David R. Klug

Bio: David R. Klug is an academic researcher from Imperial College London. The author has contributed to research in topics: P680 & Photosystem II. The author has an hindex of 43, co-authored 128 publications receiving 7992 citations. Previous affiliations of David R. Klug include University College London & École Polytechnique Fédérale de Lausanne.

Mechanism of photocatalytic water splitting in TiO2. Reaction of water with photoholes, importance of charge carrier dynamics, and evidence for four-hole chemistry.

Abstract: We show for the first time that the photogenerated hole lifetime in TiO2 is a strong determinant of the ability of TiO2 to split water. Hole lifetimes were measured using transient absorption spectroscopy over a range of excitation intensities. The lifetimes of the holes were modulated by the use of exogenous scavengers and were also found to vary systematically with the excitation intensity. In all cases the quantum yield of oxygen production is found to be linked to the light intensity used, ranging from below 1 sun equivalent to nearly 1 sun equivalent. We also provide evidence that oxygen production requires four photons for each molecule of oxygen, which is reminiscent of the natural photosynthetic water-splitting mechanism. This in turn suggests a mechanism for oxygen production which requires four-hole chemistry, presumably via three, as yet unidentified intermediates. It is also shown that at excitation densities on the order of 1 sun, nongeminate electron−hole recombination limits the quantum yie...

Parameters Influencing Charge Recombination Kinetics in Dye-Sensitized Nanocrystalline Titanium Dioxide Films

Abstract: Optical excitation of RuII(2,2‘-bipyridyl-4,4‘dicarboxylate)2(NCS)2-sensitized nanocrystalline TiO2 films results in injection of an electron into the semiconductor. This paper addresses the kineti...

The role of cobalt phosphate in enhancing the photocatalytic activity of α-Fe2O3 toward water oxidation.

Abstract: Transient absorption spectroscopy was used to probe the dynamics of photogenerated charge carriers in α-Fe2O3/CoOx nanocomposite photoelectrodes for water splitting. The addition of cobalt-based electrocatalysts was observed to increase the lifetime of photogenerated holes in the photoelectrode by more than 3 orders of magnitude without the application of electrical bias. We therefore propose that the enhanced photoelectrochemical activity of the composite electrode for water photooxidation results, at least in part, from reduced recombination losses because of the formation of a Schottky-type heterojunction.

Charge separation versus recombination in dye-sensitized nanocrystalline solar cells: the minimization of kinetic redundancy.

Abstract: In this paper we focus upon the electron injection dynamics in complete dye-sensitized nanocrystalline metal oxide solar cells (DSSCs). Electron injection dynamics are studied by transient absorption and emission studies of DSSCs and correlated with device photovoltaic performance and charge recombination dynamics. We find that the electron injection dynamics are dependent upon the composition of the redox electrolyte employed in the device. In a device with an electrolyte composition yielding optimum photovoltaic device efficiency, electron injection kinetics exhibit a half time of 150 ps. This half time is 20 times slower than that for control dye-sensitized films covered in inert organic liquids. This retardation is shown to result from the influence of the electrolyte upon the conduction band energetics of the TiO2 electrode. We conclude that optimum DSSC device performance is obtained when the charge separation kinetics are just fast enough to compete successfully with the dye excited-state decay. Th...

Electron injection and recombination in dye sensitized nanocrystalline titanium dioxide films: A comparison of ruthenium bipyridyl and porphyrin sensitizer dyes

Abstract: This paper is concerned with the parameters influencing the interfacial electron transfer kinetics, and therefore the sensitizing efficiency, for different sensitizer dyes adsorbed to nanocrystalline titanium dioxide films. We consider three sensitizer dyes: Ru(2,2‘-bipyridyl-4,4‘-dicarboxylate)2-cis-(NCS)2 (Ru(dcbpy)2(NCS)2) and zinc and free base tetracarboxyphenyl porphyrins (ZnTCPP & H2TCPP). These dyes were selected as they exhibit large differences in their oxidation potentials and photophysics, while retaining similar carboxylate groups for binding to the TiO2 surface. For example, whereas the photophysics of Ru(dcbpy)2(NCS)2 in solution is dominated by ultrafast ( 1 ns) π* singlet excited states and only weak singlet/triplet mixing. The ground and excited-state oxidation potentials also differ by up to ...

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Dye-Sensitized Solar Cells

Abstract: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

Understanding TiO2 photocatalysis: mechanisms and materials.

Abstract: Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

Solar energy conversion by dye-sensitized photovoltaic cells

Abstract: The quality of human life depends to a large degree on the availability of energy. This is threatened unless renewable energy resources can be developed in the near future. Chemistry is expected to make important contributions to identify environmentally friendly solutions of the energy problem. One attractive strategy discussed in this Forum Article is the development of solar cells that are based on the sensitization of mesoscopic oxide films by dyes or quantum dots. These systems have already reached conversion efficiencies exceeding 11%. The underlying fundamental processes of light harvesting by the sensitizer, heterogeneous electron transfer from the electronically excited chromophore into the conduction band of the semiconductor oxide, and percolative migration of the injected electrons through the mesoporous film to the collector electrode will be described below in detail. A number of research topics will also be discussed, and the examples for the first outdoor application of such solar cells wi...