Mn-N-C with High-Density Atomically Dispersed Mn Active Sites for the Oxygen Reduction Reaction

The utilization of transition metal-based catalysts as alternatives presents an attractive solution for enhancing the sluggish oxygen reduction reaction (ORR) and reducing costly platinum-based electrocatalysts in hydrogen fuel cells. Manganese-based nitrogen-carbon (Mn-N-C) is anticipated to exhibit durability due to its weaker Fenton reaction propensity. However, a key obstacle lies in boosting intrinsic electrocatalytic activity and increasing the density of Mn active sites, crucial for practical integration into fuel cell operations. Herein, a three-step method is developed to synthesize atomically dispersed Mn-N-C materials with a rich mesoporous structure as highly effective ORR catalysts. The high Mn loading (3.42 wt%) promotes the generation of Duo-MnN₄ active sites, demonstrating outstanding performance and durability for fuel cells. Specifically, the exceptional performance of proton exchange membrane fuel cells (PEMFC) reaches 649 mW cm^-2 and anion exchange membrane fuel cells (AEMFC) achieves 770 mW cm^-2. Notably, the durability of the Mn-N-C catalyst in PEMFC is reported for the first time, showing only 18.4% decay after 30 000 square-wave cycles. This work provides a unique perspective and a systematic design strategy for building feasible nonprecious metal catalysts with a high active site density, addressing the challenges of inefficiency and performance limitations across various electrocatalytic applications.