Defect-mediated high loading metal single-atom catalysts direct oxygen reduction reaction selectivity to H₂O₂...

Transition metal single-atom catalysts (TM-SACs) have emerged as promising electrocatalysts for the two-electron oxygen reduction reaction (2e^-ORR) due to their exceptional atomic utilization efficiency and tunable electronic structures. Nevertheless, the practical application of TM-SACs is constrained by their relatively low metal loading, which adversely affects their catalytic performance. Herein, we developed a universal defect-mediated strategy to fabricate TM-SACs with high metal loading. Nitrogen-doped carbon dots (NCDs) derived from ethylene diamine tetraacetic acid (EDTA) serve as an ideal support material, where the confined spatial dimensions and abundant defect sites effectively isolate metal atoms while preventing their aggregation. To validate the versatility of this synthetic strategy, we successfully prepared a series of TM-SACs (denoted as TMSA-NC, where TM = Fe, Ni, Cu) with high metal loading reaching 6.87 wt%. Intriguingly, the ORR selectivity can be precisely modulated toward the 2e^- pathway for hydrogen peroxide (H₂O₂) synthesis by varying the central metal atom. Notably, the NiSA-NC catalyst exhibits outstanding performance in neutral conditions, achieving 81.0 % H₂O₂ selectivity and a remarkable production rate of 2972.2 mmol L^-1 h^-1 g_cat.^-1, surpassing most previously reported catalysts. This work not only provides a general methodology for constructing high-loading TM-SACs but also offers new insights into the rational design of efficient electrocatalysts for sustainable chemical synthesis.