Nickel sulfide wrapped by porous cobalt molybdate nanosheet arrays grown on Ni foam for oxygen evolution reaction and supercapacitor

Hierarchical core-shelled CoMo layered double hydroxide@CuCo2S4 nanowire arrays/nickel foam for advanced hybrid supercapacitors

The development of core-shelled heterostructures with the unique morphology can improve the electrochemical properties of hybrid supercapacitors (HSC). Here, CuCo2S4 nanowire arrays (NWAs) are vertically grown on nickel foam (NF) utilizing hydrothermal synthesis. Then, CoMo-LDH nanosheets are uniformly deposited on the CuCo2S4 NWAs by electrodeposition to obtain the CoMo-LDH@CuCo2S4 NWAs/NF electrode. Due to the superior conductivity of CuCo2S4 (core) and good redox activity of CoMo-LDH (shell), the electrode shows excellent electrochemical properties. The electrode's specific capacity is 1271.4 C g-1 at 1 A g-1, and after 10, 000 cycles, its capacity retention ratio is 92.2 % at 10 A g-1. At a power density of 983.9 W kg-1, the CoMo-LDH@CuCo2S4 NWAs/NF//AC/NF device has an energy density of 52.2 Wh kg-1. This indicates that CoMo-LDH@CuCo2S4/NF has a great potential for supercapacitors.

A Review of Transition Metal Boride, Carbide, Pnictide, and Chalcogenide Water Oxidation Electrocatalysts

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of "catalytically active sites/species/phases" in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

Coordination compound-derived Fe4N/Fe3N/Fe/CNT for efficient electrocatalytic oxygen evolution: a facile one-step synthesis in the absence of extra nitrogen source

By annealing an Fe(III)-coordination compound (Fe-CC), [FeCl₃(Hbta)₂] (Hbta = benzotriazole) in the presence of a carbon nanotube precursor (PCNT) template, an Fe₄N/Fe₃N/Fe/CNT heterostructure was successfully synthesized without an extra nitrogen source. The decomposition of the Hbta in Fe-CC under high-temperature annealing can produce carbon sheets and reduced graphene oxide (rGO), and the presence of CNTs can alleviate the stacking of thein situ-generated carbon materials. Meanwhile, iron nitride nanoparticles (NPs) can be anchored on the carbon sheets, and the anchoring effect efficiently prevents the agglomeration of NPs and increases the amount of active catalytic sites for the oxygen evolution reaction (OER). Fe₄N/Fe₃N/Fe/CNT shows an excellent OER activity with a Tafel slope of 63 mV dec^-1as well as overpotentials of 121 (η₁₀) and 275 mV (η₁₀₀) at 10 and 100 mA cm^-2, respectively - far exceeding commercial RuO₂and other catalysts. Density functional theory calculations show that the excellent OER performance of Fe₄N/Fe₃N/Fe/CNT is associated with the Fe₄N/Fe₃N heterojunction, which can improve the electron conductivity and boost the electron transfer from N to Fe. The Fe₄N/Fe₃N/Fe/CNT catalyst exhibits long-term OER activity during 100 h of electrolysis at 20 mA cm^-2. This is related to the dual coatings of thein situ-generated thin carbon shell and few-layered rGO on the surface of the iron nitride NPs, which can protect the fast leaching of iron nitride during the OER process. Furthermore, the effects of the annealing temperature, the PCNT template and the heating rate on the calcined products were investigated.

Coordination Polymer-Derived Fe3N Nanoparticles for Efficient Electrocatalytic Oxygen Evolution

Based on a coordination polymer, FeCl₂(4,4'-bpy) (4,4'-bpy = 4,4'-bipyridine) and the carbon nanotube (CNT)/NaCl dual template, Fe₃N nanoparticles (NPs) were synthesized via chemical thermolysis in the absence of an extra nitrogen source. The decomposition of 4,4'-bpy under high temperature produces thin carbon coating for Fe₃N NPs. Also, the CNT template anchors the Fe₃N NPs to avoid aggregation. The sample (denoted as Fe₃N-C N) exhibits excellent electrocatalytic oxygen evolution reaction (OER) behavior even with a small molar ratio of Fe₃N (Fe: 4.9 at. %), which can deliver a current density of 10 mA cm^-2 at an overpotential of 218 mV with a Tafel slope of 84 mV dec^-1 and long-term OER activity during 60 h electrolysis at 20 mA cm^-2. Furthermore, the sample after 20 h electrolysis, denoted as Post-Fe₃N-C N (20 h), displays enhanced OER activity with a smaller Tafel slope of 41 mV dec^-1 and overpotentials of 195 and 327 mV at 10 and 100 mA cm^-2, respectively, which is mainly due to the partial transformation of Fe₃N into FeOOH. The OER mechanism is investigated by density functional theory calculations, and it is found that the surface partial oxidation of Fe₃N leads to the effective OER electrolysis, which changes the electron density of the superficial atoms and induces the moderate adsorption for the intermediates.

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.

K-doped FeOOH/Fe3O4 nanoparticles grown on a stainless steel substrate with superior and increasing specific capacity

K-doped FeOOH/Fe₃O₄ nanoparticles grown on stainless steel demonstrated a superior specific capacity of 396 mA h g⁻¹ at 1 A g⁻¹ with an increasing capacity during charge–discharge cycles.