A nanocomposite photoelectrode made of 2.2 eV band gap copper tungstate (CuWO4 and multi-wall carbon nanotubes for solar-assisted water splitting

We report on the photoelectrochemical performances of a nanocomposite photoactive material made of copper tungstate (CuWO4) and multi-wall carbon nanotubes (MWCNT). The purpose of this work was to create a light absorber/charge collector composite material with tunable electronic transport properties to minimize the bulk resistance of CuWO4 material class. Nanocomposite thin films (typically 2.0 +/- 0.1 gm) were fabricated by means of spray pyrolysis using solutions containing copper acetate, ammonium metatungstate and MWCNT. Spray-deposited polycrystalline CuWO4 films were found to be porous, though crack-free, and made of CuWO4 nanoparticles with dimensions in the 10-50 nm range. Tauc plots derived from UV-visible and photocurrent spectroscopy techniques led to a consistent band gap value of 2.20 (+/- 0.05) eV. Electrochemical impedance spectroscopy performed in pH10 buffer solution under Air Mass 1.5 global (AM1.50(G)) at 0.8 V vs. saturated calomel electrode (1.63V vs. reversible hydrogen electrode) pointed out a bulk resistance reduction by 30% on nanocomposites photoanodes when compared to un-modified CuWO4 control samples. It is worth mentioning that the reduction in bulk resistance was achieved with an extremely low MWCNT:CuWO4 weight ratio (1:10,000), in which MWCNT absorbed less than 2% of incoming light. Subsequent linear scan voltammetry (LSV) performed in the same conditions revealed a photocurrent density increase of 26% at 0.8 V-SCE (1.63 V-RHE) compared to control samples. Additional LSV and incident photon-to-current efficiency measurements demonstrated that MWCNT served as effective electron collectors distributed throughout the entire CuWO4 bulk. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.