Bandgap Engineering of Hydroxy‐Functionalized Borophene for Superior Photo‐Electrochemical Performance

Two‐dimensional (2D) semiconducting boron nanosheets (few‐layer borophene) have been theoretically predicted, but their band gap tunability has not been experimentally confirmed. In this study, hydroxy‐functionalized borophene (borophene‐OH) with tunable band gap was fabricated by liquid‐phase exfoliation using 2‐butanol solvent. Surface‐energy matching between boron and 2‐butanol produced smooth borophene, and the exposed unsaturated B sites generated by B−B bond breaking during exfoliation coordinated with OH groups to form semiconducting borophene‐OH, enabling a tunable band gap of 0.65–2.10 eV by varying its thickness. Photoelectrochemical (PEC) measurements demonstrated that the use of borophene‐OH to fabricate working electrodes for PEC‐type photodetectors significantly enhanced the photocurrent density (5.0 μA cm −2 ) and photoresponsivity (58.5 μA W −1 ) compared with other 2D monoelemental materials. Thus, borophene‐OH is a promising semiconductor with great optoelectronic potential.