Preparation And Water Splitting Performance Of Cobalt-based Oxide Electrocatalyst

Increasing energy demands and environment awareness have promoted research on green sustainable energy.Owing to its high energy density and no pollution from combustion products,hydrogen is considered to be an advanced renewable new energy source to replace fossil fuels.Water splitting is an environmentally friendly and sustainable way to produce hydrogen,but its high activation energy limits its industrial application.Precious metal-based materials such as platinum,iridium,and ruthenium are currently advanced catalysts for reducing the energy loss,but their scarce reserves and high prices cannot meet the industrial demand,so it is necessary to develop cost-effective electrocatalysts.Cobalt-based oxides have attracted more and more attention in the field of electrocatalysis due to their low cost,strong alkali resistance and potential catalytic activity.However,there is still a large optimization space for cobalt based oxides as the electrocatalyst of oxygen evolution/hydrogen evolution reaction（OER/HER）.In view of the specific problems in different reactions,this paper has made effective improvements through vacancy engineering,morphology regulation and construction of heterostructures.（1）The OER activity of Co²⁺and Co³⁺in（Co,Fe）₃O₄ with different coordination environment is significantly different,so the change of electronic structure of cobalt ion on catalyst surface will have a significant impact on OER performance.Vacancy engineering is one of the effective strategies to modify the electronic structure,the V_O-（Co,Fe）₃O₄/CC hierarchical nanosheet arrays rich in oxygen vacancies have been successfully prepared by reduction at room temperature.Oxygen defects optimize the electronic properties,increase the ratio of Co²⁺/Co³⁺,and effectively improve the electronic transmission efficiency and the number of active centers.The hierarchical nanosheet arrays morphology not only shortens the diffusion distance of ions and electrons,but also increases the number of active sites on the catalyst surface.The electrode has excellent OER activity and stability in 1M KOH,the overpotential is only 286 m V at 10 m A cm^-2,the Tafel slope is 41 m V dec^-1,and the activity almost has no decay after operation for 24 h at a constant current density of 10 m A cm^-2.（2）The strong electron interaction between different transition metal compounds is helpful to optimize the electronic structure of the catalyst.Therefore,theα-Co（OH）₂/Co₃O₄/CC heterostructure was constructed,and the formation of tight heterogeneous interface induced the electron transfer between the two phases and the formation of new active centers.The close contact with the carbon cloth give the electrode faster electron and proton transport.The optimizedα-Co（OH）₂/Co₃O₄/CC-600s has excellent OER activity in 1M KOH,and the overpotential is as low as 275 m V at 10 m A cm^-2,which is 47 and 84 m V lower thanα-Co（OH）₂/CC and Co₃O₄/CC,respectively,while the reduction of Tafel slope(76 m V dec^-1)demonstrated the improvement in kinetics.（3）In order to improve the electronic conductivity of CoO and promote its electron transfer in HER,ultra-thin amorphous carbon coated cobalt oxide nanosheet arrays（C@CoO/CC）were synthesized on carbon cloth by a simple two-step method.The carbon layer regulates the conductivity of CoO,reduces the electrochemical impedance,improves the charge and mass transfer efficiency,and accelerates the HER kinetic process.Moreover,the carbon coating also acts as a protective layer,and its HER activity and stability are obviously superior to the pure CoO/CC under the strong alkali condition.Compared with CoO/CC,the overpotential of the composite electrode at-10 m A cm^-2 is reduced by 128 m V,and the decay degree of HER activity in the stability test of 20 h is far less than that of CoO/CC,which can be almost ignored.