Structure-Sensitive Organic Functionalization on Pt and Its Impact on Oxygen Reduction Kinetics

Surface functionalization on Pt surfaces is an effective approach to enhancing the oxygen reduction reaction (ORR) activity and, in turn, the performance of proton exchange membrane fuel cells. However, the mechanism through which adsorbates impact the microenvironments of key reaction intermediates and ORR performance remains unclear. In this work, we demonstrate that melamine functionalization is effective in enhancing ORR kinetics on Pt surfaces via single-crystal electrochemistry, in situ spectroscopy, and theoretical modeling. Melamine's adsorption configurations are structure-sensitive and highly correlated with ORR activity. It adsorbs axially via a Faradaic process on the terrace sites, while adopting a flat-lying configuration on the step sites without any charge transfer. Melamine adsorbed on Pt(111) exhibits a more pronounced enhancement effect on the intrinsic ORR activity compared with that on step sites. Furthermore, melamine functionalization is able to suppress the poisoning effect of specifically adsorbed phosphate, sulfate, and sulfonate in Nafion on Pt surfaces. Incorporation of melamine-functionalized Pt/C is able to enhance the mass activity in proton exchange membrane fuel cells by ∼50%, underscoring its potential for practical applications.