Electrochemical reduction of NO by solid electrolyte cells with La0.8Sr0.2MnO3-Ce0.8Sm0.2O1.9 composite cathodes

Abstract

Solid electrolyte cells with La0.8Sr0.2MnO3-Ce0.8Sm0.2O1.9 (LSM-SDC) composite cathodes are fabricated for nitric oxide (NO) reduction. The effects of SDC content, inlet NO flow rate and concentration, operating temperature, cathodic polarization, additional gas compositions on NO conversion are investigated systematically. Various characterization methods such as XRD, TEM, SEM, BET, I-V curve, electrochemical impedance spectra (EIS), Raman spectra, XPS, and in situ DRIFT spectra are performed. It is found that the moderate SDC addition expands the three phase boundaries (TPBs) and oxygen vacancies at cathodes, thereby decreasing the polarization resistance and facilitating the gas adsorption. The cathode containing 35 wt% SDC has the highest NO conversion of 67.22% and the lowest polarization resistance of 75.24 Ω cm2 at 700 °C. The high flow rate and low temperature have the negative effects on NO conversion but the high concentration even improves the electrochemical performance of cells. The cathodic voltage promotes the cell performance because of the reduction of Mn ions and the generation of more oxygen vacancies at cathode. The cells show the relatively good tolerance for CO2 and great reversible inhibition effect on SO2, but the excess O2 can degrade the NO conversion evidently due to the competitive effect. The reaction mechanism is proposed in the end that NO2 is the possible intermediate and NO3− is the major adsorption species on cathode surfaces.