Suppression of Surface Dissolution of CdS Photoanode by Reducing Agents

Inoue, Tooru; Watanabe, Tadashi; Fujishima, Akira; Honda, Kenichi; Kohayakawa, Koichi

doi:10.1149/1.2133392

Cited by 186 publications

(89 citation statements)

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“…Although many such materials have been made and utilized a crucial factor in application is the photo-hydro-stability of the material. For example, CdS could be a much better material for water splitting because it has a band gap in the visible (*2.4 eV), but it oxidises in the presence of water and light [13] and the band positions are not properly aligned for water splitting. Titania has been shown to be generally photo-hydrostable and so is the focus here, but it is worth noting that other, less stable semiconductors have been proposed for use when coated with a fairly thick layer of titania for protection [14].…”

Section: Electronic Transitions In Titaniamentioning

confidence: 99%

The Photocatalytic Window: Photo-Reforming of Organics and Water Splitting for Sustainable Hydrogen Production

et al. 2014

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Precious metal-titania materials make good catalysts for hydrogen production from a variety of organic substrates using sunlight. These substrates essentially act as reductants for water, by intercepting electrophilic oxygen species generated by electron-hole excitation resulting from photon absorption in the titania support. As a result, the hydrogen produced comes partly from water splitting and partly from dehydrogenation of the organic substrate. Why only precious metals work for the reaction is discussed, together with the mechanism of these reactions. The oxygenate substrates are decarbonylated to produce adsorbed CO, which is removed in the presence of light by the electrophilic oxygen as CO 2 , but the level of CO 2 detected is strongly affected by the amount of liquid water present, due to absorption and reaction to form carbonic acid. The possibilities for application of this technology in the domestic environment, the 'Photocatalytic Window' is considered.Keywords Photo-catalysis Á Photo-reforming Á Water splitting Á Hydrogen production Á Methanol Setting the SceneThe human race is in a period of fast transition in all sorts of aspects of life. Perhaps the most important of these is the changing energy scene. Because of the increase in population and increased industrialisation the most convenient forms of useable energy that are available in large quantity, fossil fuels, have been utilized for energy supply. These are firstly coal, used originally for driving steam generation for the new steam engines invented and widely introduced for manufacturing and transport in England from the late 18th century. Following from this came the widespread use of crude oil for transport, in the form of refined petroleum spirit, and in more recent times increasing use of gas powered electrical power generation and domestic combustion. As a result there has been an increase of CO 2 in the atmosphere-increasing from the geologically steady value of about 280 ppm, now just breaking the 400 ppm level, a 42 % increase. The source of these increases can be traced back to the original industrialisation of the early-mid 18th century. Figure 1 illustrates this in terms of the CO 2 level in the atmosphere, combined with a derivative which traces the start of this increase to the period just after the development of more efficient forms of steam engines for mechanical power generation see Ref. [1].The consequences of this geologically fast increase in CO 2 levels can be debated, but what is absolutely certain is that, as sentient beings, humans should not be playing with dice by abnormal perturbance of natural equilibrium, over a geologically fast timescale. The results are not likely to be positive for the planet, except in the sense that it might help reduce the human population.Thus there is an urgent need to stop the CO 2 increase and to find new sustainable ways of fuelling our future. Of course we have a number of successful technologies in Electronic supplementary material The online version of this article

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Section: Electronic Transitions In Titaniamentioning

confidence: 99%

The Photocatalytic Window: Photo-Reforming of Organics and Water Splitting for Sustainable Hydrogen Production

et al. 2014

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“…Conversion of light to electricity with devices called photoelectrochemical cells has been an area of considerable activity in the last 2 years (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). Except for one cell that uses a p-type CdTe photocathode (12), the key element of such cells is an n-type semiconducting photoanode.…”

mentioning

confidence: 99%

n-Type Si-based photoelectrochemical cell: New liquid junction photocell using a nonaqueous ferricenium/ferrocene electrolyte

Legg

Ellis

Bolts

et al. 1977

Proc. Natl. Acad. Sci. U.S.A.

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n-Type Si has been shown to serve as a stable photoanode in a cell for the conversion of light to electricity. The other components of the cell are a Pt cathode and an electrolyte consisting of an ethanol solution of the electrolyte. A Si-based cell is of note for several reasons: (i) Si is one of the most widely studied and best understood semiconductors with a wealth of supporting technology behind it, (ii) Si is the second most abundant element on earth, and (iii) the small band gap of Si affords the possibility of utilizing a large fraction of the solar spectrum. Unfortunately, the 1

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“…Whether the decomposition of water or dissolution of the semiconductor takes precedence depends on the relative equilibrium potentials for the water oxidation and for the dissolution of the semiconductor materials. The redox reaction with more negative redox potential occurs by the action of holes in precedence to that with more positive redox potential [12,13]. Thermodynamic calculations [14,15] can provide information concerning this problem.…”

Section: A) Stabilitymentioning

confidence: 99%

“…There have been active studies to stabilize these photoanodes by use of suitable redox compounds [2,6,12,13,[24][25][26][27][28][29][30]. The reducing agents can react with the photogenerated holes in the valence band.…”

Section: A) Stabilitymentioning

confidence: 99%

“…Many efforts have recently been concentrated on the above problem, i.e., surppression of dissolution of unstable semiconductor photoelectrodes. It has been established that stabilization of these electrodes can be achieved by addition of suitable redox species in the electrolyte solution [12,13,[24][25][26][27][28][29][30]. We studied the competitive photoanodic oxidation at a CdS electrode in electrolytes containing various reducing agents [12,13].…”

Section: -2-3 Regenerative Electrochemical Photocellmentioning

confidence: 99%

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Photoelectrochemical Hydrogen Production

Watanabe¹,

Fujishima²,

Honda³

1979

Solar-Hydrogen Energy Systems

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The solar energy coming down onto the earth's surface amounts to ca. 3 X 10 J per year, which is approximately 10 times the world-wide yearly energy consumption. Search for the efficient conversion of solar energy into other useful forms is, in view of the increasing anxiety about the exhaustion of energy resources, one of the most important challenges of future research and technology. In systems designed for the purpose of converting solar energy into electricity and/or chemical energy, two principal criteria must be fulfilled. The first is the absorption, by some chemical substance, of solar irradiation, leading to the creation of electron (a reduced chemical moiety)-hole (an oxidized chemical moiety) pairs. The second is an effective separation of these electron-hole pairs with little energetic loss, before they lose the input energy through recombination. Such a photoinduced charge separation can proceed effectively provided an electric field (potential gradient) has been established at the position where the primary photoexcitation takes place. In general, a potential gradient can be produced at an interface between two different substances (or different phases). For example, a very thin (ca. 50 A) lipid membrane separating two aqueous solutions inside the chloroplast of green plants is believed to play the essential role for the process of photosynthesis, which is the cheapest, and probably most successful solar conversion system available so far. Another well-known example is a photocell or a solar cell, in which the photogenerated electron hole pairs are driven efficiently in opposite directions by an electric field existing at the boundary (junction) of nand p-type semiconductors (or at metal/semiconductor junctions). A potential gradient can also be created, by a process described later in more detail, at an interface of a semiconducting material and a liquid phase. Hence, if a semiconductor is used as an electrode which is connected to another (counter) electrode, photoexcitation of the semiconductor can generate an electric work through an external load and, simultaneously, make proceed chemical (redox) reaction on the surface of each electrode. On the other hand, in a system where semiconductor particles are suspended in a solution, excitation of the semiconductor can lead to redox processes at the interface region. These systems have recently drawn the attention of a large number of investigators primarily in connection with solar energy conversion. The present chapter deals with the principles and recent advances in the investigation of light energy conversion systems based on the semiconductor/liquid junctions, focusing on fuel production as well as electrical energy generation. Biophotoelectrochemical processes (photoinduced charge generation and separation using compounds or organisms of biological origin) are also reviewed.

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Suppression of Surface Dissolution of CdS Photoanode by Reducing Agents

Cited by 186 publications

References 20 publications

The Photocatalytic Window: Photo-Reforming of Organics and Water Splitting for Sustainable Hydrogen Production

The Photocatalytic Window: Photo-Reforming of Organics and Water Splitting for Sustainable Hydrogen Production

n-Type Si-based photoelectrochemical cell: New liquid junction photocell using a nonaqueous ferricenium/ferrocene electrolyte

Photoelectrochemical Hydrogen Production

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