Highly efficient and robust oxygen evolution catalysts achieved by anchoring nanocrystalline cobalt oxides onto mildly oxidized multiwalled carbon nanotubes

Abstract

Crystalline cobalt oxide nanoparticles have been densely and strongly anchored onto mildly oxidized multiwalled carbon nanotubes (Co₃O₄/mMWCNT) and applied as electrocatalysts for highly efficient water oxidation. The hybrid catalyses oxygen evolution reactions (OER) with an onset potential of 1.51 V vs. RHE and an overpotential only of 390 mV to achieve a current density of 10 mA cm⁻². The Co₃O₄/mMWCNT catalyst exhibits high Faraday efficiency (>99%) and long-term stability (>25 h) during bulk electrolysis of water. A range of carbon nanostructures including MWCNTs, single-walled CNTs (SWCNTs), and graphene, and CNTs of different oxidation states have been prepared and applied as substrates for Co₃O₄ nanocrystals and their performance is compared to reveal the interrelationship between the nanocarbon structure, surface functionalization and charge transport for rational design of OER catalysts. Furthermore, a range of techniques has been utilized to characterize the stability of MWCNT substrates during water oxidation. Importantly, it is found that the MWCNTs in the composite can sustain the harsh oxidative environment of water oxidation, with no carbon corrosion detected.