Electrochemical analysis of ascorbic acid and uric acid on defect-engineered carbon nanotube networks with increased exposure of graphitic edge planes

Sulfur-doped carbon nanotubes with hierarchical micro/mesopores for high performance pseudocapacitive supercapacitors

Increasing the specific surface area and the amount of doping heteroatoms is an effective means to improve the electrochemical properties of carbon nanotubes (CNTs). The usual activation method makes it difficult for the retention of the heteroatoms while enlarging the specific surface area, and it can be found from literatures that specific surface area and S-content of carbon-based electrode materials are mutually exclusive. Here, CNTs with high specific surface area and sulfur content are constructed by simple activation of sulfonated polymer nanotubes with KHCO₃, and the excellent electrochemical performance can be explained by the following points: first, KHCO₃can be decomposed into K₂CO₃, CO₂and H₂O during the activation process. The synergistic action of physical activation (CO₂and H₂O) and chemical activation (K₂CO₃) equips the electrode material with high specific surface area of 1840 m²g^-1and hierarchical micro/mesopores, which is beneficial to its double-layer capacitance. Second, compared with reported porous CNTs prepared by chemical activation (KOH) or physical activation (CO₂or H₂O), the mild activator KHCO₃makes the sulfur content at a high level of 4.6 at%, which is very advantageous for high pseudocapacitance performance.

High performance of filter capacitor based on nitrogen-doped carbon nanotube supercapacitor

The high-performance filter capacitor is a hot research topic in the field of filter circuits for flexible and wearable devices, whereas traditional aluminum electrolytic capacitors still experience widespread problems in terms of large error factors and poor stability. To avoid these disadvantages, in this work, we have developed a liquid dual-layer supercapacitor (SC). When it is employed as the filter capacitor in a filter circuit, any waveform signal can be transformed into a linear signal. The maximum fluctuation of the output signal is less than 16 mV; the SC also demonstrates excellent filtering stability in a frequency range of 1 ∼ 100 000 Hz, as well as an amplitude window of 0 ∼ 10 V. In this framework, our filter SC demonstrates unparalleled processing properties, and can greatly improve the stability and extend the lifetime of the entire electronic circuit. The fact that the requirements of high-end electronic products can be fulfilled due to the contribution of this filter SC are particularly significant.

Self-template/activation nitrogen-doped porous carbon materials derived from lignosulfonate-based ionic liquids for high performance supercapacitors

A simple ion exchange reaction of sodium lignosulfonate (SLS) and 1-allyl-3-methyl imidazolium chloride ([Amim]Cl) produced a new polymeric ionic liquid [Amim]LS and NaCl, and the mixture was successfully used as a precursor to prepare a nitrogen-doped porous carbon material via direct carbonization without any additional activation agent or template. It was believed that the in situ produced NaCl during the precursor synthesis process acted as the self-template and in self-activation. The introduction of imidazolium ionic liquid into the precursor raised the nitrogen content of the obtained carbon material up to 4.68% for a high yield of [Amim]LS-700 carbon material up to 34.6%. The effect of carbonization temperature on the structures and electrochemical properties of the prepared carbon were also studied systematically. It was found that the carbon material exhibits a superior gravimetric capacitance up to 230 F g-1 (0.1 A g-1) at the carbonization temperature of 700 °C, a good energy density of 7.99 W h kg-1 at the power density of 25 W Kg-1, and an excellent cycling stability of 90.3% after 20 000 cycles. This work provides a new path for the value-added utilization of biomass coupled with the field of electrochemical energy storage.

Facile preparation of porous sheet-sheet hierarchical nanostructure NiO/Ni-Co-Mn-O x with enhanced specific capacity and cycling stability for high performance supercapacitors

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination. The thermodynamic behavior was observed by TG/DTA. The chemical structure and composition, phase structure and microstructures were tested by XPS, XRD, FE-SEM and TEM. The electrochemical performance was measured by CV, GCD and EIS. The mechanism for formation and enhancing electrochemical performance is also discussed. Firstly, the precursors such as NiOOH, CoOOH and MnOOH grow on nickel foam substrates from a homogeneous mixed solution via chemical bath deposition. Thereafter, these precursors are calcined and decomposed into NiO, Co₃O₄ and MnO₂ respectively under different temperatures in a muffle furnace. Notably, NiO/Ni–Co–Mn–O_x on nickel foam substrates reveals a high specific capacity with 1023.50 C g⁻¹ at 1 A g⁻¹ and an excellent capacitance retention with 103.94% at 5 A g⁻¹ after 3000 cycles in 2 M KOH, its outstanding electrochemical performance and cycling stability are mainly attributed to a porous sheet–sheet hierarchical nanostructure and synergistic effects of pseudo-capacitive materials and excellent redox reversibility. Therefore, this research offers a facile synthesis route to transition metal oxides for high performance supercapacitors.

NiO, Ni–Co–Mn–O_x and NiO/Ni–Co–Mn–O_x on nickel foam substrates were prepared via a chemical bath deposition–calcination.

Construction and application of a nonenzymatic ascorbic acid sensor based on a NiO1.0/polyaniline3.0 hybrid

The schematic diagram for the fabrication process of NiO/PANI.

Molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon: fabrication, characterization and electrochemical detection of uric acid

An electrochemical sensor is described for determination of uric acid (UA). Carbon-enwrapped nickel nanoparticles (Ni@BC) were coated with polydopamine (PDA) that was molecularly imprinted with UA. The biomass carbon (BC) was synthesized by one-step solid-state pyrolysis from leaves of Firmiana platanifolia. The imprinted polymer was obtained by electrodeposition of DA as the monomer. The amount of monomer, the scan cycles, pH value and adsorption time were optimized. Furthermore, the selectivity of the MIP for UA on a glassy carbon electrode (GCE) was evaluated by selectivity tests. The differential pulse voltammetric responses to UA with and without interferents were consistent. The modified GCE has a linear response in the 0.01-30 μM UA concentration range, and the limit of detection is 8 nM. The MIP electrode was applied to the analysis of UA in urine for which the initial concentrations were determined by the phosphotungstic acid kit. Recoveries ranged from 91.3 to 113.4%, with relative standard deviations between 1.3 and 9.7% (n = 3). Graphical abstract Schematic presentation of electrochemical detection of uric acid by molecularly imprinted polydopamine modified with nickel nanoparticles wrapped with carbon (Ni@BC-MIP).