Synthesis of ZnO-Cu doped ZnO homojunction photoanode for photoelectrochemical water splitting under visible light irradiation

The photoelectrochemical (PEC) splitting of water utilizing sunlight to produce hydrogen has attracted much attention in light of its potential to store solar energy in a convenient way [1, 2]. Among materials for PEC applications, ZnO has been widely investigated as a photoanode because of its favorable band-edge position, high photocatalytic activity, high electron mobility, low cost, non-toxicity, thermal and chemical stability but, photocatalytic properties of ZnO often limited by recombination of photoexcited electron-hole pairs [3]. This paper describes the fabrication of a ZnO-Cu doped ZnO homojunction (ZnO/ZnO:Cu) photoanode by facile and cost-effective electrodeposition method at low temperature to improve the charge separation for enhanced photoelectrochemical water oxidation. ZnO/ZnO:Cu photoanode achieved a maximum photocurrent density of ~50 μA/cm2 at 1 V vs. saturated calomel electrode (SCE), which was about 2 orders of magnitudes higher than the pristine ZnO nanorods (ZnO NRs) under visible light irradiation. This study reveals that ZnO/ZnO:Cu photoanode could facilitate the separation and restrain the recombination of photo-generated electron–hole pairs. Although both Cu-doped ZnO (ZnO:Cu) and ZnO/ZnO:Cu photoanodes exhibit better PEC performances in compare with ZnO NRs photoanode, ZnO/ZnO:Cu photoanode presents an additional charge separation effect due to band bending structure. Motte-Schottky plots show that the flat band potential of ZnO/ZnO:Cu photoanode is more negative than that of pure ZnO NRs, which is beneficial for water splitting.