Electrochemical impedance spectra of RuO2 during oxygen evolution reaction studied by the distribution function of relaxation times

[Display omitted] •A genetic programming method is used to analyze the impedance data of an OER catalyst.•Four relaxation processes are noted, and examined at several overpotentials.•Solution resistance is not affected by stability test, but changes with overpotential.•Charge transfer resistance is dominant at high overpotentials. In this work, the distribution function of relaxation times (DFRT) of a RuO2 catalyst is determined by Impedance Spectroscopy Genetic Programming (ISGP). The resulting DFRT plots contain three peaks that vary with the overpotential. This discloses the presence of various electrochemical phenomena at different relaxation times in the catalyst. The effective resistance to charge transfer during the oxygen evolution reaction (OER) is small at low overpotential but becomes dominant at high overpotential. Moreover, we can track the change in each peak after a stability test: the resistance to both the production rate of intermediates and charge transfer show an increase while the solution resistance is almost constant. Hence, ISGP opens a new avenue for analyzing catalysts and providing detailed information about the resistance contributed by various phenomena.