Low loading inkjet printed bifunctional electrodes for proton exchange membrane unitized regenerative fuel cells

Abstract

Inkjet printing is evaluated as a feasible technique for unitized regenerative fuel cells (URFCs) electrode fabrication and to study the optimal ionomer and catalyst loading. A physical mixture of Pt, IrOx, and Nafion ionomer was inkjet printed directly on a Nafion membrane to fabricate varying loading bifunctional oxygen electrodes for a URFC and characterized via scanning electrode microscopy and cyclic voltammetry. The results show that the two catalyst do not interfere with one another and that an optimal electrode requires low ionomer loading, i.e., 10 wt%, and significantly lower amount of the IrOx catalyst compared to platinum, i.e., 3:1 Pt-IrOx ratio. A catalyst loading study shows that the highest round-trip efficiency is obtained at around 0.67 mgPt+IrOx/cm2 and further increasing the amount of catalyst does not result in a significant cell performance improvement either in water electrolysis or fuel cell mode. Overall, inkjet printing technique was used to fabricate thin bifunctional electrodes reaching round-trip efficiencies of up to 50% at 500 mA/cm2 using a bifunctional oxygen electrode with only 0.67 mgPt+IrOx/cm2 PGM catalyst loading, resulting in the highest efficiency by amount of catalyst reported to date.