Facile Two-Step Synthesis of Delafossite CuFeO2 Photocathodes by Ultrasonic Spray Pyrolysis and Hybrid Microwave Annealing

Delafossite CuFeO2 photocathodes have recently attracted attention for water splitting due to their suitable band gap (∼1.5 eV) and high stability in aqueous media. The preparation of CuFeO2 usually requires long and energy‐intense treatments in an inert atmosphere for the full conversion of spinel CuFe2O4 to delafossite CuFeO2. Herein, we report the preparation and characterization of highly uniform and stable CuFeO2 thin films obtained via a combination of inexpensive ultrasonic spray pyrolysis followed by a short hybrid microwave treatment (∼4 min). The resulting films show good stability in alkaline media and produce a photocurrent of ∼650 μA/cm2 under 1.5 AM simulated sunlight and with oxygen bubbling. The effect of the rapid transformation from the spinel to the delafossite phase induced by hybrid microwave annealing was investigated with synchrotron‐based X‐ray absorption spectroscopy (XAS) and X‐ray photoelectron spectroscopy (XPS).