Synthesis,Surface Modification Of Co-based Catalytic Nanomaterials And Their Electrocatalytic Performance

In recent years,the increasing shortage of energy and the serious threats to the ecological environment caused by fossil energy have attracted great attention from all over the world.Hydrogen production from electrolyzed water is an effective way to solve the energy crisis nowadays due to its clean,efficient and simple operation.Traditional precious metal materials are still the main catalysts to produce hydrogen from electrolyzed water.However,the scarcity and high cost of these precious metals have greatly limited their large-scale practical application.Therefore,it is of great urgancy to develop a new type of oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）electrocatalysts with excellent performance and low cost.Motivated by the outstanding OER activity,we prepared cobalt-based nanomaterials by adjusting the synthetic methods and reaction conditions.And these catalysts manifested excellent catalytic performance and stability toward the oxygen evolution reaction（OER）and hydrogen evolution reactions（HER）.The main work of this paper is as follows:（1）The precursor of Ni-Co bimetallic hydroxide doped with N,P,F was synthesized by a hydrothermal method and then calcined in NH₃ atmosphere to obtain dual-nitridation of PF/Ni_1.5Co_1.5N nanocrystalline catalyst.As a model reaction,the catalytic performance of the catalyst towards the OER was investigated in this study.The results show that the catalyst has a large specific surface area due to its one-dimensional nanostructure.The surface hetero-atom doping and dual-nitridation all provide more active surface sites for the catalyst.The synergistic coupling effect of transition metal and heteroatom is beneficial to improve the conductivity of the material and increase the electronic transport,endow the excellent catalytic performance for the PF/Ni_1.5Co_1.5N nanocatalyst towards the OER.（2）The precursors of CoM（M=Co,Ni,Zn）MOFs precursors were synthesized by an ultrasonic assisted hydrothermal method.A 3D flower-like of CoMO,Co MN,and Co MP were obtained by calcining at high temperature in different atmospheres.Interestingly,CoMS hollow spheres were prepared by adding thioacetamide in the hydrothermal process.The catalytic properties of three-dimensional flower-like materials were studied in alkaline electrolyte by using OER and HER as model reactions.The results show that the three-dimensional structure of the catalyst has a large specific surface area.And more active sites can be exposed after the oxidation,nitridation,phosphating,and sulfuration.In addition,the hollow sphere structure of CoMS can accelerate the electronic transport rates,promote the OER catalytic performance.The P atom in the phosphide,which has higher electronegativity,makes the electron more easily dissociate from the metal surface and boost the HER catalytic performance.（3）Based on the the previous chapter,Bi/Co MOFs precursor can be also obtained by the ultrasonic assisted hydrothermal method.After calcination at high temperature,a flower-like Bi/CoP electrocatalyst with complete structure was prepared in this work.Meanwhile,incorporation of Bi into CoP has an important effect on the morphology,surface element content,valence state,and HER catalytic performance in alkaline and acidic electrolytes.As the doping amount of Bi is 7%,there is a strong synergistic catalytic effect between Bi and CoP,which can enhance the electronic transfer and boost the electron transfer efficiency in alkaline solution.Notably,7%Bi doped Co P hybrid manifests excellent HER catalytic activity in alkaline solution,and 3%Bi doped CoP catalyst exhibits excellent HER catalytic activity in acid medium.The formation of Bi-doped CoP is the most stable in acidic environment,but when the doping amount of Bi increases,the CoP structure is easily destroyed in acidic environment.