Using a sequential synthesis approach to fabricate (Ni,Co)Se₂ electrodes for high-performance supercapacitors

The synthesis of bimetallic selenides, derived from bimetallic oxide precursors, has garnered considerable attention for their potential in supercapacitor applications. However, the challenge of promoting their selenization degree from bimetallic oxide precursors to optimize electrochemical performance remains a significant hurdle. In this work, (Ni,Co)Se₂ electrode materials with a rose-petal-like morphology have been fabricated through a sequential synthesis method from a NiCo-LDH precursor and their supercapacitive performance has been systematically evaluated. The results show that the as-synthesized (Ni,Co)Se₂ delivers a specific capacitance of 1565 F g^-1 at 1 A g^-1, which is better than those of other nickel-cobalt bimetallic selenides. Additionally, the as-synthesized (Ni,Co)Se₂ exhibits excellent rate capability, retaining 97.7% capacitance at 10 A g^-1. Additionally, at a current density of 20 A g^-1, (Ni,Co)Se₂ retained 87.8% of its capacity after 5000 cycles. Furthermore, the supercapacitor constructed from (Ni,Co)Se₂ and activated carbon exhibits a remarkable energy density of 44.44 Wh kg^-1 at a power density of 867.78 W kg^-1. This superior electrochemical performance benefits from the sequential synthesis strategy that not only significantly enhances the product's selenization degree, thereby boosting its electrochemical properties, but also maintains the inherent rose-petal-like morphology, ensuring optimal mass transport efficiency. Furthermore, a possible explanation for the improvement of the selenization degree is also proposed.