Photovoltage Effects of Sintered IrO2 Nanoparticle Catalysts in Water-Splitting Dye-Sensitized Photoelectrochemical Cells

Water-splitting dye-sensitized photoelectrochemical cells (WSDSPECs) utilize high surface area TiO2 electrodes functionalized with light absorbing sensitizers and water oxidation catalysts. Because water splitting requires vectorial electron transfer from the catalyst to the sensitizer to the TiO2 surface, attaching both sensitizer and catalyst to TiO2 in the correct sequence and stabilizing them under photoelectrochemical conditions has been a challenging problem. Rutile-phase IrO2 nanoparticles can be deposited directly on the TiO2 electrode by adsorbing citrate-capped amorphous IrOx and then sintering at 450 °C. Electrodes functionalized with these nanocrystalline particles show higher activity than those made from ligand-capped amorphous IrOx without sintering. In the WS-DSPEC, the Coulombic efficiency for oxygen evolution from the sintered nanoparticle photoelectrodes was near unity. The loading of colloidal IrOx and IrO2 particles onto the porous TiO2 electrodes was quantified by neutron activation analysis. Photovoltage measurements suggest that at high catalyst loading the dominant charge recombination pathway is from photoinjected electrons to IrO2.