Investigation of oxygen reduction mechanisms using cathode microelectrodes, part I: Experimental analysis of la1-xSrxMnO 3-d and platinum

Abstract

Oxygen reduction reactions (ORR) on La1-xSrxMnO 3-d are currently not well understood and no final agreement on the precise oxygen reduction rate-determining step(s) has been made. To investigate ORR, we fabricated thin-film microelectrodes of La1-xSr xMnO3-d and platinum (Pt) by RF-sputtering and patterning via photolithography to obtain precisely defined electrode geometries and features. These were then tested using impedance spectroscopy and under varying conditions such as DC bias, oxygen partial pressure, and current treatment. For the Pt microelectrode, we observed two distinct semicircles and attributed these to processes related to ionic conduction in the electrolyte and an oxygen adsorption at the Pt cathode. For La1-xSrxMnO 3-d, we found that varying annealing temperatures of the thin films after deposition resulted in different impedance response. Varying oxygen partial pressure, DC bias, and current treatment was also found to affect the electrode impedance response in both Pt and La1-xSr xMnO3-d but had no effect on the electrolyte.