ANN ARBOR, MI
High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are crucial for powering heavy-duty vehicles. A key challenge in their performance lies in the use of phosphoric acid (PA) as an electrolyte. While PA enables proton conduction at elevated temperatures, it also strongly adsorbs onto platinum catalysts, blocking active sites and hindering the oxygen reduction reaction (ORR). This leads to significant energy losses, limiting the overall efficiency of HT-PEMFCs. Phosphonated ionomers, featuring covalently bound phosphonic acid groups, have been proposed as alternative electrolytes, though their impact on ORR remains underexplored.
In a recent study by researchers from the Toyota Research Institute of North America (TRINA), Dr. Honghong Lin and Dr. Siwen Wang investigated how different acid anions, including phosphoric acid (PA) and alkyl-substituted phosphonic acids (R-PAs), influence ORR activity at the catalyst surface. Through a combination of simulations and experimental analysis, they provided a more comprehensive understanding of the anion effect.
Their research at TRINA revealed a complex dual effect of R-PAs on ORR activity. While these alternative acids bind more strongly to platinum and block active sites, they simultaneously enhance catalytic performance at neighboring locations by modifying the electronic structure and disrupting stabilizing surface water layers. This unexpected benefit suggests new design strategies for phosphonated ionomers, where carefully tailored functional groups can optimize fuel cell efficiency rather than merely mitigating anion adsorption.
For detailed information, please refer to the published paper in ACS Energy Letters.