Water Photo-Oxidation Reaction on Clean and Doped Two-Dimensional Graphitic C 2 N

In the search for new efficient photo-catalysts for hydrogen production through water splitting, the main attention has been paid to tuning the band gap width and its position with respect to vacuum level. However, actual electro-catalytic activity for the water oxidation reaction on a catalyst surface is no less important than those quantities. In this work we evaluate from first principles the thermodynamics of the reaction on relatively new candidates for water splitting: two-dimensional C2N and that doped with phosphorus. We find that the 4-step reaction usually expected for water splitting will not proceed on these systems, resulting in oxygen atoms left strongly adsorbed to the surface. Another option, a 3-step reaction, is also found to be unfavorable. We also test an effect of higher oxygen coverage on the reaction thermodynamics, as suggested elsewhere. We find that, indeed, the doubled O-coverage makes the 4-step reaction feasible for the doped C2N. However, an unacceptably high anode potential is required to make this reaction proceed. We thus conclude that the materials under consideration may not be efficient electro-catalysts for water splitting.