Protonated Ni-MOF as an Advanced Electrode material for High-Performance Hybrid Supercapacitor

Abstract Metal-organic frameworks (MOFs) with high conductivity have proven to be an exciting electrode material for energy storage devices. However, most of the MOFs exhibit a low electrical conductivity, which limits their use in supercapacitors. To overcome this issue herein, a simple acid treatment method was adopted to obtain nanoflower-like Ni-MOF to improve the electrical conductivity without disrupting its framework. The sample treated with a solution of H2SO4 at optimal pH 2 (Ni-MOF-2), exhibited improved surface texture with excellent electrochemical characteristics. The Ni-MOF-2 sample displayed a high specific capacity (Cs) of 467 C g-1 at 1 A g-1 in aqueous 6 M KOH electrolyte than that of other samples. This is mainly due to enhanced proton conduction in Ni-MOF-2 after acid treatment. In addition, a hybrid supercapacitor (HSC) device was fabricated using battery-type Ni-MOF-2 as a positive electrode and heteroatom enriched activated carbon (O, N, S@AC) as a negative electrode. The fabricated HSC exhibited a maximum specific capacity (Cs) of 38 mAh g-1 with high specific energy (Es) 39 Wh kg-1 and maximum specific power (Ps) of 11079 W kg-1. Moreover, the HSC displayed excellent cyclic stability of ∼87% for 10000 continuous galvanostatic charge/discharge (GCD) cycles.