Enhancement of the Photoelectrochemical Performance of CuWO₄ Thin Films for Solar Water Splitting by Plasmonic Nanoparticle Functionalization

The effect of plasmonic nanoparticles (NPs) on the photoelectrochemical water splitting performance of CuWO4 is studied here for the first time. CuWO4 thin films were functionalized with well-defined Au NPs in two composite configurations: with the NPs (I) at the CuWO4–electrolyte interface and (II) at the CuWO4 back contact. In both cases, the incident photon to current conversion efficiency of the film was increased (∼6-fold and ∼1.2-fold for configurations I and II (at λ = 390 nm), respectively). Two important advantages of placing the NPs on the CuWO4–electrolyte interface are identified: (1) Au NPs, coated with a 2 nm TiO2 layer, are found to significantly enhance the surface catalysis of the film, decreasing the surface charge recombination from ∼60% to ∼10%, and (2) the NP’s near-field can promote additional charge carriers within the space charge layer region, where they undergo field-assisted transport, essentially avoiding recombination. Our study shows that Au NPs, coated with a 2 nm TiO2 layer, can significantly mitigate the catalytic and optical photoelectrochemical (PEC) limitations of CuWO4. An increase from 0.03 to 0.1 mA cm–2 in the water-splitting photocurrent was measured for a 200 nm film under simulated solar irradiation at 1.23 V vs RHE.