Performance constraints of high temperature polymer electrolyte membrane fuel cells by varying the Pt/C ratio of the catalyst

Electrodes prepared from catalysts with Pt weight percentages on the carbon support (Pt/C nanoparticles) ranging from 10 up to 60 wt% are used as cathodes of membrane electrode assemblies (MEAs) and tested in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). For each Pt/C percentage in the catalyst, the cathode Pt-loading (which become proportional to the thickness of the electrode formed by the catalyst nanoparticles) is stepwise scanned from low to high loadings. Results show that when the Pt load increases, the MEA performance (measured by its power density at 0.6 V) rises initially (due to the increase in the number of active sites in the cathode) up to a maximum value limited by the mass transport of oxygen, associated to an optimum Pt-loading (different for each Pt/C ratio). Noteworthy, the peak performance is significantly different depending on the catalyst used (60 > 40 >> 20 > 10 wt% Pt/C), a fact that restricts the catalyst choice according to the performance required by the application. Furthermore, higher amounts of Pt in the cathode lead to a large catalyst waste as the FC performance even decreases as the cathode thickness increases.