Chronocoulometry

Chronocoulometry is an electrochemical technique in which a potential step is applied to a working electrode and the resulting current is integrated over time to yield the total charge versus time. The method aims to quantify the amount of electroactive species in solution and to characterize diffusion-controlled transport by separating faradaic (charge transfer) from nonfaradaic (double-layer) contributions.

Principle and data analysis

After the potential step drives a redox reaction, the current decays as diffusion governs the flux of species to the electrode. The total charge accumulated up to time t is described by Q(t) = (2 n F A C* D1/2 / sqrt(pi)) t1/2 + Qdl + Qads, where n is the number of electrons transferred, F is Faraday’s constant, A is electrode area, C* is bulk concentration, D is diffusion coefficient, Qdl is the double-layer (nonfaradaic) charge, and Qads accounts for any adsorbed species. The term proportional to t1/2 is the Anson term and reflects diffusion-controlled charge. By plotting Q(t) versus sqrt(t) (an Anson plot), a straight line should appear under diffusion-controlled conditions. The slope provides information on n, A, C*, and D, while the intercept relates to nonfaradaic contributions and adsorption. This framework also allows determination of concentration or diffusion coefficients when the other parameters are known.

Variants and applications

A common variant is double-potential-step chronocoulometry, which uses a second potential step to reverse the reaction and help subtract nonfaradaic contributions, improving accuracy. Chronocoulometry is used for quantitative analysis of electroactive species, determination of diffusion coefficients, assessment of surface coverage of adsorbed species, and studies of reaction mechanisms. It is employed in sensor calibration, electrochemical kinetics, and battery research, where precise charge measurements are essential.