Design And Oxygen Evolution Performance Study Of Ca₂CoFeO_5+δ-metal Oxides Heterointerfaces

The energy crisis and environmental problems caused by the economic development and human activities are becoming increasingly serious.In order to achieve the sustainable development of society and national economy,it is imperative to find and develop new green energy.Therefore,as a new energy technology,the metal-air battery has the advantage of high theoretical energy density in energy conversion and storage devices,which has been considered as the next generation of electrochemical energy storage devices.However,oxygen evolution reactions（OER）and oxygen reduction reactions（ORR）affect the overall performance and commercialization of these energy devices due to kinetic slowness and high energy barrier（overpotential）.There is an urgent need to develop electrocatalysts to facilitate both reactions and minimize this overpotential,thereby reducing the extra energy required to drive the reactions in these devices.Among ORR/OER electrocatalysts,Pt and Ru O₂ are regarded as the most effective.While their scarcity,costliness as well as the instability under reaction conditions hinder their wide applications.Therefore,in terms of electrochemical energy storage and conversion technologies,the low noble metal and non-noble matal electrocatalysts are one of the main research objects.In recent years,perovskite oxides in transition metal oxides have attracted great attention due to their unique electronic,ionic,magnetic,catalytic,and environmentally friendly properties.However,most of the studies are mainly focused on morphology,ion doping,introduction of defects,and coupling with conductive materials,and the performance of single-component perovskite oxides is still limited.Therefore,a new type of non-noble metal electrocatalyst with low cost,high activity and high stability is prepared by combining the Brownmillerite（BM）-type metal oxide Ca₂CoFeO_5+δ（C₂CF）with another metal oxide in this paper.The details are as follows:1.The nano Bi₂O₃ is loaded on C₂CF precursor by simple impregnation method,and then calcined at high temperature to synthesize Bi₂O₃-C₂CF composite material with heterogeneous structure.After electrochemical test,the catalyst of 0.1Bi₂O₃-C₂CF exhibites the best catalytic activity and stability.Under the current density of 10 m A.cm^-2,it shows a lower overpotential（357 m V）and Tafel slope(85.8 m V.dec^-1).Compared with C₂CF,Bi₂O₃-C₂CF loaded with two-dimensional nano-flake Bi₂O₃has smaller particle size,larger specific surface area and more abundant surface defects.Moreover,the combination of Bi₂O₃ and C₂CF produces more oxygen vacancies,which facilitates electron transfer and oxygen-containing species adsorption.And the strong interaction between them accelerates the kinetic reaction as well as improves its OER performance.2.A series of NiO-C₂CF catalysts with different proportions are obtained by ethylene glycol-citric acid complex method（EG-CA）and impregnation method.The 0.05NiO-C₂CF shows high activity for electrocatalytic oxygen evolution reaction under alkaline condition.And its overpotential is 362 m V,which is reduced 51 m V than the commercial Ru O₂.After chronoamperometric current test for 10000 s,it still maintains a high current density.These results are ascribed to:there are a large amount of defective oxygen is generated in NiO-C₂CF,which increases more active sites and makes it have higher catalytic activity.Moreover,the interface of NiO-C₂CF is conducive to electron transfer,regulating the adsorption of oxygen-containing species and improving the catalytic activity of catalytic.3.Nano CeO₂ is obtained by direct precipitation method,and then three kinds of CeO₂-C₂CF composites are obtained by sol-gel method and impregnation method.XRD shows that the synthesized CeO₂-C₂CF catalyst has both CeO₂ and C₂CF phase structure.It observes in SEM and TEM that CeO₂ particles are uniformly dispersed on the surface of C₂CF and CeO₂-C₂CF heterostructure with abundant interfaces is formed,which generates more active sites and promotes OER reaction.The presence of Ce³⁺and reactive oxygen species after loading CeO₂ promotes the effective adsorption of intermediates.Combined with the electrochemical test results,0.1CeO₂-C₂CF do show higher OER activity and better stability,indicating that the synthesis of composites can improve the catalytic activity.