Local electrocatalytic activity of PtRu supported on nitrogen-doped carbon nanotubes towards methanol oxidation by scanning electrochemical microscopy

Nitrogen-doped carbon nanotubes (NCNTs) were synthesized by treating HNO3-oxidized carbon nanotubes (CNTs) in an NH3 flow at different temperatures. PtRu nanoparticles were decorated over NCNTs. The PtRu catalysts were prepared by an impregnation–reduction method from metal chloride precursors with a total metal loading of about 10 wt%. The electrocatalytic activity with respect to methanol oxidation was studied using electrochemical and scanning electrochemical microscopy (SECM) measurements. Transmission electron microscopy revealed the spherical shape and narrow particle size distribution of the PtRu particles over NCNTs with average particle sizes of ∼3–5 nm. A detailed X-ray photoelectron spectroscopy study was performed to quantitatively identify different nitrogen functional groups and to evaluate their role in the observed enhanced catalytic activity towards methanol oxidation. The determination of the local electrocatalytic activity of the proposed catalyst towards methanol oxidation and simultaneous evaluation of the intermediates produced during methanol oxidation were achieved using SECM. Density functional theory studies were performed to understand the adsorption sites of methanol and intermediates on different reactive sites and to investigate possible reaction mechanisms.