Overall Splitting of Water by RuO₂-Loaded PbWO₄ Photocatalyst with d¹⁰s²-d⁰ Configuration

Tetragonal lead tungstate, PbWO 4, consisting of a WO 4 tetrahedron showed high and stable photocatalytic activity for the overall splitting of water, producing a stoichiometric quantity of H 2 and O 2 under UV irradiation when loading RuO 2 on the metal oxide. The activity was found to strongly depend on the preparation temperature of PbWO 4 . In the temperature range 773−1273 K, a maximum appeared at around 1023 and 973 K when prepared in air and under a N 2 atmosphere, respectively. X-ray diffraction analysis and SEM observation showed that high activity was achieved with a combination of crystallized PbWO 4 with a high dispersion of RuO 2 particles. The DFT calculation for PbWO 4 with the d 10 s 2 -d 0 electronic configuration showed that the top of the valence band (HOMO) was composed of hybridized O 2p + Pb 6s orbitals, while the bottom of the conduction band (LUMO) consisted of hybridized W 5d + O 2p + Pb 6p orbitals. Considerable dispersion was observed for both the conduction and valence bands, which differed from the small dispersion observed for the photocatalytically inactive CaWO 4 with a similar crystal structure. Photoexcited electrons and holes with high mobility were considered to be responsible for the high photocatalytic performance of PbWO 4 . The useful role of a Pb 2+ ion with the d 10 s 2 electronic configuration in photocatalysis has been elucidated.