Efficiencies, of photoelectrochemical

The quantum efficiency of photoelectrochemical reactions may vary from 2 to 4, effective dissolution valence from 2 to 4, and efficiency of hydrogen evolution from 1 to near zero depending on light intensity and potential. 

Fig. 1. (a) Optical excitation in a simple metal. The excited electron-hole pair can relax rapidly (path 1) so that the quantum efficiency of the photoemission process (2) is small. In addition, the back reaction (4) involving electron injection from the solution may occur before the photoemit-ted electron relaxes in the solvent (3). (b) Optical excitation in an insulator or semiconductor. Here, geminate recombination is slower due to the forbidden gap so that the quantum efficiency of photoelectrochemical reactions can approach unity under optimum conditions. In principle, either conduction band (1) or valence band (2) reactions can occur, but in practice the reaction of the minority carrier is most important for extrinsic semiconductors. 

The efficiency of photoelectrochemical devices is based on effective charge transfer while suppressing surface recombination and corrosion. While the photocurrent is a direct measure of the irreversibly transferred electrons, it is not trivial to obtain a measure for the losses at surfaces due to recombination. As will be shown in Section 2.3.1, stationary microwave reflectivity is a method that measures the integral of the excess minority carrier profile. Such profiles are shown in Figures 2.3-2.6. The simultaneous recording of photocurrent and excess microwave reflectivity in an electrochemical cell allows the assessment of the relative contributions of kr and Sr for well-defined systems. These parameters are defined as follows ... 

Kisumi, T., Tsujiko, A., Murakoshi, K., Nakato, Y. Crystal-face and illumination intensity dependences of the quantum efficiency of photoelectrochemical etching, in relation to those of water photooxidation, at n-Ti02 (rutile) semiconductor electrodes. J. Electroanal. Chem. 545, 99-107 (2003)... 

Subbaiyan NK, Maligaspe E, D Souza F (2011) Near unity photon-to-electron conversion efficiency of photoelectrochemical cells built on cationic water-soluble porphyrins electrostatically decorated onto thin-film nanocrystalline Sn02 surface. ACS Appl Mater Interfaces 3(7) 2368-2376... 

The redox behavior of the SeSO -Zn-EDTA system has been discussed on the basis of Pourbaix and solubility diagrams [11], Different complexes and substrates have been employed in order to optimize the electrodeposited thin films. By the selenosulfate method it is generally possible to grow ZnSe with an almost stoichiometric composition however, issues of low faradaic efficiency as well as crystallinity and compactiveness of the product, remain to be solved. Interestingly, in most reports of photoelectrochemically characterized ZnSe electrodeposits, the semiconductor film was found to be p-type under all preparation conditions (ZnSe is normally n-type unless deliberately doped p-type). 

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... 

Tenne R, Wold A (1985) Passivation of recombination centers in n-WSe2 yields high efficiency (>14%) photoelectrochemical cell. Appl Phys Lett 47 707-709 Chaparro AM, Salvador P, Peter LM (1995) The role of surface defects in the photooxidation of iodide at n-MoSe2 evidence for a local autocatalytic effect. J Phys Chem 99 6677-6683... 

Rh2 is the rate of production (moles/s) of hydrogen in its standard state per unit area of the photoelectrode. The standard Gibbs energy AG° = 237.2 kj/mol at 25°C and 1 bar, and Pt is the power density (W/m ) of illumination. The numerator and denominator have units of power and hence, as in the case of photoelectrochemical solar cells, the photoconversion efficiency is the ratio of power output to the power input. 

Antonucci V, Giordano N, Bart JCJ (1982) Structure and photoelectrochemical efficiency of oxidized titanium electrodes. Int J Hydrogen Energy 7 769-774... 

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