High performance polymer electrolyte fuel cells with ultra-low Pt loading electrodes prepared by dual ion-beam assisted deposition

Abstract

Ultra-low pure Pt-based electrodes (0.04–0.12 mg Pt/cm 2) were prepared by dual ion-beam assisted deposition (dual IBAD) method on the surface of a non-catalyzed gas diffusion layer (GDL) substrate. Film thicknesses ranged between 250 and 750 Å, these are compared with a control, a conventional Pt/C (1.0 mg Pt(MEA)/cm 2, E-TEK). The IBAD electrode constituted a significantly different morphology, where low density Pt deposits (largely amorphous) were formed with varying depths of penetration into the gas diffusion layer, exhibiting a gradual change towards increasing crystalline character (from 250 to 750 Å). Mass specific power density of 0.297 g Pt/kW is reported with 250 Å IBAD deposit (0.04 mg Pt/cm 2 for a total MEA loading of 0.08 mg Pt/cm 2) at 0.65 V. This is contrasted with the commercial MEA with a loading of 1 mg Pt(MEA)/cm 2 where mass specific power density obtained was 1.18 g Pt/kW (at 0.65 V), a value typical of current state of the art commercial electrodes containing Pt/C. The principal shortcoming in this effort is the area specific power density which was in the range of 0.27–0.43 W/cm 2 (for 250–750 Å IBAD) at 0.65 V, hence much below the automotive target value of 0.8–0.9 W/cm 2 (at 0.65 V). An attempt to mitigate these losses is reported with the use of patterning. In this context a series of patterns ranging from 45 to 80% Pt coverage were used in conjunction with a hexagonal hole geometry. Up to 30% lowering of mass transport losses were realized.