Designing an isoelectronic counterpart to group III-V semiconductors: A novel honeycomb BeCN2 monolayer with ultra-high mobility toward solar driven overall water splitting and bifunctional oxygen evolution/reduction reaction

Abstract

Like group III-V materials, which have obviously broadened the scope of group IV family and enriched the semiconducting members, a lightest representative of group II−IV−V2 family, BeCN2 monolayer, as an isoelectronic counterpart to group III-V semiconductor has for long remained unsolved for its applications in HER/OER/ORR, although previous first-principles investigations have touched the configuration and existence toward multiple crystalline forms of BeCN2. Using density functional theory calculations, the stable BeCN2 monolayer is predicted to be a direct bandgap semiconductor with high ultraviolet light absorption, achieving photocatalytic overall water-splitting within full pH, whose photogenerated electrons/holes will provide an external potential to obviously reduce the overpotential of HER and even make it achieve a spontaneous OER within pH 0–14. Meanwhile, it presents significantly anisotropic and high carrier mobilities (104 order) with preferred electron/hole transport along the x/y-direction, providing rich and required charge sources for HER/OER/ORR. After TM-decoration, the catalytic activities are greatly enhanced, achieved by the low HER and OER/ORR overpotentials of 0.05/0.07 V for V/Co@BeCN2 and 0.79/0.43 V for Ni@BeCN2, respectively. Plus, under pH 0–14, the OER overpotential of Ni@BeCN2 can be completely overcome by the external potential provided by photogenerated holes, achieving bifunctional catalysis for OER and ORR. Particularly, the Ni-d orbital is evidently hybridized with the O-p orbital for OH*Ni@BeCN2, so that the initial lone electrons located at the anti-bonding orbital pair up can populate the downward bonding orbital, allowing the species *OH to be moderately adsorbed on Ni@BeCN2, and thus redound the performance of OER/ORR.