Electrochemical Observation of Ligand Effects on Oxygen Reduction at Ligand-Stabilized Pt Nanoparticle Electrocatalysts

摘要

We have incorporated small Pt nanoparticles (1.7 ± 0.5 nm) stabilized with triphenylphosphine triphosphate (Pt-TPPTP) or triphenylphosphine oxide (Pt-TPPT-oxide) into composite polymer-Vulcan carbon thin films and measured the effects of the ligands on the oxygen reduction reaction (ORR) activity of the Pt nanoparticles using rotating disk electrode (RDE) voltammetry. We measure ORR activities for TPPTP-stabilized particles of 0.21 A/mg{sub}(Pt) at 0.9 V, which is less than the 0.25 A/mg{sub}(Pt) that we measure for the "bare" Pt nanoparticle. However, when normalizing the ORR kinetic current for Pt microscopic surface area, the specific activity, i{sub}s, for Pt-TPPTP is significantly higher than for the parent nanoparticles (0.41 mA/(cm{sup}2){sub}(real) vs. 0.29 mA/(cm{sup}2){sub}(real)), suggesting a kinetic enhancement of the ORR viz. a weakening of the Pt-O bond strength by the TPPTP ligand. Cyclic voltammetry also reveals a positive shift in Pt-oxide electrochemistry for Pt-TPPTP compared to that for bare Pt nanoparticles, which is consistent with the improved area-specific ORR kinetics.