Plasmon-Enhanced Layered Double Hydroxide Composite BiVO₄ Photoanodes: Layering-Dependent Modulation of the Water-Oxidation Reaction

Photo-electrochemical (PEC) generation of hydrogen from sunlight and water is a promising pathway to carbon-neutral energy. We describe a highly efficient three-layer photoanode, which consists of plasmonic Au-SiO2 core–shell nanoparticles (Au@SiO2 NPs), a layered double hydroxide (LDH), and semiconducting BiVO4. To understand the spatial dependence of water oxidation by the composite photoanode, we examined two configurations, LDH/Au@SiO2/BiVO4 (photoanode I) and Au@SiO2/LDH/BiVO4 (photoanode II), which differed in the order in which the LDH nanosheets and Au@SiO2 layers were grown on BiVO4. In a PEC water-splitting cell under back-side illumination, at E0′(H2O/O2) = 1.23 V versus RHE, the photocurrent density of photoanode I reached 1.92 mA·cm–2, showing a 52% increase compared to that of photoanode II; the efficiency toward water oxidation of photoanode I was 69%, 1.3 times higher than that of photoanode II. This is because light absorption by Au@SiO2 in photoanode I excites a strong localized surface plasmon resonance that promotes the charge separation in BiVO4. However, under front-side illumination, photoanode II performed better than photoanode I because less light is transmitted to the Au@SiO2 layer in photoanode I. Our findings reveal that the BiVO4 layer contributed predominantly to charge separation, while the LDH layer served to catalyze water oxidation. The spatial dependence of the components of composite photoanodes provides a route to rational design of plasmonic PEC devices for solar energy conversion applications.