Ammonia-Free Soft Urea-Derived Nickel Cobalt Nitride/CNTs as Battery-Type Electrode for Asymmetric Supercapacitors

Abstract

To meet the rising global energy demands, there has been significant interest in developing efficient and sustainable energy storage devices. Supercapacitors (SCs), renowned for their rapid charge-discharge capabilities and long cycle life, effectively bridge the energy-power gap between batteries and traditional capacitors. Transition Metal Nitrides (TMNs) have emerged as promising electrode candidates for SCs due to their excellent redox properties and high electrical conductivity. However, challenges related to their electrochemical stability considerably hinder their commercialization potential. Additionally, the toxic ammonia-based synthesis methods commonly employed for fabricating metal nitrides raise environmental and safety concerns. This study presents an ammonia-free, urea-based synthesis of Nickel Cobalt Nitrides (NiCoN) integrated with Carbon Nanotubes (CNTs) as next-generation supercapacitor electrodes. Different compositions of nickel and cobaltbased nitrides were synthesized with CNTs. The proper synthesis of the materials was validated through various morphological and structural characterizations. The electrochemical performance of the samples with different metallic ratios i.e. NiCoN(1:1)/CNTs, NiCoN(1:2)/CNTs, and NiCoN(2:1)/CNTs was tested in threeelectrode system, where NiCoN(1:1)/CNTs showed the best performance, exhibiting a remarkable specific capacitance of 1146.5 F g⁻¹ at a current density of 0.5 A g⁻¹. Its batterylike behavior was assessed using Dunn’s method. Furthermore, an Asymmetric Supercapacitor (ASC) was assembled with NiCoN(1:1)/CNTs as the cathode and Activated Carbon (AC) as an anode. The NiCoN(1:1)/CNTs // AC device achieved a high energy density of 79.7 Wh kg⁻¹ and a power density of 243.75 W kg⁻¹ at 0.35 A g⁻¹. Notably, the device demonstrated 101.8 % capacity retention and an average coulombic efficiency of 98 % after 10,000 continuous cycles, indicating excellent cyclic reversibility.