Direct Synthesis of Pt Catalyst on Multi-Walled Carbon Nanotubes

Abstract

If metal catalysts could be grown directly on their support, the resulting bonds between them may be stronger than those formed by drop casting nanoparticles as they would form by more than mere physical contact. Surface limited redox replacement (SLRR) is a process that has been used to grow epitaxial metal films on metal substrates in a layer-by-layer process, allowing for better adhesion to the substrate and the tuning of electrochemical properties through strain and ligand effects. The possibility for adapting this process to carbon-based substrates like those found in fuel cells is explored through the used of multi-walled carbon nanotubes. SEM and TEM images showed that the catalysts mostly grew in the form of nanoparticles, almost entirely coating the nanotubes by the 20th iteration. However, surface area measured via CV showed a self-limiting behavior to the growth of surface area after the 10th iteration despite the increase in nanoparticle density observed in SEM. The behavior in ORR also showed a limiting behavior, with the onset potential increasing to .6 V (vs. Ag/AgCl) by iteration 8, then remaining in the vicinity of that value with subsequent iterations.