In situ transmogrification of nanoarchitectured Fe-MOFs decorated porous carbon nanofibers into efficient positrode for asymmetric supercapacitor application

Abstract

In situ transmogrification is one of the most promising ways to synthesize positrode materials using a chemical treatment approach under optimal conditions for supercapacitor applications. The nickel salt concentration plays a vital role in the complete transmogrification of Fe-MOFs@PCNFs into Ni-Fe-OH@PCNFs (positrode). Herein, we successfully transform the tetragonal Fe-MOFs@PCNFs structure into pellet-like Ni-Fe-OH@PCNFs via in situ transmogrification under fixed temperature and pressure. The obtained Ni-Fe-OH@PCNFs-1 possess a unique porous architecture with a large surface area (74.3 m2g−1), which facilitates ion relocation and electron movement within the materials during charging/discharging. Owing to the limited surface area of electroactive materials, the double transition metal hydroxides (Ni-Fe-OH@PCNFs-D) synthesized directly (i.e., by employing two metal salts instantaneously) suffer a rapid decline in capacitance during cyclic stability test. The Ni-Fe-OH@PCNFs-1 electrode generated from Fe-MOFs@PCNFs has excellent cycling stability with ~86.7% capacitance retention and ~ 91.3% coulombic efficiency after 10,000 cycles at 10 A g−1. It also exhibits a remarkable specific capacitance of 1528 F g−1 at 1 A g−1. Additionally, the asymmetric supercapacitors (Ni-Fe-OH@PCNFs-1//Fe2O3/NPC@PCNFs) exhibit a maximum energy density of 44.3 Wh kg−1 at a power density of 907 W kg−1). The results of this work suggest the possibility of using MOF-derived nanoporous electrode materials and additional transition metal hydroxides for supercapacitors.