13 October 2013
Year: 2013Price: 10.00
Polymer electrolyte membrane fuel cells (PEMFC) continue to garner great interest particularly in the automotive sector as eco-friendly and energy efficient alternatives to internal combustion.1, 2 The heart of any PEMFC is the polymer exchange membrane (PEM) which serves the dual role of separating the anode and cathode as well as transporting protons from the former to the latter.
To stand any chance of successful application in a fuel cell, the PEM must fulfill a number of criteria. The membrane should remain mechanically stable across a range of temperatures and relative humidities. Chemical stability in a highly acidic environment and in the presence of radicals is also important. Proton conductivity should be as high as possible and fuel crossover should be as low as possible. Water management is also very important since it has direct bearing on fuel cell performance. During operation, water is generated at the cathode and an electro-osmotic drag force is produced, which depletes the water content at the anode side. To prevent the anode from drying out, PEMCs are optimally operated from 60 to 80 °C which necessitates a cooling system. Under heavy load however, cooling may not be sufficient and indeed the membranes are expected to operate up to 100 °C. These difficult criteria greatly limit applicable materials as PEMs. DuPont’s Nafion®, which is a polymer based on a perfluorinated sulfonic acid vinyl monomer, has long been heralded as the polymer de facto in this field although its high cost is a burden.3 Indeed a polymer which offers comparable performance at lower cost can truly help advance the use of PEMs and thus portable fuel cells.
To stand any chance of successful application in a fuel cell, the PEM must fulfill a number of criteria. The membrane should remain mechanically stable across a range of temperatures and relative humidities. Chemical stability in a highly acidic environment and in the presence of radicals is also important. Proton conductivity should be as high as possible and fuel crossover should be as low as possible. Water management is also very important since it has direct bearing on fuel cell performance. During operation, water is generated at the cathode and an electro-osmotic drag force is produced, which depletes the water content at the anode side. To prevent the anode from drying out, PEMCs are optimally operated from 60 to 80 °C which necessitates a cooling system. Under heavy load however, cooling may not be sufficient and indeed the membranes are expected to operate up to 100 °C. These difficult criteria greatly limit applicable materials as PEMs. DuPont’s Nafion®, which is a polymer based on a perfluorinated sulfonic acid vinyl monomer, has long been heralded as the polymer de facto in this field although its high cost is a burden.3 Indeed a polymer which offers comparable performance at lower cost can truly help advance the use of PEMs and thus portable fuel cells.
Over the last 30 years, a variety of polymers have been developed and investigated as potential replacements for Nafion®.4, 5 As with Nafion®, the majority of investigated polymers are poly sulfonic acids though alternate ionomers based on phosphonic acid6, 7 and benzimidazole8 are also considered. As a class, sulfonated aromatic polymers9 tend to be easier to synthesize and thus less expensive than Nafion®. Polymers synthesized from less expensive strong acid vinyl monomers such as 2-acrylamido-2-methylpropane sulfonic acid (AMPS) are also considered and indeed this monomer is utilized within this paper.10-13 An additional benefit of this monomer is that it is amenable to photo induced polymerization which we herein present as a relatively uncomplicated method for preparing PEMs with nevertheless quite high proton conductivity. Further tests are planned to determine the real applicability of such polymers for use in PEMFCs.
