  Magneli phases of titanium dioxide (such as Ti4O7, Ti5O9, etc.) provide
electronic properties, namely a stable metallic behavior at room temperature.
In this manuscript, we demonstrate that nanoscopic Magneli phases, formed
intrinsically in anatase during a thermal aerosol synthesis, can enable
significant photocatalytic H2 generation. This without the use of any extrinsic
co-catalyst in anatase. Under optimized conditions, mixed phase particles of 30
percent anatase, 25 percent Ti4O7 and 20 percent Ti5O9 are obtained that can
provide, under solar light, direct photocatalytic H2 evolution at a rate of 145
micromol h-1 g-1. These anatase particles contain 5-10 nm size inter-grown
phases of Ti4O7 and Ti5O9. Key is the metallic band of Ti4O7 that induces a
particle internal charge separation and transfer cascade with suitable
energetics and favorable dimensions that are highly effective for H2
generation.
