Promoting Water Activation by Photogenerated Holes in Monolayer C2N

In photocatalytic reactions, the activation of H2O is very important for achieving high energy conversion efficiency. However, its activation mechanism under photoirradiation is still not fully understood. Here, on the basis of first-principles calculations, the role of photogenerated holes on the activation of H2O is investigated in a typical photocatalytic material C2N. The H2O molecule adsorbs at the six-membered N pore of C2N with a dual H-bonding configuration. Due to the electrostatic repulsion between the O atom of H2O and six N atoms of C2N, the energy level of the H2O molecule's highest occupied molecular orbital is raised significantly to exceed the valence band maximum of C2N, so that the photogenerated holes in C2N can be quickly captured by the H2O molecule. The captured photogenerated holes boost the activation of H2O and reduce the dissociation energy barrier from 1.61 to 0.69 eV. Besides, p-type defects of C2N have similar effects as photogenerated holes.