Preparation And Electrochemical Properties Of Co₃O₄ Composite Catalysts And After Sulfuration?Phosphorization?

The development of new energy technologies such as hydrogen production from electrolytic water and metal-air batteries is closely related to the process of hydrogen evolution,oxygen evolution and oxygen reduction.However,the kinetic characteristics of these reactions are slow.Therefore,it is of great theoretical and practical significance to study and develop suitable electrocatalysts to improve the reaction efficiency.Conventional electrocatalysts are usually precious metals or alloys.Noble metal catalysts have low natural reserves,high cost and poor catalytic stability,which seriously restrict their wider application.In this paper,cobalt-based oxides and nano-carbon-based composite catalysts as the main research object,through the construction and regulation of the nanostructure of catalysts,active sites and sulfurization and phosphating treatment,the relationship between the valence of active ions in catalysts and the activity of catalysts was explored in detail,thus revealing the electrochemical reaction mechanism on the surface of these catalysts.The main research contents are as follows:?1?Cobalt-based precursor nanosheets were prepared using NaCl template,cobalt nitrate as metal source and polyvinylpyrrolidone?PVP?as carbon and nitrogen source.Nitrogen-doped cobalt oxide and carbon-based composites?Co₃O₄/C nanosheets?were obtained by secondary heat treatment.X-ray powder diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,scanning electron microscopy?SEM?and high resolution transmission electron microscopy?HRTEM?were used to characterize the phase and structure of Co₃O₄/C nanosheets.The electrochemical properties of Co₃O₄/C nanocomposites were tested under alkaline conditions.The experimental data showed that the Co₃O₄/C nanocomposites had certain ORR/OER bifunctional catalytic activity.?2?Cobalt-based sulfide-carbon composite nanosheets?Co₉S₈/C?were prepared by hydrothermal treatment of cobalt-based oxides and carbon-based composites?Co₃O₄/C nanosheets?using Na₂S as sulfur source.The results of phase and structure characterization and catalytic performance of ORR and OER in alkaline solution showed that the bifunctional catalytic activity and stability of vulcanized Co₉S₈/C were greatly improved.The starting potential of ORR was 0.892 V,60 mV left-shifted than that of Co₃O₄/C,and the overpotential of OER at 10 mA cm^-2 was 0.434 V,which was 99 mV lower than that of Co₃O₄/C.The main reason may be that the increase of Co²⁺/Co³⁺ratio is beneficial to the formation of cobalt hydroxides?CoOOH?,which favor OER catalysis,and the sulfidation process may expose more active sites to further improve the catalytic performance.The research results are expected to promote the practical application of these materials in the field of new energy devices.?3?Using sodium hypophosphite as phosphorus source,cobalt-based oxides and carbon-based composites?Co₃O₄/C nanosheets?were phosphated by nitrogen-protected thermosetting reaction,and cobalt-based phosphides and carbon-based composite nanosheets?CoP/C?were prepared.Because P has a weak negative charge,the phosphide is more conducive to the adsorption and desorption of hydrogen and the total electrochemical decomposition of water.The experimental data show that the initial potential of hydrogen evolution of CoP/C nanosheet HER under alkaline condition is only-0.053V,99 mV higher than that of Co₃O₄/C,and the overpotential of OER at 10 mA cm^-2 is 0.421 V,101 mV lower than that of Co₃O₄/C.Theoretical analysis shows that the activity of the catalyst may be related to the addition of phosphorus and the exposure of more active sites during the incorporation process.The research results provide a reference for promoting the wider application of alkaline electrolytic water in hydrogen production.