Cobalt Nanoparticle-integrated Nitrogen-doped Carbon Nanotube as an Efficient Bifunctional Electrocatalyst for Direct Methanol Fuel Cells

Abstract

Catalysts are key ingredients for direct methanol fuel cells (DMFCs). Platinum (Pt) and Pt-based catalysts are commonly used in DMFCs. The present study demonstrates highly active noble metal-free cobalt nanoparticle (NP)-integrated nitrogen-doped carbon nanotubes (Co@NC) as an efficient catalyst for the oxygen reduction reaction (ORR). The formation of the Co-Nx bond in the vicinity of Co@NC created a higher number of active sites for ORR. The Co@NC catalyst showed a half-wave potential of 0.86 V and an onset potential of 0.91 V for ORR. The Pt NP-decorated Co@NC (Pt-Co@NC) displayed high mass activity of 5.39 A/mg toward methanol oxidation reaction activity, which is 3.6-fold higher than that of the conventional Pt/C catalyst, due to the synergistic effect of Co@NC. The Co@NC cathode catalyst coupled with a Pt-Co@NC anode catalyst exhibited significantly improved performance, with a peak power density of 42.6 mW/cm2 at a discharge current density of 220 mA/cm2. The Co@NC noble metal-free bifunctional catalyst broadens the range of DMFC application, as demonstrated in a polyvinyl alcohol/potassium hydroxide (PVA/KOH) gel membrane-based room-temperature DMFC, using a synthesized cathode and anode. The PVA/KOH gel-membrane-based DMFC cell delivered a power density of 8.5 mW/cm2. Thus, the results from this study demonstrate the real applicability of the as-synthesized catalyst-integrated PVA/KOH gel membrane-based DMFC for portable electronics.