Laser irradiation-induced construction of Pt/Ag bimetallic nanourchins with improved electrocatalytic properties

Abstract

Platinum (Pt)-based nanomaterials with rough surfaces are regarded as promising catalysts in fuel cells. Herein, we report a versatile and green strategy to synthesize Pt/Ag (Pt : Ag ∼ 9 : 1) bimetallic nanourchins with mean size of ∼70 nm by laser irradiation of Ag₂S/Ag nanoparticles in a potassium chloroplatinate (K₂PtCl₄) water solution. The distinctive advantages of this novel anisotropic synthesis are as follows: (I) the enhanced anisotropic replacement reaction derived by laser-induced photothermal effect on the nanoseeds gives rise to the anisotropic deposition of Pt atoms and then the formation of rugged intermediate precursors, and (II) the subsequent anisotropic overgrowth of Pt and Ag atoms via enhanced co-reduction reaction motivated by laser-induced surface plasmon resonance will preferentially occur at protrusion surfaces on the intermediate precursors. Without any binder/stabilizer/capping additives, the pure Pt/Ag bimetallic nanourchins exhibit excellent long-term stability during repeated cyclic voltammogram (CV) tests. Electrochemically active surface area (ECSA) tests illustrate that the novel catalysts exhibit a negligible loss of 0.2% after 1500 repeated applications, while that of commercial Pt/C catalyst is 78.7% after 1000 cycles. Moreover, the ECSA-normalized CV curve and chronoamperometric (CA) measurements reveal that Pt/Ag bimetallic nanourchins possess enhanced electrocatalytic activity and stability in the methanol oxidation reaction. Correspondingly, the mass-normalized (mass of Pt) CVs show that the peak of mass current is about 302.35 mA mg_Pt⁻¹, which is 5.2 times higher than that of commercial Pt/C catalyst. For the entire time course (2000 s), the CA curves show that the current density is about 0.38 mA cm_Pt⁻², while that of commercial Pt/C electrocatalyst is 0.014 mA cm_Pt⁻². Thus the Pt/Ag bimetallic nanourchins should be established as an advanced electrocatalyst for direct methanol fuel cell application. These findings will also stimulate the investigation of using laser light as an effective tool for sculpting pure functional metal-based nanomaterials.