Anchoring of ultrafine Co3O4 nanoparticles on MWCNTs using supercritical fluid processing and its performance evaluation towards electrocatalytic oxygen reduction reaction

Abstract

Developing an efficient electrocatalyst for improving oxygen reduction reaction (ORR) kinetics is essential for various renewable energy appliances and energy-intensive technologies. The design of a low cost and robust ORR catalyst with desired durability still remains a challenging task. Here we demonstrated a facile and environmentally friendly supercritical fluid-assisted decoration of Co₃O₄ on multi-walled carbon nanotubes (MWCNTs) to generate a hybrid nanostructure electrocatalyst for ORR. The mildly oxidized MWCNTs provided functional groups on the outer walls to seed and anchor nanocrystals, while keeping the inner walls intact for a highly conducting network. In particular, the 11 wt% Co₃O₄-MWCNTs hybrid exhibited improved half wave potential by 240 mV compared to Co₃O₄ and 125 mV with respect to MWCNTs based on the rotating ring disc voltammetry results. Similarly, the observed ORR current density was superior to those of both bulk Co₃O₄ and bare MWCNTs at medium overpotential, proceeding dominantly through a 4-electron reduction pathway. Such enhancement may be attributed to the synergetic effect of the specific heterogeneous architecture, which results in improved conductivity, accessible active centres and enhanced reaction rate at Co₃O₄ decorated on the MWCNT surface.