Amino Acid Mediated Highly Ordered Carbon Dots as Phase Directing Agent for Synthesizing α-Ni(OH)₂Decorated with Nitrogen Doped CD as an Electrode for an Efficient Symmetric Supercapacitor

Abstract

The synthesis of the α-phase of layered Ni(OH)2 is desirable owing to its efficient charge storage applications. The hydrothermal route of synthesis usually leads to formation of mixed of α- and β-phases of Ni(OH)2. We present here a novel hydrothermal approach for synthesizing predominantly the α-phase of Ni(OH)2 using a nitrogen doped crystalline carbon dot ([N-CD]BA) as a phase directing agent. The reaction medium comprising [N-CD]BA led to the formation of a microflower-like structure denoted as Ni(OH)2/[N-CD]BA with more petal density than in pristine α/β mixed phases of Ni(OH)2. The structure, composition, texture, and morphology of the as-synthesized batches of Ni(OH)2/[N-CD]BA and pristine Ni(OH)2 are thoroughly characterized. The electrochemical studies recorded by cyclic voltammetry and galvanostatic charging–discharging measurements demonstrated a battery-type supercapacitor. The batch of Ni(OH)2 prepared with 12.5 vol % [N-CD]BA, denoted as Ni(OH)2/12.5%[N-CD]BA, exhibited an optimum specific capacity of 482 C g–1 recorded at 1.0 A g–1, which is 4.5 times higher than that of pristine Ni(OH)2. The enhanced charge storage and transport mechanism are explained from electrochemical impedance spectroscopy (EIS). The high power density is reflected from a small relaxation time (0.4 s), and the charging–discharging efficiency is also improved for α-Ni(OH)2/12.5%[N-CD]BA. The application of the materials as supercapacitors has been demonstrated by fabricating a symmetric supercapacitor (SSC) device, i.e., Ni(OH)2/[N-CD]BA//Ni(OH)2/[N-CD]BA, using 2 M KOH as the electrolyte. The SSC exhibited a maximum energy density of 24 Wh kg–1 and a power density of 1.5 kW kg–1. The real-time application of the symmetric supercapacitor device has been demonstrated by successfully illuminating red LED lamps and powering a motor driven 1.6 mW fan.