Adsorption of bromine complexing agents on platinum electrocatalysts and prevention through polydopamine coatings

Bromine complexing agents (BCAs) are seen as a promising route to mitigate the potential health and environmental risks of the bromine-based redox-flow batteries, like the hydrogen bromine redox flow battery (H₂–Br₂ RFB). The most studied BCAs are based on the pyridinium anion, which may adsorb and inhibit the Pt catalyst required in the H₂–Br₂ RFB system for the hydrogen reactions. Herein the effect of two BCAs (ethyl-pyridinium bromide and hexyl-pyridinium bromide) on a Pt electrocatalyst are studied, along with a potential methodology to prevent adsorption of the BCA through a polydopamine (PDA) coating. The results show that the pyridinium anion is adsorbed on Pt throughout a large potential range (−0.02 to 1.0 V), reducing the availability of the surface for the adsorption of other species. The PDA coating prevented this adsorption, but itself experiences adsorption of the BCA leading to some reduction in its porosity.