Morphology-controlled In₂O₃ nanostructures enhance the performance of photoelectrochemical water oxidation

Abstract

Nanotower- and nanowall-like indium oxide structures were grown directly on fluorine-doped tin oxide (FTO)/In2O3 seeded substrates and pristine FTO substrates, respectively, by a straightforward solvothermal method. The tower-like nanostructures are proposed to form via a self-assembly process on the In2O3 seeds. The wall-like nanostructures are proposed to form via epitaxial growth from the exposed edges of SnO2 crystals of the FTO substrate. The nanotowers and nanowalls are composed of highly crystalline and ordered nanocrystals with preferred orientations in the [111] and [110] directions, respectively. The two structures display remarkably different activities when used as photoanodes in solar light-driven water splitting. X-ray photoelectron spectroscopy results suggest an increased density of hydroxyl groups in the nanowalls, which results in a decrease of the work function and a concomitant shift in the onset potential of the photocurrent in the linear sweep voltammograms, which is further confirmed by Mott-Schottky and flat-band potential measurements, indicating the importance of hydroxyl content in determining the photoelectrochemical properties of the films. Morphology-controlled, nanostructured transparent conducting oxide electrodes of the kind described in this paper are envisioned to provide valuable platforms for supporting catalysts and co-catalysts that are intentionally tailored for efficient light-assisted oxidation of water and reduction of carbon dioxide.

Chemical‐Bath‐Deposited Indium Oxide Microcubes for Solar Water Splitting

“…In addition, the In 2 O 3 nanowires fabricated by Meng et al using CVD, exhibitedalower photocurrent density ( % 0.41 mA cm À2 )t han those of the films fabricated in this presents tudy. [38] Chen and co-workers [14] solvothermally synthesized In 2 O 3 nanotowers and nanowalls with photocurrent densities of 0.40 and 0.26 mA cm À2 ,r espectively,w hereas Lei et al [37] fabricated In 2 O 3 nanosheetsb yt he hydrothermal method with ap hotocurrent density of approximately 0.10 mA cm À2 ,w hich is significantly lower than those of the microcubes produced in the present study.…”

“…As aw ide-band-gap material (E g % 3.6 eV), In 2 O 3 is used extensively in optoelectronic devices, such as lasers, light emitting diodes,a nd flat panel displays. [14][15][16][17] It exhibits excellent conductivity and stabilityi na queous systems, [18] and has also been reportedt oh avec onduction and valence bands that are appropriately positioned for driving the necessaryr edox reactions for water splitting. [19] However,In 2 O 3 is transparent to visible light, owing to its large band gap;t his limits its potential for use in water splitting.…”

Synergistic Effect of Si Doping and Heat Treatments Enhances the Photoelectrochemical Water Oxidation Performance of TiO2 Nanorod Arrays

“…In the dark, the A–V‐Si:TiO 2 nanorod film shows very low current density, which is ≈1 µA cm −2 (Figure a, curve I′). Even in the range of 1.23–1.85 V, the dark current density still keeps such low value, indicating that the charge transfer is prevented due to the overpotential required to initiate water oxidation …”

“…Actually, the thickness of the semiconductor layer of the photoelectrodes is a contradiction: the thicker semiconductor can absorb more incident light; however, the photoexcited carriers in the bulk of the thick semiconductor layer are difficult to diffuse to the semiconductor–electrolyte interface due to their limited diffusion length. In other words, most of the charge carriers created in the bulk of the semiconductor will be lost through recombination before reaching the interface . To absorb incident light as much as possible and at the same time to maximize the utilization of the photoexcited carriers, it is very important to employ nanostructured films with characteristics of open and three dimensional structure, instead of dense, planar films.…”

Geogrid‐Inspired Nanostructure to Reinforce a CuxZnySnzS Nanowall Electrode for High‐Stability Electrochemical Energy Conversion Devices

“…The NWD demonstrated as a counter electrode in a dye-sensitized solar cell shows a power conversion efficiency of 7.44 ± 0.04%, comparable with the device using Pt as electrode, and also significantly improves device stability as compared with that afforded by an electrode comprising a CZTS nanowall without the nano-geogrid (denoted as NOD). [28] Simultaneously, various electrode nanostructures have been investigated to address the challenges associated with EEC devices; examples of such nanostructures include 1D (e.g., nanowires and nanobelts), [29,30] 2D (e.g., nanorod arrays), [31] and 3D (e.g., hierarchical nanostructures and nanowalls) [32,33] structures. Moreover, when HERs are conducted under extreme conditions, the NWD electrode remains intact, whereas the NOD electrode is completely peeled off after 10 min of reaction.…”