Junaid Ali Syed

High-Performance Flexible Solid-State Carbon Cloth Supercapacitors Based on Highly Processible N-Graphene Doped Polyacrylic Acid/Polyaniline Composites.

Improving the solubility of conductive polymers to facilitate processing usually decreases their conductivity, and they suffer from poor cycling stability due to swelling-shrinking during charging cycles. We circumvent these problems with a novel preparation method for nitrogen-doped graphene (NG) enhanced polyacrylic acid/polyaniline (NG-PAA/PANI) composites, ensuring excellent processibility for scalable production. The content of PANI is maximized under the constraint of still allowing defect-free coatings on filaments of carbon cloth (CC). The NG content is then adjusted to optimize specific capacitance. The optimal CC electrodes have 32 wt.% PANI and 1.3 wt.% NG, thus achieving a high capacitance of 521 F/g at 0.5 F/g. A symmetric supercapacitor made from 20 wt.% PANI CC electrodes has more than four times the capacitance (68 F/g at 1 A/g) of previously reported flexible capacitors based on PANI-carbon nanotube composites, and it retains the full capacitance under large bending angles. The capacitor exhibits high energy and power densities (5.8 Wh/kg at 1.1 kW/kg), a superior rate capability (still 81% of the 1 A/g capacitance at 10 A/g), and long-term electrochemical stability (83.2% retention after 2000 cycles).

Super-hydrophobic multilayer coatings with layer number tuned swapping in surface wettability and redox catalytic anti-corrosion application

The wetting characteristic of a metal surface can be controlled by employing different coating materials and external stimuli, however, layer number (n) modulated surface swapping between hydrophobicity and hydrophilicity in a multilayer structure to achieve prolonged anti-corrosion ability was not taken into consideration. In this study, we proposed a layer-by-layer (LbL) spin assembled polyaniline-silica composite/tetramethylsilane functionalized silica nanoparticles (PSC/TMS-SiO2) coating with the combined effect of super-hydrophobicity and enhanced anti-corrosion ability. Interestingly, the hierarchical integration of two coating materials with inherently different surface roughness and energy in a multilayer structure allows the wetting feature to swap from hydrophobic to hydrophilic state by modulating n with decreasing hydrophilicity. The samples with odd n (TMS-SiO2 surface) are hydrophobic while the samples with even n (PSC surface) exhibits the hydrophilic character. The TMS-SiO2 content was optimized to achieve super-hydrophobic coating with significantly high water contact angle (CA) 153° ± 2° and small sliding angle (SA) 6° ± 2°. Beside its self-cleaning behavior, the electro-active PSC/TMS-SiO2 coating also exhibits remarkably enhanced corrosion resistance against aggressive media. The corrosion resistance of the coating was remained stable even after 240 h of exposure, this enhancement is attributed to super-hydrophobicity and anodic shift in corrosion potential.

A naphthyl-imide-based epoxy resin: Cure kinetics and application in carbon fiber reinforced composites

A novel heat-resistant epoxy resin based on N, N’-bis(5-hydroxy-1-naphthyl) pyromellitic diimide was prepared and its cure kinetics with 4,4-diaminodiphenysulfone (DDS) was investigated by differential scanning calorimetry (DSC) under non-isothermal and isothermal conditions. Under non-isothermal condition, the effective activation energy calculated from the advanced isoconversional method (AICM) varies with curing conversion, which is different from that obtained by Kissinger’s model. This should be attributed to the formation of highly crosslinked network later in the curing stage. The isothermal curing process at different temperatures could be well fitted by Kamal’s model in the initial curing stage but deviates subsequently. The deviation is corrected by introducing a diffusion factor in Kamal’s model. In addition, the naphthyl-imide epoxy resin is used to prepare carbon fiber reinforced composites and their applications were explored. The composites exhibit a high glass transition temperature, low moisture absorption, sufficient flame retardance and especially very low tensile strength loss at high temperature.

Asymmetric hybrid capacitors based on novel bearded carbon fiber cloth–pinhole polyaniline electrodes with excellent energy density

It is well known that electronic conductivity and kinetics of ion diffusion determine the large current discharge capacity of electrode materials. Hence, we envisioned construction of an integrated smart structure for which fast ion and electron transfer were guaranteed. This paper presents a novel bearded carbon fiber cloth (CFC) decorated with pinhole polyaniline (PANI) formed by electro-polymerization to achieve excellent electrochemical properties. The pinhole nanostructure of redox-active PANI exposed a high electrolytic-attainable surface area and the bearded CFC would serve as an excellent 3D conductive skeleton, which would supply a direct channel for electron transport. As the current density increased from 1.3 to 16.5 A g−1, the PANI/CFC still maintained a higher specific capacitance; the specific capacitance decreased from 808 F g−1 to 749 F g−1, only ∼7% loss of capacitance, which implies that the PANI/CFC electrodes have excellent rate capability. The optimal composite electrodes achieved a high area-normalized capacitance of 3.3 F cm−2. The asymmetric hybrid capacitors based on optimal composite electrodes were tested in a cell voltage region of 0–1.6 V and exhibited high energy densities with values of 36.35 Wh kg−1 and power densities of 422.15 W kg−1. The results showed that the combination of porous PANI with bearded CFC significantly increased the capacitance of the electrode and enhanced its electrochemical performance.

Highly processible and electrochemically active graphene-doped polyacrylic acid/polyaniline allowing the preparation of defect-free thin films for solid-state supercapacitors

In the present work, we report the preparation of graphene (G) doped polyacrylic acid/polyaniline (G-PAA/PANI) composites with excellent processibility for ensuring ultrathin, defect-free and highly flexible films, as well as high electrochemical performance. The weight content of PANI is maximized under the constraint of still allowing defect-free films, and the G content is optimized. Interestingly, we combine two steps that both, if taken in isolation as a strategy, worsen the solubility. The PANI and G contents are optimized to be 20 wt% and 1.3 wt%, respectively. The optimal G-PAA/PANI composite film has a gravimetric capacitance of 399 F g−1 at 10 mV s−1, which is more than twice that of pure PANI nanoparticles. Considering the film thickness of only 50 μm, its specific areal and volumetric capacitances are as high as 1.20 F cm−2 and 240 F cm−3. The film still has a gravimetric capacitance of 342 F g−1 at a high scan rate of 100 mV s−1 (86% of that at 10 mV s−1), which promises great potential for applications needing a rapid charge/discharge. An assembled all-solid-state supercapacitor using two such flexible G-PAA/PANI films provides 93 F g−1; an eighteen-fold improvement over that of a previously reported similar device. The capacitor also exhibits excellent electrochemical stability under different bending angles.