Hybrid Plasmonic Photoanodes for Effective Photocatalytic Water Splitting

Photocatalytic water splitting by semiconductors is elucidated in many important works. At the same time, mechanisms of plasmonic enhancement of photocatalytic water splitting by metals are still debated. Here, we study hybrid photocatalysts in which a main metallic catalyst, AlB₂, is combined with a co-catalyst made of either a metal, a semiconductor or a dielectric (FeSe, WS₂ and ZrO₂). These catalysts are fabricated from AlB₂ and relevant powders by a low-cost, high-yield and scalable rolling mill technique. They demonstrate photocatalytic water/seawater splitting under solar-like radiation with high efficiency. We show that the reasons for efficiency enhancement are connected to optical impedance matching in hybrid photoanodes, reasonable light absorption that allowed total light absorption in 300 nm films, and matching the absorption spectrum of photoanodes to the spectrum of solar light. Using hybrid photoanodes composed of AlB₂ and FeSe nanostructures, we achieved a maximum applied bias photon-to-current efficiency of ∼10% under simulated solar illumination with an applied bias of 0.3 V, which brings our approach within values for the commercial viability benchmark. We also demonstrate seawater splitting using stable AlB₂-FeSe and AlB₂-WS₂ photoanodes attaining current densities of ∼5 mA/cm² by solar illumination raising efficiency of seawater splitting to ∼5%. Bifunctionality of studied hybrid photoanodes is established.