Three dimensional Ni(OH)2/rGO hydrogel as binder-free electrode for asymmetric supercapacitor

Highlights: • 3D Ni(OH)₂ nanoparticles deposited reduced oxide hydrogel (Ni(OH)₂/rGO) has been synthesized. • The 3D hydrogel is porous with large surface area. • The 3D hydrogel can be directly used as electrode without binder. • Asymmetric supercapacitor of Ni(OH)₂/rGO.||rGO has been fabricated which showed high performance. Three-dimensional Ni(OH)₂/GO hydrogel has been prepared by a two-step route: formation of rGO hydrogel and depositing of Ni(OH)₂ nanoparticles inside it. Structure and composition of the as-prepared Ni(OH)₂/GO hydrogel were measured by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Raman spectroscopy. The 3D structure of graphene and the pseudo-capacitance of nickel hydroxide are found to be remarkably effective in enhancing the specific capacitance of the composite hydrogel, up to 532 F g⁻¹. Then, asymmetric supercapacitor was assembled by using the Ni(OH)₂/rGO hydrogel and rGO hydrogel as the two electrodes in KOH (6.0 M) electrolyte, and it exhibited a high performance with an energy density of 28.88 Wh kg⁻¹ and a power density of 5829.2 W kg⁻¹. The specific capacitance can be retained 90% of the initial value after 10000 charge/discharge cycles. The results indicate that Ni(OH)₂/rGO hydrogel could be a potential candidate as binder-free electrode for supercapacitors, especially asymmetric supercapacitors, which has a wide range of applications in the near future.