Industrial hydrogen fuel typically comprises about 5 ppm of hydrogen sulfide (H2S), incurring irreversible poisoning of platinum on carbon (Pt/C) catalyst in fuel cells. For realistic use, H2S should be removed to below 4 ppb; this process, however, is challenging and costly. We describe an exceptional H2S-tolerant yet high-performing hydrogen oxidation reaction (HOR) catalyst prepared by chemical grafting of chromic oxide (Cr2O3) onto a molybdenum-nickel (MoNi4) alloy. Cr2O3 as a Lewis acid enhances the specific adsorption of hydroxyl ions, which in turn prevents from S2- diffusing to the catalyst surface via electrostatic repulsion. Meanwhile, the adsorbed hydroxyl species boost HOR kinetics through improving the hydrogen-bond networks in electrical double layers. The composite catalyst achieved HOR performance comparable to that of commercial Pt/C in an alkaline electrolyte. Moreover, a fuel cell using this catalyst as anode can survive 5 ppm of H2S without deactivation, compared with rapid degradation observed over the Pt/C counterpart.
Keywords: Electrocatalysis; Fuel cells; H2S tolerance; Hydrogen oxidation reaction; Lewis acid modifier.