Single-Step Preparation of Large Area TiO2 Photoelectrodes for Water Splitting

The fast, single-step and easily scalable production by plasma electrolytic oxidation (PEO) of large area TiO2 electrodes with excellent photoactivity in water splitting under simulated solar light is systematically investigated here. In particular, the effects that the cell voltage (100-180 V) and the processing time (0.5-15 min) have on the electrode properties are studied. The PEO-produced oxide layers are porous, the predominant crystalline structure shifting from anatase, to an anatase-rutile mixture, and finally to rutile by rising the cell voltage. The electrodes show a double-layered structure, with a more compact layer at the interface with the titanium substrate and a thick porous layer on the external surface. The photocurrent density versus wavelength reflects the phase composition, with a maximum incident photon-to-current efficiency of 90% at 320 nm. The highest H-2 production rate is attained with the mixed anatase-rutile electrode prepared by 300 s-long PEO at 150 V.