Preparation And Performance Studies Of OER/ORR Bifunctional Metal Oxides Catalysts

The Zn-air battery（ZAB）is considered as the the idea energy source for the next generation of electric vehicles due to its high safety factor,energy density and low cost.The oxygen evolution reaction（oxygen evolution reaction,OER）and oxygen reduction reaction（oxygen reduction reaction,ORR）are vital reactions that occur on the negative electrode in ZAB.Therefore,it is crucial to discover a catalyst that can improve the OER/ORR activity simultaneously to develop zinc-air batteries.However,the low reaction kinetics and conversion efficiency of these two reactions limit the application of ZAB.Moreover,due to the widespread use of proton exchange membranes in the OER,the catalyst in acidic solutions has significant value to investigate.However,the catalysts with excellent performance based on noble metals,such as Pt/Ir-based alloys or oxides,are currently the most effective.Thus,it is crucial to develop OER materials that can improve water splitting efficiency in harsh acidic environments while maintaining durability,activity,and affordability.This paper aims to improve the OER/ORR activity based on the perovskite structure Sr Ru O₃ and pyrochlorite structure Co₂Sb₂O₇（CSO）.We synthesized A-site doped Sr_0.9M_0.1Ru O_3-δ（SMRO,M=K,Na,Ag）perovskites using a sol-gel method and tested their OER/ORR bifunctional activity.Our results show that Sr_0.9Ag_0.1Ru O₃（SARO）exhibits the highest activity.In 0.1 M KOH,SARO achieves a low overpotential of 220 m V to attain a current density of 10 m A cm^-2 in OER and a half-wave potential of 0.6 V in ORR.X-ray photoelectron spectroscopy analysis confirms that the introduction of metal ions（M⁺）into the A-site results in the formation of oxygen vacancies and lattice oxygen,which is the primary reason for the improved catalytic activity.Our findings offer important insights into the design and synthesis of high-performance bifunctional electrocatalysts for energy applications.The pyrochlore structure of Co₂Sb₂O₇（CSO）was synthesized by solid-state sintering which exhibited excellent OER activity.In 0.5 M H₂SO₄,CSO achieved a current density of 10 m A cm^-2 with a low overpotential of 288 m V and its high activity can remain for 40 hours.XPS analysis confirmed that the high activity and stability were related to the presence of Co²⁺atoms and oxygen vacancies on the surface.To further investigate the changes in surface structure after the CP test,we used XRD and HRTEM analysis,which revealed the formation of Co Sb₂O₆ on the surface of CSO after the test,enhancing its stability.Furthermore,CSO showed excellent bifunctional activity in alkaline conditions,achieving a current density of 10m A cm^-2 in OER at an overpotential of 287 m V and a half-wave potential of 0.75 V in ORR with a limiting current density of 4 m A cm^-2.To improve the activity and stability of CSO in OER,the catalysts was loaded onto nickel foam（CSO-Ni）.The resulting CSO-Ni showed a low overpotential of 228m V to attain a current density of 10 m A cm^-2,reducing 60 m V compared to CSO.Additionally,in alkaline solution,the overpotential of CSO was reduced by 158 m V,and its stability was greatly improved.This was attributed to the increased dispersion and surface area of CSO on the nickel foam,which enhanced its activity in OER.