Electrochemical binders used to immobilize electrocatalysts on electrodes are essential in all fields of electrochemistry. However, conventional organic-based binders like Nafion generally suffer from oxidative decomposition at high potentials on anodic electrodes and have high charge transport resistivity. This work proposes the use of acidic redox-assisted deposition to form cobalt manganese oxyhydroxides (CMOH) as a solid-state inorganic binder. CMOH remains stable under high oxidative currents and ensures catalyst adhesion even under significant peel-off stress as shown by experiments involving the alkaline oxygen evolution reaction (OER) using RuO₂ as a catalyst immobilized on a rotating disc electrode. While the molecular structure of Nafion decays significantly after 45 minutes under OER conditions at 3.86 V, the CMOH binder is able to support the powder catalysts (RuO₂ and NiO _x ) showing stability around 1000 mA cm^-2 without significant current decay over 24 hours. The robust catalyst adhesion is a result of the formation of chemical bonds between the electrode and the binder and it can be further improved by increasing the applied loading of CMOH. Unlike Nafion, both the OER activity and the diffusion kinetics are not significantly affected by the CMOH binder. It has also been shown that using CMOH as a binder leads to lower charge transfer resistances R _ct and higher electrochemical surface areas compared to systems using Nafion. This is partially due to the presence of metal sites in different oxidation states which has been shown to increase intrinsic conductivity, facilitating the charge hopping at the binder/electrocatalyst interface. With this, the present work provides a proof-of-concept for inorganic metal oxides as promising solid-state binders for a wide range of applications in electrochemistry, demonstrating CMOH's outstanding characteristic of strong adhesion to support other highly active but adhesion-weak electrocatalysts.

Meng-Yu Lin

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