Morphology and Photoelectrochemical Properties of Sputtered WO ₃ :Mo Anodes

We present an investigation of sputtered WO 3 :Mo thin films as anodes for photoelectrochemical water splitting. The films were deposited by reactive sputtering from a W:Mo target ( w Mo = 10 at.%) on SnO 2 :F/glass with a systematic variation of the pressure p (0.40, 0.55, 0.70 Pa), the oxygen partial pressure p O2 (4–19 mPa), the substrate temperature T s (245, 280, 320 °C), the deposition rate r (0.6–7.8 nm min –1 ), and the thickness d (0.83–1.88 µm). For high T s , the layers consist of well‐defined crystals, whereas samples grown at a lower temperature show a high percentage of microcrystalline structures. The morphology correlates with the photocurrent density J , which is generally higher for crystalline layers. No correlations were found between J and p , p O2 , r , or d in the investigated parameter space. The highest measured J was 0.784 mA cm –2 at a potential of 1.23 V versus RHE.