Porous boron nitride for combined CO2 capture and photoreduction

Porous and amorphous materials are typically not employed for photocatalytic purposes, like CO2 photoreduction, as their high number of defects can lead to low charge mobility and favour bulk electron-hole recombination. Yet, with a disordered nature can come porosity, which in turn promotes catalyst/reactant interactions and fast charge transfer to reactants. Here, we demonstrate that moving from h-BN, a well-known crystalline insulator, to amorphous BN, we create a semiconductor, which is able to photoreduce CO2 in the gas/solid phase, under both UV-vis and pure visible light and ambient conditions, without the need for cocatalysts. The material selectively produces CO and maintains its photocatalytic stability over several catalytic cycles. The performance of this un-optimized material is on par with that of TiO2, the benchmark in the field. For the first time, we map out experimentally the band edges of porous BN on the absolute energy scale vs. vacuum to provide fundamental insight into the reaction mechanism. Owing to the chemical and structural tunability of porous BN, these findings highlight the potential of porous BN-based structures for photocatalysis particularly solar fuel production.