| The energy shortages and environmental degradation caused by excessive exploitation of fossil fuels have become two major issues of global attention.The development of clean,pollution-free and renewable energy sources to replace fossil fuels has become the consensus of countries around the world to achieve sustainable development.Hydrogen energy is considered as one of the most promising alternative energy sources because of its high energy density and zero carbon dioxide emission.Developing hydrogen energy is crucial to achieving the goal of carbon neutrality.Hydrogen production by water splitting is the most ideal hydrogen production technology because only hydrogen and oxygen are produced in the reaction process.However,oxygen evolution reaction（OER）in anodic water splitting involves a complex four-electron transfer process,and the slow reaction kinetics limits the speed development of water splitting technology.Therefore,the design and preparation of highly efficient OER catalyst is of great significance to promote the development of large-scale hydrogen production technology.At present,noble metals such as Ir O2 and Ru O2 are still the most ideal OER catalysts,but their scarce reserves,expensive cost and poor stability seriously restrict their large-scale applications.Transition metal sulfides（TMSs）have attracted much attention because of their low cost,good conductivity and tunable valence state.Although many efforts have been made to develop low-cost,efficient and stable transition metal sulfides to replace noble metal-based materials,their OER catalytic activity and stability still need to be further improved.In this paper,two transition metal sulfide composites were prepared using layered double hydroxides（LDHs）as the precursors by adopting multiple optimization strategies,which included（Ni,Fe）S2/Co S2/C/r GO based on Interlayer confinement effect of layered double hydroxides,and Fe-NiCo S2/C/r GO composite derived from LDHs/Prussian blue analogue（PBA）.Ultimately,the catalytic performance and stability of OER were greatly improved.The main contents of the paper are summarized as follows.（1）Preparation and electrocatalytic OER performance of（Ni,Fe）S2/Co S2/C/r GO.The product（（Ni,Fe）S2/Co S2/C/r GO）was prepared with ultra-small Co S2nanoparticles loaded on（Ni,Fe）S2 composite based on reduced graphene oxide（r GO）substrate.The composite was obtained by sulfurizing Mg Ni Fe-[Co EDTA]2--LDH/GO precursor of[Co EDTA]2-anionic intercalation and acid etching.The Co S2 in this electrocatalyst was extremely small in size and uniformly distributed（2.27±0.57 nm）,providing a rich site of activity,while the presence of（Ni,Fe）S2/Co S2 heterostructure optimized the electronic structure of the composite material,thereby improving the OER electrocatalytic activity.Under alkaline conditions,when the current density was 10 and 100m A·cm-2,the overpotential of（Ni,Fe）S2/Co S2/C/r GO was only 225 m V and282 m V,respectively,with a low Tafel slope of 50.9 m V·dec-1 and a good long-term stability of 24 h.（2）Preparation and electrocatalytic OER performance of Fe-NiCo S2/C/r GOFe-NiCo S2/C/r GO composite with hierarchical porous structure was derived from curing and acid etching three-dimensional NiCoFe PBA@NiCoAl-LDH/GO which was obtained from uniformly distributed NiCoAl-LDH nanosheet arrays on graphene oxide（GO）by[Fe（CN）6]3-secondary hydrothermal treatment.The addition of PBA introduced Fe doping,which adjusted the electronic structure of the material and greatly optimized the active center of the material,thereby significantly improved the OER performance.In addition,Fe-NiCo S2/C/r GO composite with the best alkaline OER catalytic performance were determined by adjusting the Ni/Co ratio.When the current density was 10 and 100 m A·cm-2,Fe-NiCo S2/C/r GO-2（Ni/Co=1:1）had an overpotential of only 233 and 283 m V,and the slope of Tafel was 47.1m V·dec-1.Notably,Fe-NiCo S2/C/r GO-2 had a current retention rate of up to95.2%after 24 h stability testing at the current density of 10 m A·cm-2. |
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