Magneli phases doped with Pt for photocatalytic hydrogen evolution

Abstract

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}$forUVandca.1670micromolh$^{-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.

References in corpus (4)

• Black Magic in Gray Titania: Noble-Metal-Free Photocatalytic H2 Evolution from Hydrogenated Anatase
• Suspended Pt nanoparticles over TiO2 nanotubes for enhanced photocatalytic H2 evolution
• Magneli-Phases in Anatase Strongly Promote Co-Catalyst-Free Photocatalytic Hydrogen Evolution
• A study of Ti${}_n$O${}_{2n-1}$ Magnéli phases using Density Functional Theory