Using sunlight to produce hydrogen from water requires a photocatalyst with a bandgap in the UV–visible energy range. Niobates and tantalates have bandgaps in the UV region, but Weidong Shi and colleagues, Jiangsu University, Zhenziang, China, were able to produce hydrogen from an aqueous methanol solution under UV–visible light using sodium or potassium tantalate catalysts decorated with silver particles.

Tantalate nanocubes alone produced no hydrogen under visible light, but silver-decorated cubes produced a small amount of hydrogen from aqueous methanol solutions. Hydrogen production increased under simulated sunlight, reaching 186 μmol/h·g using sodium tantalate nanocubes decorated with 0.1 wt % silver. The researchers propose that light excites surface plasmon resonances in the larger silver particles. Excited electrons transfer from the metal to the conduction band of the nanocubes, and from there to the smaller silver particles.

Hydroxyl ions diffuse from water to the nanocube surfaces. Electron holes in the larger silver particles oxidize them to form hydroxyl radicals, which oxidize the methanol molecules. Meanwhile, the photoexcited electrons move from the tantalate conduction band to the small silver particles, which reduce protons to hydrogen.

• Ag-Decorated ATaO₃ (A = K, Na) Nanocube Plasmonic Photocatalysts with Enhanced Photocatalytic Water-Splitting Properties,
  Dongbo Xu, Songbo Yang, Yu Jin, Min Chen, Weiqiang Fan, Bifu Luo, Weidong Shi,
  Langmuir 2015.
  DOI: 10.1021/acs.langmuir.5b01294