Investigations of Electrochemically Active Regions in Bifunctional Air Electrodes Using Partially Immersed Platinum Electrodes

Abstract

Oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) on glassy-carbon-supported platinum electrodes (Pt/GCs), which are partially immersed in alkaline electrolytes, are investigated as a model of the triple phase boundary (TPB) in air electrodes for metal-air secondary batteries. ORR currents are measured with changing the vertical position of Pt/GCs, and OER currents are measured by linear sweep voltammetry. Based on the electrochemical results, it is found that thin liquid film on Pt/GCs effectively serves to expand TPB regions for ORR, but the liquid film hardly increases OER currents. Therefore, we conclude that the most effective TPB form are determined by the electrode reactions (ORR or OER), which are corresponding to discharge and charge processes for metal-air secondary batteries. In practice, it is strongly necessary to control the wettability of electrode inside, in order to construct high-performance bifunctional air electrodes.