Pt–Pd alloy nanoparticle-decorated carbon nanotubes: A durable and methanol tolerant oxygen reduction electrocatalyst

Abstract

We describe the decoration of multiwalled carbon nanotubes (MCNTs) with Pt–Pd alloy nanoelectrocatalysts of three different compositions and their electrocatalytic performance toward the oxygen reduction reaction (ORR). The decoration of the MCNTs involves polymer-assisted impregnation of metal precursors PtCl^2-₆ and PdCl^2-₄ and the subsequent reduction of the impregnated precursors by a modified polyol route. The composition of the catalyst was controlled by tuning the molar ratio of the precursors during their impregnation. Electron probe microscopic analysis shows that the catalysts have compositions of Pt₄₆Pd₅₄, Pt₆₄Pd₃₆ and Pt₂₈Pd₇₂. The Pt₄₆Pd₅₄ and Pt₆₄Pd₃₆ catalysts have truncated octahedral and icosahedral shapes with a size ranging from 8 to 10 nm. On the other hand, the catalyst of Pt₂₈Pd₇₂ composition has a spherical/quasispherical shape with a size distribution of 1–2 nm. The XPS measurement confirms the signature of metallic Pt and Pd. The Pt₄₆Pd₅₄ catalyst has a pronounced electrocatalytic activity toward the ORR with a specific and mass activity of 378 μAcm^-2_Pt-Pd and 64 μA μg^-1_Pt-Pd, respectively at 0.8 V. Moreover, the Pt₄₆Pd₅₄ nanoelectrocatalyst is highly durable and it retains its initial catalytic activity even after 1000 extensive cycles. Interestingly, this catalyst has a very high tolerance toward methanol and it does not favor the oxidation of methanol in the potential window of 0.1–1.4 V. The electrocatalytic activity of the alloy electrocatalyst is compared with commercially available Pt black and MCNT-supported spherical Pt nanoparticles. The catalytic activity of the Pt₄₆Pd₅₄ nanoelectrocatalyst is higher than the other catalysts. The Pt₄₆Pd₅₄ catalyst outperforms the electrocatalytic activity of all other catalysts.