Effects of deposition parameters and cobalt hexacyanocobaltate surface modification on magnetron-sputtered ZnIn₂S₄ thin film photoanodes

For the first time, ZnIn₂S₄ (ZIS) thin films were successfully prepared by magnetron sputtering and systematically investigated as photoanodes for photoelectrochemical (PEC) water splitting. The PEC performance of the layers strongly depended on the deposition parameters. The highest photocurrent density of 2.77 mA cm⁻² at 1.62 V vs. RHE was achieved for films deposited at 200 °C for 90 min, whereas films deposited at 300 °C for 90 min exhibited improved stability. The optimized ZIS photoanode was subsequently modified with a cobalt hexacyanocobaltate (Cohcc) surface layer formed via electrooxidation of a Co layer in an electrolyte containing Co(CN)₆³⁻. This surface modification improved photoanode performance, particularly in terms of stability, likely due to enhanced oxygen evolution reaction (OER) kinetics at the electrode surface. Cohcc-modified photoanode generated almost 3 times higher photocurrent density after 100 s operation compared to unmodified photoanode. Electrochemical measurements performed under dark conditions further confirmed the role of Cohcc as cocatalyst toward OER. Overall, the results demonstrate that magnetron sputtering enables effective control over the properties of ZIS photoanodes through optimization of deposition parameters, while surface modification with cobalt hexacyanocobaltate represents a viable strategy for tuning interfacial kinetics and improving the functional performance of ZIS-based photoanodes.