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This paper presents a synthesis approach of gain-scheduling offline robust predictive controller (GSORPC) for discrete-time systems with varying parameters. The online controller gain is computed by interpolating between feedback gains of the polyhedral invariant (PI) sets constructed for each vertex of the polytopic uncertainty set so robust stability can be guaranteed as the parameters vary. At each time step, the smallest PI set containing the state is selected for each PI sets sequence. Then, the scheduling parameters are measured and employed in the interpolating between feedback gains of the PI sets. The novelty lies in the fact that the online controller gain is scheduled according to the scheduling parameters so the proposed GSORPC can achieve less conservative results as compared with the conventional offline predictive controller. All optimization problems are solved offline so the online computation is tractable.

Due to their outstanding power density, long cycle life and low cost, supercapacitors have gained much interest. As for supercapacitor electrodes, molybdenum nitrides show promising potential. Molybdenum nitrides, however, are mainly prepared as nanopowders via a chemical route and require binders for the manufacture of electrodes. Such electrodes can impair the performance of supercapacitors. Herein, binder-free chromium (Cr)-doped molybdenum nitride (Mo2N) TFEs having different Cr concentrations are prepared via a reactive co-sputtering technique. The Cr-doped Mo2N films prepared have a cubic phase structure of γ-Mo2N with a minor shift in the (111) plane. While un-doped Mo2N films exhibit a spherical morphology, Cr-doped Mo2N films demonstrate a clear pyramid-like surface morphology. The developed Cr-doped Mo2N films contain 0–7.9 at.% of Cr in Mo2N lattice. A supercapacitor using a Cr-doped Mo2N electrode having the highest concentration of Cr reveals maximum areal capacity of 2780 mC/cm2, which is much higher than that of an un-doped Mo2N electrode (110 mC/cm2). Furthermore, the Cr-doped Mo2N electrode demonstrates excellent cycling stability, achieving ~ 94.6% capacity retention for about 2000 cycles. The reactive co-sputtering proves to be a suitable technique for fabrication of binder-free TFEs for high-performance energy storage device applications. Graphical Abstract

Recently, aluminium–air batteries have received great attention because of their high specific capacity and low cost. However, corrosion of the aluminium (Al) anode is a critical problem limiting their practical applications. In this study, a decrease in the corrosion and an increase in the discharge performance of the Al anode were demonstrated through the use of nano-yttrium-stabilized zirconium (nano-YSZ). Three weight ratios of nano-YSZ blended with Al were prepared via mechanical stir casting. The surface hardness of the new Al alloys was determined using nano-indentation method and phase transition. Crystallite size measurements were conducted using X-ray diffraction analysis. Subsurface morphologies were conducted using scanning electron microscopy. Corrosion studies were carried out using electrochemical impedance spectroscopy and linear sweep voltammetry. The discharge and short-circuit studies of the prepared Al–air battery were undertaken using different Al alloy anodes. The results demonstrated that the Al anode having a higher ratio of nano-YSZ (5 wt%) had the highest discharge behaviour and excellent corrosion resistance making it a potential candidate as an electrode for the Al–air battery.

The effect of different calcination temperatures had been successfully analyzed on the LiV3O8 nanorods that were synthesized through the sol-gel method under the thermal, structural, and morphological characterizations. The thermal analysis had revealed the calcination at 400 °C to be enough for removing all the residual solvents from the sol-gel, while phase and Rietveld analyses had shown pure LiV3O8 to be successfully attained at a calcination temperature of 500 °C. The morphological observation had also indicated high calcination temperatures as inducing large-sized LiV3O8 nanorods. LiV3O8 was then mixed with graphene and evaluated by electrochemical analysis. The best electrochemical performance was with graphene content at 15 wt.%. At low cyclic voltammetry (CV) scan rates of 0.1 mV s−1, two pairs of redox peaks at ESCE = − 0.42/− 0.40 V and − 0.22/− 0.27 V were observed and consistent with Li+ diffusion coefficients at 1.910 × 10−14 cm2 s−1 (anodic) and 1.123 × 10−14 cm2 s−1 (cathodic). For specific capacity, it demonstrated a higher initial specific capacity (90.0 mAhg−1) on LiV3O8/graphene. The post-structural and morphological analyses on the anode after different CV cycles clearly provide in-depth information on the influence of the graphene addition.

This paper focuses on the problem of robustly stabilizing uncertain discrete-time systems subject to bounded disturbances. The proposed tube-based model predictive controller ensures that all possible realizations of the state trajectory lie in the time-varying tubes so robust stability and satisfaction of the state and input constraints are guaranteed. The time-varying tubes are computed off-line so the on-line computational time is tractable. At each sampling time, the precomputed time-varying tubes are included in the optimal control problem as the constraints in the prediction horizon and only a quadratic programming problem is solved. In comparison to the algorithm that calculates the time-varying tubes on-line, the proposed algorithm can achieve the same level of control performance while the on-line computational time is greatly reduced.

Amoxicillin was removed from aqueous solutions using hollow fibre supported liquid membrane system (HFSLM). After evaluation of the influencing variables, the highest permeation coefficient of amoxicillin reached 2.778 × 10−4 ms−1 when the length of hollow fibres was 15 cm and the operating time was 60 min. Then, the reaction flux models of extraction and stripping were calculated. Thereafter, the modelling results were compared with the experimental data at standard deviations of 2.07 and 3.19%. In the comparison of carrier and diluent, the best conditions were achieved when Aliquat 336 and 1-Decanol were used. Results showed that amoxicillin extraction and stripping were of first and zero reaction orders; their reaction rate constants were 0.0344 min−1 and 0.0445 mg/L·min, respectively.

Herein, the formation and electrochemical performance of a novel binder-free turbostratic stacked/ well-ordered stacked δ-MnO2-carbon fiber composite cathodes in deep eutectic solvent (DES) based zinc-ion battery (ZIB) is reported. Results of morphological, elemental, and structural analyses revealed directly grown and interconnected δ-MnO2 crumpled nanosheets on a carbon fiber substrate. Moreover, an improvement via a simple annealing strategy in the stacking, surface area and conductivity of the δ-MnO2 sheets was observed. Annealing induces the rearrangement of δ-MnO2 sheets resulting in the transformation from turbostratic stacking to a well-ordered stacking of $${\delta }$$ δ -MnO2 sheets, as indicated by the selected area electron diffraction (SAED) hexagonal single crystal pattern. Besides, the formation of the well-ordered stacking of $${\delta }$$ δ -MnO2 sheets exhibited improved electrochemical performance and cyclability, as cathode material for ZIB. The novel strategy described in this study is an essential step for the development of binder-free δ-MnO2-C fiber composite with a well-ordered stacking of δ-MnO2 sheets. This study also demonstrated comparable electrochemical performance between the turbostratic $${\delta }$$ δ -MnO2 sheets and the well-ordered stacked δ-MnO2 sheets.

Flexible zinc-air batteries were fabricated using an inexpensive screen-printing technique. The anode and cathode current collectors were printed using commercial nano-silver conductive ink on a polyethylene terephthalate (PET) substrate and a polypropylene (PP) membrane, respectively. Air cathodes made of blended carbon black with inexpensive metal oxides including manganese oxide (MnO2) and cerium oxide (CeO2), were studied. The presence of the metal oxides in the air cathodes enhanced the oxygen reduction reaction which is the most important cathodic reaction in zinc-air batteries. The battery with 20 %wt CeO2 showed the highest performance and provided an open-circuit voltage of 1.6 V and 5 – 240 mA.cm-2 ohmic loss zone. The discharge potential of this battery at the current density of 5 mA.cm-2 was nearly 0.25 V higher than that of the battery without metal oxides. Finally, the battery was tested for its flexibility by bending it so that its length decreased from 2.5 to 1 cm. The results showed that the bending did not affect characteristics on potential voltage and discharging time of the batteries fabricated.

Zinc-air flow batteries exhibit high energy density and offer several appealing advantages. However, their low efficiency of zinc utilization resulted from passivation and corrosion of the zinc anodes has limited their broad application. In this work, ethanol, which is considered as an environmentally friendly solvent, is examined as an electrolyte additive to potassium hydroxide (KOH) aqueous electrolyte to improve electrochemical performance of the batteries. Besides, the effects of adding different percentages of ethanol (0–50% v/v) to 8 M KOH aqueous electrolyte were investigated and discussed. Cyclic voltammograms revealed that the presence of 5–10% v/v ethanol is attributed to the enhancement of zinc dissolution and the hindrance of zinc anode passivation. Also, potentiodynamic polarization and electrochemical impedance spectroscopy confirmed that adding 5–10% v/v ethanol could effectively suppress the formation of passivating layers on the active surface of the zinc anodes. Though the addition of ethanol increased solution resistance and hence slightly decreased the discharge potential of the batteries, a significant enhancement of discharge capacity and energy density could be sought. Also, galvanostatic discharge results indicated that the battery using 10% v/v ethanol electrolyte exhibited the highest electrochemical performance with 30% increase in discharge capacity and 16% increase in specific energy over that of KOH electrolyte without ethanol.

Yttrium (Y) is an essential lanthanide rare earth element and can be effectively extracted and purified using a hollow fiber supported liquid membrane (HFSLM) system. However, the stability of HFSLM system is a significant challenge. Pseudoemulsion-hollow fiber strip dispersion (PEHFSD) system, providing excellent stability, is attracting research attention. In this work, the recovery of Y(III) by PEHFSD system using di(2-ethylhexyl)phosphoric acid (D2EHPA) as a carrier was investigated. The effects of several operating parameters, including the initial concentration of Y(III) in the feed phase, the flow rate of feed, the stirring speed and the volumetric ratio of feed to strip on Y(III) separation were studied. The Y(III) transport was analyzed on the concentration ratio of Y(III) ions, percent extraction, percent stripping and overall mass transfer coefficient (K p ). The PEHFSD system outperformed HFSLM system regarding separation performance and stability. K p of HFSLM system decreased after the second run, but K p of PEHFSD system remained constant even at the fifth run. The dispersed droplets in the strip dispersion phase in the PEHFSD system enhanced separation performance and stability of the membrane module.

In this work, we proposed the new method for estimation of the thickness and the optical properties of the thin metal oxide film deposited on a transparent substrate. The developed method uses only transmittance spectra measured. Our method is based on the two stage optimization where the thickness is determined in the outer stage and the optical properties are determined in the inner stage. The differential evolutionary algorithm is used in solving the formulated problem. The proposed method was illustrated in the case study of Titanium dioxide film deposited on a glass substrate. The results indicate that the thickness and the optical properties estimated agree well with the experiment. Moreover, we investigated robustness of the proposed method in the case of transmittance spectra containing noises. The data were modelled by adding random noises ranging between 0 and 30% to the transmittance spectra measured. It is seen that the proposed method has better robustness and performance than the existing method based on pointwise unconstrained minimization approach. In solving the estimation problem, the performance of the proposed method was also compared with the well-known Levenberg---Marquardt method and single stage differential evolutionary method. The results indicate that the proposed method has better performance than Levenberg---Marquardt method and single stage differential evolutionary method. Moreover, the proposed method is more robust to random noise than Levenberg---Marquardt method and single stage differential evolutionary method.

This work investigates the effects of concentration of organothiol molecules and temperature used during self-assembled monolayers (SAMs) formation on quality of the organothiol SAMs coating layer obtained in terms of wettability, corrosion inhibition efficiency and carbon to copper ratio. The organothiol SAMs were coated on copper substrates prepared by electro-polishing followed by oxygen plasma treatment for 15 s. Three types of organothiol SAMs including 1-octanethiol (OTT), 2-ethylhexanethiol (2-EHT) and 2-phenylethanethiol (2-PET) were investigated. Concentration of organothiol molecules ranging from 0.005 to 0.02 M in isopropanol and forming temperature ranging from -15 to 50°C were studied. It was found that all organothiol SAMs of 0.01 M provided the SAMs coating layer with the highest quality. The SAMs formed at 40°C with OTT and 2-EHT, and at 0°C with 2-PET were the most favorable condition with the highest water contact angle of 124.79o, 130.66o and 120.58o at corrosion inhibition efficiencies of 96.24%, 99.37% and 98.90%, respectively.

In this work, spherical copper (core) - silver (shell) nanoparticles with diameter of 40-50 nm were synthesized through polyol successive reduction process in glycerol with addition of sodium hydroxide (NaOH). The process involves microwave-assisted reduction of copper nitrate by glycerol under atmospheric conditions and successive reduction of silver nitrate at the surface of copper nanoparticles synthesized. We investigated the influence of synthesis parameters including molar ratio of NaOH:Cu (0:1, 1:1, 3:1 and 5:1), the molar ratio of Ag:Cu (0.01:1, 0.05:1, 0.10:1, 0.15:1 and 0.20:1) on the size, structure and composition of the resulting particles. High-resolution transmission electron microscopy with energy dispersive X-ray spectroscopy (TEM/EDS), scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis were used to characterize the particles obtained. The average size of the nanoparticles decreased with increasing of the ratio of sodium hydroxide. With the molar ratio of Ag:Cu greater than 0.05:1, the silver protective shell can prevent forming of copper oxide on the surface of nanoparticles.