Robust Protection of III–V Nanowires in Water Splitting by a Thin Compact TiO₂ Layer

Abstract

Narrow-band-gap III–V semiconductor nanowires (NWs) with a suitable band structure and strong light-trapping ability are ideal for high-efficiency low-cost solar water-splitting systems. However, due to their nanoscale dimension, they suffer more severe corrosion by the electrolyte solution than the thin-film counterparts. Thus, short-term durability is the major obstacle for using these NWs for practical water-splitting applications. Here, we demonstrated for the first time that a thin layer (∼7 nm thick) of compact TiO 2 deposited by atomic layer deposition can provide robust protection to III–V NWs. The protected GaAs NWs maintain 91.4% of its photoluminescence intensity after 14 months of storage in ambient atmosphere, which suggests the TiO 2 layer is pinhole-free. Working as a photocathode for water splitting, they exhibited a 45% larger photocurrent density compared with unprotected counterparts and a high Faraday efficiency of 91% and can also maintain a record-long highly stable performance among narrow-band-gap III–V NW photoelectrodes; after 67 h photoelectrochemical stability test reaction in a strong acid electrolyte solution (pH = 1), they show no apparent indication of corrosion, which is in stark contrast to the unprotected NWs that fully failed after 35 h. These findings provide an effective way to enhance both stability and performance of III–V NW-based photoelectrodes, which are highly important for practical applications in solar-energy-based water-splitting systems.

Synthesis of vertical WO3 nanoarrays with different morphologies using the same protocol for enhanced photocatalytic and photoelectrocatalytic performances

“…The illumination source used was a 500 W Xe arc lamp (CEL-HXF300) with a AM 1.5 G filter. The measured potentials vs. Ag/AgCl were converted to the potentials vs. reversible hydrogen electrode (RHE) using the following Nernst equation: 25 E RHE = E Ag/AgCl + 0.059pH + E 0 Ag/AgCl …”

Tandem Nanostructures: A Prospective Platform for Photoelectrochemical Water Splitting

“…The representative materials include Si and III‐V compound semiconductors, which possess tunable bandgaps for light absorption in the spirit of the well‐known band gap engineering including relatively narrow band gaps, e.g., 1.1 eV for Si, 1.05 eV for GaInAsP lattice‐matched to InP, 1.35 eV for InP, 1.42 eV for GaAs, or 1.90 to 2.23 eV for AlGaInP lattice‐matched to GaAs [28b,29] . For example, the GaAs‐ and Si‐based core‐shell PEC photoelectrodes had been reported by Cui's and Jaramillo's groups, respectively ( Figure ) [13a,22] . However, these materials usually suffer from corrosion during the PEC reactions.…”

“…SEM a) and higher‐magnification TEM b) images of the GaAs NW/TiO 2 photoelectrode. Reproduced with permission [13a] . Copyright 2021, American Chemical Society.…”

“…Though the mentioned above strategies have promoted the development of PEC water splitting to a great extent, the industrialized application of it still faces the challenge on account of the cost, efficiency and availability. Tandem nanostructures consisting of rationally designed nanostructured units represent an effective photoelectrode configuration to break the performance bottleneck imposed by the unitary nanostructure, which include the following types: 1) core‐shell nanostructures for single photoelectrode, which combines the highly‐absorbent material (such as Si, [ 12 ] III‐V compound semiconductors, [11c,13] etc.) as the core, while the metal oxides shell as buffer and protective layer, [12a,13a,14] and the cocatalyst anchored on the metal oxides shell [ 15 ] ; 2) two‐photoelectrode tandem cell assembled in parallel or in monolithic to realize the highly‐efficient or unassisted water splitting, where the photocathode produces hydrogen with the photoanode generating oxygen simultaneously, and the self‐driven bias depends on the difference of aligned Fermi levels in photocathode and photoanode, respectively [ 16 ] ; 3) tandem nanostructures of plasmon related devices for the improvement of PEC water splitting, where nanostructures of noble metals like Au or Ag are surrounded by semiconductors in a layered tandem structure [ 17 ] or in a Janus heteronanostructure, [3b,18] and the specific mechanisms of plasmons such as hot electron injections, local electric field enhancement, and resonance energy transfer could be clarified more clearly in the regular structure.…”

Enhanced Light Trapping in GaAs/TiO2-Based Photocathodes for Hydrogen Production

“…III–V nanowires (NWs) present a high aspect ratio improving their light-trapping efficiency and have a strong ability to be grown on low-cost silicon substrate, making them particularly attractive to design innovative photoelectrodes for light-driven water splitting . While many studies have been focusing on the use of III–V NWs as photoanodes for the OER, only few reports are available on the use of these materials as photocathodes for the HER. − A recent work by Zhou et al indicated a significant enhancement of the STH efficiency, reaching performances close to 10% using the GaP NW combined with a complex heterostructure and band gap engineering . If the corrosion of these materials has limited the viability of their use in actual devices thus far, Cui et al recently demonstrated the possibility to overcome this issue by protecting the surface of the nanowires with a thin TiO 2 oxide layer .…”