Localization of platinum in low catalyst loading electrodes to to attain high power densities in SPE fuel cells

Abstract

This paper presents the results of three methods used to attain high power densities in solid polymer electrolyte fuel cell systems. The objectives of these methods are to use relatively thin electrocatalytic layers in the gas diffusion electrodes and to localize further the platinum near the front surface of the electrodes to minimize activation, ohmic, and mass transport overpotentials. The three methods were: (i) use of a higher wt% Pt/C in the supported electrocatalysts (20 and 40 wt% Pt/C rather than 10); (ii) sputtering of a thin film of platinum (corresponding to a 50 nm film on a smooth surface) on the state-of-the-art Prototech electrode (10 wt% Pt/ C); and (iii) a combination of the two methods, i.e., sputtering of a 50 nm film of platinum on an electrode prepared with a higher Pt/ C wt ratio in the supported electrocatalyst. The optimum configuration of the electrode was found to be the one fabricated with 20 wt% Pt/C in the supported electrocatalysts onto which was sputtered a 50 nm film of platinum. At a current density of 1 A/cm 2, the cell potentials were 0.600 V and 0.540 V, with H 2/O 2 and H 2/air as reactants, at 80° C, and 3/5 atm pressure. The cyclic voltammetric technique was used to ascertain the electrochemically active surface areas of the electrodes. By use of this method, the platinum utilization of the electrode with the optimum configuration was estimated to be about 15–20%. To increase the power densities further, it is necessary to use membranes with higher specific conductivities and better water retention characteristics.