater accumulation. Considering those outstanding properties, a wearable self-powered system, converting and storing solar energy into electric energy, is designed to light up displays. This microfluidic strategy offers an effective way to design new structural materials, which will advance the development of next-generation wearable/smart industries.

Construction of hierarchical cobalt-molybdenum selenide hollow nanospheres architectures for high performance battery-supercapacitor hybrid devices

Transition metal selenides have aroused widespread attention as a class of emerging electrode materials for high-performance supercapacitors attributed to their featured with high theoretical capacitance and low electronegativity. Nevertheless, their practical applications are seriously restricted by the large volume expansion during high-rate charge/discharge. It is imperative to reasonably construct tunable composition and attractive architectures for electrode materials at nanoscale to mitigate the issues. Herein, hierarchical cobalt-molybdenum selenide (denoted as CoSe₂/MoSe₂-3-1) hollow nanospheres architectures are purposefully prepared via an efficient gas bubble-templated method combined with post-annealing process. Benefiting from the rationally hierarchical hollow structures and maximized utilization ratio of active materials, the novel bimetallic selenides acquire superior electrochemical performance with high specific capacity (211.97 mA h g^-1 at 1 A g^-1) and remarkable cycling stability (94.2% capacity retention over 2000 cycles at 3 A g^-1). Significantly, the assembled CoSe₂/MoSe₂-3-1//activated carbon (AC) battery-supercapacitor hybrid (BSH) device renders a high energy density up to 51.84 W h kg^-1 at a power density of 799.2 W kg^-1 and preeminent cycling stability with 93.4% retention over 10,000 cycles. The present work provides an effective and rational design route to engineer advanced bimetallic selenides with hierarchical hollow structures for electrochemical energy storage and conversion.