Solid-Solid Separation Approach for Preparation of Carbon-Supported Cobalt Carbide Nanoparticle Catalysts for Oxygen Reduction

Transition metal carbides have received significant attention for oxygen reduction reaction (ORR) applications primarily owing to their good conductivity. However, cobalt carbide based catalysts (CoCx) are difficult to prepare, owing to the preferential formation of metallic cobalt and cobalt oxide instead. Also, cobalt carbide nanoparticles rapidly coarsen and undergo grain growth. This is a problem as it results in low current density and poor active site exposures. In this study, carbon-supported CoCx (C@CoCx) is successfully synthesized using the solid-solid separation synthesis method. The limitations identified to be associated with cobalt carbide nanoparticle based electrocatalysts are overcome. Here, the synthetic approach ensures good distribution and protection of CoCx on in situ generated carbon nanotubes. This results in robust activities with an appreciable onset potential of ∼0.92 V, a half-wave potential of ∼0.8 V, and a durability of ∼100% (tested on ∼22 h continuous operation runs). In alkaline medium, C@CoCx compares favorably with commercial platinum dispersed on carbon (20 wt % Pt/C) and shows a higher current density of ∼300 μA/cm2 at an electrode potential of 0.6 V. All of these indicate that there is a synergistic charge transfer between CoCx and an in situ generated carbon nanotube. This is due to intimate contact that exists between the two phases; it is in fact responsible for superior methanol tolerance observed, making it a good candidate for direct methanol fuel cells.