Construction Of Transition Metal Chalcogenide Based Heterogeneous Nanosheet Array Electrocatalysts And Its Electrocatalytic Performance

With the increasing energy crisis and environmental pollution,it is extremely urgent to seek a new type of clean and environmental-friendly energy.Hydrogen is considered as an ideal energy with green,zero carbon,and high energy density,which has received widespread attentions.Electrolytic water splitting is currently one of the most safe,economical,and efficient ways to produce high-purity hydrogen,consisting of two half reactions,namely,oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）.The overall energy efficiency of water electrolysis is severely restricted by the sluggish dynamic of the OER process,as it suffers from four proton-coupled electron transfers,which requires a large overpotential to overcome equilibrium potential of 1.23V.At present,the catalyst is Ir-based noble metal,Ir-based noble metal is most effective commercial OER electrocatalysts due to their high catalytic activity and good stability.However,their scarcity and high cost seriously limit the future large-scale commercial application.Therefore,it is extremely important to construct green,efficient,inexpensive,and mass produce non-noble metal catalysts.Transition metal catalyst with easily regulated electronic structures and unique physical properties can effectively improve the catalytic activity.Heterogeneous interface engineering can optimize the coordination of electronic structures and promote catalytic activity.Thus,simple and easy synthesis methods are adopted to prepare three efficient and stable three-dimensional self-supporting transition metal chalcogenide based heterogeneous nanosheet arrays as electrocatalysts.The mechanisms of synergistic effects of interfacial heterostructures were explained by systematically studying the correlation between microstructure and electrocatalytic activity.The main research content of this paper are as follows:1.Three-dimensional（3D）self-supporting Ni₃S₂/Ni Fe O_xH_y nanosheet arrays with crystalline amorphous heterostructures were prepared by one-step hydrothermal method.In alkaline electrolyte,the Ni₃S₂/Ni Fe O_xH_y catalyst exhibits significant OER activity.To deliver a current density of 100 m A cm^-2,the OER overpotential requires only 243 m V with a Tafel slop of 79.8 m V dec^-1.In addition,as a dual functional electrocatalyst,under industrial conditions（85°C,6M KOH）,at a current density of10 m A cm^-2,only 1.32 V is required to drive the total water decomposition reaction.This Ni₃S₂/Ni Fe O_xH_y heterogeneous nanosheet array structure provides a new design idea for the preparation of high-efficiency and low-cost industrial electrocatalysts.2.A 3D heterostructure electrocatalyst consisting of crystalline Se and amorphous Ni Fe-based（oxy）hydroxide nanosheet arrays in situ grown on the surface of Ni foam via a one-step chemical reaction at ambient temperature.The Se@Ni Fe OOH catalyst requires low overpotentials of 265 m V for OER at the current density of 100 m A cm^-2,together with a low Tafel slope of 49.6 m V dec^-1 in an alkaline electrolyte,which is superior than Ir O₂.In addition,the Se@Ni Fe OOH catalyst shows excellent long-term stability over 150 h at a current density of 100 m A cm^-2.In addition to the synergistic effect,the output OER performance of Se@Ni Fe OOH is also attributed to the 3D heterostructure structure composed of 2-dimensional nanosheets,crystalline nanoparticles and hydrophilic features for fast transportation of electrolyte and release of bubbles,which offer a large specific surface area with porous pores to enrich active sites,and improve electrical conductivity to facilitate the mass transport and diffusion kinetics.This work provides a new idea and strategy for efficient catalysts in the field energy storage and conversion.3.A 3D self-supporting electrocatalyst of Co₉S₈/Ni（OH）₂ hierarchical nanoflake arrays on the surface of the Ni foam were synthesized by one-step hydrothermal method.Due to the unique hierarchical flower-like structure,the Co₉S₈/Ni（OH）₂ provides increased specific surface area with available catalytic active sites and improves electron transfer rate.The Co₉S₈/Ni（OH）₂ catalyst exhibits excellent OER performance,requiring only 307 m V to drive a current density of 300 m A cm^-2.In addition,with the irradiation of a xenon lamp,the overpotential decreases to 277 m V at current density of300 m A cm^-2.This work provides a new guidance for the design and construction of key catalytic materials in the electrochemistry and photoelectrochemistry.