Potential of Dipicolinic Acid as a Water-Dissociating Catalyst in a Bipolar Membrane

Bipolar membranes (BPMs) are increasingly being applied in chemical recovery and energy storage fields due to their unique water dissociation ability under reverse bias. BPMs capable of dissociating water at a lower potential will minimize energy consumption, and it depends on the thickness asymmetry between the cation exchange layer (CEL)/anion exchange layer (AEL) and the right catalyst material used at the interface of CEL/AEL. In this report, a heteroaromatic compound, 2,6-pyridine-dicarboxylic acid (also known as dipicolinic acid, DPA), is being proposed to be an effective interface catalyst for BPM made of sulfonated poly(ether ether ketone) (CEL) and quaternized polysulfone (AEL). The optimum concentration of DPA as an interface layer over fabric-reinforced AEL was found using an adsorption study. The thickness asymmetry between CEL and AEL (without catalyst) alone could lower the water dissociation onset potential (Udiss) to 0.72 V, which was further reduced to 0.70 V using DPA as an interface catalyst. After 5 h of electrodialysis experiments at 25 mA·cm–2, the acid (or base) concentration increased from ∼0.19 mol·L–1 (without catalyst) to 0.21 mol·L–1 due to the presence of DPA at the interface. Meanwhile, operational studies performed using synthetic reverse osmosis (RO) reject of sea water confirm the consistency in the acid–base production during multiple cycles.