Comparison of Forward and Reverse Reactions in Hydrogen Generation between GaN, InGaN, Nanocrystalline TiO₂ and Pt Electrodes during Water Electrolysis

Abstract

The electron transport between n-, p-GaN, and p-In 0:12 Ga 0:88 N electrodes and electrolyte solution is studied by cyclic voltammetry under dark conditions, and compared with that between Pt and nanocrystalline TiO 2 /Ti electrodes. Both forward and reverse reactions of 2H þ þ 2e À H 2 occur for Pt and TiO 2 /Ti electrodes. In contrast, in n-, p-GaN and p-In 0:12 Ga 0:88 N electrodes, only the forward reaction of 2H þ þ 2e À ! H 2 occurs and no reverse reaction is observed. These results are consistent with the finding that the conduction band-edge potentials of n-, p-GaN, and p-In 0:12 Ga 0:88 N are higher than the reduction potential of H þ (aq) in electrolyte, determined by flat-band potential measurement. These differences in potential work as an energy barrier for the reverse electron transfer from H 2 molecules to electrodes. These results also support the experimental results of spontaneous H 2 generation caused by the band-gap excitation of p-GaN and p-In 0:12 Ga 0:88 N electrodes without applying bias voltage.

Photoelectrochemical Properties of (In,Ga)N Nanowires for Water Splitting Investigated by in Situ Electrochemical Mass Spectroscopy

“…These values are significantly higher than those of p-In 0.12 Ga 0.88 N films which exhibited only 0.3 mA/ cm 2 at −1.9 V/NHE under 405 nm illumination with 30 mW/ cm 2 . 15 This comparison is consistent with the expected benefits of the NW geometry compared to planar films.…”

Significant improvements in InGaN/GaN nano-photoelectrodes for hydrogen generation by structure and polarization optimization

“…So far, various kinds of materials have been extensively investigated as photochemical catalysts, such as Fe 2 O 3 , BiVO 4 , Ta 3 N 5 , etc 2 7 8 . However, some of them suffer from a low carrier mobility 1 9 10 , which leads to the suppression of incident photon conversion efficiency (IPCE) 11 . BiVO 4 -based PEs have to work with the assistant of promoter under a high applied external bias 12 13 .…”

Enhanced InGaN/GaN photoelectrodes for visible‐light‐driven hydrogen generation by surface roughening

“…Visible‐light‐driven photoelectrochemical hydrogen generation has been intensively investigated as an environmental friendly and energy saving solution . Among most demonstrated photo catalysts materials, III‐nitride semiconductors are considered as promising candidates due to their adjustable direct band gap covering a very broad spectral range, especially InGaN alloys can perfectly match the solar spectrum . Furthermore, III‐nitride semiconductors have demonstrated high‐chemical stability in acid aqueous solutions as well as outstanding photoelectric characteristics .…”