Applications of cathodic Co100-XNiX (x = 0, 30, 70, and 100) electrocatalysts chemically coated with Pt for PEM fuel cells

Abstract

The present work comprises a study about the synthesis, characterization, and performance evaluation of four Co100-X-NiX (x = 0, 30, 70, and 100) electrocatalysts coated with Pt with potential catalytic activity towards ORR. Electrocatalysts were prepared through a two-stage process combining the versatile high-energy ball milling synthesis and the galvanic displacement method. On a first stage, high-energy ball milling was used to produce nanoparticles of non-noble transition metals, (M = Co100 and Ni100) and (BM = Co30Ni70and Co70Ni30). On a second stage, galvanic displacement reactions via chemical reflux treatment were employed to promote a Pt coating over the milled nanoparticles. The four electrocatalysts were dispersed on Vulcan carbon maintaining a metal:carbon (wt.%) ratio of 50:50 each one. The result was two type of systems: (M-Pt/C = Co100–Pt/C and Ni100–Pt/C) and (BM-Pt/C = Co30Ni70–Pt/C and Co70Ni30–Pt/C). All the electrocatalysts presented a final composition: ~10 wt%. of Pt, ~40 wt% of Co100-xNix, and ~50 wt% of Vulcan carbon. Physical characterization of the synthesized electrocatalysts involved XRD, STEM, AAS-ICP-MS and EDS-SEM studies confirming the formation of homogeneously-distributed metallic nanoparticles on the carbon. The electrochemical evaluation, through cyclic voltammetry and steady-state polarization curves using rotating disk electrode technique, was performed for the four synthesized electrocatalysts and for a commercial platinum-loaded carbon black (Pt Etek 20 wt%) catalysts. All four synthesized electrocatalysts were electroactive for ORR. Moreover, the Ni100–Pt/C electrocatalyst presented the highest mass activity whereas Co30Ni70–Pt/C electrocatalyst showed the major stability after 3000 cycles of accelerated degradation test than the others. Two membrane electrode assemblies (MEAs) for PEM fuel cell were fabricated with the synthesized Ni100–Pt/C and Co30Ni70–Pt/C electrocatalysts used as cathodes. Results under single-fuel cell operation showed the same performance trend for those materials that observed under electrochemical glass cell conditions.