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

<jats:title>Abstract</jats:title><jats:p>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 TiO<jats:sub>2</jats:sub> photocatalyst, which demonstrates the stoichiometric evolution of H<jats:sub>2</jats:sub> and O<jats:sub>2</jats:sub> 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 °C. Using a light-concentrated furnace, a steady hydrogen evolution rate of 40 mmol g<jats:sup>−1</jats:sup> h<jats:sup>−1</jats:sup> is demonstrated, which is of the same order of magnitude as laboratory-scale electrolysers.</jats:p>