Considering the suitability of symmetrical cell testing in developing electrodes for solid oxide fuel cells via a study of different lanthanum nickelate cathode materials

Developing solid oxide fuel cells (SOFCs) with improved performance and lifetime continues to attract research attention from around the world. One important focus in this field is the synthesis of new air electrode materials that can replace the state-of-the-art lanthanum cobaltite-type phases. A host of materials with a wide range of properties has resulted. However, the means and metrics by which promising cathode materials are best characterised are not widely agreed upon within the literature and this can often complicate comparisons between studies. One common approach to conducting analysis of electrodes is to employ so-called ‘symmetrical cell’ tests which aim to isolate the performance of a specific electrode material under open-circuit conditions. However, despite the prevalence of symmetrical cell testing in the literature, there are some widely accepted limitations of the approach (e.g. limited to study at equilibrium conditions). In this work, a selection of air electrode materials with a wide range of properties were studied in both symmetrical and single cell testing set-ups. This case-study was conducted to identify the correlation between the two approaches and to understand how successful the symmetrical cell testing approach is in identifying favourable electrode materials. The results show that, whilst symmetrical-cell testing can be used to identify open circuit behaviours, the comparison between polarisation resistance at open circuit and performance under polarisation is not always perfectly correlated. Crucially, while the symmetrical cell test can provide some guidance in determining whether a new material may show promise, it highlights the need for more detailed studies to understand material performance under polarised conditions.