Design, Synthesis, and Performance of Heme-Derived Carbon Towards Electrocatalytic Oxygen Reduction Reaction

Developing highly efficient, stable, and cost-effective non-precious metal electrocatalysts to replace traditional platinum-based materials is of great significance for advancing the commercialization of advanced energy conversion devices, such as zinc-air batteries (ZABs). Herein, we propose a facile and highly efficient strategy to successfully prepare a defect-rich, highly active nitrogen-doped porous carbon-based electrocatalyst, U-Fe-N-C (Urea-assisted synthesized iron-nitrogen-carbon material), via a high-temperature co-pyrolysis treatment of heme in the presence of urea. The study demonstrates that urea not only acts as an excellent nitrogen source during pyrolysis, introducing abundant topological defects and heteroatom doping sites, but also prompts the carbon substrate to form a hierarchical sponge-like porous structure with a high specific surface area. This unique microenvironment effectively prevents the agglomeration of iron species at high temperatures, achieving efficient anchoring and high dispersion of catalytic active centers. Electrochemical tests indicate that under optimal synthesis conditions (precursor mass ratio of 1:3, calcination at 900 °C), U-Fe-N-C exhibits outstanding oxygen reduction reaction (ORR) catalytic activity (with a half-wave potential reaching 0.731 V vs. RHE) and possesses long-term durability far exceeding that of commercial Pt/C. Furthermore, liquid rechargeable zinc-air batteries assembled with U-Fe-N-C as the air cathode demonstrate exceptional stability, achieving up to 270 h of charge-discharge cycling without attenuation. This study not only provides profound insights into the mechanisms of pore formation and assistance but also offers a novel perspective for the rational design and scalable synthesis of high-performance metal-nitrogen-carbon (M-N-C) electrocatalysts.