title: Band Gap Engineering in a 2D Material for Solar-to-Chemical Energy Conversion.
abstract: The electronic structure of 2D semiconductors depends on their thickness, providing new opportunities to engineer semiconductors for energy conversion, electronics, and catalysis. Here we show how a 3D semiconductor, black phosphorus, becomes active for solar-to-chemical energy conversion when it is thinned to a 2D material. The increase in its band gap, from 0.3 eV (3D) to 2.1 eV (2D monolayer), is accompanied by a 40-fold enhancement in the formation of chemical products. Despite this enhancement, smaller flakes also have shorter excited state lifetimes. We deduce a mechanism in which recombination occurs at flake edges, while the "van der Waals" surface of black phosphorus bonds to chemical intermediates and facilitates electron transfer. The unique properties of black phosphorus highlight its potential as a customizable material for solar energy conversion and catalysis, while also allowing us to identify design rules for 2D photocatalysts that will enable further improvements in these materials.
authors.affiliation: Department of Chemistry and ‡Department of Applied Physical Sciences, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Jun
authors.initials: J
authors.lastname: Hu
authors.affiliation: Department of Chemistry and ‡Department of Applied Physical Sciences, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Zhenkun
authors.initials: Z
authors.lastname: Guo
authors.affiliation: Department of Chemistry and ‡Department of Applied Physical Sciences, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Mcwilliams
authors.affiliation: Department of Chemistry and ‡Department of Applied Physical Sciences, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: John E
authors.initials: JE
authors.lastname: Darges
authors.affiliation: Department of Chemistry and ‡Department of Applied Physical Sciences, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Druffel
authors.affiliation: Department of Chemistry and ‡Department of Applied Physical Sciences, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Moran
authors.affiliation: Department of Chemistry and ‡Department of Applied Physical Sciences, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Scott C
authors.initials: SC
authors.lastname: Warren
keywords: Phosphorene; black phosphorus; photocatalysis; quantum confinement; solar energy; two-dimensional material