Polyselenide electrolyte

Complex equilibria among multiple species are typical also of polyselenide and polytelluride solutions. Aqueous polyselenide solutions have been employed as electrolytes in high-elRciency PEC with photoanodes made of gallium arsenide and cadmium chalcogenides (Chap. 5). Unlike polysulfides, the fundamental equilibria constraining the distribution of polyselenide species have not been meticulously characterized [19]. 

Emissive spectral features were consistent with those previously reported for CdS Te (6-13) and confirmed (Roessler s correlation, (12)) that the Te concentration was <100 ppm. TheA,5x5xl mm samples had resistivities of A,2 ohm-cm (four point probe method) and were oriented with the 5x5 mm face perpendicular to the c-axis. Samples were first etched with 1 10 (v/v) Br2/MeOH and then placed in an ultrasonic cleaner to remove residual Br2. The electrolyte was either sulfide, 1M 0H /1M S2-, or polyselenide, typically 5M 0H /0.1M Se2 /0.001M Se22- short optical pathlengths (<0.1 cm) were used to make the latter essentially transparent for A >500 nm. Electrode and electrolyte preparation as well as electrochemical and optical instrumentation employed have been described previously (8). Electrolytes were magnetically stirred and blanketed under N2 during use. 

These factors are consistent with the 10- to 20-fold decline observed in polyselenide electrolyte in those experiments there also appeared to be little potential dependence of the results (9). Similar thermal quenching data has been reported for dry CdS Te samples irradiated with UV light (10,12,13), electron beams (11), and a particles (19). The temperature dependence of the decline in emission intensity has been linked to the ionization energy of the Te-bound hole, 0.2 eV (10,11,12,13,19). 

We should point out that the temperature effects on emission intensity and photocurrent are completely reversible. Although this result suggests that electrode stability obtains over the duration of the experiments, the properties measured may not be very sensitive to variations in surface or near-surface composition. There is now considerable evidence, in fact, that surface reorganization processes do occur in CdS- and CdSe- based PECs in polychalcogenide electrolytes (17, 21-26). In particular, the occurrence of such an exchange reaction for CdS Te in polyselenide electrolyte would yield CdSe to whose lower band gap... 

Journal of the Electrochemical Society Figure 3. Current-luminescence-voltage (iLV) curves for a 100-ppm CdS Te electrode in polyselenide electrolyte. 

While this cell utilised a salt bridge to separate the two electrolytes, many systems used a membrane instead. Ang and Sammells (1980) provided an example of a membrane cell with a polycrystalline n-CdSe photoelectrode that drove a poly-sulphide/polyselenide storage couple. The cell had reasonable conversion efficiency (4%), but low output power density. The storage reaction and cell configuration are ... 

LYO/YOU] Lyons, L. E., Young, T. L., Alkaline selenide, polyselenide electrolytes Concentrations, absorption spectra and formal potentials, Aust. J. Chem., 39, (1986), 511-527. Cited on pages 135, 154, 155, 156, 157, 565. 

Fig. 14 Chemical species coexisting in polysulfide (a), ferrocyanide (b) and polyselenide (c) aqueous electrolytes used in regenerative PECs.

U sing the understanding of polyselenide speciation in solution, the rationale electrolyte modification of aqueous polyselenide photoelectrochemical solar cell gas been investigated. n-GaAs photocurrent, photovoltage, and photopower are affected by the distribution of hydroselenide. 

In this section, we review the characterization of photoetching patterns evolved on the surface of polycrystalUne CdX(X = S, Se), which are one of the most extensively studied semiconductors as photoelectrodes in photoelectrochemical cells, photoconductors, and other optoelectronic usages. Anodic photocurrent flowing through the electrode-electrolyte interface is entirely due to the oxidative dissolution of the semiconductors themselves to form Cd " " ion and elemental chalco-gen, except in certain redox solutions, such as aqueous polysulfide, polyselenide, and alkanolamine solutions. For example, in an aqueous NaCl solution, CdSe is photoanodically decomposed to form Cd + ion and elemental Se. After the photoelectrolysis of a CdSe electrode under potentiostatic conditions and a subsequent... 

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