Ba2InTaO6 - A Partially B-Site-Ordered Double Perovskite for Overall Water Splitting

Completely B-site-ordered Ba2InTaO6 has been prepared previously by prolonged heating at 1500 degrees C; here, we significantly lowered the annealing temperature to 1130 degrees C under H-2/Ar dynamic flow and obtained a partially ordered (ca. 74%) double perovskite, as determined by Rietveld refinement of the powder X-ray diffraction data. As a wide-band-gap semiconductor, Ba2InTaO6 possesses photocatalytic activity for overall water splitting under UV irradiation, though the gas evolution rates of 12.9 and 6.6 mu mol/h/g for H-2 and O-2 generation, respectively, are low. With the assistance of methanol as a sacrificial reagent, the H-2 evolution rate increases to 50.5 mu mol/h/g, which indicates that the surficial charge recombination rate is really high. We applied the typical cocatalyst-loading method to this material, and with 1 wt.-% PtOx and NiOx, the H-2 production rates in pure water were further improved to 16.0 and 18.4 mu mol/h/g, respectively. Attempts to dope Ba2InTaO6 with first-row transition metals (Ti, V, Cr, Mn, Fe, Co, and Ni) led to a general enhancement of the light-harvesting ability; however, the experimental water-splitting activity did not improve. We believe that the doped cations most likely behaved as recombination centers for photogenerated charges. Considering its structural similarity to the well-known catalyst InTaO4:Ni, Ba2InTaO6 possesses the potential to extend its photocatalytic activity to the visible-light region but needs further enhancement.