Mn3+ partially substituting the Ni3+ of NiCo2O4 enhance the charge transfer kinetics and reaction activity for hybrid supercapacitor

Rational design of positrode material with kinetics matching with negatrode is essential to achieve favorable electrochemical performance for hybrid supercapacitor. In this paper, we prepare a series of Mn substituted NiCo2O4 (MNCO) nanowires arrays with different substitution ratios via a hydrothermal-annealing strategy. We find from first-principles calculation that Mn3+ ions preferentially substitute Ni3+ ions at the octahedral sites enables Mn3+ act as an n-type dopant and induce a higher electron density of states near the Fermi level, especially for MNCO with Mn/Ni molar ratios of 2:6. In addition, the Mn substitution can increase the energy overlap between the eg, β band of Ni and Mn and d7 configuration of tetrahedral sites Co2+ and enhance the charge transfer ability from Ni to O ions, which also plays an important role in improving electrochemical activities. The electrochemical experiment results show that the optimal MNCO electrode exhibit a large specific capacity of 200.3 mAh g−1 (1441.8 F g−1) and high rate capability (62.8%). The enhanced electrochemical activity and electrochemical reaction kinetics of positrode material is crucial for high power and energy density hybrid supercapacitors.