Anion Exchange of Ni–Co Layered Double Hydroxide (LDH) Nanoarrays for a High‐Capacitance Supercapacitor Electrode: A Comparison of Alkali Anion Exchange and Sulfuration

Abstract

A facile and new anion exchange process is presented, which involves the conversion of NiCo-CO₃ layered double hydroxide (LDH) nanosheet arrays in an alkaline solution. The anion exchange between CO₃ ^2- and OH^- results in the construction of a reservoir for OH^- anions, and the decoration of thin nanoflakes on the surface of nanosheets effectively enlarges the surface area of NiCo LDH nanoarrays. The capacitance of the as-soaked NiCo LDH nanoarrays electrode increases from 1.78 F cm^-2 (684 F g^-1 ) to 6.22 F cm^-2 (2391 F g^-1 ) at 2 mA cm^-2 after soaking for 12 h. Moreover, the soaked NiCo-OH LDH electrode exhibits an enhanced rate capacity, high coulombic efficiency, and good cycling stability compared with the Ni-Co-S nanosheet electrode synthesized through a hydrothermal sulfuration process. The as-assembled all-solid-state NiCo LDH//active carbon asymmetric supercapacitor shows a maximum energy density of 83.4 W h kg^-1 at a power density of 1066 W kg^-1 .