The Electrochemistry of Colloidal Semiconductor Particles: Theory

Abstract

The distribution of majority carriers in a collection of colloidal semiconductor particles is calculated. The kinetics of electron transfer from such particles to a macroscopic electrode are considered. Although each particle may have hundreds of electrons, the kinetics are shown to obey the simple equations of classical electrochemistry, such as the Tafel relation. The effect of illuminating the particles and photogenerating majority carriers is also considered. Again, the classical results for the photoelectrochemistry on a transparent rotating disk electrode are obtained, providing that account is taken of the much slower diffusion of the particles.

Electrochemistry of titanium dioxide: some aspects and highlights

“…Small particles of titanium dioxide make stable colloidal solutions in water if the pH is sufficiently far from the isoelectric point of TiO 2 (≈pH 6). Electrochemical and photoelectrochemical investigation of such solutions has been pioneered in 1984 by Albery et al 34. using optically transparent rotating disc electrodes.…”

Nanoparticle Arrays on Surfaces for Electronic, Optical, and Sensor Applications

“…This difference results from the contribution of space charge effects, which are remarkable for the bulk CdS but not for the CdS nanoparticle, which is too small for any remarkable space charge layer to form. [196] The bandgap of the CdS nanoparticle was determined on the basis of a potential region where no appreciable current flow is observed. [64] For example, a bandgap of 2.9 eV was obtained for a 3.1 nm CdS nanoparticle.…”

Photoelectrochemistry with the optical rotating disc electrode Part 2. Steady-state and transient studies on colloidal CdS

“…1 shows a model of the particle/electrode encounter, adapted from ref. 19, in which each particle has n electrons (majority carriers, thermally or photonically generated) in the conduction band or one type of shallow electron trap at or near the particle surface (trapping times are \100 fs for CdS24h27). A similar model may be drawn for each type of trap.…”

“…Eqn. (19) shows that particle transport may be treated by the usual convective di †usion equation, implying that Tafel and Levich relations will hold for semiconductor particle systems. Let us consider these relationships for the simplest case of electron…”

“…Heyrovsky, Jirkovsky et al have examined the dark polarographic and cyclic voltammetric behaviour of a range of metal oxide colloids with mercury drop electrodes,15h18 while one of us has previously reported polarograms recorded from colloidal TiO 2 and CdS with the ORDE in the dark and in the light. 19,20 Of greater utility would be a study of the transient photocurrents generated by semiconductor colloids yielding information relating to photogenerated charge carrier kinetics. To the best of our knowledge, this has not yet been done.…”