Photocatalytic water splitting

Since for the formation of the O2 molecule a complex four hole oxidation is necessary (see Eq. 2.18), the oxidation reaction is quite difficult to achieve. In order to still be able to study the reduction reaction (Eq. 2.17) the oxidation step is replaced by the oxidation of a so called hole scavenger. The reduction potential of this scavenger lies energetically above the VB the oxidation usually requires only one or two holes and can therefore be easily achieved. In the experiments within this thesis, TEA 

In the presented case CdS, as a prominent example for nano structured n-VI semiconductors, were used since their lower band gaps compared to corresponding oxide materials make them attractive candidates for visible light assisted photocatalytic hydrogen generation. The hole scavenger TEA protects the CdS from anodic photo corrosion (caused by oxidation reactions, i.e. CdS + 2h Cd - + S) by swiftly 

In order to improve further the efficiency of the hydrogen evolution reaction, it is necessary to fully understand the underlying reaction mechanisms. Understanding and controlling the metal co-catalyst is one way to achieve higher reactivity. 

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Figure 4.12 Schematic representation of the proposed reaction mechanism for overall photocatalytic water splitting using 03 - redox mediator and a mixture of Pt-Ti02-anatase and Ti02-rutile photocatalysts. Adapted from [161] (2001) with permission from Elsevier.

Zhou et al. obtained nitrogen-doped titanium dioxide replicas via a two-step infiltration process with natural leaves as templates [220]. The replicas inherited the hierarchical structures of the natural leaf at the macro-, micro-, and nanoscales. These materials showed enhanced light-harvesting and photocatalytic hydrogen evolution activities. The photocatalytic water splitting activity of the artificial leaf structures was eight times higher than that of titanium dioxide synthesized without templates. 

Khan, M.A. and Yang, O.B. (2009) Photocatalytic water splitting for hydrogen production under visible lighton Ir and Co ionized titania nanotube. Catalysis Today, 146 (1-2), 177-182. 

A. Kudo, H. Okutomi, H. Kato, Photocatalytic water splitting into H2 and 02 over K2LnTa5C>i5 powder,... 

Iwase, A. Ng, Y. H. Ishiguro, Y. Kudo, A. Amal, R., Reduced Graphene Oxide as a Solid-State Electron Mediator in Z-Scheme Photocatalytic Water Splitting under Visible Light./. 

S.7 Hj from Photocatalytic Water Splitting Using Photobiocatalytic Method... 

Galinska, A., Walendziewski, J. 2005. Photocatalytic water splitting over Pt TiO, in the presence of sacrificial reagents. Energy Fuels 19 1143-1147. 

Ni, M., Eeung, K.H.M., Eeung, D.Y.C., Sumathy, K. 2007. A review and recent developments in photocatalytic water-splitting using TiO, for hydrogen production. Renew Sustain Energy Rev 11 401 25. 

Fig. 6.3 Band position of several semiconductors in presence of aqueous electrolyte at pH = 1. Energy scale is indicated in electron volts (eV) using either normal hydrogen electrode or vacuum level as a reference. On right energy levels for Xi02 photocatalytic water splitting are presented.

Table 6.6 summarizes photocatalytic water splitting properties of various mixed oxides prepared from two different processes, solid-state reaction (SSR) and solution based Pechini-type polymerizable complex routes [56,57,120-122], Ba5Ta40i5 prepared... 

Kim HG, Hwang DW, Bae SB, Jung JH, Lee JS (2003) Photocatalytic water splitting over La2Ti207 synthesized by the polymerizable complex method. Catal Lett 91 193-198... 

Shimizu K, Itoh S, Hatamachi T, Kodama T, Sato M, Toda K (2005) Photocatalytic water splitting on Ni-intercalated Ruddlesden-Popper type H2La2/3Ta207. Chem Mater 17 5161-5166... 

Lee K, Nam WS, Han GY (2004) Photocatalytic water splitting in alkaline aqueous solution using redox mediator 1 parameter study. Int J Hydrogen Energy 29 1343-1347... 

A. Kudo A, Okutomi H, Kato H (2000)Photocatalytic water splitting into H2 and O2 over K2LnTa50i5. Chem Lett 1212-1213. 

Zou Z, Ye J, Arakawa H (2003) Photocatalytic water splitting into H2 and or O2 under UV and visible light irradiation with a semiconductor catalyst. Int J Hydrogen Energy 28 663-669... 

Jang JS, Kim HG, Reddy VR, Bae SW, Ji SM, Lee JS (2005) Photocatalytic water splitting over iron oxide nanoparticles intercalated in HTiNb(Ta)05 layered compounds. J Gatal 231 213-222... 

Lee JS (2006) Photocatalytic water splitting under visible light with particulate semiconductor catalysts. Catal Surv Asia 9 217-227... 

Fig. 8.13 Z-scheme approach to photocatalytic water splitting using a DSSC based tandem cell.

Photocatalytic Water Splitting Under Visible Light Concept and Catalysts Development Ajay K. Ray, Photocatalytic Reactor Configurations for Water Purification Experimentation and... 

Ni et al. [5], in a review on the developments in photocatalytic water splitting using Ti02 for hydrogen production, divided the techniques used to enhance the photocatalytic efficiency in two broad groups photocatalyst modification techniques,... 

R.M. Navarro, F. del Valle, J.A. Villoria de la Mano, M.C. Alvarez-Galva n, and J.L.G. Fierro, Photocatalytic Water Splitting Under Visible Light Concept and Catalysts Development Ajay K. Ray, Photocatalytic Reactor Configurations for Water Purification Experimentation and Modeling... 

That is, photocatalytic water splitting is an oxidation-reduction process, where the oxidation process takes place in the valence band and the reduction process in the conduction band, in the subsequent manner (see Figure 2.11) ... 

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