Copper(ii) tungstate nanoflake array films: sacrificial template synthesis, hydrogen treatment, and their application as photoanodes in solar water splitting

Abstract

We report the preparation of CuWO4 nanoflake (NF) array films by using a solid phase reaction method in which WO3 NFs were employed as sacrificial templates. The SEM, TEM and XRD results demonstrated that the obtained CuWO4 films possessed a network structure that was composed of single crystalline NFs intersected with each other. The CuWO4 NF films showed superior photoelectrochemical (PEC) activity to other CuWO4 photoanodes reported recently for the oxygen evolution reaction (OER). We attributed the high activity to the unique morphological and crystalline structure of the CuWO4 film, which enhanced the photoactivity by providing a large specific area, a short hole transport distance from the inside of CuWO4 to the CuWO4/solution interface, and a low grain boundary density. Hydrogen treatment by annealing the CuWO4 NF film in mixed gases of H2 and Ar could further enhance the photoactivity, as hydrogen treatment significantly increased the electron density of CuWO4 by generating oxygen vacancy in the lattice. The photocurrent density for OER obtained on the hydrogen-treated (H-treated) CuWO4 NF film is the largest ever reported on CuWO4 photoanodes in the literature. Moreover, the CuWO4 photoanodes exhibit good stability in weak alkaline solution, while the H-treated CuWO4 photoanodes exhibit acceptable stability. This work not only reveals the potential of CuWO4 as a photoanode material for solar water splitting but also shows that the construction of nanostructured CuWO4 photoanodes is a promising method to achieve high PEC activity toward OER.

Preparation of Bifunctional CuWO4‐Based Heterostructure Nanocomposites for Noble‐Metal‐Free Photocatalysts

“…In Figure A(c), the main peak is shown at 530.5 eV for O ( 1 s ) and it can be deconvoluted into two peaks with broad at 530.3 and tail at 530.95 eV are assigned to the Cu−O of CuO and W−O of respectively ,. By comparing the results with earlier reports,,, the present study does not show any OH − related signals in particles due to the OH − groups of PEG compensated the loss of oxygen during annealing. In Figure A(d), the peaks are shown centered at 934.2 eV and 953.9 eV due to Cu ( 2p 3/2 ) and Cu ( 2p 1/2 ) respectively, of CuWO 4.…”

“…High resolution XPS patterns were also recorded for Cu ( 2p ), W ( 4 f ) and O ( 1 s ) with scan rate of 0.025 eV, time per step of 50 ms with 10 cycles of scanning. In Figure A(b), the peaks observed at 35.4, 37.6 and 41.3 eV due to the binding energies of W( 4f 7/2 ), W( 4f 5/2 ) and W( 5p 3/2 ) respectively, of W 6+ state . In Figure A(c), the main peak is shown at 530.5 eV for O ( 1 s ) and it can be deconvoluted into two peaks with broad at 530.3 and tail at 530.95 eV are assigned to the Cu−O of CuO and W−O of respectively ,.…”

Lamellar shape lead tungstate (PbWO4) nanostructures as synergistic catalyst for peroxidase mimetic activity

“…This inorganic material with variable band gap (2.9 eV-4.5 eV) occurs as tetragonal (stolzite), monoclinic (respite) with scheelite (space group I41/a) and wolframite (space group P21/a) type structures [20,21]. The emission properties of PbWO 4 were first reported in 1940s [22][23][24]. Although most of the time it is considered as dielectric materials, its semiconductor properties as independent materials and in the form of composite materials have also been explored by researchers [25][26][27].…”

Network Structured CuWO4/BiVO4/Co-Pi Nanocomposite for Solar Water Splitting

“…In previous studies, N-type semiconductors, such as TiO 2 [2], ZnO [3,4], WO 3 [5][6][7][8], Fe 2 O 3 [6,9], Ag 3 PO 4 [10], BiVO 4 [11,12], and CuWO 4 [13,14], whose valence band edges are higher than the redox potential of the O 2 /H 2 O couple, have been employed as the photoanode materials for such PEC OER. CuWO 4 has been regarded as a promising photoanode material [13][14][15][16][17][18][19][20] due to its appropriate bandgap energy (2.3-2.4 eV), positive valence band edge potential (at ca. 2.8 V vs. reversible hydrogen electrode (RHE)) [13], low toxicity, and, most importantly, high stability in neutral and acid solutions.…”

“…CuWO 4 has been regarded as a promising photoanode material [13][14][15][16][17][18][19][20] due to its appropriate bandgap energy (2.3-2.4 eV), positive valence band edge potential (at ca. 2.8 V vs. reversible hydrogen electrode (RHE)) [13], low toxicity, and, most importantly, high stability in neutral and acid solutions. However, as compared with the highly active n-type semiconductors, the activity of CuWO 4 for PEC OER is still low because of its indirect bandgap and poor charge transport property [18], which results in the accumulation of photoinduced holes, thereby increasing the recombination.…”