Synthesis And Electrochemical Performance Of Perovskite Electrocatalysts

Eff-iciently utilizing renewable and clean energy resources is critical to solve global warming and to mediate the deterioration of the ecological environment.Electrocatalytic splitting of water can potentially realize the substantial production of hydrogen and oxygen.Fuel cells can efficiently convert the chemical energy of oxygen and hydrogen into electricity.However,the efficiency of water splitting and fuel cells are drastically limited by the sluggish kinetics of the oxygen evolution reaction(OER)and oxygen reduction reaction(ORR),which cause a considerable overpotential and an obvious energy loss.To address this challenge,highly efficient electrocatalysts for electrochemical water splitting and fuel cells have been extensively investigated.Normally,state-of-the-art electrocatalysts for OER/ORR adopt noble metal or metal oxides such as IrO2,RuO2 and Pt,but the scarcity,high cost,and low stability restrict their large-scale applications Therefore,it is urgent to design novel electrocatalysts with characteristics of high activity,high stability and low cost.Among many candidates for oxygen electrocatalysis,perovskite oxides have gained increased attention in recent years thanks to the outstanding merits of the tunable structure,the employment of earth-abundant elements,and the facile preparation process.In this thesis,the non-metallic element doping and electrospinning have been applied to design and optimize the perovskite oxides as highly efficient electrocatalysts for oxygen electrocatalysisFirstly,we selectively introduced phosphorus(P)into SrCo0.8Fe0.2O3-δ(SCF)to form modified perovskite oxides,i.e.,SrCo0.8Fe0.15P0.05O3-δ,SrCo0.75Fe0.2P0.05O3-δ and Sr(Co0.8Fe0.2)0.95P0.05O3-δ.An improved OER activity and stability compared to undoped SCF was clearly observed.Meanwhile,the specific surface area,oxygen vacancy content and electronic conductivity increased due to the P doping.Moreover,a lower valence state of B-site cations induced by the high-valence P5+ was detected,which may contribute to the better activity and stability.Among them,Sr(Co0.8Fe0.2)0.95P0.05O3-δ with the dual-site substitution stands out when evaluating the activity and stability in alkaline solution.The results suggest that the P doping could be an effective strategy to develop perovskite electrocatalysts with high electrocatalytic activity and stabilitySecondly,we prepared LaBa0.85Ca0.15Mn2O5+δ(LBCM)by sol-gel and electrospinning,leading to the formation of a bulk structure and one-dimensional nanorods,respectively.The specific surface area of LBCM-ES(electrospinning)is nearly 7 times larger than that of LBCM-SG(sol-gel),which could potentially provide more active sites.Accordingly,LBCM-ES has better electrocatalytic activity towards ORR compared with LBCM-SG,exhibiting an onset potential of 0.879 V vs.RHE and a limiting current density of 6.17 mA cmdisk-2.However,the stability of LBCM-SG and LBCM-ES is still unsatisfied as the onset potential of LBCM-SG and LBCM-ES are both negatively shifted by 51 and 26 mV after 1000 cycles via cyclic voltammetry.In a zinc-air battery,the discharge voltage of LBCM-ES is higher than that of LBCM-SG under the same current density and the charge-discharge voltage gap of LBCM-ES keeps at 1.393 V after 500 charge-discharge cycles,indicating promising electrochemical performance by utilizing LBCM-ES as oxygen catalysts.