Adsorption and photocatalytic splitting of water on graphitic carbon nitride: a combined first principles and semiempirical study

Abstract

Water adsorption on graphitic carbon nitride is studied by means of first principles and semiempirical calculations. Using a thermodynamic model, the photocatalytic water oxidation reaction is found to be hindered by a very large overpotential.

Abstract

Graphitic carbon nitride, g-C ₃N ₄, is a promising organic photo-catalyst for a variety of redox reactions. In order to improve its efficiency in a systematic manner, however, a fundamental understanding of the microscopic interaction between catalyst, reactants and products is crucial. Here we present a systematic study of water adsorption on g-C ₃N ₄ by means of density functional theory and the density functional based tight-binding method as a prerequisite for understanding photocatalytic water splitting. We then analyze this prototypical redox reaction on the basis of a thermodynamic model providing an estimate of the overpotential for both water oxidation and H ⁺ reduction. While the latter is found to occur readily upon irradiation with visible light, we derive a prohibitive overpotential of 1.56 eV for the water oxidation half reaction, comparing well with the experimental finding that in contrast to H ₂ production O ₂ evolution is only possible in the presence of oxidation cocatalysts.