Enhanced photoelectrochemical stability of GaN photoelectrodes by AlO surface passivation layer.

Photoelectrochemical (PEC) water splitting is one of the most promising hydrogen production methods because of its high efficiency, renewable resources and harmless by-products. Gallium nitride (GaN) is suitable for PEC water splitting because it has excellent stability in electrolyte and band gap energy which straddles the redox potential of water (V = 1.23 V). These characteristics allow this material to split water stably without external bias. However, the stability of GaN is still not sufficient for practical applications. In this study, we investigated the properties of GaN photoelectrodes with aluminum oxide (AlO) thin film as a protection layer for increasing stability. In a long-term stability test, AlO-coated GaN showed more stable photocurrent than that of bare GaN. The total hydrogen production amount was also improved in AlO-coated samples than bare GaN. These results indicate that the AlO protection layer significantly enhances stability and hydrogen production.