Preparation of a platinum electrocatalyst by coaxial pulse arc plasma deposition

Abstract

We have developed a new method of preparing Pt electrocatalysts through a dry process. By coaxial pulse arc plasma deposition (CAPD), highly ionized metal plasma can be generated from a target rod without any discharged gases, and Pt nanoparticles can be deposited on a carbon support. The small-sized Pt nanoparticles are distributed over the entire carbon surface. From transmission electron microscopy (TEM), the average size of the deposited Pt nanoparticles is estimated to be 2.5 nm, and their size distribution is narrow. Our electrocatalyst shows considerably improved catalytic activity and stability toward methanol oxidation reaction (MOR) compared with commercially available Pt catalysts such as Pt black and Pt/carbon (PtC). Inspired by its very high efficiency toward MOR, we also measured the catalytic performance for oxygen reduction reaction (ORR). Our PtC catalyst shows a better performance with half-wave potential of 0.87 V, which is higher than those of commercially available Pt catalysts. The higher performance is also supported by a right-shifted onset potential. Our preparation is simple and could be applied to other metallic nanocrystals as a novel platform in catalysis, fuel cells and biosensors.

Keywords: Pt nanoparticles; electrocatalysts; methanol oxidation.

Figure 1.

Experimental set-up for preparation of the PtC catalyst prepared by CAPD. (a) Illustration of the generation of an arc plasma. (b) Photographs of an arc plasma and a sample holder.

Figure 2.

(a) SEM image, (b) HAADF-STEM image and (c) and (d) bright-field TEM images of Pt nanoparticles (5 wt%) deposited on carbon support. The corresponding histogram of the particle size distribution is also shown as the inset in panel (c).

Figure 3.

(a) Cyclic voltammetric and (b), (c) amperometric curves for the MOR catalyzed PtC-CAPD, PtC-5%, PtC-20% and PtB in a 0.5 M H₂SO₄ solution containing 0.5 M methanol. (d) Pt_ECSA retention of each sample during the cycling treatments. The current densities (Y-axis) are normalized by the mass of Pt (mg). A scanning speed of 50 mV s⁻¹ is used for the (a) cyclic voltammetric measurements, while constant potentials of 0.5 V and 0.4 V are used in the (b), (c) amperometric measurements.

Figure 4.

Cyclic voltammograms for MOR catalyzed (a) PtC-CAPD, (b) PtC-5%, (c) PtC-20% and (d) PtB catalysts, respectively, in a 0.5 M H₂SO₄ solution containing 0.5 M methanol at different stages.

Figure 5.

(a) ORR polarization curves of a RDE modified with PtC-CAPD, PtC-5% and PtC-20%. The plots were obtained in O₂-saturated KOH (0.1 M) at a rotation rate of 1600 rpm with a scan rate of 10 mV s⁻¹. (b) ORR polarization curves of PtC-CAPD at different rotation rates (from 100 rpm to 2000 rpm) in O₂-saturated KOH (0.1 M) with a scan rate of 10 mV s⁻¹. (c) The Koutecky–Levich (K–L) plots of PtC-CAPD at various potentials. RHE stands for reversible hydrogen electrode.