Main‐Group Magnesium Single‐Atom Lewis Acid Sites: A CO‐Tolerance Booster for Alkaline Hydrogen Oxidation Reaction

CO poisoning is notoriously intolerable for precious metal-based hydrogen oxidation reaction (HOR) electrocatalysts, which are significant technical barriers for anion exchange membrane fuel cells (AEMFCs). Herein, we separately constructed Lewis acid sites for CO oxidation, which can independently catalyze the oxidation of CO, maximizing the number of Ru active sites for HOR. Moreover, owing to the stable anchoring effect of Mg single atoms on the carbon substrate, ultra-small Ru nanoparticles exhibit no agglomeration or structural changes even after cycling, maintaining excellent material structural stability. Consequently, the Ru/Mg_s/C catalyst maintains high CO tolerance and excellent HOR performance. Excellent CO tolerance and recoverable performance (90% of initial activity) were demonstrated in fuel cell tests. In situ infrared spectroscopy and theoretical calculations collectively suggest that Mg single atoms, which function as Lewis acid sites, can favorably interact with Lewis base molecules such as CO and OH^- via Lewis acid-base interactions, boosting the electro-oxidation of CO and resulting in significantly enhanced HOR activity and resistance to CO-poisoning. When assembled in AEMFCs, its specific power density is as high as 4.11 W mg^-1 _metal with only 0.38 mg cm^-2 total platinum group metal (PGM) utilization. It also demonstrates competitive performance with ultralow precious metal loading (0.125 mg cm^-2).