Regulation mechanisms of electron-delocalized single transition metal-doped Mo2CO2 MXene hydrogen evolution reaction catalysts

Two-dimensional (2D) Mo-based MXenes (Mon+1CnTx) are recognized to have significant potential as hydrogen evolution reaction (HER) activity electrocatalysts. However, appropriate descriptors are absent to predict the H-adsorption Gibbs energy (Delta G(H)) due to the unique delocalized electronic properties of the Mo atom. In this paper, we used first-principles calculations and machine learning to study the HER activity of Mo2CO2 with single transition metal-doped (Mo2CO2-STM), and elucidate the mechanisms by which single transition metals (STMs) regulate the hydrogen evolution reaction. Our results revealed that Delta G(H) has a "W" shape as a function of the doped atom changing in one period. The electronic structure analysis indicates that the electronic delocalized Mo has a longer range affecting not only the nearest atoms, but the second-nearest neighbor (STM-Mo) bonding effect controls the periodic distribution of Delta G(H). Using machine-learning method, we quantized the STM regulation mechanism using five key structural and electronic descriptors, and predicted the Delta G(H) of Mo2CO2-STM, which were also extended to W2CO2-STM successfully. Our findings highlight the importance of considering second-nearest-neighbor bonding effects in similar delocalized materials systems research.