Last decade witnessed significant advances of polymer electrolyte membrane fuel cell (PEMFC) R&D and the exciting transition of such development into the commercialization of fuel cell vehicles. While the low temperature PEMFC represents the state-of-art technology for transportation applications, substantial challenges remain in finding better catalysts for oxygen reduction reaction (ORR), which accounts for the biggest loss of energy efficiency and the highest cost of material components of FC stacks. ORR involves multiple steps of proton coupled electron transfer processes and a “scaling” issue makes it difficult to optimize every elemental reaction step simultaneously. ^[1] In addition to the improvement of catalyst itself, engineering catalyst electrolyte interface properties may offer a separate venue to tackling the problem. One recent effort involves the modification of Pt catalyst surface with organic ligands and has demonstrated some successes in enhancing catalyst activity. The effect was mostly attributed to either the change of surface electronic structure of the catalyst or the protection of Pt active sites from poisoning by strong anion adsorption. ^[2-4] However, the impact of ligand modification on catalyst durability and the stability of the ligand itself on the catalyst surface have not been thoroughly investigated. In this study, we systematically examined a series of organic ligands with different structures and anchoring groups. Coupling material characterization with electrochemical analyses allowed us to assess both the catalyst durability and the ligand stability. Such a comparative study is expected to lead the development of design principles to further improve this technology towards MEA and FC stack applications.

References

(1) M. T. M. Koper, et al., J. of Electroanal. Chem., 2011, 660, 254-260

(2) Y. H. Chung, et al., J. Phys. Chem., Lett. 2013, 4, 1304-1309

(3) Z. Y. Zhou, et al., J. Phys. Chem., C, 2012, 116, 10592-10598

(4) D. Strmcnik, et al., Nature Chem., 2010, 2, 771