Strain-Engineered Metal-Free h‑B₂O Monolayer as\na Mechanocatalyst for Photocatalysis and Improved\nHydrogen Evolution Reaction

Abstract

Developing\nstable metal-free materials with a highly efficient\nhydrogen evolution reaction (HER) has received intense research interest\ndue to its renewable and environmentally friendly properties. In this\nwork, we systematically investigated the HER catalytic activity of\na new h-B₂O monolayer based on first-principles calculations.\nThe results show the B site in the h-B₂O structure is energetically\nfavorable for hydrogen with the calculated Gibbs free energy (Δ<i>G</i>_H*) of −0.07 eV, which is comparable\nto that of the Pt catalyst (Δ<i>G</i>_H* = −0.09 eV). Moreover, the catalytic activity of the h-B₂O monolayer is quite robust with increasing hydrogen coverages\n(from 1/9 to 9/9). Interestingly, the HER activity of the h-B₂O monolayer is sensitive to the strains-driven.\nFor example, applied tensile strains (0–2%) could weaken the\nbonding between hydrogen and the substrate, resulting in Δ<i>G</i>_H* even close to 0 eV. However, the opposite\ntrend is found for applied compressive strain. After analyzing the\ndensity of states (DOS), we found the h-B₂O monolayer with\nabsorbed hydrogen retains the metallic property, still exhibiting\nexcellent electrical conductivity. These results reveal that the metal-free\nh-B₂O monolayer is a promising candidate for HER applications.