A bilayer anion-exchange membrane with low borohydride crossover and improved fuel efficiency for direct borohdyride fuel cell

The development of membranes with low fuel crossover and high fuel efficiency is a key issue for direct borohydride fuel cells (DBFC). In previous work, we produced a polyvinyl alcohol (PVA) - anion exchange resin (AER) membrane with low fuel crossover and low fuel efficiency by introducing Co ions. In this work, a bilayer membrane was designed to improve fuel efficiency and cell performance. The bilayer membrane was prepared by casting a PVA-AER wet gel onto the partially desiccated Co-PVA-AER gel. The bilayer membrane showed a borohydride permeability of 1.34 106 cm2s-1, which was even lower than that of the Co-PVA-AER membrane (1.98 106 cm2s-1) and the PVA-AER membrane (2.80 106 cm2s-1). The DBFC using the bilayer membrane exhibited higher fuel efficiency (37.4%) and output power (1.73 Wh) than the DBFCs using the Co-PVA-AER membrane (33.3%, 1.27 Wh) and the PVA-AER membrane (34.3%, 1.2 Wh). Furthermore, the DBFC using the bilayer membrane achieved a peak power density of 327 mWcm-2, which was 2.14 times of that of the DBFC using the PVA-AER membrane (153 mWcm-2). The drastic improvement benefited from the bilayer design, which introduced an interphase to suppress fuel crossover and avoided unnecessary borohydride hydrolysis.