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

摘要

The present work comprises a study about the synthesis, characterization, and performance evaluation of four Co100-X-Ni-X (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 = Co-100 and Ni-100) and (BM = Co30Ni70 and 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 = Co-100-Pt/C and Ni-100-Pt/C) and (BM-Pt/C = Co30Ni70-Pt/C and Co70Ni30-Pt/C). All the electrocatalysts presented a final composition: similar to 10 wt%. of Pt, similar to 40 wt% of Co100-xNix, and similar to 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 Ni-100-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 Ni-100-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. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.