On the Origin of High Hydrogen Evolution Catalytic Activity and Stability in Cobalt-Embedded C₂N

Transition metal-embedded two-dimensional materials have recently drawn significant research interest because they can serve as excellent catalysts in fuel cells, hydrogen production devices, etc. Especially, cobalt oxide encapsulated in C₂N (<a href="mailto:Co@C2N">Co@C₂N</a>) was recently shown to exhibit excellent catalytic performance for hydrogen evolution reaction (HER) together with high stability [1], but their precise understanding still remains elusive. Based on first-principles calculations, we herein scrutinize the mechanisms of enhanced HER performance of <a href="mailto:Co@C2N">Co@C₂N</a>, particularly focusing on the role of C₂N. We explore three plausible mechanisms that include (i) single-atom catalyst, (ii) quantum tunneling from substrate, and (iii) atomic-cluster catalyst. Among the three, we find that the atomic-cluster catalyst mechanism, in which few-atom Co cluster encapsulated within the holey region formed between two C₂N layers explains the experimentally-observed high HER activity. The atomic-cluster catalyst might prove to be a general mechanism for the TM-embedded two-dimensional catalysts.
[1] Mahmood, J. et al, Chem. Mater. 27, 4860 (2015)