Gold/WO₃ nanocomposite photoanodes for plasmonic solar water splitting

A facile electron-charging and reducing method was developed to prepare Au/WO₃ nanocomposites for plasmonic solar water splitting. The preparation method involved a charging step in which electrons were charged into WO₃ under negative bias, and a subsequent reducing step in which the stored electrons were used to reductively deposit Au on the surface of WO₃. The electron-charged WO₃ (c-WO₃) exhibited tunable reducibility that could be easily controlled by varying the charging parameters, and this property makes this method a universal strategy to prepare metal/WO₃ composites. The obtained Au/WO₃ nanocomposite showed greatly improved photoactivity toward the oxygen evolution reaction (OER) when compared with WO₃. After Au decoration, the OER photocurrent was improved by a percentage of over 80% at low potentials (< 0.6 V vs. SCE), and by a percentage of over 30% at high potentials (> 1.0 V vs. SCE). Oxygen evolution measurements were performed to quantitatively determine the Faraday efficiency for OER, which reflected the amount of photocurrent consumed by water splitting. The Faraday efficiency for OER was improved from 74% at the WO₃ photoanode to 94% at the Au-8/WO₃ composite photoanode, and this is the first direct evidence that the Au decoration significantly restrained the anodic side reactions and enhanced the photoelectrochemical (PEC) OER efficiency. The high photoactivity of the composite photoanode toward OER was ascribed to the plasmon resonance energy transfer (PRET) enhancement and the catalytic enhancement of Au nanoparticles (NPs).