Boron-doped diamond decorated with metal-organic framework-derived compounds for high-voltage aqueous asymmetric supercapacitors

Conductive diamond has been recognized as a promising electrode material for supercapacitors due to its excellent stability and broad electrochemical potential window. To enhance the performance of diamond-based supercapacitors, this study focuses on two key strategies: incorporating redox-active species on the electrodes and/or in the electrolytes to increase the capacitance, and constructing asymmetric supercapacitors to expand the operating voltage range. In this context, pseudocapacitive Co3O4@boron doped diamond (BDD) and Bi-Bi2O3@BDD were synthesized using metal-organic framework (MOF) decorated BDD of Co-MOF@BDD and Bi-MOF@BDD as precursor materials, respectively. An aqueous asymmetric supercapacitor was then assembled using a pseudocapacitive electrode/redox electrolyte system of Co3O4@BDD | 3.0 M KOH+0.05 M K3Fe(CN)6/ K4Fe(CN)6 as the positive compartment, and Bi-Bi2O3@BDD | 3.0 M KOH as the negative compartment. The resulting device demonstrated a wide operating voltage of 1.7 V, a maximal energy density of 10.0 Wh L- 1 at a power density of 333.2 W L- 1. The remarkable performance can be attributed to the Faradaic redox reactions involving [Fe(CN)6]3-/4-, Co3+/Co4+, Bi0/Bi2+/Bi3+ in the electrode materials and electrolytes. This work presents a novel way for fabricating aqueous supercapacitors with high voltage, high energy and power densities, offering significant potential for various energy storage applications.