Optimized magnetron-sputtered CuFeO₂ thin films for PEC water spitting application

CuFeO₂ (CFO) has been recently identified as a promising photocathode material for photoelectrochemical (PEC) water splitting. However, this p-type semiconductor suffers from poor photo-induced electron–hole separation and charge collection. In this study, CFO thin films were successfully sputtered via a magnetron sputtering technique, and their PEC experiments were carried out under front-side chopped illumination in 1M NaOH electrolyte against a Ag/AgCl reference electrode. In argon, the thin films produced low photocurrent, while in oxygen, it enhanced the photocurrent and rose to 0.55 mAcm^-2 at 0.4 V vs. RHE (V_RHE). The synthesis parameters dictated the water splitting efficiency; when the power of the Fe target increased from 160 W to 200 W, the photo-current density enhanced and reached the highest value of 0.55 at 0.4 V vs. RHE (V_RHE) due to its lower charge transfer resistance according to EIS data. Similarly, the Cu power was optimized in which the highest J-V was produced with a power of 40 W rather than 60 and 80 W. The other constituent of CFO that affects the PEC activity is oxygen; an oxygen flow rate of 2 sccm (with O₂:Ar = 1:9) was optimal; increasing this further reduced the J-V. AFM spectroscopy revealed that the roughness of the thin films increased as a function of Fe and Cu sputtering power, whereas SEM-EDAX inferred a homogeneous distribution of the elemental constituents.