Structural Regulation And High Temperature Electrochemical Performance Of Pr_2-xCe_xCuO₄-based Cathode Catalyst

Solid oxide fuel cells（SOFC）are devices that effectively convert chemical energy into electricity and heat,typically operating between 800 and 1000℃.This high temperature condition is designed to promote electrode reactions and promote rapid ion movement in the electrolyte.The current research work is aimed at the optimization of batteries operating in the temperature range of 500-700℃,with very strict material requirements.In addition to mechanical and chemical compatibility requirements,the material must exhibit a high degree of oxygen ion mobility and electrochemical activity at this medium and low temperature.Current research on cathode materials focuses on mixed ion and electron conductor（MIEC）with strong electrochemical catalytic activity.In this paper,based on cobalt-free perovskite oxide Pr_2-xCe_xCuO₄,cathode materials were modified by element doping,second phase composite and the introduction of A-site defects.Pr_2-xCe_xCuO₄,Pr_1.95Ce_0.05CuO_4-xCe0.8Pr0.2O1.9 and Pr_1.90-xCe_0.1CuO₄ series cathode materials were synthesized respectively,and the performance of the above materials as SOFC cathode materials was discussed.1.Pr_2-xCe_xCuO₄（PCCx,x=0.05,0.10）series oxides were synthesized by sol-gel method.PCCx has stable tetroidal structure and good high-temperature chemical compatibility with electrolyte（Ce0.9Gd0.1O1.95,GDC）.At 700 ℃,the polarization resistance（Rp）of PCC0.05 can reach 0.14 Ω cm2 and the output power density of the whole battery is 0.75 W cm-2.The kinetics of the oxygen reduction reaction on the cathode was studied.The fitting results showed that the adsorption and diffusion process of oxygen molecules on the electrode surface was the main rate control step.2.Pr_1.95Ce_0.05CuO_4-xCe0.8Pr0.2O1.9（PCC-xCPO,x=10,20,30）series of composite cathode materials were synthesized by one-step co-assembly method using Pr_1.95Ce_0.05CuO₄ as parent material.The electrochemical behavior was analyzed systematically.The test results of O2-TPD proved that the introduction of CPO phase effectively increased the oxygen vacancy concentration of the material and provided more reaction sites for the electrocatalytic process.At 700℃,the polarization resistance of the PCC-30CPO half-cell is as low as 0.042 Ω cm2,and the peak output power density of the whole battery with the PCC-30CPO as the cathode is 1.04 W cm-2.The performance of the PCC-30CPO half-cell does not degrade after 60 h operation at a constant voltage of 0.5 V.Through a series of analysis of relaxation time distribution（DRT）,characteristic capacitance and relaxation frequency,it can be known that oxygen adsorptiondissociation process is the main process of oxygen reduction reaction of PCC-30CPO materials.In the semi-cell polarization test,the exchange current density（i0）of PCC30CPO is 70.22 mA cm-2,and it shows high current density in both SOFC and solid oxide electrolytic cell（SOEC）,which indicates that PCC-30CPO is a potential bifunctional material.3.Pr_1.90-xCe_0.1CuO₄（P1.90-xCC,x=0.05,0.10,0.15）series oxides were synthesized by sol-gel method.The absence of Pr ion improved the electrical conductivity of the materials,among which P_1.75CC showed the highest conductivity in the series,reaching 275 S cm-1 at 800℃.At the same time,the introduction of A site defect increased the oxygen vacancy concentration of the materials,contributing to the enhancement of electrocatalytic activity.At 700℃,the polarization resistance of P1.90-xCC cathode decreases with the increase of the number of defects,and the Rp value of P_1.75CC cathode is 0.025 Ωcm2,which is significantly lower than that of the material without defects.The power density of the whole battery assembled with P_1.75CC as the cathode is 1.11 W cm2,and the long-term stability is maintained for 100 h.The electrochemical impedance spectra of P_1.75CC at different oxygen partial pressures showed that the adsorption and diffusion process of oxygen on the electrode surface was the control step of oxygen reduction reaction on P_1.75CC electrode.