Generation of Plasmonic and Chemical Hot Spots near the Reaction Sites in Solar-Driven Photoelectrochemical Ammonia Splitting

From the perspective of energy and environmental issues, separating NH3, a CO2-free hydrogen carrier, into N2 and H2 has become a major challenge. Research on photocatalytic and photoelectrochemical (PEC) decomposition of NH3 has begun, but there is much room for improvement in the performances. We have shown that a faceted Au nanoparticle (NP)-loaded TiO2 nanowire array (Au/TiO2 NWA) is a promising photoanode for PEC NH3 splitting. Two-compartment cells consisting of a Au/TiO2 NWA photoanode, Pt cathode, and Nafion membrane separator were fabricated to separately quantify the products at the anode and cathode. A PEC cell using an Au(3.4 nm)/TiO2 NWA photoanode selectively decomposes NH3 to H2 and N2 with an efficiency of ∼70% at 380 nm. Under illumination of simulated sunlight (AM 1.5), the rates of H2 and N2 production increase in proportion to light intensity to reach 78.0 μmol cm–2 h–1 and 24.9 μmol cm–2 h–1, respectively, at four sun. These performances can originate from simultaneous concentration of light, holes, and NH3 near the triphase interface with the recombination effectively inhibited through the synergy between TiO2 photocatalysis and Au NP plasmonic photocatalysis. This is the first report of plasmon-assisted PEC NH3 splitting.