  Defined substoichiometric titanium oxides (Ti$_x$O$_{2x-1}$ with $3 < x <
10$) called Magneli phases have been investigated mostly for their unusual high
conductivity and metal-like behavior. In photocatalysis, Magneli phase
containing titania particles have been reported to provide favorable charge
separation resulting in enhanced reaction efficiency. In the current work we
describe a one-step synthesis of Magneli-containing mixed phase nanoparticles
that carry directly integrated minute amounts of Pt. Phase optimized
nanoparticles that contain only a few hundred ppm Pt are very effective
photocatalysts for H$_2$ evolution (they provide a 50-100 times higher H$_2$
evolution than plain anatase loaded with a similar amount of Pt). These
photocatalysts are synthesized in a setup combining a hot-wall reactor that is
used for TiOx synthesis with a spark generator producing Pt nanoparticles.
Different reactor temperatures result in various phase ratios between anatase
and Magneli phases. The titania nanoparticles (ca. 24 - 53 nm) were
characterized using XRD, HRTEM, XPS and EPR spectra as well as ICP-OES
analysis. The best photocatalyst prepared at 900$^\circ$C (which consists of
mixed phase particles of 32% anatase, 11% rutile and 57% Magneli phases loaded
with 290 ppm of Pt) can provide a photocatalytic H$_2$ evolution rate of ca.
5432 micromol h$^{-1} g$^{-1}$ for UV and ca. 1670 micromol h$^{-1} g$^{-1}$
for AM1.5 illumination. For powders converted to higher amounts of Magneli
phases (1000$^\circ$C and 1100$^\circ$C), a drastic loss of the photocatalytic
H$_2$ generation activity is observed. Thus, the high photocatalytic efficiency
under best conditions is ascribed to an effective synergy between
multi-junctions of Magneli titania and Pt that enable a much more effective
charge separation and reaction than conventional Pt/anatase junctions.
