Eliminating the Need for Craftsmanship: Facile and Precise Determination of Oxygen Reduction Reaction Activity by Spraying Catalyst Ink on Rotating Disk Electrode

Abstract Fabricating uniform catalyst thin films on rotating disk electrodes (RDEs) is crucial for the accurate and reproducible evaluation of the oxygen reduction reaction (ORR) activity of high surface area catalysts via the thin film (TF)-RDE method. For the conventional methods, a catalyst thin film is fabricated by drying one droplet of the catalyst ink on the surface of a glassy carbon (GC) disk electrode under the optimized conditions. However, the optimization of the drying conditions is time-consuming or sometimes impossible depending on the catalyst samples. In this study, we proposed a facile method of fabricating highly-uniform catalyst thin films using a commercial ultrasonic atomizer, which can forcibly deposit the catalyst particles evenly on the GC electrode. Although the catalyst loading is not precisely controlled by the atomizer, it can be determined using the total electrochemical surface area (ECSA) of Pt and a calibration line. By employing the developed method for two different commercial Pt/C catalysts, the ORR activities, which are comparable to the highest values reported in the previous literature, were obtained. Moreover, the developed method was also successfully applied to the ORR activity evaluation of a homemade Pt/NbB2 catalyst, which could not be properly tested by a conventional ink deposition method because of the difficulty of preparing a uniform catalyst thin film. Thus, the developed method eliminates the need for setting a specific film fabrication condition for each catalyst sample and enables the easy and precise ORR activity determination of any kind of high surface area catalyst as long as well-dispersed catalyst inks are available.