Photocatalytic Activity of Rutile Titania for Hydrogen Evolution

Abstract

Herein, we demonstrate the high photocatalytic activity of rutile particles for H 2 evolution from aqueous ethanol solution. The rutile particles were prepared by successive calcination at 900°C and H 2 reduction treatment at 700°C of commercial anatase-rich TiO 2 powder, Evonik/Degussa P25. Photocatalytic water splitting to generate H 2 and O 2 using oxide photocatalysts has potential for large-scale fuel production from solar energy.1 Titanium dioxide has been a widely studied photocatalyst since the photoelectrolysis of water by singlecrystal rutile TiO 2 electrode was reported in 1969.2 However, a feasible design concept for highly efficient photocatalysts, including conventional TiO 2 photocatalysts, for water splitting has yet to be developed.The photocatalytic activity of rutile is considered to be lower than that of anatase.36 Rutile particles are generally larger than anatase particles, as rutile is the thermodynamically stable phase of TiO 2 . 4 The low photocatalytic activity might be due to the small specific surface area of rutile particles. Rutile is also reported to exhibit higher rates of recombination compared to those displayed by anatase. 3 The difference in the energy levels of anatase and rutile is also important for photocatalytic water splitting. Electrochemical studies indicate that the flat band potential of rutile (001) is more positive than that of anatase (101) by 0.2 V.7 This indicates that the reducing ability of rutile is lower than that of anatase. Considering the band gaps of anatase (3.2 eV) and rutile (3.0 eV), the position of the valence band maxima are similar, as shown in Figure 1. The energy level of the conduction band minimum of rutile is comparable to the redox potential of H + /H 2 (0 V vs. SHE); thus, nearly no overpotential is available for H 2 evolution. 7 In contrast, there is no evidence that the photoexcited electrons in the conduction band of rutile are thermodynamically inefficient for the reduction of water to H 2 . A better understanding is required for evaluating the photocatalytic activity of rutile TiO 2 particles in H 2 evolution.Herein, we examined the photocatalytic activity of rutile particles for H 2 evolution from aqueous ethanol solution. The rutile particles were prepared from commercial anatase-rich TiO 2 , Evonik/Degussa P25 (Nippon Aerosil, Yokkaichi, Japan), as a precursor. P25 is a well-known standard photocatalyst displaying high photocatalytic efficiency for H 2 evolution in the presence of supported Pt nanoparticles, as a cocatalyst, and sacrificial electron donors such as alcohols. 8,9

Hydrogen Reduced Rutile Titanium Dioxide Photocatalyst

“…Contrary to this viewpoint, we demonstrated that H 2 -reduced rutile TiO 2 is much more active than mixed-phase P25 for photocatalytic H 2 evolution from aqueous ethanol solution [17,18]. To confirm that the anatase phase does not work as an active component, we investigated H 2 reduction treatment of pure single-phase rutile particles [17]. P25 was first calcined in air at 900 C to induce complete phase transition from anatase to rutile, and then the pure rutile phase was reduced by H 2 at 700 C( Figure 7A).…”

“…The mixture of anatase and rutile phases in P25 is reportedly more active than the individual polymorphs of TiO 2 . Contrary to this viewpoint, we demonstrated that H 2 -reduced rutile TiO 2 is much more active than mixed-phase P25 for photocatalytic H 2 evolution from aqueous ethanol solution [17,18]. To confirm that the anatase phase does not work as an active component, we investigated H 2 reduction treatment of pure single-phase rutile particles [17].…”

Light-driven oxygen evolution from water oxidation: TiO2 engineering in the performance of the immobilised photocatalysts

“…As displayed in Fig. 6, the performance of the photocatalytic water oxidation for O 2 evolution was achieved when the ratio between anatase and rutile crystalline phases are superior (88%, Table 1), corroborating with the reported investigations 33,34 .…”

“…Nevertheless, for the synthesised TiO 2 calcined at 900 ºC 100% rutile (Table 1) the performance for O 2 production was lower compared with the TiO 2 -700 and also with TiO 2 -800 samples, suggesting that the other factors account to the e ciency of the process using the TiO 2 samples prepared by sol-gel method. As documented, the ratio between surface anatase and rutile particles increases the photocatalytic activity in water splitting reactions 32,33 . As displayed in Fig.…”

Water Splitting on Rutile TiO2‐Based Photocatalysts

“…Amano et al. reported that H 2 ‐reduced rutile TiO 2 was much more active than mixed‐phase P25 for photocatalytic H 2 evolution under ultraviolet irradiation . The AQY for H 2 evolution of H 2 ‐reduced rutile TiO 2 was 46 % under 390 nm irradiation .…”