The Electrochemistry of Colloidal Semiconductor Particles: Experiments on and

Abstract

Results are presented for the dark electrochemistry and photoelectrochemistry of CdS and TiO2 colloidal particles studied with the optical rotating disk electrode (ORDE). The electron-transfer reactions between the particles and the electrode are found to be irreversible. However, in agreement with theoretical predictions, the kinetics obey both the Tafel and Levich relations. Several hundred electrons may be transferred on each encounter between a particle and the ORDE. Added halide ions are shown to be good scavengers for photogenerated holes. Results for the quantum efficiencies for the photogeneration of majority carriers are reported.

Spectroelectrochemistry of Colloidal CdSe Quantum Dots

“…30,31 Bard and colleagues have measured the passage of around 50 electrons between electrodes and colloids during electrochemistry of CdS QDs. 57,58 Another calculation based on electrochemical measurements of CdS nanocrystals has likewise yielded electron counts in the hundreds. 58 By correlating the broad band edge tail in the absorbance of chemically reduced CdSe with electrons present in surface states, Gamelin et al estimated that around 8−10 electrons can reside in surface states, 11 (with d = 3.4 nm and a similar surface chemistry to that used in our experiments) and they calculated that around 50 electrons were localized on surface states.…”

“…Nevertheless, large electron injection numbers are regularly reported during redox reactions with nanocrystals. In the cases of colloidal silver and colloidal gold, thousands of electrons are injected per particle. , Bard and colleagues have measured the passage of around 50 electrons between electrodes and colloids during electrochemistry of CdS QDs. , Another calculation based on electrochemical measurements of CdS nanocrystals has likewise yielded electron counts in the hundreds . By correlating the broad band edge tail in the absorbance of chemically reduced CdSe with electrons present in surface states, Gamelin et al estimated that around 8–10 electrons can reside in surface states, while Dempsey and co-workers carried out titrations of chemically reduced CdSe QDs (with d = 3.4 nm and a similar surface chemistry to that used in our experiments) and they calculated that around 50 electrons were localized on surface states .…”

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

“…Sols used in the study of ref. 20 were signiÐcantly older, so explaining why the surface states have a wider distribution of energies in this new study than in that of ref. 20.…”

“…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.…”

“…CdS colloids were prepared by the method of as modiÐed by Albery et Gra tzel23 al. 20 Experiments on these particles were carried out in a sol containing 10 mM and 10 mM sodium hexa-KC1O 4 metaphosphate (HMP) ; the concentration of CdS was 5 mM. Experiments were conducted in the absence of added charge scavengers.…”