High-Shell Sulfur Doping Enhances Mn-N₄ Spin States and Boosts Oxygen Reduction Reaction Performance in both Acidic...

The development of platinum group metal-free catalysts for the oxygen reduction reaction (ORR) is critical to advancing sustainable energy conversion technologies. Manganese (Mn)-based catalysts, known for their reduced toxicity and promising durability, have traditionally exhibited lower ORR activity compared to state-of-the-art iron-nitrogen-carbon (Fe-N-C) catalysts. In this study, a highly efficient Mn-N-C-S catalyst is presented, engineered through a sulfur-mediated high-shell coordinated doping strategy, that markedly enhances ORR activity and stability. The Mn-N-C-S catalyst achieves a record-high half-wave potential of 0.94 V in alkaline media, among the highest values reported for Mn-based catalysts. Additionally, in acidic media, it exhibits a half-wave potential of 0.80 V, placing it among the top-performing M-N-C catalysts. The catalyst also demonstrates a high peak power density of 0.82 W cm^-2 in H₂-O₂ fuel cells and 0.264 W cm^-2 in Zn-air batteries, outperforming previously reported Mn-based catalysts. Both experimental findings and theoretical computations suggest that the high-shell S-doping can increase the spin density of Mn sites, strengthen Mn-N bonds, and thereby improve the durability of Mn-N₄ sites. This work underscores the effectiveness of high-shell sulfur doping and paving the way for their deployment in the cathodes of fuel cells and metal-air batteries.