All Platinum Group Metal-Free and Durable Catalysts for Direct Borohydride Fuel Cells

Platinum group metal-free catalysts (e.g., Fe-N-C and Co-N-C) are used as hydrogen peroxide reduction reaction (PRR) catalysts in direct borohydride fuel cells (DBFCs). Fe-N-C is more active in the PRR and demonstrates high performance at the beginning of the DBFC test, whereas Co-N-C exhibits more stability in long-term operation. In the DBFC-accelerated durability test, Fe-N-C displays an activity decline of 18.6%, whereas Co-N-C exhibits a more stable performance, with an activity decrease of only 6.7%. In addition, the active site of Fe-N-C degrades more rapidly than that of Co-N-C in terms of demetalation of the central atom, as revealed by X-ray photoelectron spectroscopy. Furthermore, density functional theory simulations indicate that Co-N-C is more stable than Fe-N-C in both O-2 and H2O2 environments. Overall, this study demonstrates that non-noble transition metal catalysts can fully replace platinum group metal catalysts at the cathode and anode in liquid-fuel-powered DBFC systems.