Interfacial synthesis of micro-cuboid Ni0.55Co0.45C2O4 solid solution with enhanced electrochemical performance for hybrid supercapacitors.

Efficient charge and energy storage relies essentially on the development of innovative electrode materials with enhanced electrochemical kinetics. Herein, Ni0.55Co0.45C2O4 solid solution was successfully synthesized by a liquid-liquid interfacial reaction. The observation of the morphologies of Ni0.55Co0.45C2O4 depicts a peculiar micro-cuboid structure composed of nanoparticles in the size range of 13 to 23 nm, benefiting the increase in the contribution of surface-controlled reactions to charge storage processes. The results from X-ray diffraction and thermogravimetric analysis demonstrate the similarity of the crystal structure and thermal decomposition behavior between Ni0.55Co0.45C2O4 and CoC2O4, and indicate that the CoC2O4 lattice plays a role as the fundamental framework in the solid solution instead of NiC2O4. The electrochemical measurements show that Ni0.55Co0.45C2O4 achieves a higher specific capacity of 562 C g-1 at a current density of 1 A g-1 than its counterpart NiC2O4/CoC2O4 hybrids, due to this the alternative arrangement of nickel and cobalt species in the solid solution expedites the diffusion process of active ions during the electrochemical reaction. Depending on the enhancement of the electrochemical stability in the solid solution, Ni0.55Co0.45C2O4 electrodes retain 87.4% of the initial capacity after 4000 cycles. The assembled Ni0.55Co0.45C2O4//AC hybrid supercapacitor attains an energy density of 38.5 W h kg-1 at a power density of 799 W kg-1 with a long cycling life (80% of the initial capacitance after 10 000 cycles). The excellent electrochemical performance suggests that Ni0.55Co0.45C2O4 is a promising candidate electrode material for supercapacitors.