Iridium oxide, a water oxidation co-catalyst, plays an important role in mediating the hole transfer process of a UV-irradiated TiO2 system.
Spectroscopic identification of trapped holes has enabled their characterization in colloidal TiO2 suspension and monitoring of the transfer of trapped holes to IrO2.
Titration of trapped holes with potassium iodide yields an estimate of 3 holes per particle during 7 min of UV-irradiation of TiO2 suspension in ethanol containing 5% acetic acid. An extinction coefficient of 11,230 M-1 cm-1 at 360 nm, corresponding to the absorbance of the trapped holes, has been calculated.
The hole transfer to IrO2 occurs with a rate constant of 6×105 s-1.
Interestingly, IrO2 also catalyzes the recombination of trapped holes with reduced oxygen species.
So what does it mean? Photocatalytic water splitting with IrO2 as the water oxidation catalyst could be hindered by this unexpected and undesirable side reaction For a pure photo-driven water splitting setup to be viable, it will be necessary to separate photogenerated electrons quickly to prevent scavenging by oxygen One way to get around this is to use a “reverse” fuel cell, which separates the working electrode (where O2 is produced) and the counter electrode (where H2 is produced). This facilitates both charge separation and removes the gas separation step, as they are generated in different compartments!
Schematic of our “reverse” fuel cell Brian Seger; Prashant V. Kamat; J. Phys. Chem. C 2009, 113, 18946-18952.
This work can be found in the Journal of Physical Chemistry Letters (DOI: 10.1021/jz200852m) J. Phys. Chem. Lett., 2011, 2, pp 2304–2310 Thank you for watching! More information on the Kamat group can be found at: http://www.nd.edu/~pkamat Thanks to: