Photoelectrochemical

A. J. Nozik, in Photovoltaic and Photoelectrochemical Solar Energy Conversion, F. Cardon, W. P. Gomes, and W. Dekeyser, eds.. Plenum, New York, 1981. 

Luminescence has been used in conjunction with flow cells to detect electro-generated intennediates downstream of the electrode. The teclmique lends itself especially to the investigation of photoelectrochemical processes, since it can yield mfonnation about excited states of reactive species and their lifetimes. It has become an attractive detection method for various organic and inorganic compounds, and highly sensitive assays for several clinically important analytes such as oxalate, NADH, amino acids and various aliphatic and cyclic amines have been developed. It has also found use in microelectrode fundamental studies in low-dielectric-constant organic solvents. 

N. Serpone, E. Pehzzetti, and H. Hidaka, in Z. W. Tian and Yi Cao, eds.. Photochemical and Photoelectrochemical Conversion and Storage of Solar Energy International Academic PubUshers, Beijing, China, 1993. 

Metal oxide electrodes have been coated with a monolayer of this same diaminosilane (Table 3, No. 5) by contacting the electrodes with a benzene solution of the silane at room temperature (30). Electroactive moieties attached to such silane-treated electrodes undergo electron-transfer reactions with the underlying metal oxide (31). Dye molecules attached to sdylated electrodes absorb light coincident with the absorption spectmm of the dye, which is a first step toward simple production of photoelectrochemical devices (32) (see Photovoltaic cells). 

Electrodes Rechargeable batteries (accumulators) fuel cells, photoelectrochemical cells, analytical sensors (pH, O2, NO, SO2, NH3, glucose), electrocardiography (ECG)... 

Chronoamperometry (kinetics) Photoelectrochemical methods (electronic properties, heterogeneity)... 

Bullock, K. R., Trischan, G.M. and Burrow, R. G., Photoelectrochemical and Microprobe Laser Raman Studies of Lead Corrosion in Sulphuric Acid , J. Electrochem. Soc., 130, 1283 (1983)... 

The Ni(OH)2/NiOOH reaction is a topo-chemical type of reaction that does not involve soluble intermediates. Many aspects of the reaction are controlled by the electrochemical conductivity of the reactants and products. Photoelectrochemical measurements [86, 871 indicate that the discharged material is a p-type semiconductor with a bandgap of about 3.7eV. The charged material is an n-type semiconductor with a bandgap of about 1.75eV. The bandgaps are estimates from absorption spectra [87]. 

Stationary microwave electrochemical measurements can be performed like stationary photoelectrochemical measurements simultaneously with the dynamic plot of photocurrents as a function of the voltage. The reflected photoinduced microwave power is recorded. A simultaneous plot of both photocurrents and microwave conductivity makes sense because the technique allows, as we will see, the determination of interfacial rate constants, flatband potential measurements, and the determination of a variety of interfacial and solid-state parameters. The accuracy increases when the photocurrent and the microwave conductivity are simultaneously determined for the same system. As in ordinary photoelectrochemistry, many parameters (light intensity, concentration of redox systems, temperature, the rotation speed of an electrode, or the pretreatment of an electrode) may be changed to obtain additional information. 

These three equations (11), (12), and (13) contain three unknown variables, ApJt kn and sr The rest are known quantities, provided the potential-dependent photocurrent (/ph) and the potential-dependent photoinduced microwave conductivity are measured simultaneously. The problem, which these equations describe, is therefore fully determined. This means that the interfacial rate constants kr and sr are accessible to combined photocurrent-photoinduced microwave conductivity measurements. The precondition, however is that an analytical function for the potential-dependent microwave conductivity (12) can be found. This is a challenge since the mathematical solution of the differential equations dominating charge carrier behavior in semiconductor interfaces is quite complex, but it could be obtained,9 17 as will be outlined below. In this way an important expectation with respect to microwave (photo)electro-chemistry, obtaining more insight into photoelectrochemical processes... 

As mentioned in the introduction, before an adequate theory was developed, it was difficult to understand the experimentally determined pho-toinduced PMC signals, especially the minority carrier accumulation near the onset of photocurrents.The reason was that neither conventional solid-state semiconductor theory nor photoelectrochemical theory had taken such a phenomenon into account. But we have shown that it is real and microwave (photo)electrochemical experiments clearly confirm it. 

It is well known that photoelectrochemical measurements do not indicate photocurrents in the accumulation region of an illuminated semiconductor. The reason is that majority carriers control interfacial reactions, which... 

On the basis of our theoretical considerations and preliminary experimental work, it is hoped that fast processes of charge carriers will become directly measurable in functioning photoelectrochemical cells, Typical semiconductor electrodes are not the only systems accessible to potential-dependent microwave transient measurements. This technique may also be applied to the interfacial processes of semimetals (metals with energy gaps) or thin oxide or sulfide layers on ordinary metal electrodes. 

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. 

Badawy,W.A. Photovoltaic and Photoelectrochemical Cells 30 Based on Schottky Barrier Heterojunctions... 

Newman, J. Photoelectrochemical Devices for Solar Energy Conversion 18... 

Taniguchi, I. Electrochemical and Photoelectrochemical Reduction of Carbon Dioxide 20... 

Photoelectrochemical Kinetics and Related Devices Khan, S. U. M. Bockris, J. O M. 14... 

Photoelectrochemical conductivity, and microwave conductivity, 437 Photo electrodes... 

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