Boosting durability of fuel cell membranes EU-funded scientists developed novel durable membranes for stationary fuel cells, breaking the paradigm of trade-offs in membrane materials by improving both mechanical stability and conductivity. Energy © Thinkstock A fuel cell can produce electricity through a chemical reaction between a fuel and oxygen. Those that use a proton-conducting polymer membrane as the electrolyte are known as proton exchange membrane (PEM) fuel cells. These are semipermeable membranes generally made from ionomers and designed to conduct protons while being impermeable to gases. However, until now, PEM fuel cells have failed mostly because of mechanical failure of the membrane. To increase their durability and lifetime, the 'Membranes for stationary application with robust mechanical properties' (MAESTRO) project was established. One of the most common and commercially available PEM materials is the fluoropolymer perfluorosulfonic acid (PFSA). MAESTRO made great strides in obtaining low equivalent-weight (EW) PFSA ionomers with improved mechanical properties compared to the state of the art. Benchmark ionomers may have been hitherto the best materials in the lab. However, MAESTRO proved that they were not the best in terms of durability when membrane electrode assemblies (MEAs) were evaluated after 100 hours of continuous operation. To this end, scientists used lower EW ionomers in their bid to prepare membranes with robust mechanical properties. Their approaches relied on the use of chemical, thermal, and processing and filler reinforcement methods. In particular, the focus was on exploring ionic cross-links during emulsion polymerisation and membrane casting. This approach leads to non-linear ionomer molecules with high molecular weight that overcome issues associated with membrane dimensional changes – i.e. swelling. Scientists also used electrospinning to produce organic and inorganic fibres for mechanically reinforcing the low EW benchmark ionomers. Through nanofibre reinforcement, scientists reported significant improvement of mechanical properties of the final membranes and greater durability, with conductivity being higher compared to the benchmark membrane. Another method to mechanically reinforce the benchmark ionomers was through ionic cross-linking based on nanoparticles. A number of membranes were prepared using nanoparticle fillers of different hydrophobicity. With in situ tests designed to accelerate mechanical degradation, the stabilised MEAs demonstrated improved durability, with less than 3 % voltage loss after 2 000 hours of operation. Project findings were disseminated in publications and on the project website. Keywords Fuel cell membranes, mechanical stability, proton exchange membrane, mechanical properties, PFSA ionomers
