Borophene-supported single transition metal atoms as potential oxygen evolution/reduction electrocatalysts: a density functional theory study.

Due to the maximal atom utilization, high activity, and selectivity, the two-dimensional (2D) matrix supported single-atom catalysts (SACs) have attracted substantial research interests. In this work, we carried out the theoretical study on the stability, activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), and its dependence on the electronic structure of transition metal (TM) anchored on two types of borophene (called β12 and χ3) by density functional theory (DFT) calculations. The results show that the early- and VIII-TM anchored β12 and χ3 borophenes are structurally and thermodynamically stable. The overpotentials of OER (ηOER) over the Ni supported on β12 and χ3 borophene SACs, designated as β12-Ni and χ3-Ni, are 0.38 and 0.35 V, respectively. The ηORR of β12-Ni and χ3-Ni are estimated to be as low as 0.34 and 0.39 V, respectively. The OER/ORR activity of the SACs can be well correlated with their electronic structures. The high ηOER values of early TM supported on borophene SACs correspond to high d-band center of TM. Both β12-Ni and χ3-Ni have a moderate d-band center. Since the overpotentials for OER and ORR on β12-Ni and χ3-Ni are comparable to those of Pt group metals and their oxides, β12-Ni and χ3-Ni can be considered as the promising bifunctional catalysts for OER and ORR.