KTaO3 was
doped with Sr cations, and its photocatalytic
activity for the overall water splitting was investigated. By doping
with Sr, a Sr-rich shell was formed over a Sr-poor core. Extended
X-ray absorption fine structure spectroscopy revealed the simultaneous
occupation of the K sites and Ta sites by Sr cations. A concentration
gradient of Sr cations occupying the Ta sites was suggested to be
produced after doping with Sr. The concentration gradient of Sr cations
simultaneously induced an energy gradient of the conduction band edge
bottom. Hence, photoexcited electrons are separated, which are driven
away to the bulk by the energy gradient, from the complementary holes
present on the surface. The higher the Sr cation concentration, the
higher the energy gradient produced. Thus, the electron-hole separation
is improved and the electron population accordingly increases
with the increase in the Sr cation concentration. Nevertheless, the
increase in the Sr cation concentration led to the decrease in the
water splitting activity. The highest water splitting activity was
observed for bare KTaO3. The decreased water splitting
activity was proposed to be primarily due to the blockage of the electron
transfer to the cocatalysts by the Sr-rich shell and the poor O2 evolution ability of the Sr-rich shell.
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