Nitrogen-doped carbon nanofiber catalyst for ORR in PEM fuel cell stack: Performance, durability and market application aspects

A noble metal-free catalyst based on N-doped carbon nanofibers supported on graphite (N-CNF/Fe) was employed for the oxygen reduction at the cathode of a Nafion PEMFC with a commercial Pt/C anode. Obtained performance in pure H2 and O2 indicated the presence of significant mass-transport limitations when utilizing catalyst loading between 1 and 10 mg cm−2. Strategies to reduce the limitations were explored by optimization of the cathode ionomer content, catalyst loading and application technique. Pore-formers (Li2CO3, (NH4)2CO3 and polystyrene microspheres) were utilized to improve the mass-transport within the layer. A maximum of 72 mW cm−2 and 1400 A g−1 or 300 W g−1 at peak power was demonstrated. The catalyst was then applied to the cathode of a 10-cell fuel cell stack, and a 400-h durability test was conducted. The average cell voltage decay amounted to 162 μV h−1. Finally, a market application analysis was conducted to illustrate the potential and challenges of replacing platinum as cathode catalyst. It was shown that even a near-complete elimination of the cathode catalyst cost by substitution of platinum with a carbon-based catalyst cannot produce a cost competitive product unless both the performance and the durability of the fuel cell with the new catalyst are very close to that of the state-of the art Pt-based system.