Well-dispersed and size-tuned bimetallic PtFexnanoparticlecatalysts supported on ordered mesoporous carbon for enhanced electrocatalytic activity in direct methanolfuel cells

Abstract

Ordered mesoporous carbon (OMC) supported well-dispersed PtFe_x nanoparticles with a controllable size distribution were prepared via a modified polyol synthesis route, using hexachloroplatinic acid and ferric chloride as Pt and Fe source, and ethylene glycol as a reducing agent. The catalytic activities relevant to direct methanol fuel cell of the PtFe_x/OMC composites were investigated using cyclic voltammetry, single-cell proton exchange membrane fuel cell (PEMFC) test and electrochemical impedance spectroscopy (EIS) technique. Due to the existence of more Pt⁰ species and Fe ion corrosion caused by the formation of the alloyed PtFe_x catalyst, Pt⁰ can provide the more active sites for methanol oxidation reaction, and the methanol oxidation activity of the PtFe_x/OMC electrode is evidenced to be enhanced by the increased anodic peak current with increasing the incorporation content of Fe. The oxygen reduction reaction (ORR) current density of 0.662 A cm⁻² and power density of 237.2 mW cm⁻² generated by the PtFe₃/OMC sample are more than two times the values of 0.32 mA cm⁻² and 102.6 mW cm⁻² by the Pt/OMC sample. The PtFe₃/OMC catalyst in 0.5 M H₂SO₄ + 1 M CH₃OH displays the highest specific catalytic activity of 100.6 mA m⁻², which is almost 3 times lower than that of 283.7 mA m⁻² in 0.5 M H₂SO₄. The enhanced higher activity for the PtFe₃/OMC sample can be firstly attributed to a highly homogeneous dispersion of the PtFe₃ nanoparticles on the mesoporous channels within OMC, such PtFe₃ nanoparticles with a diameter of 3.3 nm can accelerate the formation of Pt–OH groups. Meanwhile, the alloyed PtFe₃ nanoparticles can provide a lower onset potential for the electrooxidation of CO/H₂ than that of pure Pt, and would contribute more to the promotion of C–H breaking and CO_ad tolerance. Furthermore, the larger surface area, the favorable pore structure and the structural integrity between the PtFe₃ nanoparticles and the OMC matrix, will effectively facilitate the transportation of reactants and products in liquid electrochemical reactions.