Proceedings of nanoGe Fall Meeting 2018 (NFM18)
Publication date: 6th July 2018
Solar energy converted hydrogen is becoming much more attractive as an energy storage material recently. GaN is one of a suitable material for evaluate this solar energy conversion by photoelectrochemical (PEC) reaction because GaN has good chemical stability and high crystal quality. However, n-type GaN photoanode shows anodic corrosion in the PEC reactions. NiO loading on the n-type GaN surface prevents this anodic corrosion. We investigated the effects of NiO loading on n-type GaN sample with and without PEC treatment in order to evaluate the carrier transfer mechanisms.
The working electrode was (0001) Ga-face n-type GaN (C.C. 2.0×1017 cm-3) grown by MOVPE. The NiO was deposited as NiO island shape by Ni(OH)2 dispersed solution [1]. The counter electrode was Pt and the light was Xe-lamp. The electrolyte was 1.0M NaOH (pH 13.4). The photocurrent density was measured for 180 min at zero bias.
The photocurrent density of the NiO loading sample was higher than the bare GaN sample and almost stable for 180 min. The sample surface after the reaction was mirror-like and not change. In contrast, the photocurrent density without NiO sample decreased 20% during 180 min treatment. The sample surface changed frosted glass like due to surface corrosion. The photocurrent density of the sample with NiO loading on the rough surface was also observed for 180 min. The increasing and stable photocurrent, which is observed the NiO loading sample before the treatment, did not occur. That is, the photocurrent density kept decreasing with the same rate of the bare GaN. The result shows that the reaction mechanisms with NiO loading were different between the smooth and rough surface. The suppression of anodic corrosion occurred only for the NiO loading on the GaN smooth surface. The majority number of hole are thought not to move from n-type GaN to NiO particle for the NiO loaded on the GaN rough surface. The carrier transfer mechanism probably related to the n-type GaN surface roughness from these results.
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