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-SiO 2 core–shell nanoparticles (Au@SiO 2 NPs), a layered double hydroxide (LDH), and semiconducting BiVO 4 . To understand the spatial dependence of water oxidation by the composite photoanode, we examined two configurations, LDH/Au@SiO 2 /BiVO 4 (photoanode I) and Au@SiO 2 /LDH/BiVO 4 (photoanode II), which differed in the order in which the LDH nanosheets and Au@SiO 2 layers were grown on BiVO 4 . In a PEC water-splitting cell under back-side illumination, at E 0 ′(H 2 O/O 2 ) = 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@SiO 2 in photoanode I excites a strong localized surface plasmon resonance that promotes the charge separation in BiVO 4 . However, under front-side illumination, photoanode II performed better than photoanode I because less light is transmitted to the Au@SiO 2 layer in photoanode I. Our findings reveal that the BiVO 4 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.