Wood-derived single-atom catalysts via scalable in situ chloride etching strategy for zinc-air batteries

Abstract

Carbon-supported nitrogen-coordinated single metal-site (M-N-C) catalysts are considered ideal platinum group metal (PGM)-free cathode catalysts for zinc-air batteries (ZABs) due to their high metal utilization efficiency, unique size-dependent quantum effects, and excellent catalytic activity. However, large-scale, sustainable preparation of M-N-C catalysts remains a significant challenge owing to the complex synthesis procedures and the difficulty in achieving an optimal coordination environment between metal atoms and the carbon matrix. In this study, we develop a large-scale preparation method for Fe-N-C catalysts, which directly utilizes lignocellulosic materials through in situ etching and carbonization, without the need for pickling. During the in situ etching process, chloride ions (Cl−) weaken the hydrogen bonds in lignocellulose, facilitating the dissolution of cellulose, hemicellulose, and lignin, thus creating abundant micropores. The Fe-N4 active site is successfully formed during the subsequent carbonization process. The resulting SA-FeN4/PC catalyst, benefiting from its porous structure and homogeneous dispersion of Fe-N4 sites, exhibits enhanced oxygen reduction and evolution reaction (ORR/OER) performance and superior stability. When used as the cathode in ZABs, SA-FeN4/PC demonstrates long-term stability, maintaining 520 h of operation at a current density of 5 mA/cm2. Furthermore, by varying the metal cation, we successfully prepare other metal-nitrogen-carbon catalysts (SA-MN4/PC, where M refers to Co, Ni, and Cu). This scalable synthesis strategy shows significant potential for the preparation of wood-based single-atom catalysts for high-temperature applications.