61st Annual Report on Research 2016

Platinum nanoparticles are commonly developed for heterogeneous catalysis. The shape and exposed crystal structure of the platinum plays a large factor in determining catalytic activity. However, the presence of molecular ligands, which are often used in synthesis, will also affect catalytic activity. There are few systematic studies of the effects of molecular ligands on platinum catalytic activity. We have investigated the influence of amine-base ligands on platinum activity towards electrocatalytic methanol oxidation. We have studied amines with straight alkyl chains of varying length and investigated both aromatic and non-aromatic ring structures. We find that amine structure has a small influence on platinum electrocatalytic activity towards methanol oxidation. Longer straight chain amines cause a more significant decrease in activity than shorter chain amines. By combining catalytic measurements with measurements of the molecular layer ordering and density, we are able to connect differences in catalytic activity to fundamental molecular structure. We find that long-chain amines such as octadecylamine form ordered molecular layers on the platinum surface at high concentrations and functionalization times. Shorter amines such as hexylamine do not form ordered molecular layers, likely contributing to the higher electrocatalytic activity. We also find that longer chain amines have higher onset potentials for methanol electrocatalysis, while shorter molecules require a lower applied potential. We have also investigated surface blocking of the amine molecular layers using the redox active probe ferricyanide. We find minimal blocking for all amine structures, demonstrating that the presence of the amine ligands does not prevent access to the platinum surface. As we conclude our work on the effects of amine binding on electrocatalytic methanol oxidation we will next move to the second aim of the grant and investigate controlling catalytic selectivity through the binding of amine ligands. We will be able to use our previous experience in attaching and evaluating amine-based molecular layers, and in obtaining reproducible electrocatalytic measurements on platinum surfaces. Two undergraduate students have worked on this project in the past year. One received academic credit for her work, and the second was supported by a Holy Cross summer science fellowship for work over the summer. As a result, PRF funds were not needed for student support this year, despite active involvement of undergraduate research students.