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 in direct borohydride fuel cells (DBFCs). In previous work, we produced a poly(vinyl alcohol) (PVA)-anion-exchange resin (AER) membrane with a low fuel crossover and a low fuel efficiency by introducing Co ions. In this work, a bilayer membrane was designed to improve the 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 cm ² ·s ^-1 , which was even lower than that of the Co-PVA-AER membrane (1.98 ×10 ^-6 cm ² ·s ^-1 ) and the PVA-AER membrane (2.80 × 10 ^-6 cm ² ·s ^-1 ). The DBFC using the bilayer membrane exhibited a 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.