Iron Sulfide Microspheres Supported on Cellulose-Carbon Nanotube Conductive Flexible Film as an Electrode Material for Aqueous-Based Symmetric Supercapacitors with High Voltage.

Nanostructured iron disulfide (FeS2) was uniformly deposited on regenerated cellulose (RC) and oxidized carbon nanotube (CNT)-based composite films using a simple chemical bath deposition method to form RC/CNT/FeS2 composite films. The RC/CNT composite film served as an ideal substrate for the homogeneous deposition of FeS2 microspheres due to its unique porous architecture, large specific surface area, and high conductivity. Polypyrrole (PPy), a conductive polymer, was coated on the RC/CNT/FeS2 composite to improve its conductivity and cycling stability. Due to the synergistic effect of FeS2 with high redox activity and PPy with high stability and conductivity, the RC/CNT/FeS2/PPy composite electrode exhibited excellent electrochemical performance. The RC/CNT/0.3FeS2/PPy-60 composite electrode tested with Na2SO4 aqueous electrolyte could achieve an excellent areal capacitance of 6543.8 mF cm-2 at a current density of 1 mA cm-2. The electrode retained 91.1% of its original capacitance after 10,000 charge/discharge cycles. Scanning electron microscopy (SEM) images showed that the ion transfer channels with a pore diameter of 5-30 µm were formed in the RC/CNT/0.3FeS2/PPy-60 film after a 10,000 cycle test. A symmetrical supercapacitor device composed of two identical pieces of RC/CNT/0.3FeS2/PPy-60 composite electrodes provided a high areal capacitance of 1280 mF cm-2, a maximum energy density of 329 µWh cm-2, a maximum power density of 24.9 mW cm-2, and 86.2% of capacitance retention after 10,000 cycles at 40 mA cm-2 when tested at a wide voltage window of 1.4 V. These results demonstrate the greatest potential of RC/CNT/FeS2/PPy composite electrodes for the fabrication of high-performance symmetric supercapacitors with high operating voltages.

Polypyrrole/Carbon Nanotube Freestanding Electrode with Excellent Electrochemical Properties for High-Performance All-Solid-State Supercapacitors.

In this study, a facile and environmentally friendly method was used to prepare a freestanding supercapacitor electrode displaying excellent areal capacitance and good cycle life performance. First, we prepared polypyrrole nanoparticles (PPyNP) through a simple in situ chemical polymerization using the plant-derived material curcumin as a bioavailable template. A PPyNP/f-CNT freestanding composite electrode of high mass loading (ca. 14 mg cm-2) was prepared after blending the mixtures of the prepared PPyNP and functionalized CNTs (f-CNTs). The performance of the as-prepared material as a supercapacitor electrode was evaluated in a three-electrode setup using aqueous 1 M H2SO4 as the electrolyte. The PPyNP/f-CNT freestanding composite electrode exhibited a high areal capacitance of 4585 mF cm-2 and a corresponding volumetric capacitance of 176.35 F cm-3 at a current density of 2 mA cm-2. A symmetric all-solid-state supercapacitor assembled using two identical pieces of PPyNP/f-CNT composite electrodes exhibited maximum areal energy and power density of 129.24 µW h cm-2 and 12.5 mW cm-2, respectively. Besides, this supercapacitor device exhibited good cycle life performance, with 79.03% capacitance retention after 10,000 charge/discharge cycles. These results suggest practical applications for these PPyNP/f-CNT freestanding composite electrode-based symmetric all-solid-state supercapacitors.