Nature of Charge Carrier Recombination in CuWO₄ Photoanodes for Photoelectrochemical Water Splitting

Abstract

CuWO 4 is a ternary semiconductor oxide with excellent visible light harvesting properties up to 550 nm and stability at high pH values, which make it a suitable material to build photoanodes for solar light conversion to hydrogen via water splitting. In this work, we studied the photoelectrochemical (PEC) performance of transparent CuWO 4 electrodes with tunable light absorption and thickness, aiming at identifying the intrinsic bottlenecks of photogenerated charge carriers in this semiconductor. We found that electrodes with optimal CuWO 4 thickness exhibit visible light activity due to the absorption of long-wavelength photons and a balanced electron and hole extraction from the oxide. The PEC performance of CuWO 4 is light-intensity-dependent, with charge recombination increasing with light intensity and most photogenerated charge carriers recombining in bulk sites, as demonstrated by PEC tests performed in the presence of sacrificial agents or cocatalysts. The best-performing 580 nm thick CuWO 4 electrode delivers a photocurrent of 0.37 mA cm −2 at 1.23 V SHE , with a 7% absorbed photon to current efficiency over the CuWO 4 absorption spectrum.

Nanocellulose@gallic Acid-Based MOFs: A Novel Material for Ecofriendly Food Packaging

“…A similar observation has been reported in another study. , Overall, the FESEM images clearly illustrated how varying concentrations of NC and MOF affected film morphology, elucidating their individual and combined effects on the microstructure (Figure S11). , The thickness of the synthesized films was determined by the cross-sectional FESEM images because the cross-sectional FESEM is a common and efficient technique to examine the morphology as well as film thickness. − The thickness of films was measured at 5 different positions, and their mean ± standard deviation values are given in Table . The thickness of the CH film increased after the incorporation of NC and the MOF due to increased solid content in the film …”

Improving the photoelectrocatalytic efficiency of CuWO4 through molybdenum for tungsten substitution and coupling with BiVO4

“…2.3 eV corresponding to an absorption edge of 550 nm, represents a good candidate material for PEC devices, also thanks to its good stability in PEC water oxidation under prolonged solar irradiation in neutral and slightly basic solutions and high selectivity towards the oxygen evolution reaction. 15–19 However, best-performing CuWO 4 electrodes produce no more than 0.4 mA cm −2 under 1 sun illumination at 1.23 V RHE , quite far from the theoretical limit. 20 Doping-level substitution of Cu 2+ ions with Fe 3+ or Ni 2+ was reported to increase both photocurrent generation 21 and charge separation efficiency, 22 while increased visible-light sensitised photoanodes were obtained by partial substitution of W 6+ with Mo 6+ ions in the CuWO 4 structure, due to a band gap energy reduction from 2.3 to 2.0 eV.…”

Partial Substitution of Cu Sites by Mg for the Improvement of CuWO4 Photoanodes Performance

“…A three-layer film was selected as a photoanode based on its average thickness (further information can be found in Section ). Due to the reduced hole diffusion length of CuWO 4 (∼25 nm), the utilization of films with a thickness larger than 600 nm significantly hampers the photoelectrochemical performance of CuWO 4 photoelectrodes …”