Photocatalysis is a promising advanced water treatment technology, and recently the possibility of using hydrogenation to improve the photocatalytic efficiency of titanium dioxide has generated much research interest. Herein we report that the use of high-temperature hydrogenation to prepare black TiO2 primarily results in the formation of bulk defects in the material without affecting its electronic band structure. The hydrogenated TiO2 exhibited significantly worse photocatalytic activity under simulated sunlight compared to the unhydrogenated control, and thus we propose that high-temperature hydrogenation can be counterproductive to improving the photocatalytic activity of TiO2, because of its propensity to form bulk vacancy defects.