Growth of Ni₃Se₂ nanosheets on Ni foam for asymmetric supercapacitors

We present a facile one-step hydrothermal method to in situ grow nickel selenide (Ni₃Se₂) nanosheets on nickel (Ni) foam (Ni₃Se₂/Ni) by using SeO₂ as selenide source, Ni foam as nickel source and NaBH₄ as reducing agent. The mole ratio of NaBH₄/SeO₂ is optimized as 4:1. An asymmetric supercapacitor (ASC) is fabricated by using as synthesized Ni₃Se₂/Ni as positive electrode and activated carbon (AC) as negative electrode. The synthesized materials and assembled devices are measured and characterized by a field emission scanning electron microscopy, powder X-ray diffraction, cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. The results shows that the as-synthesized Ni₃Se₂/Ni electrode possesses a high specific capacitance of 854 F g⁻¹ at 1 A g⁻¹. The ASC can steadily operate with a high voltage of 1.6 V in 3 M KOH electrolytes, and possesses a superior energy density of 23.3 W h kg⁻¹ at a power density of 398.1 W kg⁻¹. In addition, the Ni₃Se₂//AC ASC shows excellent charge/discharge stability, after 5000 cycles the capacitance retention reaches 91.11%. The excellent performance of Ni₃Se₂/Ni electrode is mainly due to the pseudo-capacitive by Ni₃Se₂ and the 3D structure of Ni foam.