Electrolyte-assisted polarization leading to enhanced charge separation and solar-to-hydrogen conversion efficiency of seawater splitting

Photocatalytic splitting of seawater for hydrogen evolution has attracted a great deal of attention in recent years. However, the poor energy conversion efficiency and stability of photocatalysts in a salty environment have greatly hindered further applications of this technology. Moreover, the effects of electrolytes in seawater remain controversial. Here we present electrolyte-assisted charge polarization over an N-doped TiO2 photocatalyst, which demonstrates the stoichiometric evolution of H2 and O2 from the thermo-assisted photocatalytic splitting of seawater. Our extensive characterizations and computational studies show that ionic species in seawater can selectively adsorb on photo-polarized facets of the opposite charge, which can prolong the charge-carrier lifetime by a factor of five, leading to an overall energy conversion efficiency of 15.9 +/- 0.4% at 270 degrees C. Using a light-concentrated furnace, a steady hydrogen evolution rate of 40 mmol g-1 h-1 is demonstrated, which is of the same order of magnitude as laboratory-scale electrolysers. Photocatalytic overall water splitting on particulate systems represents a possibility for clean energy storage, yet efficiencies for the process are typically low. Here, highly concentrated saltwater is used to polarize photoexcited N-doped TiO2, resulting in enhanced charge separation and a solar-to-hydrogen efficiency approaching 20%.