The role of hydrophobicity and active layer thickness on degradation and durability of the air cathode in alkaline fuel cells

Abstract

The limited cycle life due to the degradation of the cathode is a major problem for commercializing alkaline fuel cells. In this work, a novel combination of in situ and post-mortem analyses have been conducted, along with modifying the thickness and ratio of carbon/binder within the active layer, to investigate the degradation and durability of an alkaline air cathode. In situ analyses such as monitoring the electrode potential and electrochemical impedance spectroscopy are applied. The increased potential loss is likely due to the flooding of electrolyte inside the primary macro structure of the active layer, increasing the mass transfer resistance for oxygen transport. Scanning electron microscopy analysis during the first 24 h of operation reveals that the degree of binder loading has no effect on the electrolyte ingress in the active layer. Higher durability is observed for the cathode with a thicker active layer. X-ray photoelectron spectroscopy data indicates that Pt loss is associated with the elimination of the carbon functional group. Volume rendering of the active layer from Nano-scale X-ray computed tomography has shown a higher porosity and larger pores for the failed cathode. Pt loss, and diminishing of side chain in the binder are observed by thermogravimetric analysis.