UV Photon-Induced Water Decomposition on Zirconia Nanoparticles

Formation of H2 from photolysis of water adsorbed on zirconia (ZrO2) nanoparticles using 254 nm (4.9 eV) and 185 nm (6.7 eV) photon irradiation was examined. The H2 yield was approximately an order of magnitude higher using monoclinic versus cubic phase nanoparticles. For monoclinic particles containing 2 monolayers (ML) of water, the maximum H2 production rate was ∼0.4 μmole h–1 m–2 using 185 + 254 nm excitation and a factor of 10 lower using only 254 nm. UV reflectance reveals that monoclinic nanoparticles contain fewer defects than cubic nanoparticles. An H2O coverage dependence study of the H2 yield is best fit by a sum of interactions involving at least two types of adsorbate–surface complexes. The first dominates up to ∼0.06 ML and is attributed to H2O chemisorbed at surface defect sites. The second dominates at coverages up to a bilayer. H2 formation is maximum within this bilayer and likely results from efficient energy transfer from the particle to the interface. Energy transfer is more efficient for the monoclinic ZrO2 nanoparticles and likely involves mobile excitons.