TY - JOUR

T1 - Photoelectrochemistry with the optical rotating disc electrode - Part 3. The theoretical analysis for photophysical-chemical-electrochemical (PCE) processes

AU - Boxall, C

AU - Albery, W. John

PY - 2000

Y1 - 2000

N2 - Exact and asymptotic analytical expressions are obtained for the diffusion-controlled light-on transient photocurrents exhibited at an optical disc electrode (ODE) by two types of photoelectrochemical systems: (i) the photophysical-reversible-chemical-electrochemical (PrCE) system wherein the decay of the photogenerated excited species, S*, and the reversible chemical reaction of S* with a solution phase charge scavenger, A, obey pseudo-first-order kinetics with rate parameters k(0), k(1) (forward chemical) and k(2) (reverse chemical) respectively; and (ii) the photophysical-irreversible-chemical-electrochemical (PiCE) system wherein the chemical reaction between S* and A is considered to be irreversible i.e. k(2)=0. Exact descriptions of [S*] as a function of distance from the electrode surface at t -->infinity are given for both systems for a range of values of k(0), k(1) and, where appropriate, k(2). The photoelectrochemical collection efficiency of the ODE is also presented as a function of t and the rate parameters. Pre-existing approximate expressions for the rotation-speed dependence of the diffusion-controlled steady-state photocurrent recorded at an optical rotating disc electrode (ORDE) are extended and applied to the PiCE process allowing ORDE diffusion layer profiles for [S*] to be calculated for the first time. The asymptotic expressions for the transient and steady-state photocurrent behaviour at stationary and rotating electrodes are combined, producing fourteen composite cases that completely describe the behaviour of PrCE and PiCE systems at ODEs. Each case is discussed and procedures are given for extracting values of k(0), k(1), k(2) and phi (the quantum efficiency for the photogeneration of S*) from experimental data. The relationship between the cases is illustrated by a series of case diagrams. A case assignment flow diagram is also presented. For the purposes of illustration, the colloidal CdS/Fe(CN)(6)(3-) system is case-assigned and its associated rate parameter values are calculated.

AB - Exact and asymptotic analytical expressions are obtained for the diffusion-controlled light-on transient photocurrents exhibited at an optical disc electrode (ODE) by two types of photoelectrochemical systems: (i) the photophysical-reversible-chemical-electrochemical (PrCE) system wherein the decay of the photogenerated excited species, S*, and the reversible chemical reaction of S* with a solution phase charge scavenger, A, obey pseudo-first-order kinetics with rate parameters k(0), k(1) (forward chemical) and k(2) (reverse chemical) respectively; and (ii) the photophysical-irreversible-chemical-electrochemical (PiCE) system wherein the chemical reaction between S* and A is considered to be irreversible i.e. k(2)=0. Exact descriptions of [S*] as a function of distance from the electrode surface at t -->infinity are given for both systems for a range of values of k(0), k(1) and, where appropriate, k(2). The photoelectrochemical collection efficiency of the ODE is also presented as a function of t and the rate parameters. Pre-existing approximate expressions for the rotation-speed dependence of the diffusion-controlled steady-state photocurrent recorded at an optical rotating disc electrode (ORDE) are extended and applied to the PiCE process allowing ORDE diffusion layer profiles for [S*] to be calculated for the first time. The asymptotic expressions for the transient and steady-state photocurrent behaviour at stationary and rotating electrodes are combined, producing fourteen composite cases that completely describe the behaviour of PrCE and PiCE systems at ODEs. Each case is discussed and procedures are given for extracting values of k(0), k(1), k(2) and phi (the quantum efficiency for the photogeneration of S*) from experimental data. The relationship between the cases is illustrated by a series of case diagrams. A case assignment flow diagram is also presented. For the purposes of illustration, the colloidal CdS/Fe(CN)(6)(3-) system is case-assigned and its associated rate parameter values are calculated.

U2 - 10.1039/B001339K

DO - 10.1039/B001339K

M3 - Journal article

VL - 2

SP - 3651

EP - 3662

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 16

ER -