Role of Ultrathin Carbon Shell in Enhancing the Performance of PtZn Intermetallic Nanoparticles as an Anode Electrocatalyst for Direct Formic Acid Fuel Cells

Abstract

Introducing a carbon shell to Pt-based intermetallic nanoparticles (iNPs) is an effective approach to prepare structurally ordered electrocatalysts for fuel cell applications. However, it remains a huge challenge to synthesize small-sized Pt-based iNPs with a concisely controlled carbon shell based on fully understanding the role of the carbon shell in the electrocatalytic performance. Herein, we report the preparation of ultrathin carbon shell (UCS)-coated, small-sized PtZn iNPs, which are obtained by using the simple heat treatment of polypyrrole-coated PtZn/C (PPy−PtZn/C), which can produce a carbon shell in situ and simultaneously transfer a disordered PtZn alloy into ordered intermetallic PtZn. Interestingly, the thickness of the carbon shell can be well-controlled by tuning the polymerization time of pyrrole (Py). The obtained PtZn iNPs (an average diameter of ca. 4 nm) coated with UCS (ca. 0.5 nm thickness) shows the best electrocatalytic performance toward the formic acid oxidation reaction. Moreover, the UCS−PtZn iNPs offers remarkable long-term stability as an anode electrocatalyst in a constructed direct formic acid fuel cell. The results demonstrate that the UCS formed in situ only acts as a physicochemical protecting shell with high permeability for the reactants, but it does not block the catalytic reaction sites of iNPs.