Iodine-Doping-Induced Electronic Structure Tuning of Atomic Cobalt for Enhanced Hydrogen Evolution Electrocatalysis

The development of strategies for tuning the electronic structure of the metal sites in single-atom catalysts (SACs) is the key to optimizing their activity. Herein, we report that iodine doping within the carbon matrix of a cobalt-nitrogen-carbon (Co-N-C) catalyst can effectively modulate its electronic structure and catalytic activity toward the hydrogen evolution reaction (HER). The iodine-doped Co-N-C catalyst shows exceptional HER activity in acid with an overpotential of merely 52 mV at 10 mA cm^-2, a small Tafel slope of 56.1 mV dec^-1, making it among the best SACs based on both precious and nonprecious metals. Moreover, this catalyst possesses a high turnover frequency (TOF) value of 1.88 s^-1 (η = 100 mV), which is about 1 order of magnitude larger than that (0.2 s^-1) of the iodine-free counterpart. Experimental and theoretical studies demonstrate that the introduction of iodine dopants lowers the chemical oxidation state of the Co sites, resulting in the optimized hydrogen adsorption and facilitated HER kinetics. This work provides an alternative strategy to regulate the electronic structure of SACs for improved performance.