Site-Blocking Strategy Boosts H₂S Tolerance in Platinum-Based Hydrogen Oxidation Catalysts

Proton exchange membrane fuel cells (PEMFCs) show great potential for energy conversion, but their platinum-based hydrogen oxidation reaction (HOR) catalysts are easily and irreversibly poisoned by trace impurities like H₂S, causing performance degradation with unclear mechanisms. Here, combining in situ Raman spectroscopy with theoretical calculations, we found that on pure Pt surfaces, H₂S dissociates into S* and HS* intermediates that occupy active sites of continuous Pt atoms in an acidic solution under 50 ppm H₂S/H₂ atmosphere. However, on PtRu alloy surfaces, while *OH species were observed on Ru sites, no sulfur-containing species were detected on Pt sites. Comparative experiments revealed that the sulfur-related Raman peaks of PtRu exhibited a redshift compared to Pt, indicating that Ru alloying weakens the *S adsorption on Pt sites through electronic effects. These results demonstrate that Ru not only creates discontinuous Pt sites to block sulfur adsorption but also significantly weakens sulfur binding through electronic modulation. Based on these insights, small-sized site-blocking PtRu/C catalysts were developed, exhibiting only 9.2% activity decay after 700s in 50 ppm H₂S/H₂ atmosphere, a 4.3-fold improvement over commercial Pt/C catalysts (39.3% decay). This work provides fundamental understanding of H₂S poisoning mechanisms and practical guidelines for designing robust, poison-resistant catalysts.