Electrode in photoelectrochemical

Cojucaru A, Simashkevich A, Sherban D, Tiginyahu I, Ursaki V, Tsiulyanu I, Usatyi (2005) Use of porous GaAs electrodes in photoelectrochemical cell. Phys Stat Sol A 202 1678-1682... 

During the last 15 years, many investigations have been performed with semiconductor particles or nanocrystals, either dissolved as colloids or used as suspensions in aqueous solutions. Recently films of nanocrystalline layers have also been produced which were used as electrodes in photoelectrochemical systems. Essential results have already been summarized in various reviews [1-9]. All kinds of systems, containing small or large particles have been used in various investigations. In this chapter, the essential properties of semiconductor particles will be described. Small particles, i.e. nanocrystals, are of special interest because of quantum size effects. 

Traditional ceramics are quite common, from sanitary ware to fine chinas and porcelains to glass products. Currently ceramics are being considered for uses that a few decades ago were inconceivable applications ranging from ceramic engines to optical communications, electrooptic applications to laser materials, and substrates in electronic circuits to electrodes in photoelectrochemical devices. Some of the recent applications for which ceramics are used and/or are prime candidates are listed in Table 1.1. 

In this chapter we have attempted to summarize and evaluate scientific information available in the relatively young field of microwave photoelectrochemistry. This discipline combines photoelectrochemical techniques with potential-dependent microwave conductivity measurements and succeeds in better characterizing the behavior ofphotoinduced charge carrier reactions in photoelectrochemical mechanisms. By combining photoelectrochemical measurements with microwave conductivity measurements, it is possible to obtain direct access to the measurement of interfacial rate constants. This is new for photoelectrochemistry and promises better insight into the mechanisms of photogenerated charge carriers in semiconductor electrodes. 

A photoelectrochemical cell is an electrochemical cell that uses light to carry out a chemical reaction. This type of cell is being considered for the production of hydrogen from water. The silicon electrodes in a photoelectrochemical cell react with water ... 

In their pioneering work on the formation of photoelectrochemically active metal sulfides by oxidation of the parent metal electrode. Miller and Heller [29] reported the anodic formation of polycrystalline Bi2S3 on a bismuth metal electrode in a sodium polysulfide cell, wherein this electrode was used in situ as photoanode. When a Bi metal electrode is anodized in aqueous sulfide solutions a surface film is formed by the reaction... 

A thorough insight into the comparative photoelectrochemical-photocorrosion behavior of CdX crystals has been motivated by the study of an unusual phenomenon consisting of oscillation of photocurrent with a period of about 1 Hz, which was observed at an n-type CdTe semiconductor electrode in a cesium sulfide solution [83], The oscillating behavior lasted for about 2 h and could be explained by the existence of a Te layer of variable width. The dependence of the oscillation features on potential, temperature, and light intensity was reported. Most striking was the non-linear behavior of the system as a function of light intensity. A comparison of CdTe to other related systems (CdS, CdSe) and solution compositions was performed. 

The photoelectrochemical behavior of ZnSe-coated CdSe thin Aims (both deposited by vacuum evaporation on Ti) in polysulflde solution has been described by Russak and Reichman [112] and was reported to be similar to MIS-type devices. Specifically, Auger depth profiling showed the ZnSe component of the (ZnSe)CdSe heterostructures to convert to ZnO after heat treatment in air, thus forming a (ZnO)CdSe structure, while the ZnO surface layer was further converted to a ZnS layer by cycling the electrode in polysulfide electrolyte. This electrochemically generated ZnS layer provided an enhanced open-circuit potential compared to CdSe alone. Efficiencies as high as 5.4% under simulated AM2 conditions were recorded for these electrodes. 

Efficient photoelectrochemical decomposition of ZnSe electrodes has been observed in aqueous (indifferent) electrolytes of various pHs, despite the wide band gap of the semiconductor [119, 120]. On the other hand, ZnSe has been found to exhibit better dark electrochemical stability compared to the GdX compounds. Large dark potential ranges of stability (at least 3 V) were determined for I-doped ZnSe electrodes in aqueous media of pH 0, 6.3, and 14, by Gautron et al. [121], who presented also a detailed discussion of the flat band potential behavior on the basis of the Gartner model. Interestingly, a Nernstian pH dependence was found for... 

Fan and Bard [140] employed capacitance and voltammetric measurements to investigate the photoelectrochemical behavior of n-WSe2, p-WSe2, and n-MoSe2 single-crystal electrodes in aqueous solutions containing various redox couples, namely Br /Br2, I /I, Fe(CN)6" /Fe(CN)6 , Fe /Fe, and... 

Bard AJ, Wrighton MS (1977) Thermodynamic potential forthe anodic dissolution of n-type semiconductors - A crucial factor controlling durability and efficiency in photoelectrochem-ical cells and an important criterion in the selection of new electrode/electrolyte systems. J Electrochem Soc 124 1706-1710... 

Russak MA, Reichman J (1982) Photoelectrochemical performance of ZnSe/CdSe thin film electrodes in aqueous polysulfide electrolyte. J Electrochem Soc 129 542-545... 

The first observations of photoelectrochemical phenomena were made in 1839 by Antoine Becquerel (1788-1879). He used symmetric galvanic cells consisting of two identical metal electrodes in a dilute acid. When illuminating one of the electrodes he observed current flow in the closed electric circuit. 

The photoanodic dissolution also occurs in the electrochemistry and photoelectrochemistry of compact electrodes of these materials. In fact, it is the most serious obstacle to the practical use of semiconductors such as CdS in photoelectrochemical cells The product of corrosion in the absence of oxygen is sulfur. In the presence of oxygen, sulfate ions are formed as in the case of the colloidal particles... 

GaAs, CuInS2, CuInSe2- Semiconductor electrodes have received increasing attention as a consequence of their potential application in photoelectrochemical energy conversion devices. In order to achieve optimum efficiency, the knowledge of the surface composition plays a crucial role. Surface modifications may occur during operation of the photo electrode, or may be the result of a chemical or electrochemical treatment process prior to operation. 

Recently, results of careful experiments were reported by Ito et a/.101 They claimed that formic acid, formaldehyde, and methanol, which had been previously reported as photoelectrochemical reduction products of carbon dioxide, were observed also by photolysis of cell materials, such as electrolytes, including 15-crown-5 ether, and epoxy resin, which has often been used as the molding material of semiconductor electrodes in aqueous solutions. Previously reported reduction products were obtained also under nitrogen with (Table 4) and without (Table 5) a p-GaP photocathode under illumination. These precise experiments under improved conditions, where no photolytic products were observed, gave the result that the main reduction product of carbon dioxide at a p-GaP photocathode in aqueous electrolytes was formic acid. Thus, many kinds of products reported in previous papers83,97,100 were suggested to be due to photolysis of cell materials. 

Scheme I. Semiconductor-based photoelectrochemical cell. Energy output may be in the form of electricity by putting a load in series in the external circuit, or the output can be in the form of chemical energy as redox products formed at the electrodes. N-type semiconductors effect uphill oxidations upon illumination, and p-type semiconductors effect uphill reductions under illumination. Either or both electrodes in the cell can be a photoelectrode.

Prior to the 1970 s, electrochemical kinetic studies were largely directed towards faradaic reactions occurring at metal electrodes. While certain questions remain unanswered, a combination of theoretical and experimental studies has produced a relatively mature picture of electron transfer at the metal-solution interface f1-41. Recent interest in photoelectrochemical processes has extended the interest in electrochemical kinetics to semiconductor electrodes f5-151. Despite the pioneering work of Gerischer (11-141 and Memming (15), many aspects of electron transfer kinetics at the semiconductor-solution interface remain controversial or unexplained. 

There are several non-oxide semiconductor electrodes that have been studied for use in photoelectrochemical cells for water splitting. Materials used as photocathodes include p-Si, p-lnP, p-GaAs, and p-CdTe. Materials used as photoanodes include n-Si, n-InP, n-GaAs, n-CdTe and n-CdSe. Similar to CdS, unfortunately most of these non-oxide semiconductors undergo photocatalytic corrosion under the conditions of oxygen evolution. 

Kainthala RC, Khan SUM, Bockris JOM (1987) The theory of electrode matching in photoelectrochemical cell for the production of hydrogen. Int J Hydrogen Energy 12 381-392... 

---