Photoanodes stability

Various other semiconductor materials, such as CdSe, MoSe, WSe, and InP were also used in electrochemistry, mainly as n-type photoanodes. Stability against photoanodic corrosion is, naturally, much higher with semiconducting oxides (Ti02, ZnO, SrTi03, BaTi03, W03, etc.). For this reason, they are the most important n-type semiconductors for photoanodes. The semiconducting metal oxide electrodes are discussed in more detail below. 

Strontium Titanate Photoelectrodes. Efficient Photoassisted Electrolysis of Water at Zero Applied Potential. As above but the water photosplitting driven by light only with no external bias. Photoanode stability also confirmed as in the evolution of H2 and O2 in the correct 2 1 stoichiometric ratio. 287... 

Approaches to photoanode stabilization based on polymer films containing redox functionalities have been reviewed elsewhere, e.g., Refs. [6, 373j. 

PTh 333 - 335) evidently materials which are suitable for such applications and which stabilize the photoanodes considerably. 

The reaction occurring at the photoanode (CdS or CdSe) is the oxidation of sulfide or polysulfide, while at the cathode (Pt) some polysulfide species are reduced, so that the electrolyte undergoes no net chemical change. Here, the previous problem of poor stability in Fe(CN)g solutions could be minimized, at the expense of lowering the driving potential (and thus the conversion efficiency), by using fhe... 

Added stability in PEC can be attained through the use of non-aqueous solvents. Noufi et al. [68] systematically evaluated various non-aqueous ferro-ferricyanide electrolytes (DMF, acetonitrile, PC, alcohols) for use in stabilizing n-CdSe photoanodes. Selection of the solvent was discussed in terms of inherent stability provided, the rate of the redox reaction, the tendency toward specific adsorption of the redox species, and the formal potential of the redox couple with respect to the flat band potential (attainable open-circuit voltage). On the basis of these data, the methanol/Fe(CN)6 system (transparent below 2.6 eV) was chosen as providing complete stabilization of CdSe. Results were presented for cells of the type... 

Diaz AF, Logan JA(1980)Electroactive polyanihne films. JElectroanalChem 111 111-114 Noufi R, Nozik AJ, White J, Warren LF (1982) Enhanced stability of photoelectrodes with electrogenerated polyanUine films. J Electrochem Soc 129 2261-2265 Noufi R, Tench D, Warren LE (1981) Protection of semiconductor photoanodes with photoelectrochemicaUy generated polypyrrole films. J Electrochem Soc 128 2596-2599 Jaeger CD, Fan FRF, Bard AJ (1980) Semiconductor electrodes. 26. Spectral sensitization of semiconductors with phthalocyanine. J Am Chem Soc 102 2592-2598 Gerischer H (1977) On the stability of semiconductor electrodes against photodecomposition. J Electroanal Chem 82 133-143... 

Cahen D, Mirovsky Y (1985) Ternary Chalcogenide-Based Photoelectrochemical cells. 6. Is There a Thermodynamic Explanation for the Output Stability of CulnS2 and CulnSe2 Photoanodes J Phys Chem 89 2818-2827... 

This chapter considers photoanodes comprised of metal oxide semiconductors, which are of relatively low cost and relatively greater stability than their non-oxide counterparts. In 1972 Fujishima and Honda [1] first used a crystal wafer of n-type Ti02 (rutile) as a photoanode. A photoelectrochemical cell was constructed for the decomposition of water in which the Ti02 photoanode was connected with a Ft cathode through an external circuit. With illumination of the Ti02 current flowed from the Ft electrode to the... 

The use of polycrystalline La doped SrTiOs as a photoanode has also been investigated [31]. La is considered an appropriate dopant because of its stability in trivalent state and the similarity of the ionic radii for Sr (1.40 A) and La " (1.32 A), which ensures its incorporation at Sr sites. Doping leads to the formation of a new energetic deep donor sub-level (Ti sd) in the band gap, thereby shifting its response towards the visible region. Similarly doping of polyciystalline Ti02 has shown an increase... 

Spray pyrolysis of ethanolic solutions of Fe(acetylacetone)3 or FeCls between 370°C and 450°C onto a glass substrate are reported for the fabrication of a-Fe20s thin-film photoanodes [75]. Upon illumination by a 150 W Xe lamp samples consistently demonstrate photocurrents of 0.9 mAcm , IPCE values up to 15%, and robust mechanical stability with no signs of photocorrosion for the undoped samples. With simultaneous multiple doping of 1% A1 and 5% Ti, an IPCE of 25% can be reached at 400 nm. Zn doping is known to induce p-type character in Ee20s thin film electrodes [76]. 

ZnS-CdS (bandgap = 2.3-2.4 eV) composite semiconductor photoelectrodes show a broad spectral response and n-type behavior, with saturation of the anodic photocurrent upon increasing anodic potential making the system suitable for use as a photoelectrochemical cell photoanode [72], Nanostructured ZnS-CdS thin film electrodes show that anodic photocurrent saturation can be attained with the application of a small, 0.1 V, bias [73], while hydrogen evolution is observed at the Pt cathode. The performance of the ZnS-CdS photoanodes appear strongly dependent upon the method of film preparation [72,73], with Zn rich films demonstrating superior photocurrent generation, and stability, in comparison to Cd rich films. 

Ellis AB, Bolts JM, Wrighton MS (1977) Characterization of n-type semiconducting indium phosphide photoelectrodes stabilization to photoanodic dissolution in aqueous solutions of telluride and ditelluride ions. J Electrochem Soc 124 1603-1607... 

Ginley DS, Baughman RJ, Butler MA (1983) BP-stabilized n-Si and n-GaAs photoanodes. Electrochem Soc 130 1999-2002... 

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