Electron-hole recombination kinetics was observed in NaTaO₃ photocatalysts doped with Ca, Sr, Ba, and La using time-resolved infrared absorption. The recombination rate was compared with the ultraviolet light-derived H₂ production rate in the water splitting reaction to estimate the electron-to-H₂ conversion efficiency. The conversion efficiency was sensitive to the nanometer-scale topography of the photocatalyst surface. The particularly high efficiency on the nondoped and 0.5 mol% Sr-doped photocatalysts was related to the flat (100) crystalline surfaces exposed on the photocatalyst particles. In the presence of NiO cocatalysts, the rate of electron trasfer across the La-doped photocatalyst surfaces was enhanced. These results demonstrate intense demand to do surface science on metal oxide particles.