Controllable reduced black titania with enhanced photoelectrochemical water splitting performance. 
Black titania prepared by metal-reduction methods is systematically studied and found the best controllable Mg-reduction method.  Colored titania products from white, light blue, dark blue, to black were obtained with a crystalline/amorphous core-shell structure.  The black titania shows a five times higher H2 production rate in photoelectrochemical (PEC) water splitting.