Tailoring d-p Orbital Hybridization to Decipher the Essential Effects of Heteroatom Substitution on Redox Kinetics

The heteroatom substitution is considered as a promising strategy for boosting the redox kinetics of transition metal compounds in hybrid supercapacitors (HSCs) although the dissimilar metal identification and essential mechanism that dominate the kinetics remain unclear. It is presented that d-p orbital hybridization between the metal and electrolyte ions can be utilized as a descriptor for understanding the redox kinetics. Herein, a series of Co, Fe and Cu heteroatoms are respectively introduced into Ni₃Se₄ cathodes, among them, only the moderate Co-substituted Ni₃Se₄ can hold the optimal d-p orbital hybridization resulted from the formed more unoccupied antibonding states π*. It inevitably enhances the interfacial charge transfer and ensures the balanced OH^- adsorption-desorption to accelerate the redox kinetics validated by the lowest reaction barrier (0.59 eV, matching well with the theoretical calculations). Coupling with the lower OH^- diffusion energy barrier, the prepared cathode delivers ultrahigh rate capability (~68.7 % capacity retention even the current density increases by 200 times), and an assembled HSC also presents high energy/power density. This work establishes the principles for determining heteroatoms and deciphers the underlying effects of the heteroatom substitution on improving redox kinetics and the rate performance of battery-type electrodes from a novel perspective of orbital-scale manipulation.