Huaihao Zhang

Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol)-assisted synthesis of graphene/polyaniline composites as high-performance supercapacitor electrodes

Graphene/polyaniline (GN/PANI) composites were synthesized by in situ polymerization with the assistance of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123). We show that the addition of P123 enhanced the wettability of GN and hence improved its uniformity in aqueous solution and the dispersity of PANI loaded on GN surface. Structural and morphological analyses indicate that GN has been successfully coated with PANI. P123 was mainly acted as soft temples to improve the control of morphology and increase composites effective specific surface area. Furthermore, it can improve composites capacitive performance as evidenced by electrochemical tests. When the molar ratio of P123 to ANI is 0.0108, the composites exhibit the best performance, in terms of the rate capability, the lowest equivalent series resistance (0.31xa0Ω) and the charge-transfer resistance (1.46xa0Ω). Additionally, it achieves a capacity retention of 91.8xa0% after 1000 charge–discharge cycles at the current density of 500xa0mAxa0g−1, an increase of 82xa0% over the composites without P123. A mechanism for interactions of P123, GN, and PANI is proposed in this work.

Effects of sodium dodecyl sulfate on the electrochemical behavior of supercapacitor electrode MnO2

Supercapacitor electrode material MnO2 was prepared by liquid co-precipitation with different concentration of anionic surfactant sodium dodecyl sulfate (SDS). As evidenced by X-ray diffraction, the obtained MnO2 are all typical amorphous α-MnO2 with poor crystallinity. Scanning electron microscopy reveals that the dispersity of MnO2 initially get better and then worse with the increase of SDS, and the particle sizes first become smaller then larger as well. It is worthwhile noting that the morphology of MnO2 tested by transmission electron microscopy undergoes a changeable process: fibrous, pine needle like, cotton like, round bubble like, flocculent, and nervous tissue like as SDS increases. Through cyclic voltammetry and galvanostatic charge/discharge tests, SDS addition amount 0.2xa0g (0.017xa0molxa0L−1) is found to be the optimal effect value, and the as-prepared Mn-0.2 obtains the highest specific capacitance (Csp) of 154.5xa0Fxa0g−1 at a current density of 500xa0mAxa0g−1. Compared with the sample Mn-0 synthesized without SDS, the Csp increases by about 50xa0% (±5xa0%), which can be attributed to its largest Brunauer–Emmett–Teller–specific surface area of 255.9xa0m2xa0g−1, best particle dispersity, and smallest particle size of approximately 50–80xa0nm. Meanwhile, the rate capability and cycle stability of Mn-0.2 also improves obviously, and the equivalent series resistance decreases a lot, only 0.120xa0Ω.

One-step synthesis of nickel cobalt sulphides particles: tuning the composition for high performance supercapacitors

NiS2–CoS2 composites with different Ni and Co molar ratios for supercapacitors (SCs) were synthesized by one-step hydrothermal co-deposition method using cheap Na2S2O3·5H2O as sulfur source. With the increase of Ni content, the composites particle size increases gradually and the hollow sphere structure becomes more obvious. The electrochemical measurements demonstrate that these composites possess a high specific capacitance (Cm) performance, good rate capability and long cycle stability. To be specific, the Cm of Ni/Co/S-1 composite is the largest, up to 954.3 F g−1 at 1 A g−1, and as high as 309.5 F g−1 even at large current density of 20 A g−1. Furthermore, the Ni/Co/S-1 maintains 99.9% of its initial Cm after 1000 cycles at 5 A g−1. Moreover, the asymmetric supercapacitors with Ni/Co/S-1 as positive electrode and active carbon as negative electrode are of prominent energy density of 29.3 W h−1 kg−1 at the power density of 0.7 kW kg−1, and superior cycling stability of 99.1% initial value retention after 1000 cycles.

Effect of sulfate in mineral precursor on capacitance behavior of prepared activated carbon

Analog sulfur-containing precursors (ASCPs) were employed to prepare activated carbon (AC) for supercapacitor by potassium hydroxide (KOH) chemical activation. The influence of sulfate, K2SO4, FeSO4, and CaSO4 on pore structure of resultant AC and its capacitance performance was investigated extensively. The results indicate that FeSO4 and K2SO4 in ASCPs can be involved deeply in activation reaction. K2SO4 can play a synergistic activation role in increasing porosity and capacitance performance, while FeSO4 can react with and consume a certain amount of KOH, thus decreasing the performance of AC. Compared with K2SO4 and FeSO4, CaSO4 in ASCPs has low reactivity; namely, only a small part of CaSO4 was involved in activation reaction, while most of it was transformed into CaCO3 residued in AC during washing process. Due to coexistence of CaCO3 with AC, the porosity and capacitance performance of AC were decreased obviously. Furthermore, it is noteworthy that in comparison with K+ and Ca2+, Fe2+ in ASCPs is more beneficial for transformation of inorganic sulfate into organic thioether in AC.

Sodium dodecylbenzene sulfonate-assisted synthesis of a carbon-cloth-based polyaniline flexible material for supercapacitors

Carbon-cloth-based polyaniline flexible electrode materials were fabricated by a simple chemical oxidation method with the assistance of sodium dodecylbenzene sulfonate (SDBS) at different concentrations, where SDBS acts as a surfactant and dopant to control the morphology, structure and capacitance performance of the electrode material. TGA, BET, XRD, FT-IR, UV-vis and SEM analyses showed that a suitable amount of SDBS can enhance the interchain spacing of the polyaniline and the regularity of its main-chain structure as well as helping to vary its morphology (e.g., networks, spherical, or rod-like structures) on carbon cloth. More importantly, SDBS facilitated the bonding between polyaniline and carbon cloth, leading to the formation of good three-dimensional networks and spherical and rod-like structures, respectively. The insertion/de-insertion of electrolyte ions was easier due to the unique morphology and structure of materials prepared with SDBS, and the utilization ratio of polyaniline was also higher. Cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy tests revealed that of the three composites studied (PANI/CC-0,1,2, depending on the SDBS amount), PANI/CC-1 achieved the optimal capacitance performance, i.e., a high specific capacitance (up to 537 F g−1 at the current density of 0.5 A g−1, which is 31.9% higher than that without SDBS), high capacity retention (83.4% after 1000 charge–discharge cycles, compared to 46.9% for PANI/CC-0), and high energy density (74.5 W h kg−1 at a power density of 0.25 kW kg−1) as well as the best rate capability and the lowest impedance. In summary, the addition of a suitable amount of SDBS has a positive effect on improving the capacitance performance of carbon-cloth-based polyaniline electrodes.