Construction Of Cobalt-based Phosphide/Sulfide Electrocatalytic Materials And Their Performance For Hydrogen Evolution Reaction

The rapid development of human society has led to an increasing demand for energy.In the context of the global greenhouse effect,it is urgent to require the use of clean energy to replace fossil fuel-based energy patterns.Hydrogen is considered to be an ideal energy carrier due to its high heating value,renewable and environmentally friendly characteristics.However,current hydrogen production mainly depends on steam methane reforming,and the released CO and/or CO₂ will again have an adverse impact on the environment.The electrocatalytic hydrogen evolution reaction（HER）provides an effective and clean method for large-scale hydrogen production.However,larger potentials and lower electrochemical energy conversion efficiency are the main obstacles to achieving this goal.Therefore,there is an urgent need to develop a high-efficiency HER electrocatalyst with low overpotential and abundant element content.Cobalt-based phosphide/sulfide electrocatalysts have been widely studied to replace precious metal electrocatalysts due to their diverse structures and high catalytic activity.However,there are still some challenges to fine-tune the phase,composition,structure,size/morphology,surface electronic structure and charge transport of the cobalt-based phosphide/sulfide to further improve its catalytic activity and stability,so that its catalytic performance still cannot meet people’s expectations.Based on this,a series of cobalt-based phosphide/sulfide electrode materials were constructed by using a novel two-dimensional layered cobalt hydroxide salt as a precursor through low-temperature phosphating or sulfidation treatment.systematically studying its phase,composition,microstructure,size/morphology,three-dimensional structure,surface electronic structure and charge transport,etc.,through the adjustment of composition,structure and surface characteristics,the optimization of the catalyst’s electrocatalytic active site,conductivity,surface charge transfer and electron transport is achieved,which greatly improves the electrocatalytic HER reaction of the cobalt-based phosphide/sulfide electrocatalyst activity and stability,in-depth reveal the catalyst composition?structure?performance structure-activity relationship,for the development of new high-efficiency cobalt-based electrocatalytic hydrogen evolution catalyst provides effective preparation methods and theoretical guidance.In the first part of this paper,we studied graphene oxide as the substrate and grown two-dimensional layered cobalt hydroxide salt（Co-LHSs）precursors on it in situ.The cobalt phosphide nanorod electrocatalyst（CoP-Co₂P/rGO）uniformly dispersed on the graphene substrate was constructed by low temperature phosphating,and the phase,composition,structure,size/morphology and surface properties of the obtained CoP-Co₂P/rGO nanorod electrocatalyst were studied by various characterization methods.The electrocatalytic HER performance of the CoP-Co₂P/rGO electrocatalyst was evaluated over the entire pH range.The effects of preparation conditions such as graphene compounding,nitrogen/-phosphorus doping,and cobalt phosphide on their electrocatalytic performance were investigated.The results show that due to the presence of rGO,the conductivity of CoP-Co₂P/rGO electrocatalyst is greatly improved,and the number of exposed active sites also increases.There is a strong synergy between graphene and CoP-Co₂P,which can induce enhanced electron transfer.As a result,its electrocatalytic HER activity is greatly enhanced.In the second part of this thesis,the study used a two-dimensional layered ytterbium-cobalt hydroxide salt（Yb-Co-LHSs@Yb-Co-TEOA）as a precursor for phosphating,and constructed an amorphous rare earth oxide（Yb₂O₃）hybrid in the form of nanorods cobalt phosphide electrocatalyst（Yb₂O₃-CoP-Co₂P）,The phase,composition,structure,size/morphology and surface characteristics of the obtained Yb₂O₃-CoP-Co₂P nanorod electrocatalyst were studied,the electrocatalytic HER performance of the Yb₂O₃-CoP-Co₂P electrocatalyst was evaluated,the effect of rare earth doping/composite control effect on its electrocatalytic performance was also investigated.The research results show that the amorphous rare earth Yb₂O₃hybridization can effectively control the CoP/Co₂P crystal phase,catalytic structure and morphology,and surface electron configuration,thereby greatly improving the electrocatalytic HER performance of the catalyst,thereby achieving a high Yb₂O₃-CoP-Co₂P electrocatalyst catalytic activity and strong stability,its overpotential in acidic media can be as low as 88 mV,and its overpotential in alkaline media can reach110 mV,and its stability is excellent.In the third part of this paper,we studied the use of highly conductive and easily functionalized carbon fiber cloth as the substrate for electrocatalyst growth,thioacetamide as the sulfur source,and triethanolamine as the carbon source.After hydrothermal vulcanization,an open structure was obtained.The boron-doped graphene quantum dot hybrid cobalt sulfide three-dimensional self-supporting monolithic electrode material（B-GQD@Co₃S₄/CC）was obtained,and the phase,composition,structure,the three-dimensional structure,size/morphology and surface characteristics were studied,the electrocatalytic HER performance of the B-GQD@Co₃S₄/CC electrocatalyst was evaluated,the effects of non-metallic elements N,S and B doping and carbon quantum dot recombination on their electrocatalytic performance were investigated.The results show that carbon quantum dot recombination and heteroatom doping can effectively regulate the electronic structure of the catalyst,thereby greatly improving its electrocatalytic HER performance.It shows excellent electrocatalytic HER activity in acidic media with a current density of10 mA cm^-2,the overpotential can be as low as 29 mV.