Problem of in situ real-area determination in evaluation of performance of rough or porous, gas-evolving electrocatalysts. Part 1.—Basis for distinction between capacitance of the double layer and the pseudocapacitance due to adsorbed H in the H2evolution reaction at Pt

Abstract

A procedure is described for evaluating the real, electrochemically active, electrode surface area of porous electrodes based on in situ measurements of the double-layer capacitance, C_dl, in the overpotential region by means of analysis of open-circuit potential relaxation transients and impedance spectra, recognizing the complications that arise in porous electrode materials owing to distributed electrode and matrix resistance, and distributed interfacial capacitance. The reliability and effectiveness of the recently developed initial potential-decay rate method for evaluation of double-layer capacitance is examined and confirmed by both a model theoretical kinetic analysis and the experimental determination of C_dl in the H₂ evolution reaction (HER) at a Pt electrode. It is shown how C_dl can be distinguished at an electrocatalytic cathode (e.g. Pt), from the adsorption pseudocapacitance, C_ϕ, associated with H electrosorption, by means of the initial potential-decay rate and a.c. impedance methods.