Solar hydrogen production from seawater splitting using mixed-valence titanium phosphite photocatalyst

A unique magnesium salt of titanium phosphite (MgTiP) was synthesized by the hydrothermal method and applied for the photocatalytic hydrogen evolution using seawater. The spent MgTiP was analyzed by XPS after photocatalytic reaction indicating that Ti3+ in MgTiP structure was oxidized to Ti4+ by photo-induced holes in a pure water environment, i.e., photo-corrosion. A sacrificial agent, 2 mM FeCl2 in the photocatalytic system, could enhance hydrogen evolution and prevent photo-corrosion of MgTiP. Thus this research conducted the reaction of photocatalytic hydrogen evolution using seawater. Two seawater sources were taken from the estuary of the Tamsui River and the east coast of Taiwan. The ions in seawater could act as a sacrificial agent. The result showed that the ions of seawater could enhance photocatalytic hydrogen evolution and also prevent MgTiP from photo-corrosion. The unique 12-membered ring (12 R) channels structure of MgTiP with tunable hexa-hydrated magnesium ions showed excellent photo-stability. The concentration of proton (pH) and chloride ions as hole scavenger were favorable factors. Its H2 production rate could reach up to 629.3 µmol·gcat−1·h−1 under simulated sunlight. Furthermore, the hydrogen evolution from photocatalytic seawater splitting showed better stability than pure water in a long-term test. [Display omitted] •We synthesized unique visible-light titanium phosphite MgTiP photocatalyst.•Photocatalytic seawater splitting can prevent the photo-corrosion of MgTiP.•Hydrogen evolution from natural seawater showed long-term stability.