Unveiling composition/crystal structure-dependent electrochemical behaviors via experiments and first-principles calculations: rock-salt NiCoO2 vs. spinel Ni1.5Co1.5O4

Ni–Co binary oxides hold enormous promise in hybrid supercapacitors as cathodes thanks to remarkable electrochemical behaviors. However, current research efforts are always focused on morphological and compositional design towards enhanced electrochemical properties, and no further investigations are in-depth conducted to elucidate intrinsic reasons for their distinct electrochemical properties. Herein, the rock-salt NiCoO 2 (r-NCO) and spinel Ni 1.5 Co 1.5 O 4 (s-NCO) with similar acquired parameters in terms of morphology, surface area, pore structure and Ni/Co molar ratio are purposefully constructed as the ‘models’ to investigate composition/crystal structure induced differences in charge-storage capabilities via first-principles calculations along with electrochemical experiments. Remarkably, both the r-NCO and s-NCO are featured with half-metallic electronic conductivity. Projected density of state confirms that the d -orbitals of Co atoms in r-NCO contribute much more electronic states than that of s-NCO at the Fermi level, making the r-NCO more easily gain/loss electrons for efficient redox reactions. The investigations of hydroxyls adsorption behavior on the surfaces of Ni–Co oxides reveal the lower adsorption energy and more charge transfer thus high electrochemical performance of the r-NCO. These congenital genic merits make the r-NCO deliver even larger specific capacitance of ~923.2 F g −1 than the s-NCO (~299.2 F g −1 ) at 2 A g −1 . Intrinsic composition/crystal structure-dependent electrochemical behaviors of rock-salt and spinel Ni–Co binary oxides are unveiled via comprehensive experiments and first-principles calculations. • Intrinsic difference in charge-storage capabilities of rock-salt NiCoO 2 and spinel Ni 1.5 Co 1.5 O 4 is figured out via fist-principles calculations and electrochemical evaluation. • The rock-salt NiCoO 2 owns better redox-reactivity and can provide more charge transfer for the redox reactions. • The rock-salt NiCoO 2 exhibits favorable hydroxyl adsorption capability for rapid electrochemical reactions. • The congenital composition/structure merits render the NiCoO 2 with even higher rate electrochemical properties.