Synthesis Of Mesoporous Cobalt Ferrit Based Catalysts And Their Electrocatalytic Performance For Water Splitting

Benefiting from the advantages of high energy density and zero carbon dioxide emission,hydrogen energy is generally considered as a potential energy carrier for future sustainable energy system.Hydrogen production from electrocatalytic water splitting is an attractive technology of energy conversion,but the sluggish kinetics of water splitting needs to overcome a high overpotential,so the construction of high-efficiency electrocatalytic catalysts has been the primary task.Transition metal catalysts with excellent catalytic activity are considered as ideal substitutes for noble metal catalysts,which have attracted the attention of scholars.Based on the above factors,the purpose of this dissertation is to construct the novel Co Fe based catalysts,and to effectively improve the catalytic activity of transition metal-based catalysts by controlling their surface composition and introducing carbon materials and metal doping.Co Fe₂O₄ electrocatalysts with different mesoporous structures were prepared by impregnation,calcination and etching using mesoporous Si O₂ as hard template.The performance of electrocatalytic oxygen evolution under alkaline condition was systematically studied.Due to the mesopores,electrocatalysts possess a large specific surface area to expose more active sites,which is conducive to the rapid transmission of electrons and the rapid escape of product gas,so the mesoporous Co Fe₂O₄ catalysts show excellent electrocatalytic oxygen evolution activity.Compared with that of Co Fe₂O₄ nanoparticles,mesoporous SBA-Co Fe₂O₄ catalyst only need 342 m V to obtain the current density of 10 m A cm^-2 with a low Tafel slope of 57.1 m V dec^-1,and exhibits the superior stability in 1 M KOH electrolyte.Anion regulation was carried out to further optimize the catalytic activity of cobalt iron-based catalysts.After phosphating,sulfurization and selenidation,cobalt iron-based catalysts show excellent OER catalytic performance.The mesoporous structure was destroyed after sulfurization and selenidation,so the cobalt iron phosphide is discussed in depth.By changing the ratio of cobalt to iron,the kinetic barrier can be effectively reduced and the oxygen evolution activity of mesoporous cobalt iron phosphide was improved.Mesoporous Co_0.75Fe_0.25P exhibits a low overpotential of 270 m V at a current densitiy of 10 m A cm^-2 toward oxygen evolution reaction and can be stable for a long time at current densities of 10 m A cm^-2 and 40 m A cm^-2.The overall water splitting activity of the mesoporous Co_0.75Fe_0.25P was further evaluated in 1 M KOH solution by using two-electrode configurations.The alkaline electrolytic cell needs a low voltage of 1.69 V at a current density of 10 m A cm^-2.Graphene was introduced in the mesoporous Si O₂ to form the KIT-6/r GO template,which was used to the successful preparation of mesoporous Co_0.5Fe_0.5P/r GO.Compared with that of the mesoporous Co_0.5Fe_0.5P,mesoporous Co_0.5Fe_0.5P/r GO exhibits better catalytic performance toward water splitting and1.66 V is needed when the current density reaches 10 m A cm^-2.On one hand,the strong interaction between transition metal phosphide and graphene accelerates the charge transfer,and the mesoporous structure can expose more active sites,which is conducive for the rapid adsorption and transfer of reactants and catalytic intermediates.On the other hand,the introduction of graphene can effectively protect the oxidation of transition metal phosphide in OER,and enhance the stability of mesoporous Co_0.5Fe_0.5P/r GO.Cerium(Ce)with variable valence possesses good conductivity and high oxygen storage capacity,which can effectively regulate the electronic structure of the catalyst,thus improving the electrocatalytic performance of the catalysts.Doping a small amount of Ce into the mesoporous Co_0.5Fe_0.5P can improve the oxygen evolution performance of the catalyst.When current density reaches 10 m A cm^-2,the overpotential of 5%Ce-Co_0.5Fe_0.5P is 250 m V toward oxygen evolution reaction.Compared with that of mesoporous Co_0.5Fe_0.5P,the overpotential of 5%Ce-Co_0.5Fe_0.5P decreased from 253 m V to 186 m V toward hygrogen evolution reaction at a current density of 10 m A cm^-2.At the same time,the alkaline electrolytic cell assembled by 5%Ce-Co_0.5Fe_0.5P can reach the current density of 10m A cm^-2,with a required voltage of 1.652 V.