Herein, lignin‐rich KOH‐activated porous carbon from eucalyptus wood (named as PACE) is presented as an efficient electrode for supercapacitors (SCs). Compared with the most commonly used higher activation temperature, i.e., 800 °C with KOH (PACE‐800), a more efficient SC is developed by activating carbon with KOH at lesser temperature, i.e., 600 °C (PACE‐600). The high specific capacitance (i.e., 230 F g−1 at 1 A g−1 measured in a 2 m NaCl electrolyte) measured by galvanostatic charge–discharge (GCD) studies is not primarily due to larger surface area, but due to the inherent electron‐rich oxygen‐based functionalities that persist at the lower activation temperature, contributing to the hydrophilic nature to PACE‐600. The mechanism of the capacitive charge storage is deduced from electrochemical impedance spectroscopy (EIS). The application of PACE‐600 as a SC electrode is confirmed from insignificant loss in the specific capacitance after 10 000 charging–discharging cycles, recorded at 10 A g−1. Further, fabrication of higher‐voltage (1.6 V) symmetric SC PACE‐600//PACE‐600 in aqueous neutral electrolyte (2 m NaCl) is presented, which illuminates a red LED (1.8 V) for 1 min after charging for 5 s. The corresponding energy density is calculated to be 41 W h kg−1, and at a power density of 2396 W kg−1.

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.

No abstract