Scanning electrochemical microscopy. 9. Theory and application of the feedback mode to the measurement of following chemical reaction rates in electrode processes

Abstract

The use of the scanning electrochemical microscope (SECM), in both the steady-state and chronoamperometric feedback modes, is proposed as a new method for measuring the kinetics of following chemical reactions in electrode processes. Particular attention is given to the E,Ci mechanistic case (first-order irreversible chemical step following reversible electron transfer). Theory for the problem, relating the SECM feedback current to the tip-substrate distance, tip electrode radius, and rate constant for the chemical step, is developed numerically by using the alternating-direction implicit finite-difference scheme. The theoretical results demonstrate that both the chronoamperometric and steady-state feedback modes are sensitive techniques for accurate kinetic determinations, and that homogeneous chemical rate constants in excess of 2 X 104 s-' should be accessible to measurement with current SECM technology. The theoretical predictions are verified experimentally with the measurement of the rate of deamination, in aqueous basic solution (pH 10.2-1 2.4), of oxidized N,N-dimethyl-p-phenylenediamine, produced at a platinum electrode.