A sharp peak in the performance of sputtered platinum fuel cells at ultra-low platinum loading

Abstract

Proton exchange membrane fuel cells were fabricated by direct sputter deposition of platinum on the surface of Nafion 117 membranes. A sharp spike in the performance of these sputtered platinum fuel cells was observed at ultra-low platinum thickness values of 5–10 nm. Within this narrow thickness range, the power output capability of sputtered platinum fuel cells is several orders of magnitude better than the performance produced by thinner or thicker coatings. The spike in performance is explained by rapid changes in the sputtered film microstructure at the nanometer thickness level. When the membrane surface is deliberately modified by abrasion prior to sputtering, this sharp peak is not seen. Instead, a broad plateau is observed, where the performance is insensitive to the amount of sputtered platinum. This behavior stems from how surface roughening affects the sputtered catalyst layer continuity. The performance of a sputter-deposited membrane with a platinum loading level of 0.04 mg/cm 2 is compared to a commercial membrane electrode assembly (MEA) with a platinum loading of 0.4 mg/cm 2. The maximum power output of the sputtered cell is three-fifths that of the commercial MEA, but uses one-tenth the platinum.