Synergistic incorporation of Fe and Co into nickel boride/NiCoHydroxide nanosheets to tune voltage plateau and charge storage in supercapacitors

For designing efficient redox metal-assisted electrodes, an understanding of the inclusive role of metal ions and their influence on the electrochemical window is a prerequisite. Herein, a trimetallic boride (NiCoFe-B)/NiCoHydroxide nanosheet is employed as an integrated electrode explicitly discussing the roles of all the metal ions through electrochemical and work function studies. The UPS study and theoretical calculations highlights the reduction of work function after insertion of Co in Ni-B framework, which increases the number of active sites and enhance charge transfer kinetics, whereas Fe insertion results in an extended electrochemical window (1.35 V). In an integrated electrode, NiCoFe-B/NiCoHydroxide (NCFB), the difference in work function of Fe-B and NiCo-B results in generation of an electric field near the interface that acts as a potential barrier, further countering the external electric field and resulting in an extended potential window. Notably, a symmetric cell with the extended potential of NCFB delivers a high energy density of 45.05 Wh kg−1 at 585.52 W kg−1 and restores 86.6% of initial capacitance over 10k cycles with excellent energy delivering ability (relaxation time constant of 2.20 s). This work provides an insight into tuning the voltage plateau by varying metal ions of different work functions.