Multi-walled carbon nanotubes supported porous nickel oxide as noble metal-free electrocatalysts for efficient water oxidation

Herein we report for the first time to use multi-walled carbon nanotubes (MWCNTs) supported porous nickel oxide (NiOx) as non-precious electrocatalysts for oxidation of water at low overpotentials. The nickel oxide catalyst was facilely electrodeposited on MWCNTs in a 0.1 M KBi buffered solution at pH 9.2 containing 0.1 mM Ni2+ with an applied anodic potential. The current density of bulk electrolysis is 2.2 mA/cm2 at +1.1 V (vs Ag/AgCl) using NiOx-MWCNTs as the working electrode at pH 9.2, which is much higher than that in a system containing no MWCNTs. Tafel plot indicates that the present NiOx-MWCNTs catalyst requires the overpotential of only 200 mV to catalyze the water oxidation reaction at pH 9.2. The Faradaic efficiency of >95% has been achieved at +1.1 V. The highly porous character of the NiOx catalyst materials were further studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray analysis (EDX).