New analytical approximation of feedback approach curves with a microdisk SECM tip and irreversible kinetic reaction at the substrate

Available approximate expressions used in the kinetic data treatment of (scanning electrochemical microscopy) SECM experiments in the case of steady-state feedback currents with irreversible reaction at the substrate and a microdisk tip are discussed. The necessity of new expressions is thus pointed out. A new expression of the current is then produced and discussed. It covers all usual experimental configurations (microdisks with Rg below 20, Rg characterizing the surrounding insulator thickness) and dimensionless tip-substrate distances larger than 0.1, with an accuracy of ±0.025 for any kinetics.