Oxygen vacancy-enriched NiCo2O4 spinels/N-doped carbon nanotubes-graphene composites for the ethylene glycol electro-oxidation

Abstract

The efficient electro-oxidation of alcohol fuels on non-platinum group metals (non-PGMs) is a crucial challenge in advanced fuel cell technology. This study presents a novel approach, focusing on systematically designing highly efficient composites through strategic interface engineering. The method harnesses the intrinsic potential of oxygen vacancies (Ov) in the NiCo2O4 spinel, while synergistically incorporating nitrogen heteroatoms into multi-walled carbon nanotubes mixed with graphene (N-CNTG). Ethylene glycol (EG) was employed as defect promoter at 0, 33, 66 and 100 % v/v EG. Micrographs showed that nanobars were the predominant morphology at 0 % v/v EG, and this shape shifted to nanometric hemispheres with the shift to EG. X-ray photoelectron spectroscopy (XPS) showed that the Ov increased from 23 % to 36 % shifting from 0 to 100 % v/v EG. Comparative electrocatalytic studies showed the remarkable performance of the engineered composites compared to Vulcan carbon (C), a standard support. The best onset potential (1.08 V) was found on NiCo2O4 EG33/N-CNTG. The onset potential was 330 mV higher to that of a gold nanomaterial, but the peak potential difference was only 140 mV. This was associated with the improvement of the electronic structure as revealed by chemical calculations, changing adsorption energies, apparent activation energies and resistances to charge transfer. These findings highlight the potential of interface engineering in achieving non-PGMs electrocatalysts.