Well-dispersed and size-tuned bimetallic PtFe_x nanoparticle catalysts supported on ordered mesoporous carbon for enhanced electrocatalytic activity in direct methanol fuel cells

摘要

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 Pt~0 species and Fe ion corrosion caused by the formation of the alloyed PtFe_x catalyst, Pt~0 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.