High performance of polyoxometalate/PtPd nanoparticles/carbon nanotubes electrocatalysts for the methanol electrooxidation

摘要

A novel method was put forward to synthesize PtPd nanoparticles deposited on multi-walled carbon nanotubes (MWCNTs) in the presence of polyoxometalate (PMo). In the synthesis of PMo/PtPd/MWCNT electrocatalysts, PMo plays an important role in the formation and distribution of PtPd nanoparticles on the surface of MWCNTs. It is founded that PtPd nanoparticles are deposited uniformly on the surface of MWCNTs in high density by the assistant of PMo; most of PtPd nanoparticles are aggregated, and their dispersion is uneven without PMo in synthesis. The composition of PtPd nanoparticles is optimized by tuning the Pt/Pd ratio. Among these Pt-based catalysts, it is founded that PMo/Pt_4Pd_1/ MWCNT catalysts have smallest PtPd nanoparticles with an average diameter of 1.9 nm. The smallest size of PtPd nanoparticles enables PMo/Pt_4Pd_1/MWCNT catalysts to possess a highest electrochemical surface area, and thus a largest current density in methanol oxidation. In long-term methanol oxidation, PMo/Pt_4Pd_1/MWCNT catalysts show higher stability than Pt_4Pd_1/MWCNT catalysts. The current density of PMo/Pt_4Pd_1/MWCNT catalysts remain 203 mg~(-1) even after 3000 s continuous electrocatalysis at 0.6 V, being 12 times higher than that of Pt_4Pd_1/MWCNT catalysts. CO-stripping voltammetry reveals PMo is beneficial to oxidative removal of adsorbed CO at Pt active site. On the other hand, Pd content also has important effect on CO tolerance of Pt catalysts. It can reduce the over-potential of CO oxidation at these Pt catalysts, gives a high CO removal efficiency.