Metal-Doped CB Monolayer as the Promising Electrocatalyst for Hydrogen/Oxygen Evolution Reaction: A Combined Density Functional Theory and Machine Learning Study.

The development of high-efficiency electrocatalysts for hydrogen evolution reduction (HER)/oxygen evolution reduction (OER) is highly desirable. In particular, metal borides have attracted much attention because of their excellent performances. In this study, we designed a series of metal borides by doping of a transition metal (TM) in a CB monolayer and further explored their potential applications for HER/OER via density functional theory (DFT) calculations and machine learning (ML) analysis. Our results revealed that the |Δ| values of Fe-, Ag-, Re-, and Ir-doped CB are approximately 0.00 eV, indicating their excellent HER performances. On the other hand, among all the considered TM atoms, the Ni- and Pt-doped CB exhibit excellent OER activities with the overpotentials smaller than 0.44 V. Together with their low overpotentials for HER (<0.16 V), we proposed that Ni/CB and Pt/CB could be the potential bifunctional electrocatalysts for water splitting. In addition, the ML method was employed to identify the important factors to affect the performance of the TM/CB electrocatalyst. Interestingly, the results showed that the OER performance is closely related to the inherent properties of TM atoms, i.e., the number of d electrons, electronegativity, atomic radius, and first ionization energy; all these values could be directly obtained without DFT calculations. Our results not only proposed several promising electrocatalysts for HER/OER but also suggested a guidance to design the potential TM-boron (TM-B)-based electrocatalysts.