An Efficient H₂S-Tolerant Hydrogen Oxidation Electrocatalyst Enabled by a Lewis Acid Modifier for Fuel Cells

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 S^2- 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.