Rotating disc electrode (RDE) technique is a useful and commonly accepted technique for the performance evaluation of electrocatalysts for the oxygen- reduction (ORR) and evolution (OER) reactions.^[1] To characterize new catalysts, composite thin film electrodes are casted on RDE tips (TF-RDE) where polymers are typically utilized as binders to immobilize the powder electrocatalysts onto the substrate.^[1b] Literature surveys show Nafion® as a feasible binder for the investigation of alkaline OER catalysts. However, Nafion® was developed for application in PEM fuel cells that rely on the transport of protons rather than anions.^[2] To our best understanding, there is no systematic investigation on the influence of polymer binders in alkaline OER. As shown in Figure 1, Nafion® can affect the OER performance, especially described by the phenomenon of gas bubble retention on the electrode surface during chronopotentiometry (Figure 1C) and a significant influence of the amount of binder added to the thin film.^[3]

Here we will present a TF-RDE study of a benchmark catalyst (Ni, Co- Oxide, Sigma Aldrich) on glassy carbon and gold substrates, prepared with commercially available binders (Nafion®, Aquivion®, PTFE and Fumion®). We used a standardized preparation and measurement protocol to ensure comparability and reproducibility. The results show a significant influence of the choice of binder on the measured OER performance. These differences are discussed with respect to the binder properties in terms of hydrophilicity or functional groups, as well as their corrosion behavior under OER conditions.

[1] a) K. J. J. Mayrhofer, D. Strmcnik, B. B. Blizanac, V. Stamenkovic, M. Arenz, N. M. Markovic, Electrochimica Acta 2008, 53, 3181-3188; b) J. Suntivich, H. A. Gasteiger, N. Yabuuchi, Y. Shao-Horn, Journal of The Electrochemical Society 2010, 157, B1263-B1268; c) T. Reier, M. Oezaslan, P. Strasser, ACS Catalysis 2012, 2, 1765-1772.

[2] a) M. Paidar, K. Vazac, M. Roubalik, K. Bouzek, in Hydrogen Days, Prague, Czech Republic, 2015; b) S. Jung, C. C. L. McCrory, I. M. Ferrer, J. C. Peters, T. F. Jaramillo, Journal of Materials Chemistry A 2016, 4, 3068-3076.

[3] K. Zeng, D. Zhang, Progress in Energy and Combustion Science 2010, 36, 307-326.