Evaluation of the flat-band potentials by measurements of anodic/cathodic photocurrent transitions

Abstract

The photoprocesses on semiconducting n-Ti02 and n-SrTiO, electrodes in the presence of reducible surface species are described. These species are generated by pre-illumination with the band-gap light of the electrodes being operated under reverse bias. The amount formed in the course of this preillumination can be re!ated to the negative charge required to reduce them. This charge correlates proportionally with V,,, the voltage at which transition from anodic to cathodic photocurrent occurs. The influence on Vt, of the parameters surface coverage as function of pre-illumination time, wavelength, photon flux and pH of the electrolyte is investigated. The occurrence of the cathodic photoprocess is discussed in terms of an electron-tunnelling mechanism through the space-charge barrier to the solution and a joint model proposed by Bard and Gerischer.The influences of the cathodic photoeffect on the onset potential of the usual anodic photoprocess may affect flat-band potential determinations from curves of iph against V. Experimental evidence is provided that the most reliable values of Vfb from this method can be obtained by scanning from cathodic to anodic potentials. Also irradiation with long-wavelength light, close to the band-gap energy, and high light intensity are recommended.

Highly photoactive Brookite and Anatase with enhanced photocatalytic activity for the degradation of indigo carmine application

“…These results reveal that the capacitance Csc of the material seems to be influenced by the surface states, as pointed out by other authors [38]. To verify these observations, the onset potential, Eonset, was determined from both, photocurrent transients and linear sweep voltammetry under darkness and illumination to compare to Efb since it is an equivalent method for such measurements [41]. In both samples the concordance between these techniques seems to be good confirming the suitability of the methods.…”

Laser‐Induced Photoelectrochemical Transients at a Dye Solution/Semiconductor Interface: Presence of a Slow Photosensitized Process

“…These observations suggest that the modification could result from the 05 chemisorption on the polycrystalline electrode under anodic bias, generating a great number of surface states. This possibility has already been proposed by different authors with TiO2 electrodes (18,19). Moreover, the irreversibility of the modification suggests that this oxygen chemisorption would result in a more oxygenated electrode surface.…”

(Photo)electrochemical Methods for the Determination of the Band Edge Positions of TiO2‐Based Nanomaterials

“…The diminished potential gradient and thickness of the space-charge layer will lead to enhanced recombination of photogenerated charges, which will, in turn, lead to constant decrease of photocurrents during the cathodic potential sweep. Finally, at the flatband potential, the photocurrent should disappear totally [184]. Hence, this so-called "photocurrent onset" potential can be considered to coincide with the flatband potential and to merge practically with the conduction band edge.…”