Figure 24.

(Top, (a)) Schematic of the water splitting system using a wide bandgap TiO₂ semiconductor photoelectrode and a Pt counter electrode demonstrated by Fujishima and Honda in their landmark work in 1972. Adapted with permission from Ref [50] Copyright Nature Publishing Group (1972). (Bottom, (b)) Photocurrent measurements made on TiO₂–Pd nanosheet and nanotetrahedron samples and compared to that of bare TiO₂ samples. The higher photocurrent of TiO₂–Pd nanosheets confirms plasmonic hot electron injection, while there is not too much difference in photocurrent magnitudes between bare TiO₂ and TiO₂–Pd nanotetrahedrons. This provides evidence of the poor hot electron injection abilities of Pd nanotetrahedrons as compared to Pd nanosheets. (c) Hydrogen production rates under vis-NIR light irradiation are shown, and as can be seen the TiO₂–Pd nanosheets exhibit photocatalytic hydrogen evolution activity unlike bare TiO₂ and TiO₂–Pd nanotetrahedrons [271]. These experiments provide simple insights on the application of hot electrons in photoelectrochemical water splitting. Reprinted with permission from Ref [271] Copyright Royal Society of Chemistry (2016).