Morphological characteristics of PTFE bonded gas diffusion electrodes

We have investigated the morphological and absorptive characteristics of the electrocatalyst layer of PTFE bonded gas diffusion electrodes. The electrocatalyst layer microstructure was varied by using different preparative conditions (320-360°C sintering temperature and 20-60% PTFE content). We measured the pore size distribution and the electrolyte uptake for each electrode. From these data we calculated porosities and electrolyte volume fractions of the electrocatalyst layer and agglomerate regions The electrocatalyst layer porosity and electrolyte volume fraction depend directly on the preparative conditions, while the agglomerate porosity and the macropore porosity are not influenced significantly. We proposed and evaluated a theoretical expression for the Pt utilization in the electrocatalyst layer using our measured porosities and electrolyte volume fractions. These results agree well with electrochemical measurements of active Pt surface area using cyclic voltammetry. The percentage acid occupation (PAO) was also found to be a good property for correlating morphological-absorptive characteristics and Pt utilization.