Glucose-Derived Carbon Layer Coated on Mixed-Phase Nickel Sulfide Nanoparticles for Hybrid Supercapacitors

Glucose can form carbon material under hydrothermal conditions. Thus, carbon-layer-coated nickel sulfide nanoparticles were prepared using a one-step hydrothermal method with nickel sulfide as the primary phase. The effect of the glucose mass on the structure and electrochemical properties of nickel sulfide was studied in detail. The size of nanoparticles decreased after the nickel sulfide surface was coated by using the carbon layer, forming uniform spherical particles of 200–300 nm. The carbon layer thickness on the surface was ∼3 nm. The nitrogen adsorption–desorption test revealed that the specific surface area of the pristine nickel sulfide was 2.7 m2 g–1. Under optimal conditions, the prepared carbon-layer-coated nickel sulfide (NixSy-0.5) depicted a surface area of 15.2 m2 g–1. The high specific surface area provided additional electrochemically active sites. The glucose-derived carbon layer could be utilized as a conductive agent to enhance electron transport in the electrode. Electrochemical test results depicted a high capacitance of NixSy-0.5 of 612.5 C g–1 at 1 A g–1, higher than that of pristine nickel sulfide (381.7 C g–1). The hybrid supercapacitor (HSC) assembled with NixSy-0.5 as the positive electrode and commercial activated carbon (AC) as the negative electrode exhibited a high energy density of 47 Wh kg–1. The capacitance retention rate is high (99%) after 20 000 cycles. This study demonstrated the simultaneous preparation of nickel sulfide–carbon layer composites and provided a feasible strategy for preparing economical and efficient electrode materials.