Constructing a Two-Dimensional SnWO₄ Nanosheet Array Film for Enhanced Photoelectrochemical Performance

Abstract

Stannous tungstate (α-SnWO4) is a promising photoanode material for photoelectrochemical (PEC) water splitting, but its practical performance is severely limited by the charge recombination problem that results from poor bulk charge transport ability. Herein, SnWO4 with a two-dimensional (2D) sheet-like array morphology (SnWO4-NS) was formed to provide pathways for accelerating charge transport, which is demonstrated by the small radius of electrochemical impedance spectroscopy and a short charge transport time of intensity-modulated photocurrent spectroscopy. The carrier separation efficiency and hole collection efficiency of SnWO4-NS were improved to 6.84 and 40.66% compared to those (4.83 and 13.18%) of SnWO4 without controlled morphology at 1.23 V versus the reversible hydrogen electrode. As a result, the photocurrent density increased from 0.086 to0.41 mA cm–2, and a larger amount of oxygen was obtained in the same period. This 2D morphology modification method will provide a new idea for developing α-SnWO4 with efficient PEC performance.

Development of ABO4‐type photoanodes for photoelectrochemical water splitting

“…The addition of fluoride ions in a hydrothermal process was used to fabricate 2D sheet-like arrays of SnWO 4 , which improved the photocurrent density from 0.086 to 0.41 mA cm −2 . 297 The reason for the improvement of optoelectronic performance is that the morphology of the 2D sheet array provides a high-speed movement path for the migration of carriers. The hydrothermal F − added SnWO 4 film was annealed in argon at 500°C to obtain a long sheet-like SnWO 4 film, which exhibited a photocurrent density of 0.79 mA cm −2 at 1.23 V versus RHE in the absence of any sacrificial agent.…”

“…In addition to the size of nanoparticles affecting the carrier transport performance, the nanostructure affects the carrier transport performance. The addition of fluoride ions in a hydrothermal process was used to fabricate 2D sheet‐like arrays of SnWO 4 , which improved the photocurrent density from 0.086 to 0.41 mA cm −2 297 . The reason for the improvement of optoelectronic performance is that the morphology of the 2D sheet array provides a high‐speed movement path for the migration of carriers.…”

Recent progress in the development of tin tungstate (α-SnWO4) photoanodes for solar water oxidation

“…This method was further improved by several researchers, including He et al [55][56][57] They synthesized nanostructured α-SnWO 4 thin films on fluorine-doped tin oxide (FTO) substrates using approximately the same method as described by Pyper et al, but with the addition of a post-annealing process conducted at 500 °C under an Ar atmosphere. 57 It was argued that the annealing step under an inert atmosphere would influence the oxidation state of α-SnWO 4 , preventing the formation of Sn 4+ . As a result, as shown in Fig.…”

Spectroscopic Evidence of Intraband Gap States in α‐SnWO4 Photoanodes Introduced by Interface Oxidation

“…The material shows n-type conductivity, which means that it should be employed as the photoanode in PEC water splitting devices. Several studies have been reported in the last few years on α-SnWO 4 films prepared by different techniques, [10][11][12][13][14][15][16][17][18][19][20][21][22] e.g., hydrothermal synthesis, reactive magnetron sputtering, pulsed laser deposition, and chemical vapor deposition. The attractive properties of this material as a photoanode include the bandgap of 1.9 eV, which is close to ideal for use as a top absorber in a tandem configuration, and the favorably low onset potential of %0 V versus RHE.…”

“…[18,25] Epitaxial or highly oriented films are therefore expected to have much improved charge transport, and indeed recent reports on two-dimensional α-SnWO 4 crystalline nanosheets with preferred {001} orientation demonstrated superior performance. [18][19][20] Another limitation is the modest photovoltage that can be extracted from the material, despite the fact that the band positions straddle the water reduction and oxidation potentials (which would enable a maximum quasi-Fermi level splitting of at least 1.23 V under operating conditions). In our earlier study on NiO x -coated α-SnWO 4 , in which the NiO x serves as the protection layer, we showed that the limitation of the photovoltage can be correlated with the formation of an interfacial oxide layer at the interface of α-SnWO 4 and NiO x .…”