Incorporation of Ag nanowires in CuWO 4 for improved visible light-induced photoanode performance

We report the sol-gel synthesis of a CuWO₄ (E_g ∼ 2.0-2.15 eV) thin film loaded with Ag nanowires. The incorporation of Ag nanowires into the semiconductor matrix significantly improves the performance of CuWO₄ as a photoanode for use in photochemical water splitting (PEC). Here, we have developed a planar electrode to test the photoactivity of the catalyst using standard electrochemical procedures under simulated solar light. The sol-gel synthesis of CuWO₄ is modified such that we add Ag nanowires during sol aging. We demonstrate that there is negligible change to the CuWO₄ matrix microstructure, morphology or crystal structure. When we compare the pristine CuWO₄ to the material with Ag nanowires embedded in the CuWO₄ matrix there is a fourfold improvement of photocurrent at 1.23 V vs. NHE to ca. 1.5 mA cm^-2 (pH 9) under simulated AM1.5G illumination. This photocurrent is very competitive against more well developed photoanode structures when consideration for surface area is allowed. The Ag nanowires increase carrier mobility film enabling a sufficiently thick sample of catalyst, measured at 750 nm, to effectively harvest incident light. The addition of the Ag nanowires removes the plateau region found for CuWO₄ further indicating that there is a good flow of carriers to the surface of the catalyst, a significant improvement as carrier mobility has been shown to be low in CuWO₄. The Faradaic efficiency of the catalyst was measured at 31%. Our flat band potential is found to be 0 vs. NHE. The ability to make a highly photoactive catalyst using a simple chemical process opens up opportunities in a wide range of areas that focus on PEC and other light harvesting processes.