Controllable Construction And Oxygen Evolution Performance Of Multiphase Cobalt Ang Nickel Phosphide Electrocatalysts

With the continuous development of modern society,the increasing growth of population has brought about a surge in the demand for traditional fossil fuels.As a result,a series of problems such as environmental pollution and energy shortage have become increasingly apparent.Therefore,it is urgent to develop environmentally friendly,efficient and sustainable new energies to meet the huge energy demand.Hydrogen energy is considered as the most ideal secondary energy source for breaking away from excessive dependence on fossil fuels due to its advantages cleanliness,high energy density,ease of storage and transportation,and renewable characteristics.As we all know,steam reforming technology is the main process of H₂production at present,but its production and preparation process releasing large amounts of CO₂,which seriously violates the original intention of environmental protection and sustainable development,so it is a top priority of environmentally friendly energy preparation and transformation technology.As a carbon-free hydrogen production method,water electrolysis technology has been paid more and more attention.Then,the development of OER electrocatalyst with high catalytic activity,low cost and universality is the key to improve the efficiency of hydrogen electrolysis of aquatic products.In this paper,multiphase cobalt-and nickel-based phosphide electrocatalysts were successfully prepared for OER performance,and the structure,composition,morphology,size and surface chemical state and electron transport of the electrocatalysts were systematically characterized with a variety of characterization methods.The electrocatalytic activity and long-term stability of the electrocatalysts were further improved by introducing heterojunction structure,modulating electrocatalyst surface and combining with rare earth species.The research may provide a theoretical guidance for the development of highly efficient cobalt-and nickel-based OER electrocatalysts.In the first part of the thesis,the bimetallic oxide nanosheet precursor of CoMoO₄ was successfully grown on carbon cloth via a hydrothermal method.Subsequently,the CoMoO₄precursor was treated under a high-temperature phosphating process using sodium hypophosphate as a phosphorus source to achieve MoP/CoMoP₂OER electrocatalyst.The microstructure,crystalline phase,size and morphology,surface chemical state,and electronic configuration were systematically characterized by means of techniques,and the OER performance of the electrocatalyst was evaluated through electrochemical techniques.The results shows that the overpotential of MoP/CoMoP₂electrocatalyst only requires 306 m V when the current density attains 10 m A.cm^-2,showing a relatively superior performance for OER.The existence of heterojunction in MoP/CoMoP₂electrocatalyst may result in the strong synergistic effect existing in bimetallic phosphide compounds,which leads to the strong electronic interaction between MoP and CoMoP₂to adjust its surface electronic structure for promoting the OER performance.In the second part of the thesis,based on the previous work,the rare earth compound of CePO₄was introduced into MoP/CoMoP₂electrocatalyst to further improve its OER performance.CePO₄/MoP/CoMoP₂/CC electrocatalyst was prepared by depositing a thin layer of Ce（OH）₃on pre-obtained bimetallic oxide nanosheet precursor of CoMoO₄via a electrodeposition process,following the similar phosphating process,The microstructure,composition,morphology,size,surface chemical state and electron transportation and active species of the electrocatalyst were systematically studied by coupling multiple characterization techniques.Interestingly,when it was tested in 1.0 M KOH electrolyte for OER performance,the surface reconstruction of the electrocatalyst was occurred.Thus,the CePO₄/MoP/CoMoP₂/CC electrocatalyst owns a superior OER performance,showing a overpotential of 91 m V much lower than that of MoP/CoMoP₂/CC electrocatalyst,and possesses a much better stability well.The superiority of the electrocatalyst for OER performance may be attributed to the existence of three phases of CePO₄,MoP and CoMoP₂in the electrocatalyst,which may induce strong synergistic effect to optimize the surface electronic structure,accelerate the charge transfer,increase the catalyst active site,thus greatly enhancing the OER performance.In the third part of the thesis,the bimetallic oxide precursor of NiMoO₄ nanoarray was prepared on carbon cloth via a hydrothermal method.Then,the rare earth Cespecies was deposited on the surface of NiMoO₄precursor through a electrodeposition process following a high-temperature phosphating process using sodium hypophosphate as a phosphorus source to obtain the three phased CePO₄/MoP/MoNiP/CC electrocatalyst,The composition,microstructure,morphology,size,surface chemical state and electron transportation,and active species of the electrocatalyst were systematically characterized by a variety of techniques.CePO₄/MoP/MoNiP/CC electrocatalyst showing a overpotential of 47m V much lower than that of MoP/MoNiP/CC electrocatalyst,Compared with the MoP/MoNiP/CC electrocatalyst,CePO₄/MoP/MoNiP/CC electrocatalyst possesses much abundant active sites,superior electron transfer ability and reactive kinetic performance.As a fine cocatalyst,CePO₄may further accelerate the proton coupling and electron transfer process during the OER process and promote the formation and transformation of oxygen-containing intermediates.thus greatly enhancing the OER performance of the CePO₄/MoP/MoNiP/CC electrocatalyst.