Efficient NH₃-Tolerant Nickel-Based Hydrogen Oxidation Catalyst for Anion Exchange Membrane Fuel Cells

Abstract

Converting hydrogen chemical energy into electrical energy by fuel cells offers high efficiencies and environmental advantages, but ultrapure hydrogen (over 99.97%) is required; otherwise, the electrode catalysts, typically platinum on carbon (Pt/C), will be poisoned by impurity gases such as ammonia (NH₃). Here we demonstrate remarkable NH₃ resistivity over a nickel-molybdenum alloy (MoNi₄) modulated by chromium (Cr) dopants. The resultant Cr-MoNi₄ exhibits high activity toward alkaline hydrogen oxidation and can undergo 10,000 cycles without apparent activity decay in the presence of 2 ppm of NH₃. Furthermore, a fuel cell assembled with this catalyst retains 95% of the initial peak power density even when NH₃ (10 ppm)/H₂ was fed, whereas the power output reduces to 61% of the initial value for the Pt/C catalyst. Experimental and theoretical studies reveal that the Cr modifier not only creates electron-rich states that restrain lone-pair electron donation but also downshifts the d-band center to suppress d-electron back-donation, synergistically weakening NH₃ adsorption.