Synthesis of Pt3Co Alloy Nanocatalyst via Reverse Micelle for Oxygen Reduction Reaction in PEMFCs

Monodispersed, uniformly alloyed Pt3Co alloy nanoparticle electrocatalysts were synthesized via reduction of metallic precursors by sodium borohydride in heptane/polyethylene glycol dodecylether (Brij)/water reverse micelles. These particles were further adsorbed on XC-72R carbon powder, separated from micelles, and characterized using X-ray diffraction (XRD), transmission electronic microscopy (TEM). The electrochemical activity for the oxygen reduction reaction (ORR) was characterized using a Rotating Disk Electrode (RDE) technique. Even though residual surfactants on the metallic nanoparticle reduced the active surface area of the electrocatalytic particles, the catalytic activity of the prepared Pt3Co nanoparticles exhibited higher Pt mass and Pt surface area specific activities compared to pure Pt. The impact of heat treatment on the mean particle size, the electrochemical surface area (ESA), and on the activity was investigated and correlated to the residual surfactant coverage. Intermediate annealing temperatures resulted in larger ESA, despite particle growth pointing to lower surfactant coverage. Higher annealing temperatures caused large particle growth and reduced ESA, yet significant activity gains. A surface segregation mechanism resulting in a catalytically active Pt skin structure is hypothesized.