(Invited) Chronoculometric Approach to Diagnosis of Oxygen Reduction at Low Pt-Content Electrocatalysts

Abstract

Development of catalytic systems for oxygen reduction reaction is still one of the most issues with respect to potential applications in low-temperature fuel cells,. Considerable research efforts have centered on the development of Pt-free or low-Pt-content catalytic systems. The serious research has been focused on improving the catalytic activity of Pt-based catalysts in acid media with less Pt loading.A useful mode for recording the electrochemical responses is to integrate the current and to report charge passed as a function of time. Chronocoulometry offers important advantages including good signal-to-noise ratio because the act of integration smooths random noise on the current transients. In comparison to chronoamperometry, by integrating the response, it is possible to separate surface phenomena more readily from bulk electrochemical responses. When it comes to the oxygen reduction, the double-potential-step chronocoulometry permits, in principle, estimation of the number of electrons (n) involved in the oxygen reduction and diagnosis of formation of the H2O2 intermediate. The problem lies in understanding the reaction kinetics and mechanisms in order to define properly experimental parameters.The usefulness of the double-potential step chronocoulometric data in a form of the charge vs. square root of time plots is in the fast and reliable diagnosis of the mechanisms and dynamics of charge propagation. It is clearly apparent that, by proper adjustment of pulse times and other experimental parameters within the double-potential-step experiment, mechanistic considerations permitting estimation of the number of electrons involved and the percent of formation of the H2O2 intermediate are feasible. We demonstrate that not only Vulcan-supported platinum but also Pt nanoparticles dispersed over SiO2-derivatized reduced graphene oxide induce reduction of oxygen according to almost 4-electron mechanism. Acknowledgements: This work was supported by the National Science Center (Poland) under Opus Project (2018/29/B/ST5/02627) and under auspices of the European Union EIT Raw Materials ALPE 19247 Project (Specific Grant Agreement No. EIT/RAW MATERIALS/SGA2020/1).