Exploring the hydrogen evolution reaction performance on a borophene monolayer

Borophene, a unique two-dimensional boron-based material with a graphenelike structure, has attracted growing interest due to its special configurations and remarkable physical and chemical properties. This study focuses on four different borophene phases: <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mi>α</a:mi> <a:mo>,</a:mo> <a:mo> </a:mo> <a:mrow> <a:mi>β</a:mi> <a:mn>12</a:mn> </a:mrow> <a:mo>,</a:mo> <a:mo> </a:mo> <a:mrow> <a:mi>γ</a:mi> <a:mn>3</a:mn> </a:mrow> </a:math> , and trigonal, and systematically investigates their hydrogen evolution reaction (HER) performance. By using density functional theory (DFT), we evaluate the intrinsic catalytic activity of freestanding borophene monolayers as well as the influence of an Ag(111) substrate on their HER behavior. The results indicate that the freestanding <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mi>α</b:mi> <b:mo>,</b:mo> <b:mo> </b:mo> <b:mrow> <b:mi>β</b:mi> <b:mn>12</b:mn> </b:mrow> </b:math> , and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mi>γ</c:mi> <c:mn>3</c:mn> </c:mrow> </c:math> phases exhibit excellent HER activity, characterized by optimal Gibbs free energies for hydrogen adsorption. Especially, the on-top site with the lowest coordination number is identified as the most active site. However, interaction with the Ag(111) support significantly modifies the hydrogen binding, leading to suppressed HER performance in these phases. In contrast, the trigonal phase displays relatively poor HER performance, attributed to its fully saturated bonding environment, while the silver substrate significantly modifies its geometric configuration and slightly enhances the HER performance. This work highlights both the promising intrinsic HER potential of borophene monolayers and the critical impact of substrate interactions, guiding the design of efficient borophene-based electrocatalysts.