Designing and development of stable asymmetric bipolar membrane for improved water splitting and product recovery by electrodialysis

Abstract

The stability and the performance of the bipolar membrane (BPM) are the critical issues to be resolved. The layer thickness plays an important role in improving the performance of bipolar membrane. Here, an efficient transparent asymmetric bipolar membrane has been fabricated by a layer-by-layer solution casting technique comprising cation and anion exchange layers. The thickness of the anion exchange layer was reduced to improve the performance in term of product purity and recovery by minimizing the co-ion leakage. The interface of BPM acts as a catalytic junction for dissociating the water into H+ and OH− ions. A clear membrane interface was confirmed by the scanning electron microscopy (SEM). All three BPMs show the adequate physicochemical and electrochemical properties in term of ionic conductivity and water uptake. Effect of applied potential was studied on the membrane performance through BMED for the dissociation of NaCl. We also performed the bipolar membrane electrodialysis (BMED) for the hydrolysis of different organic and inorganic salts into corresponding acid and alkali. Among the bipolar membranes, BPM with 40 % less AEL thickness (BPM-60 membrane) shows the better performance. BPM-60 shows the highest water splitting rate and alkali recovery of 0.491 g h−1 and 95.5 %, respectively with lowest energy consumption of 1.11 kW h kg−1 and high current efficiency of 90.32 %. Conversion of NaCl in to NaOH and HCl gives the highest product recovery as compared to other salts, due to higher dissociation of NaCl. BPM-60 with higher water splitting rate, lower energy consumption and higher current efficiency for conversion of salt into corresponding acid and alkali made asymmetric bipolar membrane as industrially applicable with high performance.