Design Of Interfacially Coupled And Doped Cobalt-based Catalysts And Their Electrocatalytic Hydrogen Evolution Performance

Electrocatalytic water splitting for hydrogen production is a potential hydrogen production technology,which can meet the future energy conversion demands.Hydrogen evolution reaction(HER)is one of the half reactions of water splitting,which involves two-electron transfer processes.In order to promote the kinetics of HER,highly efficient electrocatalysts are usually used to lower down the energy barrier.Cobalt-based compound materials with low cost,high efficiency and abundant reserves show excellent electrocatalytic HER performance.To accelerate the alkaline HER kinetics,interface engineering represents one of the effective approaches to enhance the HER activity in alkaline media.The abundant interfaces are experimentally and theoretically believed to reduce the energy barrier for water dissociation and optimize the hydrogen binding energy,thereby significantly facilitating the HER pathway.In addition,heteroatom doping can change the electronic structure and coordination environment around the active site to optimize the adsorption free energy of the intermediate,thus improving the electron transport capacity and catalytic performance.In terms of nanostructure engineering,the construction of porous and hierarchical structure can effectively enlarge the electrochemical active areas,promote the penetration of electrolyte and gas release,consequently accelerating the reaction kinetics and improving the electrochemical stability.The main contents of this thesis are as follows:1.A feasible template-engaged strategy has been innovatively designed for the in-situ growth of ultrasmall Pt nanoparticles on Co₃O₄ microflowers by using Pt Co-based Hofmann compound as reactive templates and precursors.The highly dispersed tiny Pt nanoparticles,abundant intimate metal/oxide heterointerfaces and hierarchical flower-like architecture endow the formed hybrid Pt/Co₃O₄ microflowers with rich active sites,lowered energy barrier for water dissociation,optimized hydrogen binding energy and facilitated reaction kinetics.As a result,when evaluated as a HER electrocatalyst in alkaline solution,the formed Pt/Co₃O₄ microflowers display a competitive activity,which is evidenced by the low onset overpotential(34 m V at 10 m A cm^-2),small Tafel slope(34 m V dec^-1)and remarkable electrochemical stability.2.Porous Co P/Co O heterostructure nanotubes have been successfully synthesized by manipulating the oxidation degree and subsequent phosphating of the Co-Asp complex precursors.The porous Co P/Co O heterostructure nanotubes exihibit significantly increased specific surface area,which is beneficial to expose more active sites.The experimental and theoretical calculations show that the abundant intimate Co P/Co O heterointerfaces can effectively reduce the energy barrier for water dissociation and optimize the adsorption free energy of H to significantly improve the intrinsic activity of Co P/Co O porous nanotubes,thus further facilitating the HER pathway.Compared with pure Co P,Co P/Co O nanotubes exhibit better HER performance in alkaline solution,which is evidenced by the low onset overpotential(61m V at 10 m A cm^-2),small Tafel slope(78 m V dec^-1)and remarkable electrochemical stability.3.A feasible topological conversion strategy has been developed for the fabrication of O-Co P microflowers by phosphating the presynthesized cobalt glycolate complex microflowers.The O atom content can be readily adjusted by controlling the phosphating time to optimize the electronic structure of Co P and thus improve the HER activity.The O-Co P microflowers with abundant pores,hierarchical flower-like architecture and appropriate O atom doping exhibit the optimal electronic structure,which is beneficial to accelerate the electron transfer and optimize the hydrogen binding energy to improve the electrocatalytic activity.The compositional and structural advantages enable the formed O-Co P microflowers to exhibit excellent HER performance,which is evidenced by the low onset overpotential(125 m V at 10 m A cm^-2),small Tafel slope(64 m V dec^-1)and remarkable electrochemical stability.