Optimizing the morphology of titania nanorods for enhanced solar seawater splitting

Nanorod-TiO2 electrodes were obtained by a hydrothermal method in the presence of different concentrations of sodium chloride. The addition of NaCl during the synthesis promoted the formation of thinner, well-crystallized nanorods growing along the [001] crystallographic direction, while still, the most intense reflection is related to (101). The optimal electrode demonstrated applied bias photon to current efficiency (ABPE) of 0.24% in solar seawater splitting, which is among the highest reported efficiencies for the pristine TiO2 nanorods. Noteworthy, the ABPE of the obtained electrodes stayed intact during variation of the solar irradiation in the range of 0.2-1 Sun. It was also demonstrated that the efficiency of nanorod-TiO2 electrodes is higher for seawater splitting (0.5 M NaCl) than for water photoelectrolysis in the presence of 0.5 M Na2SO4. This phenomenon is the result of chloride evolution reaction taking place in addition to water oxidation. A gradual decrease in efficiency resulting from the low mobility of holes was observed for all electrodes. This conclusion was confirmed by experiments with a hole-scavenger (improved performance of the cell), as well as surface photovoltage measurements and electrochemical impedance spectroscopy.