DIGITAL SIMULATIONS WITH THE FAST IMPLICIT FINITE-DIFFERENCE (FIFD) ALGORITHM .2. AN IMPROVED TREATMENT OF ELECTROCHEMICAL MECHANISMS WITH 2ND-ORDER REACTIONS

A serious problem in the application of the fast implicit finite difference (FIFD) algorithm to second-order mechanisms results from the simple linear approximation of the second-order terms. Depending on the nature of the mechanism and the kinetic parameters, negative concentrations may be obtained under certain conditions. The non-linear terms can then force the simulation to proceed in the direction of increasing negative concentrations. In the present paper we will describe an improved FIFD algorithm which allows the solution of second-order equations in a (quasi-) exact way. The method is demonstrated for the square scheme under such conditions where the cross-reaction plays an important role in the cyclic voltammetric behaviour.