Ultra-low loading electrochemical characterisation methods: best practices and design principles

Abstract This article presents the best practices, design principles, and common pitfalls of two recently developed electrochemical characterisation techniques, the floating electrode (FE) and the ultra-low loading catalyst-coated membranes (ULL-CCMs). These modern characterisation techniques aim to bridge the gap between electrochemical characterisation of catalysts using the rotating disk electrode setup and the technological application: the membrane electrode assembly. In this method paper, we offer background on the development of these setups and highlight the importance of each preparatory step when applying these assessment methods. Representative results are provided, demonstrating the ability of the FE and ULL-CCM catalyst characterisation methods to achieve high specific and high mass activities over a wide range of potentials, enabling the extraction of valuable electrokinetic parameters. In addition to oxygen reduction, hydrogen oxidation, and hydrogen evolution reactions, for which catalyst evaluation has been shown to work in FE and ULL-CCM, we also introduce how oxygen evolution reaction catalysts can be evaluated in these systems. Lastly, we offer possible explanations for common issues encountered when utilising these techniques and ways to address them. This article aims to encourage researchers to use and improve the FE and ULL-CCM methods by providing more detailed descriptions than in previous articles.