Photocurrent vs. potential

Fig. 9.25. (d) Tafel plots of log-photocurrent vs. potential for p-lnP and p-GaP. Curvel, p-lnP in 1 M NaOH curve 2, p-lnP in 1 M NaOH + 3 mftf methyl viologen curve 3, p-GaP in 1 M NaOH. (Reprinted from K. Uosaki and H. Kita, Solar Energy Materials, Vol. 7, p. 424, Fig. 2,1983, with kind permission from Elsevier Sdence-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)... 

A surface of p-InP was modified by the electrodeposition of submonolayer amounts of various metals and the photocurrent vs. potential behavior studied. The photocurrents observed at 0 V vs. NHE for various surface treatments are shown in the Table E.2. Calculate the maximum efficiency of energy conversion in each case and comment on the observed trend. The light source was an Xe lamp and incident light intensity was 50 mW cm-2. (Contractor)... 

Fig. 5 Photocurrent vs potential plot recorded for a ca. 45 pm thick nanoparticulate Ti02 film, immersed in a 0.1 M HCIO4/0.1 M HCOOH solution and irradiated with a 300-nm monochromatic light (700 pW cm ) from the side of the film/solution boundary. On the left axis is represented the corresponding incident photon-to-current conversion efficiency (IPCE). In the insert is represented schematically (marked in grey ) the illuminated part of the Ti02 film where the electron injection takes place. (Reproduced with permission from [12])...

Figure 7. Photocurrent vs potential dependence for (1) the FANl film and (2) the PANI/Ti02film on orderedAu/p-ATP substrate in 0.05M K3Fe(CN)6/K4Fe(CN)6 aqueous solution under illumination ofaXe lamp without filtering...

Figure 1. Photocurrent vs. potential and PL intensity vs. potential for activated n -Ti02 in 0.05M H2SO4 (pH 1.20) containing methanol of a 0.0 M, b 0.1 M, c 1.0 M, and d 6.0 M. U flat-band potential.

Figure 3 shows the photocurrent vs. potential plots for solutions containing iodide, hydroquinone or bromide as the electron donor. The photocurrent onset for iodide-containing solutions is at -0.3 V vs. SCE,... 

Fig. 3 Photocurrent vs. potential dependence for the photoelectrochemical cell based on tris(4,4 -dicarboxy,2,2 -bipyridyl)ruthenium(ll), Ru(dcbpy)3, in the presence of 1M Nal or NaBr as the electron donor.

Figure 5.38 illustrates the experimental setup for water photoelectrolysis measurements with the nanotuhe arrays used as the photoanodes from which oxygen is evolved. The 1-V characteristics of 400 nm long short titania nanotuhe array electrodes, photocurrent density vs. potential, measured in IM KOH electrolyte as a function of anodization hath temperature under UV (320-400 nm, lOOmW/cm ) illumination are shown in Fig. 5.39. The samples were fabricated using a HF electrolyte. At 1.5V the photocurrent density of the 5°C anodized sample is more than three times the value for the sample anodized at 50°C. The lower anodization temperature also increases the slope of the photocurrent—potential characteristic. On seeing the photoresponse of a 10 V 5°C anodized sample to monochromatic 337 nm 2.7 mW/cm illumination, it was found that at high anodic polarization, greater than IV, the quantum efficiency is larger than 90%.

The discrete charge model of equation [8] is suggested by combined capacitance-photocurrent vs. bias studies (9, 10). These results indicate that the adsorbed charge is localized, yielding a local potential distribution which can not be simply described by an averaged charge density approach, such as is obtained from solution of Poisson s equation. 

This is only possible if the factor k is known. Roy et al. obtained it from the slope of the voltage/pH plot above the inflection point whereas Bard et al. calculated it from the slope of the onset of photocurrent vs. pH (26). However, only poorly reproducible values were obtained by the former and latter method due to high voltage fluctuations and too low photocurrents, respectively. We have determined the k value by a new method through variation of the redox couple (A,2 +/A, + ). In this case a linear relation between the pH0 value and the redox potential of the pH-independent redox couple is expected [Eq. (4)]. 

To compare these methods, in Fig. 40 we show (a) EIX vs. J and (b) /Ph vs. E plots for a CVD single crystal thin-film electrode. We see that with increase in illumination intensity J, the open-circuit potential E(X approaches a limit of 0.7 V, which is close to the photocurrent onset potential (0.75 V). [The photocurrent density squared vs. potential dependence for this electrode, although far from linear (unlike that of Fig. 38), by the extrapolation to yph -> 0 gives the potential value of approx. 0.65 V.] It is concluded that, on the whole, methods (i) and (ii) are in a good agreement and can be used in the determination of the flat-band potential. Similar results were obtained with HTHP single crystals. 

Fig. 11. Mott-Schottky plot upperfigure) smii photocurrent vs. electrode potential (tower gurc) for H-RuSa [79]...

One example, oxidation of iodide at n-GaAs, is illustrated in terms of photocurrent vs shift of flatband potential in Fig. 23. These authors found a very high stability factor of about s = 0.97. On the basis of Eqs. (57) and (59), they were able to simulate the experimental curves very well if k = 0, i.e. the reaction rate between S and Red is negligible (not shown). For details, one must refer to their paper [119]. Similar results have been obtained with polysulfide. 

Fig. 23. Photocurrent vs flatband potential at -GaAs in H2SO4 with 7 M NaJ dots experimental values solid lines theoretical curves [119]...

The ohmic loss in this system was found to be approximately 50 ohms using an 1-R compensator when galvanostatic electrolysis was conducted. The open circles in Fig. 1 show the photocurrent vs. the IR-free potential, assuming that the solution resistance does not change with potential. Thus, for current densities exceeding 100 mA cm-2, the IR correction exceeds 1 V with the present geometry. 

Fig. 7.29 Cathodic photocurrent vs. electrode potential for p-GaAs in the presence of various redox system in lO M M2SO4...

Fig. 8.20 a) Anodic photocurrent vs. electrode potential for an n-WSe2 electrode in the absence and in the presence of a redox. system, b) Position of energy bands at the surface of WSe2 in the dark and under illumination. (After ref. [64])... 

Fig. 10.11 Sensitized photocurrents vs. electrode potential for 10" M solution (pH 9) of rhodamine-B at an Sn02 electrode (excitation wavelength 570 nm) at different light intensities. SCE, saturated calomel electrode. (After ref. [9])...

Fig. 10.12 Sensitized photocurrents vs. electrode potential for rhodamine-B at GaP electrodes in 1 M KCl solution (excitation wavelength 570 nm).

The photocurrent onset potential is at 0.95 V vs. RHE. This is much more positive than the flatband of a-FeaOs, which is at 0.3 Vrhe [34, 35]. The difference is due to slow oxidation kinetics (catalysis) [36] and/or to recombination in the space... 

Figure 24. Photocurrent vs. electrode potential (a) n-GaAs (b) n-WOs (photocurrent plotted as /ph see text).

Figure 29. (a) Cathodic photocurrent vs. electrode potential at p-GaAs at pHl (b) electron transfer via surface states. ... 

Time-resolved measurements of electron transfer times for quantum well photoelectrodes which can be compared with hot electron relaxation times, have not yet been reported. Only some excitation spectra, that is, photocurrent vs photon energy for MQWs and single quantum wells (SQWs), have been published so far [2]. In both cases, the photocurrent spectra show distinct structures corresponding to transitions between the hole and electron wells as shown for SQW electrodes in Figure 9.32. The MQW electrodes are not very suitable because the externally applied potential occurs across many quantum wells which leads to a... 

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