Effect of different surface functional groups on carbon supports toward methanol electro-oxidation of Pt nanoparticles

Abstract

With an increased demand for efficient energy conversion system, nanoscale electrocatalysts have been intensively studied for high activity and stability. However, carbon support for nanoparticulate electrocatalyst has been generally thought to be inert for reaction pathway on metal nanocrystals. Therefore, material design for carbon support has mainly focused on development of high surface area with engineered pore structure, while surface state of the support has been largely neglected. Here, we demonstrate that surface functionalization of carbon support can modulate catalytic performance of Pt nanoparticle towardmethanol electro-oxidation. Vulcan carbon (VC) surface was successfully modified by either acid oxidation or urea annealing, resulting in oxygen-rich (O-VC) and nitrogen-rich (N-VC) surface states, respectively. Modified surface state of carbon supports were investigated with XPS spectra. With controlled experiments, uniform Pt nanoparticles (d similar to 5 nm) were deposited on each carbon support for the same electrochemical surface area. Through high-resolution XPS analysis, electronic transfer from nitrogen to Pt was monitored in Pt/N-VC. With electron-enriched surface, Pt/N-VC reveals less oxophilic surface property compared to Pt/VC and Pt/O-VC. Notably, methanol electro-oxidation reaction largely depended on types of functional groups. Compared to Pt/VC, methanol oxidation decreased 30% in oxygen-rich Pt/O-VC after surface oxidation, while reaction rate increased double in nitrogen-rich Pt/N-VC. From CO bulk oxidation result, improved MOR activity of Pt/N-VC is attributed to larger number of available Pt active sites from attenuated adsorption of oxygen species. Therefore, this study highlights the importance of surface engineering in carbon supports for electrocatalysis.