Evaluation of multivalent phosphate cross-linked chitosan biopolymer membrane for direct borohydride fuel cells

The direct borohydride fuel cell (DBFC) is a promising power supply for stationary and mobile devices. A high performance and low cost membrane electrolyte would reduce fuel cell stack cost and may help in its commercialization. In the work presented here, a cost-effective and eco-friendly chitosan membrane has been prepared and modified by phosphate or triphosphate salt. The paper describes the membrane preparation method, and various studies performed on it, which includes thermal analysis, water uptake, mechanical strength, ionic conductivity, and fuel cross-over measurements. These studies show that the triphosphate chitosan membrane has slightly higher figure of merit than phosphate chitosan membrane for application in a DBFC. A chitosan chemical hydrogel has been synthesized and used as the electrode binder. A borohydride-oxygen fuel cell employing triphosphate chitosan membrane and chitosan binder has achieved a peak power density of 685 mW cm ^-2 at 60 °C, which is over 50% higher than the power performance of a DBFC using commercial Nafion ^® materials. In addition to the far superior power density, this chitosan-based DBFC has exhibited comparable stability and efficiency as Nafion ^®-based DBFC.