Cobalt-Based MOF Derived Metal Sulfides Supported Rhenium Disulfide Composite For Overall Water Splitting

The hydrogen production by water electrolysis is an environmentally friendly and sustainable energy conversion technology,which can effectively address the problems of global energy shortage.The process of water electrolysis involves two reactions,namely the cathodic hydrogen evolution reaction(HER)and the anodic oxygen evolution reaction(OER).However,the OER process,which is a four-electron reaction,is slow in kinetics,and significantly hinders the overall efficiency of the water electrolysis process.Therefore,the development of both efficient HER and OER catalysts is crucial for improving the energy conversion efficiency of overall water splitting.This study aims to design the metal-organic frameworks(MOFs)derived cobalt sulfide as a high OER activity component,and combine with the layered rhenium disulfide(ReS2)with the potential application of HER.The composite is loaded on the carbon papers.Meanwhile,the morphology and electronic structure of the ReS2-based catalyst are adjusted and the the cost of catalysts is reduced.Finally,the catalysts with a highly active for water splitting is constructed following the three researches.1)The controllable morphology and composition of catalysts are crucial to improving the electrocatalytic activity of oxygen evolution reaction(OER).Herein,we construct a bimetallic composite material by vertically aligned layered ReS2 on Prussian blue-derived hollow Co9S8 nanocubes(Co9S8@ReS2)by sulfidation and hydrothermal methods.The PBA nanocubes act as the precursor to prepare the hollow Co9S8@ReS2.The Co9S8@ReS2 composite material have excellent catalytic OER properties,such as high catalytic stability and fast charge transfer kinetics.Co9S8@ReS2 requires only 288 mV of overpotential to drive a current density of 10 mA cm-2 in 1 M KOH with the Tafel slope of 73.3 mV dec-1 and demonstrates remarkable catalytic stability after CA tests for 10 hours,which can be attributed to the synergistic effect of ReS2 coupled Co9S8 nanocube and the core-shell structure to expose more active sites.2)The development of catalytic HER activity is necessary due to their poor electronic conductivity.To address this issue,we introduced a highly conductive substrate(carbon fiber paper)to the CoS2@ReS2 composite material,which can work as a self-supported electrode.Co-MOF was first deposited on carbon fiber paper surface with further sulfidation treatment,and then ReS2 were grown on CoS2 through a hydrothermal reaction.The resulting CoS2@ReS2/CFP composites exhibit excellent HER and OER activity in alkaline electrolyte.The electronic conductivity of catalysts is increased by introducing carbon fiber papers,which can effectively prevent the restacked ReS2 layers and expose abundant active sites.CoS2@ReS2/CFP only requires an overpotential of 85 mV to drive to drive a current density of 10 mA cm-2 during HER process with a low Tafel slope of 144 mV dec-1 and good electrochemical stability after CA test for 10 h.For OER,it only requirs an overpotential of 260 mV at 10 mA cm-2 with the lowest Tafel slope(63.8 mV dec-1)and excellent catalytic stability.3)To further improve the intrinsic catalytic activity of composites,the electronic structure of ReS2 is modified by doping transition metal Mo elements.The cobalt sulfides are prepared by depositing Co-MOF on carbon fiber papers with further sulfidation,and then Mo doped ReS2 nanosheets are grown on CoS2 surface.The obtained Mo-ReS2/CoS2/CFP composites show excellent HER and OER activity in alkaline electrolyte.The Mo-doping not only induces the generation of unsaturated electrons and improves the electronic conductivity to promote fast charge transfer,but also activates the inert basal plane of ReS2 to introduce more active sites.Mo-ReS2/CoS2/CFP exhibits excellent electrocatalytic activity for HER,achieving a benchmark current density of 10 mA cm-2 with an overpotential of 78 mV,the lowest Tafel slope(130.3 mV dec-1),and good electrochemical stability.For OER,only 249 mV of overpotential is required to reach a current density of 10 mA cm-2,with a Tafel slope of 83.6 mV dec-1 and excellent electrochemical stability.By optimizing the conductive matrix and the element doping system,this work provides a feasible strategy to prepare the highly active catalysts for overall water splitting.