fumapem® High performance membranes for fuel cells

Perfluorosulfonic acid / PTFE copolymer is a standard type of proton-exchange material for fuel cell application. The membranes feature high chemical and mechanical durability that can be further improved by applying of reinforcement in order to secure longevity and handling.

Membrane materials for LT-PEM
The membrane for fuel cells applications is based on a PFSA polymer that is available as long-side chain one (LSC) or short-side chain one (SSC). As for stationary one, so called long-side-chain PFSA is historically used since 1990’s. This kind of membrane produced by FUMATECH is named fumapem F-940-RFS. It is comprehensively characterized by various electrochemical methods suggesting very good durability chemical- and mechanical-wise.

For those aiming on broad range of power density and relative humidity, short side chain PFSA material is proper off. The membrane fumapem FS-930-RFS shows low resistance and particularly good ability to equalize short term fluctuation of humidity during the operation without performance being affected.

Both membranes F-940-RFS and FS-930-RFS have been tested under diverse stress conditions with excellent result with respect to estimated lifetime. Regarding automotive application, short-side-chain fumapem FS-715-RFS is typically used. The 15-µm thin reinforced membrane is characterized by particularly low resistance and ability of self-humidification under dry conditions when high current density applies so the cathode-produced water contributes to increase of membrane’s conductivity. Considering the thickness the membrane displays very good mechanical properties and low hydrogen cross-over in broad range of conditions.

Some naval and aerospace applications are utilizing the PFSA fumapem membranes in thickness 80 - 120 µm since high reliability is required. The system runs on pure Hydrogen and Oxygen and the fuel cell unit is operated at increased pressure on cathode side. Both LSC and SSC materials, either as plain or reinforced films meet the target values with respect power, durability, pressure operation and very low hydrogen cross-over. All fumapem fuel cell’s membranes comply well with most common membrane-electrode-assembly techniques, such as hot pressing of membrane with GDE or transferring the electrode by decal method onto membrane’s surface or direct coating of membrane by catalytic ink. Selected properties of PEMFC membranes are summarized in the table below

Hydrocarbon membranes are used for its superior properties in special type fuel cells, such as high-temperature PEM without humidification operated above 150 °C, in DMFC application where low fuel cross-over is required.

High Temperature Proton-Exchange-Membrane (HTPEM) is the core of the fuel cells running above 150 °C. As in classical PEM fuel cells technology, Hydrogen is electrochemically split to proton and electron on anode. Proton is transported through membrane to cathode while electricity is yielded in external circuit. At cathode protons recombine with electron and reacts further with Oxygen to water and heat. Two modes of operation can be assumed with respect to source of fuel. One mode is based on natural gas conversion to Hydrogen by means of steam reforming, which represents stationary application. The second mode is based on operation of Hydrogen with Oxygen obtained by electrolysis and these suits well the space application. As for coupling to natural gas, the HTPEM technology is particularly interesting in sense of no need for additional expensive periphery such as preferential-oxidation catalyst for CO removing from steam reformate gas, since it can accommodate on anode side also high concentration of substances such as CO and CO2 without sacrificing major loss of power. Also no additional humidification is required and the heat management is simplified compared to low temperature PEM system. The HTPEM technology can achieve efficiency approaching 90% calculated as combined yield of electricity and heat.

Direct Methanol Fuel Cells (DMFC) are particularly interesting for its portable feature as they can be used very conveniently as source of power at any place where grid or connection to natural gas is not available. As fuel, methanol is used and converted at anode to protons and CO2 while current is drawn. At cathode protons and electrons recombine and are oxidized with Oxygen to water while heat is released.

Membrane materials for HTPEM
There are two materials that can be used for this kind of technology; both are based on poly-benzimidazole (PBI) molecules. The classical membrane version based on PBI is fumapem AP and the new one is ultra-high molecular weight PBI membrane fumapem AM. While the fumapem AP suits well the wet anode operation, fumapem AM is advantageous for operation with equalized humidity on both cathode and anode side and for its superb durability against temperature above 170 °C. Both membranes feature very good thermo-durability and conductivity. Very high level of performance can be achieved with both of them over period of 3,000-20,000 hrs, depending on operational conditions.

Membrane materials for DMFC
One of the most important features of membranes for DMFC application is high retention of fuel on anode side, as crossover not only reduces the efficiency, but also increases risk of cells malfunction. For this reason a robust membrane that does not suffer from excessive swelling or shrinking is the key component of each DMFC system. There are two membranes fumapem E-730 characterized by very low methanol crossover and good performance and fumapem F-1850 characterized by low methanol cross over and very good performance.