NiC <sub>2</sub> O <sub>4</sub> ⋅ 2H <sub>2</sub> O Nanoflakes: A Novel Redox‐mediated Intercalative Pseudocapacitive Electrode for Supercapacitor Applications in Aqueous KOH and Neutral Na <sub>2</sub> SO <sub>4</sub> electrolytes
Neeraj Kumar Mishra, Abhijeet Kumar Singh, Rakesh Mondal, Preetam Singh
Abstract
Abstract Pseudocapacitors with the accessibility of different oxidation states for redox‐mediated charge storage can achieve higher energy density compared to EDLC. NiC 2 O 4 ⋅ 2H 2 O is envisaged here as a potential pseudocapacitive electrode that works with the accessibility of the Ni 2+/3+ redox couple in the flexible structural network due to the presence of planar oxalate anions (C 2 O 4 2− ) supported by the 3‐dimensional hydrogen bonding network of crystal water. The NiC 2 O 4 ⋅ 2H 2 O electrode showed a superior specific capacitance equivalent to 990 F/g in the potential window of 0 to 0.45 V observed in aqueous KOH electrolyte and 440 F/g in 1 M neutral Na 2 SO 4 electrolyte in the potential window of 0 to 0.85 V. Predominant intercalative mechanism seems to play an important role behind the high charge storage capacity of NiC 2 O 4 ⋅ 2H 2 O electrode and the interactive contribution was found to be ∼84 % and surface contribution was found to be ∼16 % respectively. Further, in full cell asymmetric supercapacitor (AAS) mode in KOH electrolyte, in which NiC 2 O 4 ⋅ 2H 2 O is made as the positive electrode and Activated Carbon (AC) is made as the negative electrode, the highest specific energy of 141.5 Wh/kg and specific power of ∼559 W/kg at 0.2 A/g current density was obtained with superior cyclic stability. The detailed electrochemical studies confirm high cyclic stability and stable performance that makes NiC 2 O 4 ⋅ 2H 2 O a potential pseudocapacitive electrode for large‐scale energy storage applications.