关键词: 锶掺杂的锰酸镧, 氧电化学还原, 交流阻抗

Abstract: Electrochemical reaction of oxygen on the La 0.8 Sr 0.2 MnO 3/YSZ electrode has been investigated in detail with AC impedance. The results demonstrated that the rate determining step(rds) of the reaction varies with the temperature, oxygen partial pressure and overpotential applied. At open circuit potential, the rds is the dissociative adsorption of oxygen on the LSM surface. A large number of electron holes are generated at high anodic overpotentials, while oxygen vacancies are formed at high cathodic overpotentials. The formation of the electron holes results in the electronic conduction of the YSZ electrolyte and the extension of the electrochemical active area. While the formation of oxygen vacancies leads to the ionic conduction in the LSM electrode and the extension of the electrochemical active area over the LSM electrode surface. The extension of active area and the increase of the conductivity induce some special phenomena reflected in AC impedance spectra, such as the decrease of both the electrode resistance and the ohmic drop, the increase of the double layer capacitance, and the appearance of the low frequency inductive arc at low temperature. The rds of the reaction at low temperature and high overpotentials is the charge transfer step, while at high temperature the rds of the reaction at high anodic and cathodic overpotential are the charge transfer step and the diffusion of oxygen over LSM surface respectively.