Quasi-solid-state hybrid supercapacitors assembled by Ni-Co-P@C/Ni-B nanoarrays and porous carbon nanofibers with N-doped C nanocages

In recent times, a lot of research effort has been performed to develop hybrid supercapacitors (HSCs) because of their ability to produce high energy density as well as superb power density. The key issue for realizing highperformance HSCs is to minimize the kinetic mismatch between rapid capacitor-type anode and sluggish battery-type cathode. Optimizing the interface, morphology and microstructure of the electrode material is a favorable approach to surmount kinetic imbalance. Herein, a core-shell nanoarrays of ultrathin carbon layercoated crystalline Ni-Co-phosphide (Ni-Co-P@C) and amorphous Ni-boride (Ni-B) is fabricated on a nickel foam substrate as a positive electrode material (Ni-Co-P@C/Ni-B). Theoretical analyses validate the best metallic characteristic and most stable OH* absorption energy for Ni-Co-P@C/Ni-B, which enhance its charge storage performance than analogous Ni-Co-P and Ni-Co-P/Ni-B. The porous nitrogen (N)-doped carbon (C) nanofibers consisting of tightly embedded metal-organic framework (ZIF-8)-derived interconnected N-C nanocages (HP-NCFs) showed excellent charge storage kinetics as a negative electrode. The battery-type Ni-Co-P@C/Ni-B electrode revealed a specific capacity of 306.2 mA h g-1 at 3 mA cm-2, while highly porous capacitive HP-N-CFs electrode showed the highest capacity of 56 mA h g-1 at 2.5 mA cm-2. In addition, the assembled quasisolid-state (Ni-Co-P@C/Ni-B//HP-N-CFs) HSCs exhibited the highest energy density of 68.3 W h kg- 1 at a power density of 472 W kg- 1 with a superb rate capability (68% at 50 mA cm-2) and decent cyclic durability (90% retention over 10,000 cycles).