Ab-initio Characterization of a Novel Photocathode for Water Splitting: Bulk and Surface Properties of CuFeO2

Recent experiments have highlighted the delafossite CuFeO2 (CFO) as a promising candidate in the role of the photocathode in photoelectrochemical water splitting cells, yet in spite of these encouraging results, improvement in the catalytic activity and charge separation is required. Currently, we lack an adequate theoretical characterization to provide insight that can direct further experimental investigations. In this work, we present a theoretical characterization of CFO based on the DFT+U approach and refined with hybrid calculations. In particular, we characterized the stability of bulk CFO with respect to other iron and copper oxides in the air and in an aqueous environment, coupling Density Functional Theory with Ab-Initio Thermodynamics. We investigated the structure, electronic properties and thermodynamic stability of CuFeO_2 surfaces, both in vacuum and in an electrochemical environment. To estimate the alignment of the band edges on the electrochemical scale, we perform ab-initio molecular dynamics in explicit water, unravelling the structure of the solid/liquid interface for various surface terminations. We consider both the system in the dark and under illumination, showing that light absorption can induce a partial reduction of the surface. Using the free energy of adsorption of hydrogen as a descriptor of the catalytic activity for HER, we show that hydride species formed at oxygen vacancies can be highly active, and could therefore be an intermediate of reaction.