Honeycomb-like Ni3S2 supported on Ni foam as high performance free-standing cathode for lithium oxygen batteries

Facile fabrication of binder-free photoelectrode for sensitive glucose sensing

A novel carbon nitride particle-decorated three-dimensional porous nickel foam (CN/NF) was fabricated by a simple thermal polymerization deposition method for photoelectrochemical glucose detection. In this PEC sensing system, the synergetic effect of the photoactive CN and conductive current collector NF with multi-charge transfer channels contributed to the efficient separation of photoexcited charge carriers. The CN/NF electrode showed an excellent response for glucose detection and good anti-interference properties. A wide linear detection up to 1000μM and sensitivity of 460.2μA cm^-2mM^-1were obtained. This work provides a new strategy for designing binder-free electrodes for PEC sensing.

One-pot synthesis of N,S-doped pearl chain tube-loaded Ni3S2 composite materials for high-performance lithium-air batteries

To improve the high reversibility of lithium-air batteries, an air electrode needs to have excellent electrochemical performance and spatial structure. Ni3S2 nanoparticles are loaded onto an N,S-doped pearl chain tube (N,S-PCT) by a method called quasi-chemical vapor deposition (Q-CVD). Additionally, N and S are doped during the synthesis process, thereby forming an ideal pipe rack-like structure. The large amount of space in the tube rack can provide sufficient storage to act as a buffer for the discharge products, and the interconnected tubes can effectively promote the dispersion of O2 and electrolyte. The addition of Ni3S2 nanoparticles effectively reduces the charge transfer resistance, thereby increasing the electron mobility of the cathode. Ni3S2@N,S-PCT cathodes effectively improve the cycling and high-rate performance of lithium-air batteries, demonstrating an ultrahigh discharge capacity of 16 733.7 mA h g-1 at a current density of 400 mA g-1 and an ultrahigh discharge capacity of 5088.1 mA h g-1 at a current density of 1000 mA g-1. When the cut-off capacity is 1000 mA h g-1, the battery with the Ni3S2@N,S-PCT-800 electrode can achieve cycling stability for 148 cycles. This research provides a new solution for the design of lithium-air batteries with high electrocatalytic performance.

A novel electrode for supercapacitors: efficient PVP-assisted synthesis of Ni3S2 nanostructures grown on Ni foam for energy storage

In this academic research, we report the polyvinylpyrrolidone (PVP) assisted synthesis of a Ni3S2 electrode material containing a plentiful number of active sites on Ni foam by a novel hydrothermal approach. Interestingly, the Ni3S2 electrode is a highly efficient electroactive material, as evidenced by the physical and electrochemical characterization. Based on the physical characterization, the constructed Ni3S2 nano architecture exhibited plentiful electroactive sites, quick charge/discharge transportation and better maximum conductivity, which gave rise to enhanced electrochemical activity for large-scale supercapacitors (SCs). Besides, the electrochemical characterization of the as-developed Ni3S2 electrode obviously displayed a faradaic battery-based redox profile, which is distinct from the profiles of carbon-type materials. The battery-based PVP-assisted Ni3S2 electrode achieved impressive electrochemical activity, namely exceptional SC activity with a superior specific capacity of ∼316.8 mA h g-1 at 2 A g-1 current density, high rate capability with ∼91.4% of capacity retained at 20 A g-1, and superb cycling performance with ∼96.7% of capacity retained at 6 A g-1 after 4000 cycles. Thus, considering the best findings above, the as-developed PVP-assisted Ni3S2 is a highly efficient candidate for SCs and could effectively serve in various advanced energy storage applications.

A 3D free-standing Co doped Ni2P nanowire oxygen electrode for stable and long-life lithium-oxygen batteries

Exploring oxygen electrodes with superior bifunctional catalytic activity and suitable architecture is an effective strategy to improve the performance of lithium-oxygen (Li-O₂) batteries. Herein, the internal electronic structure of Ni₂P is regulated by heteroatom Co doping to improve its catalytic activity for oxygen redox reactions. Meanwhile, magnetron sputtering N-doped carbon cloth (N-CC) is used as a scaffold to enhance the electrical conductivity. The deliberately designed Co-Ni₂P on N-CC (Co-Ni₂P@N-CC) with a typical 3D interconnected architecture facilitates the formation of abundant solid-liquid-gas three-phase reaction interfaces inside the architecture. Furthermore, the rational catalyst/substrate interfacial interaction is capable of inducing a solvation-mediated pathway to form toroidal-Li₂O₂. The results show that the Co-Ni₂P@N-CC based Li-O₂ battery exhibits an ultra-low overpotential (0.73 V), enhanced rate performance (4487 mA h g^-1 at 500 mA g^-1) and durability (stable operation over 671 h). The pouch-type battery based on the Co-Ni₂P@N-CC flexible electrode runs stably for 581 min in air without obvious voltage attenuation. This work verifies that heterogeneous atom doping and interface interaction can remarkably strengthen the performance of Li-O₂ cells and thus pave new avenues towards developing high-performance metal-air batteries.

Configuration of gradient-porous ultrathin FeCo2S4 nanosheets vertically aligned on Ni foam as a noncarbonaceous freestanding oxygen electrode for lithium-oxygen batteries

The degradation of oxygen electrodes caused by oxygen species in lithium-oxygen (Li-O2) batteries deteriorates their energy efficiency and cyclability and seriously hinders their commercial application. To achieve high energy efficiency and long-term cycle life, gradient-porous ultrathin FeCo2S4 nanosheets on Ni foam (FeCo2S4@Ni) were deliberately designed as a noncarbonaceous freestanding oxygen electrode for Li-O2 batteries. Notably, the gradient-porous structure in FeCo2S4@Ni can offer sufficient active sites as well as mitigate polarization caused by the mass transfer during discharge and charge. The synergistic effect of the two transition metals, Fe2+ and Co3+, optimizes their d-band electronic structure and enhances the intrinsic activity of the oxygen electrode. Benefiting from the above merits, the FeCo2S4@Ni based Li-O2 battery demonstrates greatly increased discharge capacity (8001 mA h g-1), improved rate capability (with a high capacity of 4401 mA h g-1 at 500 mA g-1), and enhanced cycling stability (with a low overpotential of below 1 V after 109 cycles). Our work demonstrates that the battery performance can be improved by regulating the structure and composition of the oxygen electrode and provides a promising strategy for developing high performance Li-O2 batteries.

Fabrication of resorcinol-based porous resin carbon material and its application in aqueous symmetric supercapacitors

Carbon materials with porous structures with their unique surface area and charge transport properties have been attracting significant attention as electrode materials in renewable energy storage devices. The rapid agglomeration of layered materials during electrochemical processes reduces their shelf life and specific capacitance, which can be prevented by the introduction of suitable pores between the layers. In this study, resorcinol-based porous resin carbon was facilely prepared via a simple carbonization of the potassium salts of resorcinol-potassium resin. The morphology, structure and surface properties of the carbon materials were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption and energy dispersive spectroscopy (EDS). It is proposed that the fast nucleophilic addition between the phenols and formaldehyde produces nano-sized gel particles, followed by carbonization into carbon particles, finally packing to the mesopores. Due to the synergistic effects of the tailored porosity and O-doping, the prepared carbon materials show a high specific capacitance (198 F g⁻¹ for RC700), good capacitance retention (96.5% for RC700) at 2 A g⁻¹ in 6 M KOH and the specific area of RC700 is 540 m² g⁻¹.

Activated preparation of environmentally friendly and sustainable carbon materials and their successful application in supercapacitor devices.

In Situ Fabricating Oxygen Vacancy-Rich TiO2 Nanoparticles via Utilizing Thermodynamically Metastable Ti Atoms on Ti3C2Tx MXene Nanosheet Surface To Boost Electrocatalytic Activity for High-Performance Li-O2 Batteries

Catalysts with high performance are urgently needed in order to accelerate the reaction kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in lithium-oxygen (Li-O₂) batteries. Herein, utilizing thermodynamically metastable Ti atoms on the Ti₃C₂Tx MXene nanosheet surface as the nucleation site, oxygen vacancy-rich TiO₂ nanoparticles were in situ fabricated on Ti₃C₂Tx nanosheets (V-TiO₂/Ti₃C₂Tx) and used as the oxygen electrode of Li-O₂ batteries. Oxygen vacancy (Vo) can boost the migration rate of electrons and Li⁺ as well as act as the active sites for catalyzing the ORR and OER. Based on the above merits, V-TiO₂/Ti₃C₂Tx-based Li-O₂ battery shows improved performance including the ultralow overpotential of 0.21 V, high specific capacity of 11 487 mA h g^-1 at a current density of 100 mA g^-1, and excellent round-trip efficiency (93%). This work proposes an effective strategy for researching high-performance oxygen electrodes for Li-O₂ batteries via introducing Vo-rich oxides on two-dimensional MXene.

Engineering Ternary Copper-Cobalt Sulfide Nanosheets as High-performance Electrocatalysts toward Oxygen Evolution Reaction

The rational design and development of the low-cost and effective electrocatalysts toward oxygen evolution reaction (OER) are essential in the storage and conversion of clean and renewable energy sources. Herein, a ternary copper-cobalt sulfide nanosheets electrocatalysts (denoted as CuCoS/CC) for electrochemical water oxidation has been synthesized on carbon cloth (CC) via the sulfuration of CuCo-based precursors. The obtained CuCoS/CC reveals excellent electrocatalytic performance toward OER in 1.0 M KOH. It exhibits a particularly low overpotential of 276 mV at current density of 10 mA cm−2, and a small Tafel slope (58 mV decade−1), which is superior to the current commercialized noble-metal electrocatalysts, such as IrO2. Benefiting from the synergistic effect of Cu and Co atoms and sulfidation, electrons transport and ions diffusion are significantly enhanced with the increase of active sites, thus the kinetic process of OER reaction is boosted. Our studies will serve as guidelines in the innovative design of non-noble metal electrocatalysts and their application in electrochemical water splitting

2D Free-Standing Nitrogen-Doped Ni-Ni3 S2 @Carbon Nanoplates Derived from Metal-Organic Frameworks for Enhanced Oxygen Evolution Reaction

2D metal-organic frameworks (2D MOFs) are promising templates for the fabrication of carbon supported 2D metal/metal sulfide nanocomposites. Herein, controllable synthesis of a newly developed 2D Ni-based MOF nanoplates in well-defined rectangle morphology is first realized via a pyridine-assisted bottom-up solvothermal treatment of NiSO₄ and 4,4'-bipyridine. The thickness of the MOF nanoplates can be controlled to below 20 nm, while the lateral size can be tuned in a wide range with different amounts of pyridine. Subsequent pyrolysis treatment converts the MOF nanoplates into 2D free-standing nitrogen-doped Ni-Ni₃ S₂ @carbon nanoplates. The obtained Ni-Ni₃ S₂ nanoparticles encapsulated in the N-doped carbon matrix exhibits high electrocatalytic activity in oxygen evolution reaction. A low overpotential of 284.7 mV at a current density of 10 mA cm^-2 is achieved in alkaline solution, which is among the best reported performance of substrate-free nickel sulfides based nanomaterials.

Understanding the Reaction Chemistry during Charging in Aprotic Lithium-Oxygen Batteries: Existing Problems and Solutions

The aprotic lithium-oxygen (Li-O₂ ) battery has excited huge interest due to it having the highest theoretical energy density among the different types of rechargeable battery. The facile achievement of a practical Li-O₂ battery has been proven unrealistic, however. The most significant barrier to progress is the limited understanding of the reaction processes occurring in the battery, especially during the charging process on the positive electrode. Thus, understanding the charging mechanism is of crucial importance to enhance the Li-O₂ battery performance and lifetime. Here, recent progress in understanding the electrochemistry and chemistry related to charging in Li-O₂ batteries is reviewed along with the strategies to address the issues that exist in the charging process at the present stage. The properties of Li₂ O₂ and the mechanisms of Li₂ O₂ oxidation to O₂ on charge are discussed comprehensively, as are the accompanied parasitic chemistries, which are considered as the underlying issues hindering the reversibility of Li-O₂ batteries. Based on the detailed discussion of the charging mechanism, innovative strategies for addressing the issues for the charging process are discussed in detail. This review has profound implications for both a better understanding of charging chemistry and the development of reliable rechargeable Li-O₂ batteries in the future.

Component-Interaction Reinforced Quasi-Solid Electrolyte with Multifunctionality for Flexible Li-O2 Battery with Superior Safety under Extreme Conditions

High-performance flexible lithium-oxygen (Li-O₂ ) batteries with excellent safety and stability are urgently required due to the rapid development of flexible and wearable devices. Herein, based on an integrated solid-state design by taking advantage of component-interaction between poly(vinylidene fluoride-co-hexafluoropropylene) and nanofumed silica in polymer matrix, a stable quasi-solid-state electrolyte (PS-QSE) for the Li-O₂ battery is proposed. The as-assembled Li-O₂ battery containing the PS-QSE exhibits effectively improved anodic reversibility (over 200 cycles, 850 h) and cycling stability of the battery (89 cycles, nearly 900 h). The improvement is attributed to the stability of the PS-QSE (including electrochemical, chemical, and mechanical stability), as well as the effective protection of lithium anode from aggressive soluble intermediates generated in cathode. Furthermore, it is demonstrated that the interaction among the components plays a pivotal role in modulating the Li-ion conducting mechanism in the as-prepared PS-QSE. Moreover, the pouch-type PS-QSE based Li-O₂ battery also shows wonderful flexibility, tolerating various deformations thanks to its integrated solid-state design. Furthermore, holes can be punched through the Li-O₂ battery, and it can even be cut into any desired shape, demonstrating exceptional safety. Thus, this type of battery has the potential to meet the demands of tailorability and comformability in flexible and wearable electronics.

Free-Standing Three-Dimensional CuCo2S4 Nanosheet Array with High Catalytic Activity as an Efficient Oxygen Electrode for Lithium-Oxygen Batteries

In this work, a novel free-standing CuCo₂S₄ nanosheet cathode (CuCo₂S₄@Ni) with high catalytic activity is fabricated for aprotic lithium-oxygen (Li-O₂) battery. This deliberately designed oxygen electrode is found to yield lower overpotential (0.82 V), improved specific capacity (9673 mA h g^-1 at 100 mA g^-1), and enhanced cycle life (164 cycles) as compared to the traditional carbonaceous electrode. The improved performance can be ascribed to the superb spinel structure of CuCo₂S₄, in which both Cu and Co exhibit more abundant redox properties, improving oxygen reduction reaction and oxygen evolution reaction kinetics effectively and boosting the electrochemical reactions. Furthermore, the well-designed architecture also plays a critical role in the improved performance. Encouraged by the excellent catalytic activity of this free-standing cathode, large-scale pouch-type Li-O₂ cell based on CuCo₂S₄@Ni cathode is fabricated and can work under different bending and twisting conditions. This free-standing electrode provides a new strategy for developing Li-O₂ batteries with excellent performance and flexible wearable devices.