Wednesday, 16 May 2018: 14:00
Room 611 (Washington State Convention Center)
Direct borohydride fuel cells (DBFCs), operating with NaBH4 as a fuel and H2O2 as the oxidant have attracted a lot of attention due to their high theoretical cell voltages and tactical advantages, particularly for defense-related applications. DBFCs have a high energy density of 9.3 kWh kg-1 and specific capacity of 5.67 kAh kg-1 based on NaBH4 oxidation in alkaline media [1]. Using liquid hydrogen peroxide as the oxidant, the DBFC is a safe and attractive low temperature power source for unmanned underwater vehicles (UUVs) as they exhibit excellent energy and power density, are safe, given the high flash point of NaBH4, and do not release any gaseous effluents, enabling operation at neutral buoyancy[2]. One challenge for this system is the separation between the anolyte fuel (1.5M NaBH4 in 3M KOH) and catholyte oxidant streams (15% H2O2 in 1.5M H2SO4), while another is the high instability of NaBH4 in acidic or even neutral pH. Herein, a bipolar interface membrane electrode assembly is demonstrated for maintaining pH control of the anolyte and catholyte compartments of the fuel cell. The bipolar interface employed to separate anolyte and catholyte was based on an anion exchange membrane (AEM) interface in conjunction with a cation exchange membrane (Nafion®) separator. Studies of ion-containing block copolymers have provided clear evidence that the phase separation between hydrophilic and hydrophobic phases can produce materials with excellent ionic conductivity [3, 4]. The DBFC with the bipolar interfaces yielded a promising peak power density of 300 mW cm-2 in a 5-cm2 active area cell. Different operating conditions such as catalyst loading, operation temperature, flow rate and thickness of separator were investigated. The bipolar junction offers improved performance in the DBFC when compared with the use of a typical AEM or PEM configuration in the MEA.
References
[1] J. Milikić, G. Ćirić-Marjanović, S. Mentus, D.M.F. Santos, C.A.C. Sequeira, B. Šljukić, Electrochim. Acta, 213 (2016) 298-305.
[2] C.G. Arges, V. Prabhakaran, L. Wang, V. Ramani, Int. J. Hydrogen Energy, 39 (2014) 14312-14321.
[3] Y. Ye, S. Sharick, E.M. Davis, K.I. Winey, Y.A. Elabd, ACS Macro Letters, 2 (2013) 575-580.
[4] L. Sun, J. Guo, J. Zhou, Q. Xu, D. Chu, R. Chen, J. Power Sources, 202 (2012) 70-77.