Photoelectrochemical hydrogen production with concentrated natural seawater produced by membrane process

Water shortages are anticipated to occur all over the world and are likely to have a significant effect on the availability of water for processes such as photocatalysis and electrolysis, as well as for drinking and industrial water. To overcome this problem, it has been suggested that seawater could be used as an alternative resource for the various water industries, such as hydrogen production, industrial and drinking water. Seawater contains a large amount of dissolved ion components, thus allowing it to be utilized as an electrolyte in photoelectrochemical system for producing hydrogen. Especially, the concentrated shows higher salinity (total dissolved solids, TDS) than the general seawater fed to the membrane process, because the permeate has a lower salinity and the retentate is more concentrated than the original seawater. For these reasons, the hydrogen evolution rate was investigated in a photoelectrochemical system, including anodized tubular TiO₂ and platinum as the photoanode and cathode, an external bias (solar cell) and the use of various types of seawater prepared by the nanofiltration membrane process as the electrolyte in the photoelectrochemical system. The results showed that the rate of hydrogen evolution obtained using the relatively tight nanofiltration membrane, NF90, operated at 20MPa in the photoelectrochemical system is ca. 270μmol/cm²h, showing that the retentate with a higher TDS than the general TDS of seawater acts as a more effective seawater electrolyte for hydrogen production.