Transition metal oxides are nowadays one of the most important materials in the manufacture of capacitive electrodes. The most important problems with these materials for applied energy storage ...devices are low specific energy and poor electrical conductivity. In this research nickel ferrite nanoparticles (NiFe2O4) and also hybrid of NiFe2O4/rGO are synthesized by hydrothermal method and characterized by XRD, Raman, and XPS analysis. The amount of porosity and specific surface area is studied by BET analysis as and surface morphology is studied by SEM and TEM. To investigate the effect of adding rGO to NiFe2O4 nanoparticles, from a hybrid electrode superconducting electrochemical tests are performed, including CV, EIS, and charge-discharge. This electrode with a capacitance of 584.63 F/g and capacitance retention of 91% after 2000 consecutive cycles can be a tempting option for supercapacitor applications.
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•Synthesis of NiFe2O4/rGO by the hydrothermal method.•Electrochemical reactions occur during a diffusion-controlled process.•NiFe2O4/rGO shows a great capacitance retention of 91% after 2000 cycles.
Bipartite consensus of multiple fractional-order nonlinear systems with output constraints is assessed under signed graph. The agents’ model is completely unknown with high-order heterogeneous ...strict-feedback dynamics and external disturbances, which cover single- and double-integrator integer-order systems as special forms. To ensure the bipartite consensus task, a novel fully distributed controller is developed based on backstepping technique and neuro-adaptive update mechanism. A barrier Lyapunov function is introduced to limit the followers’ outputs within the preset bounds. Algebraic graph theory and Lyapunov fractional-order stability theorem are employed to deal with the analysis difficulties caused by the network of fractional-order dynamics. Sufficient conditions on bipartite consensus is established, and it is also shown that all the closed-loop error signals are uniformly ultimately bounded. The simulation results are carried out to demonstrate the effectiveness of the proposed approach.
A new sulfonated aromatic diamine monomer containing nitrogen heterocycles was synthesized and employed to prepare a novel sulfonated polyimide (SPI). To develop proton exchange membranes, new ...nanocomposite blend membranes consist of the prepared SPI and polybenzimidazole (PBI) were fabricated with incorporation of SrCe0.9Yb0.1O3-δ (SCYb) doped-perovskite nanoparticles with a solution-casting method. The goal of this work is to study the effect of SPI and SCYb doped-perovskite nanoparticles on the important parameters of the PBI membrane specially proton conductivity and fuel cell performance. The proton conductivity and phosphoric acid doping level of the PBI-SPI-SCYb nanocomposite blend membranes improved due to an interaction of –SO3H group and thiazole rings of SPI and N–H groups of PBI in the oxygen vacancies of SCYb doped-perovskite nanoparticles. Substitution of Ce4+ by Yb3+ in the SCYb doped-perovskite nanoparticles produce oxygen vacancies and decrease the columbic repulsion between protons and positive ions. Furthermore at highest phosphoric acid doping level of 14 mol phosphoric acid per monomer unit, the nanocomposite blend membranes displayed proton conductivity of 131 mS/cm at 180 °C and 8% relative humidity. The increase in power density from 0.31 W/cm2 in PBI-SPI blend membranes (SPI/PBI: 25 wt%) to 0.59 W/cm2 in PBI-SPI-SCYb nanocomposite blend membranes (SPI/PBI: 25 wt% and 7 wt% of SCYb) was achieved at 0.5 V, 8% RH and 180 °C, which demonstrates that these developed nanocomposite blend membranes have a high potential to be regarded as the most promising candidates for high-temperature fuel cell with improved proton conductivity.
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•SrCe0.9Yb0.1O3-δ (SCYb) doped-perovskite nanoparticles acted as one of the fastest available proton conductors.•Substitution of Ce4+ by Yb3+ in the SCYb nanoparticles produce oxygen vacancies.•The oxygen vacancies in the SCYb nanoparticles act as hydrogen traps.•Interaction of sulfonated polyimide (SPI) and PBI in the oxygen vacancies increase the proton conductivity.•The SPI/PBI/SCYb nanocomposite blend membranes show a power density of 0.59 W/cm2.
Finite-time bipartite synchronization of multi-agent systems is assessed here. To cover a wide range of practical systems, the agents dynamics are modeled as nonlinear nonstrict-feedback dynamics ...with unknown time-varying control coefficients. Moreover, to conform to many real-world applications, the agents dynamics are assumed unknown and their state information is assumed not available for measurement. First, a virtual affine variable is introduced, and to eliminate the algebraic-loop in control design, neural network along with minimal learning parameter principle are employed to approximate composite uncertainties including unknown functions in the system dynamics, unknown control coefficients and control inputs. A local linear state-observer is then designed for each follower agent to estimate unmeasured states, and finally dynamic surface control scheme and finite-time approach are adopted in the distributed bipartite control design to guarantee finite convergence time. It is ensured that under this proposed protocol, the bipartite error surfaces and boundary error layers are converged to a neighborhood of the origin in the sense of finite-time stability. Finally, two simulation examples clarify the efficiency of the designed controller.
Transition metal oxides can be performant electrode materials for supercapacitors and alcohol oxidation if their conductivity and capacity are improved. Herein, an advanced nanocomposite material ...made of NiO‐Co3O4 on reduced graphene oxide (rGO) is synthesized by a one‐step hydrothermal method for supercapacitors and methanol/ethanol oxidation. It is demonstrated that the nanocomposite is a promising material for energy storage as NiO‐Co3O4‐rGO supercapacitor electrodes achieve a specific capacity of 149 mAh g−1 (894 F g−1) at a current density of 0.5 A g−1, the discharge time of 689 s, and excellent stability of 95% after 6000 cycles. Moreover, NiO‐Co3O4‐rGO shows a current density of 15 and 10 mA cm−2 in methanol and ethanol oxidation reactions, respectively, along with excellent stability.
NiO‐Co3O4 and NiO‐Co3O4/rGO multicomponent nanocomposites are used for supercapacitors and alcohol oxidation. The synergistic effects between the two metal oxides and the hybridization with reduced graphene oxide lead to supercapacitors with high specific capacity and long discharge time as well as methanol and ethanol oxidation processes with high current density and reduced overvoltage.
Summary
A ternary nanocatalyst consisting of nickel cobalt oxide (NiCo2O4), reduced graphene oxide (rGO), and platinum (Pt) was introduced as a promising catalyst for application in the sorbitol ...oxidation reaction (SOR) process for use in fuel cells. Other catalysts such as NiCo2O4, NiCo2O4‐rGO, and NiCo2O4/Pt were prepared for comparison. The structure and morphology of the synthesized nanocatalysts were examined by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The efficiency of the as‐synthesized materials was assessed by electrochemical tests of cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA). The comparison of the SOR process for the synthesized nanocatalysts showed that NiCo2O4‐rGO/Pt has the highest current density (57.2 mA cm−2, 45.04 mA/mg) at a scan rate of 10 mV/s and the lowest peak potential (0.64 V) as well as the highest cyclic stability than other materials. The superior electrocatalytic performance is attributed to the synergistic effect of the components. Moreover, the charge transfer resistance of SOR for NiCo2O4‐rGO/Pt catalyst is 702 Ω, lower than that for NiCo2O4/Pt (930 Ω). Thus, NiCo2O4‐rGO/Pt constitutes an efficient and promising nanocatalyst for SOR.
The binary transition metal oxide (NiCo2O4) coupled with reduced graphene oxide and Pt (NiCo2O4‐rGO/Pt) shows promising catalytic properties for sorbitol oxidation. The superior electrocatalytic performance is attributed to the synergistic effect of the components. Thus, this ternary catalyst constitutes an efficient and promising nanocatalyst for sorbitol oxidation.
In this brief, we contribute to adaptive neural network (NN) backstepping control design for the nonlinear double-integrator fractional-order (FO) systems comprising unknown dynamics and disturbances ...by the event-triggered procedure. To this end, a new triggering rule with a dynamical variable is first introduced, including some available static triggering rules as its particular form. Then, by using the contradiction and some properties of the Mittag-Leffler function, it is proved for the first time that the applied dynamical variable is positive and bounded for the FO systems. Hence, the inter-event time between any two successive triggering moments can be enlarged than static event-triggered results. By integrating the backstepping approach into the NN, an adaptive NN controller is constructed, which introduces a new analysis viewpoint on the Zeno phenomenon avoidance for the FO controllers. Under this controller, the tracking error converges to a small compact set including the origin. Finally, an example is given to show the feasibility of the proposed method.
The present work reports the synthesis of MgCo
2
O
4
-rGO nanohybrid by a simple method. The nanohybrid was characterised by XRD, Raman spectroscopy, EDX, SEM, and TEM. An effective electrochemical ...sensing platform to detect Sudan I based on MgCo
2
O
4
-rGO nanohybrid modified screen-printed electrode (MgCo
2
O
4
-rGO/SPE) is reported. Electrocatalytic sensing of Sudan I is carried out using cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CHA) as well as differential pulse voltammetry (DPV) measurements. Interestingly, this newly developed sensor showed greater peak currents with the decreased anodic potential than that of the bare SPE. The modified electrode demonstrated distinctive electrocatalytic activities to detect Sudan I with the longer linear response range between 0.04 and 580.0 µM, low limit of detection (LOD) of 9.0 nM, and high sensitivity of 0.0838 µA µM
−1
. In addition, MgCo
2
O
4
-rGO/SPE sensor exhibited excellent electrochemical stability, repeatability and reproducibility for Sudan I detection. Analytical utility of our method revealed acceptable detection outputs for Sudan I. Therefore, it could be concluded that this sensor (MgCo
2
O
4
-rGO/SPE) exhibited very good electrochemical behaviour for electrochemical detection of Sudan I oxidation.
The potential of metal oxides in electrochemical energy storage encouraged our research team to synthesize molybdenum oxide/tungsten oxide nanocomposites (MoO3/WO3) and their hybrid with reduced ...graphene oxide (rGO), in the form of MoO3/WO3/rGO as a substrate with relatively good electrical conductivity and suitable electrochemical active surface. In this context, we presented the electrochemical behavior of these nanocomposites as an electrode for supercapacitors and as a catalyst in the oxidation process of methanol/ethanol. Our engineered samples were characterized by X-ray diffraction pattern and scanning electron microscopy. As a result, MoO3/WO3 and MoO3/WO3/rGO indicated specific capacitances of 452 and 583 F/g and stability of 88.9% and 92.6% after 2000 consecutive GCD cycles, respectively. Also, MoO3/WO3 and MoO3/WO3/rGO nanocatalysts showed oxidation current densities of 117 and 170 mA/cm2 at scan rate of 50 mV/s, and stability of 71 and 89%, respectively in chronoamperometry analysis, in the MOR process. Interestingly, in the ethanol oxidation process, corresponding oxidation current densities of 42 and 106 mA/cm2 and stability values of 70 and 82% were achieved. MoO3/WO3 and MoO3/WO3/rGO can be attractive options paving the way for prospective alcohol-based fuel cells.
Summary
Hierarchical porous ZnCo2O4 nanosheets and ZnCo2O4‐coated reduced graphene oxide (ZnCo2O4/rGO) were synthesized by the hydrothermal method followed by the annealing process. The composition ...of materials was proved by X‐ray electron spectroscopy and X‐ray photoelectron spectroscopy. The size and morphology of the as‐prepared samples were evaluated by scanning electron microscopy and transmission electron microscopy. The result showed ZnCo2O4 nanosheets with porous morphology and a sheet thickness of about 5 nm was well synthesized. The electrochemical tests used to prove the catalytic performance of the prepared catalysts were cyclic voltammetry and impedance spectroscopy, and the analysis was performed in alkaline environments. The electrochemical investigations on ZnCo2O4 and ZnCo2O4/rGO showed the rGO has an effective role in electrooxidation of methanol in alkaline media. In addition to the synergic effect between Zn and Co, the synergistic effect between ZnCo2O4 (make active sites for adsorption of methanol) and rGO (provide more conductivity and make more sites by preventing from the agglomeration of ZnCo2O4) has an important role for this excellent performance. The polarization curves of ZnCo2O4/rGO showed a maximum power density of 24.3 mW cm−2, which proved its potential capability for the direct methanol fuel cell.
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