MOF-derived nickel and cobalt metal nanoparticles in a N-doped coral shaped carbon matrix of coconut leaf sheath origin for high performance supercapacitors and OER catalysis

Abstract

Coconut leaf sheath-derived nitrogen doped carbon framework is developed and incorporated with nickel and cobalt metal nanoparticles in the carbon matrix by a facile process of growing ZIF-67 metal organic framework particles on the graphitised carbon, followed by annealing it in inert atmosphere. Various parameters are modified to obtain three different samples. These samples are tested for high performance supercapacitors and oxygen evolution reaction (OER) catalysts. The optimised sample NiCo–C-1 gave a high specific capacity of 308 mAh g−1 at a current density of 1 A g−1 in a 2 M KOH electrolyte. An asymmetric supercapacitor assembly prepared from NiCo–C-1 as the positive electrode and the nitrogen-doped carbon as the negative electrode, exhibited an energy density of up to 31.8 Wh Kg−1 for a high power density of 6.2 kW kg−1 over a potential window of 0–1.55 V. Two of our best samples were also tested for OER, giving good water oxidation kinetics, revealed by their lower Tafel slopes of around 107 mV and a low over potential (η) of around 420 mV at a current density of 10 mA cm−2. Hence, this work opens great avenues for biomass-derived materials for high performance supercapacitors and catalysis.