Photoelectrolysis semiconductor electrodes

Gerischer H (1979) Solar Photoelectrolysis with semiconductor electrodes. In Solar energy conversion Solid-state physics aspects, Seraphin BO (Ed), pp.l 15-172 Springer-Verlag New York... 

Ghosh AK, Maruska HP (1977) Photoelectrolysis of water in sunlight with sensitized semiconductor electrodes. J Electrochem Soc 124 1516-1522... 

Gerischer H (1979) Solar photoelectrolysis with semiconductor electrodes. In Seraphin BO, Aranovich JA (Eds.) Solar energy conversion solid state physics aspects. Springer, Berlin, pp. 114-172... 

Fujishima A, Honda K (1972) Electrochemical photolysis of water at a semiconductor electrode. Nature 238 37-38 Nozik AJ (1976) p-n photoelectrolysis cell. Appl Phys Lett 29 150-153... 

Figure 6.25 Outline of a cell for the photoelectrolysis of water. The photoexcited semiconductor electrode is made of SrTi02...

The possibility of solar photoelectrolysis was demonstrated for the first time with a system in which an n-type Ti02 semiconductor electrode, which was connected through an electrical load to a platinum black counter electrode, was exposed to near-UV light (Fig 2.2).l9) When the surface of the Ti02 electrode was... 

Nishida, M., Charge Transfer by Surface States in the Photoelectrolysis of Water Using a Semiconductor Electrode, Nature, 277, 202, 1979. 

One other approach to the photoelectrolysis of water that has been adopted involves the photosensitization of semiconductor electrodes such as Ti02,362,364,365 SrTi03365,366 or Sn02 265,365,367 by, for example, [Ru(bipy)3]2+. The photochemically excited state of the chromophore injects an electron into the conduction bond of a semi-conductor this is then passed via an external circuit to a platinum electrode for H2 production. The oxidized form of the quencher then forms 02 apparently in an uncatalyzed reaction. Unfortunately, all such systems... 

Electromagnetic radiation, besides being a probe of surface structure, can excite electrons in the species in solution (especially in organic compounds) or in the electrode itself (especially in semiconductor electrodes). This photon excitation can lead to electron transfer between electrode and solution. The study of these phenomena is photoelectrochemistry and can be very important in conversion of solar energy into electricity in order to convert substances (photoelectrolysis). 

There has recently been interest in the photoelectrolysis of water (Section 12.4). In this process a large part of the energy necessary for electrolysis is provided photochemically by solar radiation, promoting the reactions by exciting the valence electrons in semiconductor electrodes. This electronic energy is then transferred to the water molecules, helping to break the O-H bonds. Efficiencies achieved so far are still not high, and it is not clear at present what future this will have. 

Hydrogen Evolving Solar Cells Principles in the design of semiconductor electrodes, surface modification strategies, p-n junction cells, and photoelectrolysis by suspended semiconductor particles, discussed. 66... 

Solar Photoproduction of Hydrogen Review mainly addresses potential and experimental efficiencies for four types of systems of which one comprises photoelectrolysis cells with one or more semiconductor electrodes. 70... 

A photoelectrochemical (photoelectrolysis) system can be constructed using a n-type semiconductor electrode, a p type semiconductor, or even mating n- and p-type semiconductor photoelectrodes as illustrated in Figs. 2a c respectively. In the device in Fig. 2a, OER occurs on the semiconductor photoanode while the HER proceeds at a catalytic counterelectrode (e.g., Pt black). Indeed, the classical n-Ti02 photocell alluded to earlier,53 57 belongs to this category. Alternately, the HER can be photo-driven on a p type semiconductor while the OER occurs on a "dark" anode. 

Photoelectrolysis of Water in Sunlight with Sensitized Semiconductor Electrodes Similar observations as in Ref. 236 for Al3+-doped Ti02. 237... 

The p-n photoelectrolysis approach,60 on the other hand, simply combines a n-type semiconductor photoanode and a p-type semiconductor photocathode in an electrolysis cell (Fig. 2c). The pros and cons of this twin-photosystem approach (which mimicks plant photosynthesis) were enumerated earlier in this Chapter (see Section 2). Table 16 provides a compilation of the semiconductor photocathode and photoanode combinations that have been examined. Reference 67 may also be con suited in this regard for combinations involving n WSe2, n MoSe2, n WS2, n TiCH, p InP, p GaP and p Si semiconductor electrodes. 

The whole field received a new impetus after the first oil crisis, when Fujishima and Honda reported on the photoelectrolysis of water at Ti02-electrodes [13], Whereas, before the oil crisis, most basic models and results had been published only by 3-4 research groups in the world, many other scientists entered the field after this crisis and studied solar applications, and hundreds of papers were published. Since then, many processes at semiconductor electrodes have been studied more quantitatively by using not only standard electrochemical methods, but also new techniques, such as spectroscopic surface analysis (see e.g. [12]). Naturally, photoeffects played a dominant role in these investigations. These were not only restricted to reactions induced by light excitation within the semiconductor electrode [11], but were also extended to the excitation of adsorbed dye molecules [14,15]. 

The application of semiconductor-liquid junctions is of special interest for the direct production of a chemical fuel. Especially the production of hydrogen by photoelectrolysis of H2O has been studied by many research groups (compare with [114,194]. It has been demonstrated by many authors that H2-formation is rather easy at semiconductor electrodes. The crucial point is the simultaneous oxidation of H2O. So far, photoelectrolysis was only achieved with SrTiOs, a semiconductor of a large bandgap (Eg = 3.1 eV) [206]. Very recently, photocleavage of HjO was also found with some niobates under open... 

Dye sensitization of semiconductor surfaces is not considered here, nor are issues related to semiconductor particles, photocatalysis and photoelectrolysis per se. These companion topics may be found elsewhere in Volumes I, IV and V. The discussion is phenomenological and is designed to provide an intuitive grasp of the key issues rather than detailed derivations that would have been prohibitive in terms of space constraints in any case. Indeed, the available theoretical framework is only examined in terms of how and with what confidence the pertinent conclusions can be experimentally verified with semiconductor electrodes. 

One other approach to the photoelectrolysis of water that has been adopted involves the photosensitization of semiconductor electrodes such as SrTi03or... 

High-rate photoelectrolysis of CO2 was conducted in a high pressure CO2 + methanol medium using p-type semiconductor electrodes. Current densities of up to 100 mA cm 2 were achieved, with current efficiencies of up to 93 % for CO production on a p-InP photocathode. The effect of CO2 pressure on the product distributions was examined for p-InP and p-GaAs. 

Gerischer H. (1979), Solar photoelectrolysis with semiconductor electrodes , in Topics Appl. Phys., Vol. 31, Seraphin B. O., ed.. Springer Verlag, Berlin, pp. 115-172. 

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