Ultrathin Ni(OH)2 nanosheets: Microemulsion assisted hydrothermal synthesis and application in advanced hybrid supercapacitors

Abstract

Nickel hydroxide (NH) has garnered considerable attention in supercapacitors due to its large theoretical capacity, low cost, and eco-friendliness. However, insufficient accessible surface area and poor cyclic stability have hindered its large-scale application. In this study, ultrathin NH nanosheets were synthesized using a microemulsion-assisted hydrothermal strategy. The H2O/EtOH volume ratio (K(H2O/EtOH)) significantly influences the specific surface area (SA) of the prepared NH nanosheets. The Ni(OH)2 nanosheets (NH-1–1) exhibited a thickness of ca. 4 nm and a remarkable SA of 285.0 m2 g–1 at a K(H2O/EtOH) value of 1/1. The NH-1–1 electrode demonstrated an impressive specific capacity of 824.5 C g–1 at a current density of 500 mA g–1. Additionally, the NH-1–1//activated carbon hybrid supercapacitor (NH-1–1//AC HSC) delivered 91.3 F g–1 at 500 mA g–1 with an energy density of 34.5 Wh kg–1 at 412.5 W kg–1. Even when the power density was increased to 8,250 W kg–1, the NH-1–1//AC HSC still provided 22.4 Wh kg–1. After 20,000 consecutive cycles at 5.0 A g–1, the capacitance retention of this device was 89.5 %. Impressively, the NH-1–1//AC HSC operated a clock for ca. 32 min. The exceptional energy storage capability of the NH-1–1 is attributed to its large SA and ultrathin structure.