Phase Engineering Of Electrodeposited Cobalt And Its Application In Hydrogen Evolution

With the rapid development of renewable energy,hydrogen energy has attracted extensive attention because of its high energy density,wide sources and green environmental protection.Electrolysis of water for hydrogen production is the main way to produce high-purity hydrogen in industry.However,the high price of commercial precious metal catalysts and the low abundance of earth crust make it difficult to solve the problem of high cost of water electrolysis,which limits its large-scale use.Therefore,the development of high activity and low cost non-noble metal catalysts has broad application prospects.With the development of crystalline phase engineering of nanomaterials,the use of metastable phases to construct metal heterogeneous structures has become an effective way to design high performance catalysts.In catalysts,the metastable phase usually has higher catalytic activity,and the polymorphic interface formed by the metastable phase and the stable phase has a synergistic effect,which often has better catalytic activity.In this paper,a heterogeneous structure catalyst containing metastable phase was prepared by cathode plasma electrodeposition,and the structure-activity relationship between the structure and catalytic performance was studied.Then,a cobalt-based hydrogen evolution catalyst with high activity and stability was prepared by adjusting the electrolyte composition.It is found that the formation of Co_fcc in the deposition film is related to cathodic hydrogen evolution during the electrodeposition of cobalt sulfate electrolyte.The presence of sodium citrate in electrolyte can increase the deposition potential of cobalt ions.During electrodeposition of cobalt salt,anions significantly affect its deposition characteristics.Cobalt sulfate electrolyte was used to explore the formation mechanism of heterogeneous structure,and Co_hcp/Co_fcc heterogeneous structure material was prepared.After stability test,metastable Co_hcp in the film layer would be transformed.The hydrogen evolution performance of cobalt-based materials is poor.By adding sodium molybdate into cobalt-based electrolyte and adjusting the concentration of sodium citrate,the microstructure and composition of the film layer are optimized.A cobalt-based hydrogen evolution catalyst with heterogeneous structure is successfully prepared.Metastable phase Co_hcp has more excellent catalytic activity of hydrogen evolution,but its thermodynamic instability leads to its easy transformation.Mo has good hydrogen adsorption energy and can store active hydrogen,which can effectively avoid the conversion of Co_hcpinto hydrogen-rich phase Co_fcc after forming cobalt-molybdenum alloy.After the optimization of the molybdenum content in the catalyst,the overpotential of the heterogeneous structure cobalt catalyst for hydrogen evolution decreased from 64 m V to 42 m V.After the stability test of 12 h,the overpotential basically remained unchanged,showing excellent catalytic activity and stability of hydrogen evolution.