Highly active and durable non-precious metal catalyst for the oxygen reduction reaction in acidic medium

Polymer electrolyte fuel cells exhibit high potentials at the cathode during start-stop cycles in automotive applications, which leads to carbon support corrosion, and concomitant loss of electrocatalytic activity. In this study, carbon nanomaterials (CNM), predominantly composed of nitrogen doped multi-walled carbon nanotubes (N-MWCNTs) with encapsulated cobalt nanoparticles, were synthesized in-situ by the solid-state pyrolysis (SSP) of melamine and cobalt Oxide (Co₃O₄). The best formulation of the catalyst exhibited an ORR activity of of 2.3 mA cm^-2 at 0.75 V vs. RHE (4.6 mA mg^-1). The role played by cobalt to complete the active site was demonstrated as follows: Upon complexing the cobalt site with bipyridine, the ORR onset potential decreased by ∼90 mV. The stability of the above non-precious metal (NPM) catalyst was studied through accelerated stress tests (ASTs) designed to mimic load cycling and start-stop cycling protocols, wherein the catalyst was exposed to high anodic potentials (up to 1.5 V vs. RHE) in an acidic medium. In rotating disk electrode mode, the ORR polarization curve shifted to more negative values by about 20 mV and 14 mV, respectively, after the load cycling and start-stop cycling AST protocols, suggesting high stability. Similar stability was observed in fuel cell mode.