Electrode potential shift, with illumination

To determine the conductivity type, note the direction of potential shift with illumination. If OCP moves Positive (towards more anodic potentials) with illumination, the material is p-type. If OCP moves Negative (towards more cathodic potentials), the material is n-type. If the potential did not change with illumination, there may be an issue with electrode fabrication/contacts, the material may be photo-inactive under these conditions, or the material may not be viable for PEC applications. If no response to illumination is observed, it is doubtfiil that the material, as mounted, wiU respond to any other photoelectrochemical characterization techniques. However, the researcher may still wish to perform CV scans as described in section Three-Electrode j-V and Photocurrent Onset to completely rule out photoactivity of the material. 

C60 has been used to produce solvent-cast and LB films with interesting photoelec-trochemical behavior. A study of solvent-cast films of C60 on Pt rotating disc electrodes (RDEs) under various illumination conditions was reported [284]. Iodide was used as the solution-phase rednctant. The open-circuit potential shifted by 74 mV per decade of illumination intensity from a continuous wave (cw) argon-ion laser. The photocurrent versus power was measured at -0.26 V under chopped illumination (14-Hz frequency, vs. SCE) up to 30 mW cm and was close to linear. The photoexcitation spectrum (photocurrent versus wavelength) was measured at 0.02 V (vs. SCE) from 400 to 800 mn and found to be... 

Due to the anodic shift of the OCP potential with illumination [Be9], a p-type Si electrode under anodic bias in HF is preferably etched in the dark areas. 

Under the open circuit conditions, the illumination of BiOHal electrodes with a full spectrum of mercury quartz lamp causes the shift of the electrode potential to the anodic direction (typical for p-type semiconductors). In this case, in the indifferent electrolytes (neutral or acidified KHal solutions) saturated with oxygen, the high positive potential values are attained for BiOCl and BiOBr electrodes (Table 6.2). 

The transition metal chalcogenides such as n-WSe2 are a particular class of electrode materials, and their photoelectrochemical behaviour is of interest from the fundamental point of view. If the basal planar surfaces (perpendicular to the c-axis) with a low density of steps are contacting the electrolyte, these layered materials are relatively stable. Since the corrosion rate is very small, the anodic photocurrent occurs at a high overvoltage with respect to the flatband potential in the dark. As discussed in Section 2.3.1 (Fig. 2.15), the flatband potential t/fb is shifted on illumination because holes accumulate at the surface. On addition of a redox couple such as [Fe(phen)3] ... 

Figure 2 shows the energy band diagrams for n-Si electrodes in pure HF (pH = 2.3) and HF/oxidant solutions without and with light illumination (Xu and Adachi 2006). The electron affinity (Xs) of Si is —4.05 eV. At zero pH, the redox coupling is defined as the normal hydrogen electrode with a potential of —4.5 eV with respect to vacuum. This potential shifts towards more positive values with the increase in pH (+0.059 eV/pH). Thus, the electron energy of the pure HF solution with... 

The onset potential for the freshly etched p-CdTe for the photo-electrochemical reduction of carbon dioxide is -0.76V NHE. When the electrode was cycled between -0.56 to -2.24V under illumination, the onset potential for the photocurrent shifts to less cathodic potentials and remains constant at -0.66V after about c. 20 minutes. When the electrode is potentiostated at -2.0V the photocurrent remained constant for about 24 hours. These results are reproducible and consistent with the published data. Surface analysis of the etched surface of p-CdTe using XPS and SEM showed only trace amounts of carbon and oxygen. 

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