NaCl-Assisted Pyrolysis of Zn (II) Complexes with BTC and PDC to Synthesize Cl, N-Codoped Carbon Highly Efficient for Oxygen Reduction

The design of high-performance, cost-effective, and durable electrocatalysts for the oxygen reduction reaction (ORR) is essential for the widespread deployment of clean energy technologies, including fuel cells and metal-air batteries. Carbon-based metal-free catalysts (CMFCs) have emerged as promising alternatives to Pt-based materials, with their ORR performance tunable through heteroatom doping and defect engineering. In this study, we report a novel Cl, N-codoped porous carbon catalyst (Cl, N-C) enriched with structural defects, synthesized via a modified metal-organic framework (MOF) strategy. Zinc-1,3,5-benzenetricarboxylate (Zn-BTC) was employed as the MOF precursor, with partial substitution of BTC by pyridine-3,5-dicarboxylate (PDC) to introduce nitrogen and defect sites. During Zn-BTC-PDC pyrolysis, NaCl was added to enable Cl doping and promote further defect formation. Structural characterization reveals that the optimized catalyst (Cl, N-C-2) possesses abundant mesopores, high defect density, and a favorable distribution of pyridinic and graphitic nitrogen species. As a result, Cl, N-C-2 exhibits outstanding ORR activity in alkaline media, achieving a half-wave potential of 0.891 V vs RHE, which ranks among the highest reported to date for CMFCs. Electrochemical analyses demonstrate enhanced electrochemically active surface area, faster kinetics, and excellent durability. In situ ATR-SEIRAS measurements further reveal that Cl doping promotes the formation and stabilization of key OOH intermediates, facilitating a dominant four-electron ORR pathway. When applied as an air cathode in Zn-air batteries, Cl, N-C-2 delivers higher discharge voltage and power density than Pt/C. This work provides an effective strategy for designing high-performance metal-free carbon electrocatalysts through synergistic heteroatom doping and defect engineering.