Data collection and processing of open-circuit potential-decay measurements using a digital oscilloscope

A data collection and processing procedure, using a digital oscilloscope and PDP computer for treating open-circuit potential-decay behaviour, is described. Greatly improved accuracy is obtained compared with that in previous work employing analogue traces. The improved accuracy attainable allows a new technique to be employed for handling the potential-decay behaviour. Previous procedures utilize integration of the differential equation for potential decay, V(t) in time t, giving a V(t) vs. log t plot. However, when a pseudocapacitance C, associated with electroactive intermediates, e.g. H is involved, the decay equation can only be integrated after some assumption is made regarding a limiting form of C as f(V). With the new method, this is avoided by directly using the differential equation for V(t) with digitally acquired data being differentiated in a computer; then the form of C as f(V) is obtained from the experimental V(t) behaviour. Examples are given of the behaviour of the adsorbed H intermediate in the H2 evolution reaction at high activity Ni-Mo-Cd electrode materials in relation to the kinetics of H2 evolution at the same electrodes: the electroactive H is in at least 2 states at these electrodes.