Thermodynamic Stability and Native Point Defects of CuFeO₂ Photocathodes in Dry and Electrochemical Environments

CuFeO₂ has been recently identified as a promising photocathode material for photoelectrochemical water splitting cells. In spite of the first encouraging results, improvements in the catalytic activity and charge separation are required and an adequate theoretical characterization is currently not available to complement experimental results. We present a first-principles investigation of the bulk properties of CuFeO₂, focusing in particular on its stability in air and in an aqueous environment. Here, we show that while the material is in a metastable phase in air at ambient conditions, the electrochemical environment strongly stabilizes it. In fact, at conditions of applied bias and pH used in the experiments, the material operates within its region of thermodynamic stability, thus explaining its remarkable resistance to corrosion. We investigated the formation energy of native point defects in the stability region, predicting a small formation energy for an antisite defect, which could be detrimental for the performance of CuFeO₂ as a photocathode, since defect states lying inside the gap may favor the electron–hole recombination.