(A) study on the electrochemical characteristics of platinum-dispersed carbon electrode for phosphric acid fuel cell

Abstract

The corrosion behaviour of carbon catalyst support has been investigated in 96\% phosphoric acid solution at $145\,^\circ\!C$ as a function of surface oxides by using potentiodynamic and current decay transient methods in connection with Fourier Transform Infrared (FTIR) spectroscopy. The surface oxides were identified by FTIR spectroscopy. Cyclic voltammetry curve showed an anodic current peak at $0.8 V_{RHE}$ and an abrupt increase in anodic current above $1.4 V_{RHE}$. The results of FTIR spectroscopy demonstrated that the surface oxides consist of carboxyl and quinone and that the amount of carboxyl decreases markedly, while that of quinone decreases slightly with increasing applied potential from 0.8 to $1.3 V_{RHE}$. The current decay transients showed the two-staged variation of passivation index with time for applied anodic potentials. The second stage of the passivation index exhibited the stronger time dependence, the lower the applied anodic potential, indicating the occurrence of a promoted passivation on carbon black surface. The raised passivation is attributable to the increase in the amount of carboxyl with decreasing applied anodic potential and with oxygen-blowing. The abrupt increase in anodic current above $1.4 V_{RHE}$ appears to be due to the decrease in the amount of carboxyl. The experimental results suggested that corrosion behaviour of carbon black with concurrent oxygen-blowing is determined by surface oxide of carboxyl, which provides the more enhanced passivity of the carbon black, the lower the passivation potential. In other to investigate the corrosion behaviour in actual fuel cell condition, platinum-catalyzed carbon electrode was also used. The amount of surface oxide which was formed during the electrochemical ageing in hot phosphoric acid solution at $0.7 V_{RHE}$ with oxygen-blowing and with nitrogen-blowing was determined by use of linear sweep voltammetry experiment in $25\,^\circ\!C$, 1M $H_2SO_4$ solution The result of t...