Tailoring the d-band center by borophene subunits in chromic diboride toward the hydrogen evolution reaction

Abstract

Transition metal diborides (TMdBs AlB₂-type P6/mmm) electrocatalysts have aroused much attention toward the hydrogen evolution reaction (HER), because MoB₂ (P6/mmm) exhibits superior catalytic activity. However, the understanding of the activity in the different lattice planes of TMdBs is still limited, which impedes the accurate design of new superior catalyst based on TMdBs. In this work, a borophene subunit was utilized to form AlB₂-type CrB₂ (P6/mmm) for modulating the d-band center. It was revealed that the d-band center in CrB₂ has almost a linear relation with the ΔG_H* value in the different lattice planes of metallic Cr and CrB₂, and that the modulation of the electronic structure by borophene subunits was more effective at the edge side than in the basal plane of CrB₂. Single-phase CrB₂ was synthesized via a high pressure and high temperature (HPHT) approach as an electrocatalyst for HER. The performance of CrB₂ revealed a higher catalytic activity with overpotentials of 355 and 522 mV at 10 and 200 mA cm⁻² in acidic conditions and a Tafel slope of 77.84 mV dec⁻¹. These results indicate that CrB₂ is a promising alternative to noble metal-based catalysts, and that modulating the d-band center by borophene subunits is an efficient way to develop novel Cr-based catalysts.