Fe7S8 coupled with VS4 heterogeneous interface engineering driven by FeV bimetallic MOFs: An efficient all-pH and durable hydrogen evolution.

Rational design and preparation of a multiphase electrocatalyst for hydrogen evolution reaction (HER) has become a hot research topic, while applicable and pH versatility of vanadium tetrasulfide (VS4) and heptairon octasulfide (Fe7S8) composites have rarely been reported. Here, the facile topological sulfide self-template sacrifice method using FeV bimetallic MOFs is designed to obtain Fe7S8 coupled with VS4 heterostructures, enhancing the electron precipitation in the catalysts and attracts electrons to migrate. According to DFT simulations, the electronic coupling at the atomic orbital level and the modulation of interfacial electrons among various interfaces play a crucial role in enhancing the intermediate state process of the hydrogen evolution reaction (HER) across the entire pH range, promoting the optimal d-band centroid value (εd). Reassuringly, the prepared 3D Fe7S8/VS4 electrodes possessed excellent performances of η10 = 53 mV, η10 = 135 mV and η10 = 38 mV in a conventional three-electrode configuration in a 1 M KOH, 1 M Na2SO4, and 0.5 M H2SO4, and the stabilized currents can all be maintained for 48 h. This innovative design of in situ heterostructured materials constructed from dual transition metal sulfides provides inspiring ideas for the preparation of all-pH catalysts.

The dual active sites reconstruction on gelatin in-situ derived 3D porous N-doped carbon for efficient and stable overall water splitting.

The exploration of bifunctional electrocatalysts with high activity, stability, and economy is of great significance in promoting the development of water splitting. Herein, a dual active sites heterostructure NiCoS/NC was designed to be derived in situ on 3D N-doped porous carbon (NC) using gelatin as a nitrogen and carbon source. The characterization of experiments suggests that nanoflower-like Ni2CoS4 (abbreviated as NiCoS) was randomly distributed on the NC substrate, and the sheet-like NC formed a highly open porous network structure resembling a honeycomb, which provided more accessible active sites for electrolyte ions. In addition, the special nanostructures of the catalyst materials help to promote the surface reconstruction to the real active substance NiOOH/CoOOH, and the double active sites synergistically reduce the overpotential of OER and improve its kinetics. DFT (Density-functional theory) calculations reveal the electronic coupling of NiCoS/NC in atomic orbitals, modulation of electrons by the heterointerface and N-doping, and synergistic effect of dual active sites improving the inherent catalytic activity. The NiCoS/NC composite electrocatalyst exhibited a 177 mV small OER overpotential and a 132 mV small HER overpotential with Faraday efficiencies as high as 96 % and 98 % at 10 mA cm-2 current density. In the two-electrode system, it also requires only an ultra-low voltage of 1.52 V to achieve a 10 mA cm-2 current density, and it shows excellent long-term water splitting stability. This provides a new idea for the development of transition metal-based bifunctional electrocatalysts.

Interface engineered hydrangea-like ZnCo2O4/NiCoGa-layered double hydroxide@polypyrrole core-shell heterostructure for high-performance hybrid supercapacitor.

Rationally constructing advanced battery-type electrodes with hierarchical core-shell heterostructure is essential for improving the energy density and cycling stability of hybrid supercapacitors. Herein, this work successfully constructs hydrangea-like ZnCo2O4/NiCoGa-layered double hydroxide@polypyrrole (denoted as ZCO/NCG-LDH@PPy) core-shell heterostructure. Specifically, the ZCO/NCG-LDH@PPy employs ZCO nanoneedles clusters with large open void space and rough surfaces as the core, and NCG-LDH@PPy composite as the shell, comprising hexagonal NCG-LDH nanosheets with rich active surface area, and conductive PPy films with different thicknesses. Meanwhile, density functional theory (DFT) calculations authenticate the charge redistribution at the heterointerfaces between ZCO and NCG-LDH phases. Benefiting from the abundant heterointerfaces and synergistic effect among different active components, the ZCO/NCG-LDH@PPy electrode acquires an extraordinary specific capacity of 381.4 mAh g-1 at 1 A g-1, along with excellent cycling stability (89.83% capacity retention) after 10,000 cycles at 20 A g-1. Furthermore, the prepared ZCO/NCG-LDH@PPy//AC hybrid supercapacitor (HSC) exhibits a remarkable energy density (81.9 Wh kg-1), an outstanding power density (17,003.7 W kg-1), and superior cycling performance (a capacitance retention of 88.41% and a coulombic efficiency of 93.97%) at the end of the 10,000th cycle. Finally, two ZCO/NCG-LDH@PPy//AC HSCs in series can light up a LED lamp for 15 min, indicating its excellent application prospects.

NiFe-layered double hydroxide/CoP2@MnP heterostructures of clustered flower nanowires on MXene-modified nickel foam for overall water-splitting.

Exploiting efficient and economical electrocatalysts is indispensable to promoting the sluggish kinetics of overall water-splitting. Herein, we designed a phosphate reaction and two-step hydrothermal method to construct a 3D porous clustered flower-like heterogeneous structure of NiFe-layered double hydroxide (NiFe) and CoP2@MnP (CMP) grown in-situ on MXene-modified nickel foam (NF) substrate (denoted as NiFe/CMP/MX), with favorable kinetics. Density functional theory calculations (DFT) demonstrate that the self-driven transfer of heterojunction charges causes electron redistribution of the catalyst, and optimizes the electron transfer rate of the active site and the d-band center near the Fermi level, thereby reducing the adsorption energy of H and O reaction intermediates (H*, OH*, OOH*). As expected, the combination of CMP and NiFe with naturally conductive MXene forms a strong chemical and electron synergistic effect, which enables the synthesized NiFe/CMP/MX heterogeneous structure exhibits good activity for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with a low overpotential of 200 mV and 126 mV at 10 mA cm-2, respectively. Furthermore, the overpotential of 1.58 V is enough to drive a current density of 10 mA cm-2 in a two-electrode configuration, which is better than noble metals (RuO2(+)//Pt/C(-)) (1.68 V).

Recent advances in cobalt-based catalysts for efficient electrochemical hydrogen evolution: a review.

Hydrogen (H2) is a new type of renewable energy that can meet people's growing energy needs and is environmentally friendly. In order to improve the industrial application prospects and electrochemical performance of hydrogen evolution catalysts, extensive research on transition metal materials has been carried out. Among the many catalytic materials, cobalt is an element with potential for the hydrogen evolution reaction (HER) due to its abundant reserves, low cost, and small energy barrier for H adsorption. This review classifies the latest research on cobalt-based catalysts according to the types of compound, including cobalt-based sulfides, phosphides, carbides, borides, oxides, etc., and summarizes the latest research progress of cobalt-based compound catalysts in acidic and alkaline media. Strategies to tune the properties of cobalt-based compound catalysts for high catalytic activity for HER are focused on, including structural engineering, defect engineering, and doping, etc. The advantages and limitations of each modified approach are reviewed. Not only that, but also the catalytic activity and advantages of the catalyst are evaluated by using density functional theory (DFT) calculation-related descriptors, activity evaluation parameters, etc. Finally, limitations and challenges of cobalt-based materials for HER are presented, as well as prospects for future research. This paper aims to understand the chemical and physical factors that affect cobalt-based catalysts, and to find directions for future research on cobalt-based catalysts.

Hierarchical CuCo2O4@CoS-Cu/Co-MOF core-shell nanoflower derived from copper/cobalt bimetallic metal-organic frameworks for supercapacitors.

Rational design of composite materials with unique core-shell nanoflower structures is an important strategy for improving the electrochemical properties of supercapacitors such as capacitance and cycle stability. Herein, a two-step electrodeposition technique is used to orderly synthesize CuCo2O4 and CoS on Ni foam coated with Cu/Co bimetal metal organic framework (Cu/Co-MOF) to fabricate a hierarchical core-shell nanoflower material (CuCo2O4@CoS-Cu/Co-MOF). This unique structure can increase the electrochemically active site of the composite, promoting the Faradaic redox reaction and enhancing its electrochemical properties. CuCo2O4@CoS-Cu/Co-MOF shows a prominent specific capacitance of 3150 F g-1 at 1 A g-1, marvelous rate performance of 81.82% (2577.3 F g-1 at 30 A g-1) and long cycle life (maintaining 96.74% after 10,000 cycles). What is more, the assembled CuCo2O4@CoS-Cu/Co-MOF//CNTs device has an energy density of 73.19 Wh kg-1 when the power density is 849.94 W kg-1. It has unexpected application prospects.