Influence of nickel hydroxide catalyst ink formulation on direct bar coating of anion exchange membranes

Achieving uniform and high-performing catalyst-coated membranes (CCMs) is a critical challenge in the field of electrochemical energy conversion technologies. This challenge is particularly pronounced in the coating of catalyst inks, where optimizing ink formulations and mixing conditions is essential for producing homogeneous catalyst layers that enhance electrochemical performance. In this study, we investigate the influence of mixing parameters and solvent composition on the rheological behavior and performance of nickel hydroxide-based anode inks, specifically for application in anion exchange membrane (AEM) electrolysis. We systematically explored the effects of roller mixing speed (30 and 80 rpm), mixing duration (4, 24, and 48 hours), and water content (0, 25, 34, and 51 %) on the morphology and homogeneity of the catalyst layers. Our findings reveal that a mixing speed of 80 rpm and a duration of at least 24 hours are necessary to achieve desirable catalyst layer morphology. Additionally, the presence of water in the ink formulation was critical, with an optimal water content of 34 % (3 : 1, water : IPA) yielding the best morphological homogeneity and reproducible electrochemical performance. The study demonstrates a 70 mV reduction in overpotential, resulting in a voltage of 2.05 V at a current density of 1 A cm^-2. While mixing parameters minimally impacted the rheological behavior of the inks, they significantly influenced the electrochemical performance and morphology of the CCMs.