Potentiostatic deposition of CoNi₂Se₄ nanostructures on nickel foam as efficient battery-type electrodes for supercapacitors

Bimetallic CoNi₂Se₄ nanostructures on nickel-foam substrates were fabricated by a potentiostatic deposition method by adjusting the deposition solution p^H, and used as electrode materials in battery-type supercapacitors. The electrodeposition solution p^H had an important role in the fabrication of the desirable CoNi₂Se₄ nanostructures. At a deposition solution p^H of 2.0, the synthesized product contained CoNi₂Se₄ nanoparticles. In contrast, a partially converted flake-like morphology was obtained at p^H = 2.5. The appropriate flake-like morphology was formed by increasing the deposition solution p^H to 3.0. The robust flake-like structure facilitated the electron transport during redox reactions, providing an excellent electrochemical behavior in terms of specific capacity, rate capability, and cyclic stability. A battery-type supercapacitor based on the flake-like CoNi₂Se₄ structure exhibited a maximum specific capacity of 632.5 C g⁻¹ at a current density of 1 A g⁻¹ and excellent rate performance (capacity retention of 91%) in the range of 1 to 40 A g⁻¹. The material retained 83.31% of its initial capacity after 3000 cycles of charging/discharging at a current density of 40 A g⁻¹, which suggests a high long-term cycling stability. The excellent electrochemical performance of the CoNi₂Se₄ electrode material make it very promising for application in supercapacitors.