Surface Interface/Electronic Structure Regulation Of Low-Dimensional Transition Metal-Based Phosphides And Their Electrolytic Water Performance

Hydrogen energy can replace traditional fossil energy to solve the environmental pollution problem in the process of fossil energy use.Electrolysis of water to produce hydrogen is promising to be an effective means of large-scale hydrogen production.However,the slow reaction kinetics of electrodes in practice can lead to the actual voltage of water decomposition being much larger than the theoretical value.The use of electrocatalysts in the electrolysis of water can directly and effectively reduce the energy consumption of electrolytic water.In recent years,the development of economical and high performance electrocatalysts for water decomposition has become a hot research topic.Transition metal phosphides are a class of electrolytic water catalysts that have received much attention in recent years due to the advantages of abundant sources,low cost and good electrical conductivity properties.However,their electrocatalytic water decomposition performance still needs to be improved.In this paper,the surface interfaces and electronic structures of two typical transition metal phosphides electrocatalysts（Cu₃P and CoP）were effectively regulated through the strategies of low-dimensional structure design,porosity,heterogeneous atomic doping and heterogeneous interface construction,and then their resulted electrocatalytic water decomposition performance（including hydrogen precipitation,oxygen precipitation and total water decomposition）was significantly improved.Based on the experimental results,the electrocatalytic mechanism was further investigated in depth by combining electrochemical characterization and theoretical calculations.The details of the study are as follows:（1）Co-doped Cu₃P porous nanosheet arrays were controllably prepared on nickel foam substrates by hydrothermal combined with low-temperature phosphorylation technique.The nanosheet arrays showed good activity and stability for hydrogen evolution reaction（HER）under alkaline conditions,requiring only a low overpotential of 99 mV to reach a current density of 10 mA cm^-2 and 272 mV to reach the same overpotential for oxygen evolution reaction（OER）.The driving voltage of the nanosheet array was 1.66 V at a current density of 10 mA cm^-2 when it was applied to a two-electrode system for overall water splitting,implying that it also had great potential for overall water splitting.The excellent performance of the porous nanosheet array came from the synergistic effect of its unique two-dimensional mesoporous structure and Co doping,which not only provided a large electrochemically active surface and fast electrocatalytic reaction kinetics,but also weakened the binding strength of the electrode surface to the electrocatalytic reaction intermediates.（2）A Mn-doped CoP/Ni（PO₃）₂ heterostructure array electrocatalyst was designed and synthesized,which consisted of highly dispersed Ni（PO₃）₂ nanoclusters tightly wrapped around an array of Mn-doped CoP nanowires.Electrocatalytic performance tests showed that the heterostructured array exhibited outstanding electrocatalytic performance for both HER and OER,requiring only overpotentials of 116 and 245 mV to drive a current of 10 mA cm^-2,respectively.In particular,when the heterostructured array was used as both cathode and anode in a overall water splitting system,only a low voltage of 1.529 V was required to drive a current of 10 mA cm^-2.The first-principles calculations coincided with the experimental results,further elucidating the electrocatalytic mechanism.On the one hand,the effective doping of Mn atoms could optimize the surface electronic structure of CoP and promote its intrinsic activity.On the other hand,the compact and rich heterogeneous interface between Ni（PO₃）₂ and CoP not only exposed more active sites but also promoted the effective adsorption of intermediate reactants on the catalyst surface.