Study Of Structures,Crystal Phase And Electrocatalytic Properties Of Cobalt-based Catalysts

In recent decades,because of the depletion of fossil fuels and the increasingly serious environmental problems,it is urgent to develop renewable,clean and sustainable energy to ensure the rapid and healthy development of the economy.The oxygen reduction reaction?ORR?and the oxygen evolution reaction?OER?play a major role in the complex redox reactions of these energy conversion/storage systems?including fuel cells,water-splitting and metal-air batteries?.However,due to the kinetically sluggish of ORR and OER,it is highly necessary to develop an effective bifunctional catalyst to promote the reaction processes and to enhance the catalytic stability.Transition-metal catalysts have recently attracted much attention thanks to their earth-abundant nature,low cost and environmentally friendliness.Among them,a large number of studies have shown that cobalt-based materials?including their hydroxide,oxide,and sulfide?have considerable catalytic properties,electrochemical stability and reversibility for both ORR and OER,which can be used as bifunctional electrocatalysts.Cobalt hydroxide can be prepared by simple method with stable electrochemical properties,but its ORR performance is relatively poor.The micro-morphology and chemical composition of the electrocatalysts can be changed by introducing the doping of nonmetallic elements,thus enhancing their electrocatalytic performance.In this paper,electrodeposition method is the main preparation method,with carbon cloth as substrate,cobalt hydroxide nanosheets can obtained by one-step electrodeposition.Cobalt hydroxide doped with different non-metallic elements is synthesized by the introduction of different nonmetallic elements in the electrolyte.The effects of nonmetallic elements on its morphology and properties were investigated and its electrocatalytic properties were further tested.Through the test,it is found that after electrochemical oxidation,the internal structure of Cl-doped Co?OH?₂ is destroyed with some defects introduced by the removal of chlorine atoms.The defective structure can obviously increase the electrochemical active surface area and enhance the conductivity of the catalyst,and thus provide more active sites for both ORR and OER reaction.Cl-doped Co?OH?₂ with defective structures exhibits much better electrocatalytic performance thus can be used as an effective bifunctional oxygen catalyst.By introducing sulfur ions into the electrolyte,the sulfur ions are distributed evenly in the catalyst,and formed cobalt sulfide.The subsequent heat treatment can improve the crystallization and enhance the conductivity of the catalyst,which can improve the bifunctional properties of the electrocatalysts,and also have good stability.This study also provides a new approach for in situ activating catalysts.