Scanning electrochemical microscopy .33. Application to the study of ECE/DISP reactions

The scanning electrochemical microscope (SECM) is used to measure the kinetics of ECE/DISP type reactions. The theory of the steady-state feedback response is developed in terms of numerical simulation. The theoretical curves show that the variation of the tip and substrate current with the tip-substrate separation can readily be used to differentiate between an ECE and a DISP1 pathway. The theoretical results suggest that rate constants up to 1.6 x 10(5) s(-1) can be measured with tip sizes usually employed in SECM. The theory is validated using the experimental example of the reduction of anthracene in DMF in the presence of phenol. The reaction is shown to follow a DISP1 pathway, in agreement with previous studies. Good agreement is found between theory and experiment for all the phenol concentrations explored, and a rare constant of (4.4 +/- 0.4) x 10(3) M(-1) s(-1) has been determined for the protonation of the anthracene radical anion by phenol.