Hierarchically Organized NiCo2O4 Microflowers Anchored on Multiwalled Carbon Nanotubes: Efficient Bifunctional Electrocatalysts for Oxygen and Hydrogen Evolution Reactions

Abstract

Hierarchical flower-like NiCo2O4 anchored on multiwalled carbon nanotubes (NiCo2O4-MCNTs) act as robust bifunctional electrocatalysts towards O2 (OER) and H2 (HER) evolution reactions. The NiCo2O4-MCNTs hybrid is synthesized in a facile surfactant-free hydrothermal process, and its flower-like morphology was shown to consist of 1D nanowires. The MCNT support is beneficial for enhanced reactive sites, efficient charge transfer, and durability of the composite. The material shows low overpotentials of 350 mV and 209 mV for OER and HER, respectively at 10 mA cm−2. Such values are comparable to contemporary noble-metal catalysts and even lower than reported non-precious catalysts. Moreover, this hybrid shows high current density, lower Tafel slope, and excellent stability. The synergistic coupling effects between the MCNTs and NiCo2O4 are key factors for the superior catalytic activity of these hybrid materials.