Dendrimer-encapsulated PtSn bimetallic ultrafine nanoparticles supported on graphitic mesoporous carbon as efficient electrocatalysts for methanol oxidation

Abstract

Catalytic performance of Pt based nanocatalysts significantly depends on their morphologies, compositions and structures. In this work, the generation-4 phenylazomethine-tetraphenylmethane dendrimer (TPMG4)-encapsulated PtSn bimetallic ultrafine nanoparticles with tunable ratio of Pt and Sn (PtnSn60-n@TPMG4/GMC, n = 56, 48, 32) supported on graphitic mesoporous carbon (GMC) were fabricated through co-reduction method by using the phenylazomethine dendrimer as a template. The morphologies, compositions, and structures of resulting PtnSn60-n@TPMG4/GMC were detected by UV–vis absorption spectra (UV–vis), inductively coupled plasma-optical emission spectroscopy (ICP-OES), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements. These physical characterizations show that dendrimer-encapsulated PtnSn60-n nanoparticles are anchored on the surface of graphitic mesoporous carbon with highly dispersion and uniformly ultrafine size of ∼1 nm, The atomic ratio of Pt and Sn in PtnSn60-n bimetallic nanoparticles can be accurately controlled. The electrochemical characterizations demonstrate that all PtnSn60-n@TPMG4/GMC samples exhibit more excellent electrocatalytic performance for methanol oxidation than single metal Ptm@TPMG4/GMC and commercial carbon supported platinum catalyst (Pt/C). Especially, the Pt56Sn4@TPMG4/GMC displays the highest catalytic activity with 1.6 times higher than Pt60/GMC and 1.9 times higher than Pt/C. Also, the Pt56Sn4@TPMG4/GMC exhibits the high carbon monoxide (CO) tolerance and superior catalytic stability towards methanol oxidation. Consequently, constructing Pt based bimetallic nanoparticles with controllable compositions and structures is an effective way to improve the catalytic performance and reduce the amount of Pt used in the catalysts, which will be widely concerned in the field of direct methanol fuel cells.