Preparation And Investigation Of Cobalt-based Catalyst For Electrocatalytic Oxygen Evolution Reaction

Increasing energy consumption and the challenge of global warming have promoted the upsurge of clean energy research and development.Hydrogen energy that has the advantages of zero carbon emissions,high conversion efficiency,and recyclability,has been considered as acandidate for replacing fossil fuels.Water electrolysis is a clean production process that can decompose water into O₂and H₂by applying a certain voltage.It includes hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.However,OER is a four-electron coupling reaction with high reaction overpotential and low energy conversion efficiency,which is a bottleneck for the upgrade of hydrogen production technology by water electrolysis.The design of high-performance anode catalysts is an important step to achieve high-efficiency water splitting.Noble metal iridium（Ir）-and ruthenium（Ru）-based materials are often used as OER catalysts,but factors such as price and reserves limit their technical promotion.Transition metal cobalt-based materials have aroused great research interest because of their abundant reserves and low prices on the earth.The cobalt element undergoes redox transformation during the OER process,that is Co²⁺/Co³⁺and Co³⁺/Co⁴⁺.This process requires a large amount of conversion energy,and reducing the conversion energy can improve the catalytic activity.Therefore,in this dissertation,phosphorus-doped spinel Cu Co₂O₄oxides have been prepared by combining solvothermal and annealing methods,and amorphous Co Fe,Co Fe V,Co Fe V-C hydroxide catalysts have been synthesized by one-step reduction method,for the investigation of their electrocatalytic OER performance.The main content includes the following aspects:1.A series of Cu Co₂O₄catalysts with partial amorphous phases with different phosphorus contents were obtained by first solvothermal reaction in isopropanol solvent and then annealing treatment.XPS and TEM element mapping distribution measurements confirmed the successful synthesis of phosphorus-doped Cu Co₂O₄.The effect of phosphorus content on the performance of Cu Co₂O₄electrocatalytic OER was explored.The electrochemical test results show that the electrocatalytic OER performance of all phosphorus-doped samples has been greatly improved.With the increase of phosphorus doping amount,the catalytic performance of Cu Co₂O₄is improved.However,when the optimal doping amount is reached,the catalyst performance decreases with the increase of doping amount.Cu Co₂O₄-0.5(CCP_0.5)is the catalyst with the best phosphorus doping content,in which the phosphorus content is 16.75%.It has a low overpotential of 290m V,a Tafel slope of 68 m V dec^-1,and stability of up to 19 h.The characterization results can also show that the synergistic effect of the amorphous phase and the elements caused by phosphorus doping can help improve the conductivity of Cu Co₂O₄and the electrocatalytic OER activity.2.Amorphous Co Fe,Co Fe V,and Co Fe V-C hydroxide catalysts were prepared by adopting sodium borohydride one-step reduction strategy in aqueous solution.Using XRD,SEM,TEM,IR,XPS,and TEM element mapping distribution tests to analyze the structure and composition of the amorphous sample,it was confirmed that the synthesized catalyst was an amorphous multi-metal hydroxide.The effect of introducing vanadium on Co Fe and compounding it on a self-made carbon shell on its electrocatalytic OER performance was explored.The results show that the introduction of vanadium to form the ternary metal hydroxide Co Fe V can promote the synergistic effect of multiple elements and effectively improve the OER performance of Co Fe.The combination with the self-made carbon shell to increase the specific surface area of the catalyst is beneficial to the exposure of active sites and promotes the OER performance.Co Fe V-C is the best catalyst under the combined action of two influencing factors.It has a low overpotential of 280 m V,a Tafel slope of 48.6 m V dec^-1,and electrochemical stability of up to 20 h.It is a promising OER electrocatalyst.