Towards zero bias photoelectrochemical water splitting: onset potential improvement on a Mg:GaN modified-Ta₃N₅ photoanode

Nurlaela, Ela; Sasaki, Yutaka; Nakabayashi, Mamiko; Shibata, Naoya; Yamada, Taro; Domen, Kazunari

Towards zero bias photoelectrochemical water splitting: onset potential improvement on a Mg:GaN modified-Ta₃N₅ photoanode

2018

Tantalum nitride (Ta₃N₅) based photoanodes were overlaid with magnesium-doped gallium nitride (Mg:GaN) thin films by using a plasma-enhanced chemical vapor deposition (PCVD) technique, and subjected to photoelectrochemical activity tests, aiming for a negative shift of onset potential for O₂ evolution. A remarkable negative shift of the onset potential was observed after annealing Mg:GaN in N₂ gas, reaching 0 V vs. RHE, despite a lower photocurrent than that on bare Ta₃N₅. Mg:GaN annealed in NH₃ exhibited an improvement of the photocurrent. A detailed study of the photoelectrochemical performance for various samples and a thorough characterization have revealed the effects of N₂/NH₃ post annealing on Mg activation/Ta₃N₅ damage recovery, controlling the onset potential shift and the current density improvement. N₂ post annealing shifted the onset potential to 0 V vs. RHE but decreased the current density. On the other hand, NH₃ post annealing slightly shifted the onset potential and increased the current density largely. Despite the current density loss, this onset potential shift unlocks the prospect of unassisted photoelectrochemical water splitting on Ta₃N₅.

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