Effect of cation substitution on the pseudocapacitive performance of spinel cobaltite MCo₂O₄ (M = Mn, Ni, Cu, and Co)

Cation substitution is a promising strategy for modulating the structural properties and optimizing the electrochemical performance of spinel cobalt oxide (Co₃O₄); however, the underlying mechanism of this action induced by different cation substitutions has not yet been clearly addressed. Herein, a systematic investigation is performed to elucidate the effect of cation substitution on the pseudocapacitive performance of spinel cobaltite (MCo₂O₄; M = Mn, Ni, Cu, and Co) mesoporous nanowires grown on nickel foam (NF). Theoretical and experimental analyses reveal that the substitution of Co by transition metals (i.e., Mn, Ni, and Cu) in the lattice of Co₃O₄ can simultaneously improve charge transfer and ion diffusion, thereby exhibiting enhanced electrochemical properties. Herein, as a representative example, MnCo₂O₄ achieves a high specific capacitance of 2146 F g^-1 at a current density of 1 A g^-1, while 92.1% of its initial capacitance is retained after 5000 cycles. An asymmetric supercapacitor with MnCo₂O₄ as the positive material and activated carbon (AC) as the negative material delivers a high energy density of 56.1 W h kg^-1 at a power density of 800 W kg^-1, and a favorable energy density of 29.3 W h kg^-1 at a power density as high as 8000 W kg^-1.