Electrochemical energy conversion efficiencies at lower temperatures were materials costs are low, are many times that of carnot limited heat engines. Yet only the hydrogen powered proton exchange membrane (PEM) fuel cell has garnered serious commercial interest. This is because the hydrogen oxidation reaction in acid on Pt is extremely fast and when coupled with a thin perfluorosulfonic acid (PFSA) membrane, a fuel cell with a very high power density, suitable for automotive applications can be realized. It can be argued that the electrochemical oxidation of all other fuels, or electrolysis to produce fuels from water, nitrogen or carbon dioxide is limited by the PFSA electrolyte, that is only effective when wet and so limited in temperature of operation to 80°C. Redox flow cells are also limited by PFSAs which do not have sufficient ion selectivity.<br/>Research in the Herring group, with an extensive list of collaborators, over the last decade has focused on in depth scientific studies of new PEMs and anion exchange membranes (AEMs). These efforts have led to the scale up and deployment of new polymer electrolytes that we are now deploying to extend the number of fuels that can be deployed to produce electrical power and the general versatility of fuel cells, electrolyzers, and redox flow cells. Using heteropoly acids (HPAs) to extend the range of the phosphoric acid/polybenzimidazole electrolyte we demonstrate both direct methane and direct hydrogen storage liquid fuel cells can produce practical fuel cell current densities. We show that a PEM can be constructed by functionalizing a perfluorelastomer with HPAs to give a PEM with unprecedented chemical stability while exceeding the performance of PFSAs. This same material when deployed in redox flow cells gives very high proton conductivity and can be tuned to exclude all other ions. AEMS allow us to access electrochemistry in base, where typically precious metals are not mandated and more complex fuels can be oxidized. Our work on advanced AEMs has led to the discovery of a versatile polymer platform that can be tuned to have high ion exchange capacity, low water swelling, good mechanical properties and high chemical stability. These AEMs are being deployed in direct methanol fuel cells, electrolyzers, and in water applications.

Converting fuels to electrical energy and electrical energy to fuels, enabled by advancements in polymer electrolyte membranes

256th National Meeting (2018)

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