Researchers at the University of California at Riverside (UCR), led by Dr. Yushan Yan, have been awarded a $760,705 grant from the Department of Energy’s ARPA-E program (earlier post) to support the development of a new generation of hydroxide (OH-) exchange membranes (HEM) for fuel cells that are dramatically more ion-conductive, durable and tolerant of abuse than previous devices. Their work was featured as a cover story in an issue of the journal Angewandte Chemie earlier this year.
In a hydroxide exchange membrane fuel cell, the membrane conducts hydroxide ions instead of hydrogen ions. Hydroxide exchange membranes fuel cells (HEMFCs) have the potential to solve the catalyst cost and durability problems of proton exchange membrane fuel cells (PEMFCs) while achieving high power and energy density.
In addition, HEMFCs can completely avoid the electrolyte leakage and potentially eliminate the metal (bi)carbonate formation problems of the traditional liquid alkaline fuel cells (AFCs). Further, HEMFCs can offer fuel flexibility (e.g., methanol, ethanol, ethylene glycol, etc.) because of their low over-potential for hydrocarbon fuel oxidation and reduced fuel crossover.
The hydroxide exchange membrane (HEM) usually directly decided the performance of HEMFCs through its hydroxide-conductivity and membrane-thickness. Current HEMs are based on the quaternary-ammonium-hydroxide (QAOH) functional groups, and have low performance due to the hydroxide conductivity.
Yan and his group switched from the QAOH to the quaternary-phosphonium-hydroxide (QPOH), opening up the potential to solve the low hydroxide-conductivity problem and thus improve the HEMFC performance drastically.
In one of their recent studies, to be presented this coming week at the AIChE annual meeting, the team synthesized and prepared a quaternary-phosphonium functionalized hydroxide exchange membrane (TPQPOH152) with typical thickness of 50-100 µm. TPQPOH showed a 45 mS/cm (20 °C) of hydroxide-conductivity that is substantially higher than those of the commercial and currently experimental QAOH functionalized membranes.
In addition, the HEMFC single cell with a 50 µm TPQPOH152 as HEM, at 70 °C, exhibited substantially high peak power density of 258 mW/cm2 and significantly low internal resistance of 0.21 Ωcm2. The researchers suggest that the high hydroxide-conductivity and high-performance of HEMFC indicate that the quaternary-phosphonium functionalized TPQPOH152 HEM is highly promising for use in HEMFC.
Shuang Gu, Rui Cai, Ting Luo, Zhongwei Chen, Minwei Sun, Yan Liu, Gaohong He, and Yushan Yan (2009) A Soluble and Highly Conductive Ionomer for High-Performance Hydroxide Exchange Membrane Fuel Cells. Angewandte Chemie International Edition Volume 48, Issue 35 Pages: 6499-6502 doi: 10.1002/anie.200806299
Shuang Gu, Rui Cai, Ting Luo, Kurt Jensen, Yushan Yan (2009) A Highly Conductive Quaternary-Phosphonium Functionalized Membrane for High-Performance Hydroxide Exchange Membrane Fuel Cells (AIChE 2009 Annual Meeting)
Shuang Gu, Rui Cai, Ting Luo, Yushan Yan (2009) A Soluble and Highly Conductive Ionomer for High Performance Hydroxide Exchange Membrane Fuel Cells (AIChE 2009 Annual Meeting)