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The development of materials and electrochemical energy storage (EES) technologies are currently taking the lead and showing excellent performance in the global effort to tackle the issues of sustainable energy supply. Supercapacitors have been widely studied among the EES technologies as they exhibit quick charging rates under high‐power conditions. Manganese dioxide (MnO2) has attracted renewed interest as a promising material due to its high theoretical capacitance and high energy density. However, the widespread application is immediately impacted by low conductivity. Hence, combining nanomaterials and various morphologies of MnO2 can improve the electrochemical performance of supercapacitors. This paper presents a review based on the composites of nanomaterials/MnO2 with various morphologies. Their mechanism and practical applications in supercapacitors are introduced in detail. Finally, the challenges and next steps in developing MnO2 electrode materials are proposed. [ABSTRACT FROM AUTHOR]

The study of mental models and creative thinking skills in students' physics learning with the problem-based learning model has been scarce. This study aimed to analyze the relationship between mental models and creative thinking skills in high school students. Many previous research findings explain a relationship between mental models and creative thinking skills among students at the university level and workers. This mixed-methods study was conducted on high school students in Malang, East Java, Indonesia, aged between 14 and 15 years. The instrument used is in the form of mental models and creative thinking skills test questions. This finding explains no relationship between mental models and creative thinking skills because learning has not fully empowered mental models and creative thinking skills. On the other hand, learning at the previous level, students' knowledge is still fragmented, so that is incomplete. Therefore, at the high school level, they need help to improve their mental models and creative thinking skills. This finding implies that teachers in developing learning materials, tools, and instruments must pay attention to the level of student knowledge so that learning can be more optimal. [ABSTRACT FROM AUTHOR]

The dynamics of spin and charge-ordered phases in La1.67Sr0.33NiO4 single crystal have been investigated using high-frequency dielectric spectroscopy. The measurements were carried out in frequencies between 0.156 and 316 MHz and temperatures from 50 to 320 K. The intrinsic part of the response by excluding the Maxwell–Wagner relaxation region is obtained below TSDW ∼ 120 K. The intrinsic frequency-dependent real dielectric constant ɛ′ and conductivity σ′ can be well described in terms of the constant phase element revealing a complex charge-hopping process. Our results are in agreement with the spin-density-wave puddles' picture observed by the scanning micro-x-ray diffraction technique. These demonstrate that high-frequency dielectric spectroscopy can be utilized for investigating the various order phases in other transition metal oxides by considering their intrinsic responses. [ABSTRACT FROM AUTHOR]

Some of the technical problems that appear are obtaining solar cell parameters from I-V curve measurement data. One simple method is using linear graphical fit at zero current or voltage conditions. Although the accuracy of the obtained values is acceptable, other problems may arise regarding the number of parameters which could be obtained. We report a comparison between manual or graphical fit and fit using Shockley’s equation. The single I-V curve under the lighting was inferred to obtain the intrinsic parameters of the solar cells’ performance. The fittings were performed using the nonlinear equation of Shockley by determining some initial values of fittings such as Rs, Rsh, n, I0, Iph, and T. In the case of the Shockley equation fit, the iteration was performed several times to obtain the least possible inferred parameters. We have successfully obtained a better result of nonlinear Shockley fitting compared to the manual linear fit. [ABSTRACT FROM AUTHOR]

Abstract One of the key barriers to commercial development of thermoelectric materials for conversion of heat into electricity is the issue of thermal transport, which diminishes the temperature gradient needed for sustaining the thermoelectric conversion process. The translation of bulk thermoelectric materials into nanostructures such as superlattices, nanowires and quantum dots is useful to mitigate thermal conductivity, through an increase in the mechanisms responsible for phonon scattering. Theoretical principles behind superlattices, phonon glass electron crystals (PGECs) and energy filtering are introduced within the context of thermal conductivity reduction. Case studies using SrTiO 3 based oxide materials and titanium-based sulfide materials are used to illustrate structural modifications of the thermoelectric crystal lattice which have been successfully employed to reduce thermal conductivity and hence improve the thermoelectric figure of merit. In particular, the SrTiO 3 , a perovskite-type oxide class of materials was selected because of the high tunability of its crystal structure through introduction of selective doping, ability to create of an elastic strain field due to radii mismatch of the dopant atom which produces a wider range of phonon scattering and buildable crystal architecture through interleaving with dopant cations to form superlattices. On the other hand, design of TiS 2 compounds are a variant on the concept of dichalcogenides, which produce highly anisotropic layered crystal structures, which in turn lend itself to quantum confinement and enhanced phonon scattering effects. Notable nanoarchitectural design of the TiS 2 crystal lattice includes nanoblock integration, metal and organic layer intercalation, and misfit layer sulfides which give rise to interesting transport characteristics of the resulting crystal. These strategies all point towards further enhancement of the thermoelectric figure of merit through mitigation of thermal conductivity for ultimate utilization in energy harvesting applications. Highlights • Thermoelectricity is a promising renewable energy conversion technology with the ability to convert a temperature gradient into useful electricity without any need for moving parts. • One of the powerful strategy to improve the thermoelectric performance is reducing the thermal conductivity, in particular the lattice thermal conductivity so that its thermal conduction is comparable with glass thermal conduction. • Nanostructure approach is a useful strategy to mitigate thermal conductivity through an increase in the mechanisms responsible for phonon scattering. • Titanium-based thermoelectric materials play a role in the search for superior thermoelectric material due to their unique electronic structure. [ABSTRACT FROM AUTHOR]

An ionic liquid (IL) 1-ethyl, 2-methyl imidazolium thiocyanate incorporated biopolymer system is reported in this communication for applications in dual energy devices, i.e., electric double-layer capacitors (EDLCs) and dye-sensitized solar cells (DSSCs). The solution caste method has been used to synthesize ionic-liquid-incorporated biopolymer electrolyte films. The IL mixed biopolymer electrolytes achieve high ionic conductivity up to the order of 10−3 S/cm with good thermal stability above 250 °C. Electrical, structural, and optical studies of these IL-doped biopolymer electrolyte films are presented in detail. The performance of EDLCs was evaluated using low-frequency electrochemical impedance spectroscopy, cyclic voltammetry, and constant current charge–discharge, while that of DSSCs was assessed using J–V characteristics. The EDLC cells exhibited a high specific capacitance of 200 F/gram, while DSSCs delivered 1.53% efficiency under sun conditions. [ABSTRACT FROM AUTHOR]

Shaded conditions cause a decrease in the performance of photovoltaic (PV) systems. In this situation, the power versus voltage curve shows two maximum power points, namely local (LMPP) and global (GMPP). The main challenge for extracting the maximum power from a PV system during shading conditions is the existence of a false maximum or LMPP along with a true maximum or GMPP. Traditional maximum power point tracking (MPPT) has faced hurdles in overcoming the situation. Therefore, this paper describes the implementation of Queen Honey Bee Migration (or QHBM for short) to track GMPP of PV systems, which called QHBM MPPT. The highlight of this paper is the simulation results of QHBM MPPT on PV systems under various shading conditions. We implemented QHBM MPPT on a boost converter installed on a 1200 Wp PV system. We conducted a simulation using MATLAB® with five scenarios which aim to show the various shadows that PV systems might encounter in reality. The MPPT QHBM is tested repeatedly and then the average value is taken to measure performance in MPP tracking. The average value is used to calculate tracking efficiency, number of iteration or convergence time. We also compared QHBM with other methods, namely incremental conductance (IC) and Particle Swarm Optimization (PSO). The results obtained show that the QHBM and PSO MPPTs outperform the IC MPPT in terms of efficiency, convergence time and the number of iterations. IC MPPTs oscillate under shading conditions since no knowledge of GMPP. Both PSO and QHBM MPPTs know GMPP from scouts or particles, respectively. Therefore, PSO and QHBM MPPTs are better than IC MPPT in various shading cases. [ABSTRACT FROM AUTHOR]

Among various types of energy storage, the supercapacitor is regarded as the most promising device due to its long cycling life, good cycling stability, and high power density. A supercapacitor is generally composed of electrodes, electrolytes, and a separator. The separator is one of the most important components, serving to prevent internal short circuits between the anode and the cathode. Herein, a nanostructured-based separator in a PAN/PVDF nanofiber scheme is introduced for improving the electrochemical performance of the supercapacitor. Briefly, the membranes were produced via the electrospinning technique. All of the raw materials were blended in various compositions of PVDF for optimization purposes. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were carried out to identify the microstructure of the nanofibers. The electrochemical properties of the membrane were measured using galvanostatic charge-discharge (GCD). Based on GCD, it was shown that the PAN/PVDF 20 wt% membrane exhibited the optimum gravimetric capacitance at 54.104 Fg-1 as evidenced by a high porosity percentage. Thus, the PAN/PVDF nanofiber has good potential as a separator for application in supercapacitors. [ABSTRACT FROM AUTHOR]

Ferrogels based on polyvinylpyrrolidone/polyvinyl alcohol (PVP/PVA) matrices with Mn0.6Fe2.4O4–polyethylene glycol (Mn0.6Fe2.4O4–PEG) were synthesized using the freezing–thawing method. The phase structure and morphology of ferrogels with Mn0.6Fe2.4O4–PEG filler were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The Mn0.6Fe2.4O4–PEG/PVP/PVA ferrogel was characterized using small-angle X-ray scattering to determine the distribution of Mn0.6Fe2.4O4–PEG nanoparticles through two-lognormal data analysis; the semicrystallite distribution of the PVP/PVA was investigated using the Beaucage and Teubner–Strey models. The optical and electrical properties of the Mn0.6Fe2.4O4–PEG nanoparticles were characterized using a UV–Vis spectrophotometer. The XRD analysis showed that the Mn0.6Fe2.4O4–PEG exhibits an inverse-spinel cubic structure with an average particle size of 10.2 nm. This result was corroborated by TEM analysis, which revealed an average size of 10.9 nm through the Image-J software analysis. The two-lognormal method was used to analyze the distribution of Mn0.6Fe2.4O4–PEG nanoparticles in the ferrogel, revealing a secondary particle size of approximately 9.8 nm. These secondary particles are, on average, evenly arranged with respect to the primary particles with a diameter of 3.3 nm. UV–Vis data analysis showed that the refractive index and energy gap of the Mn0.6Fe2.4O4–PEG nanoparticles were approximately 2.79 and 2.24 eV, respectively. The optical conductivity and electrical conductivity calculated from the refractive-index and energy-gap data were 1.27 × 108 and 70 Ω−1 cm−1, respectively. These results indicate that the Mn0.6Fe2.4O4–PEG nanoparticles exhibit strong potential for use as a base material in optoelectronics applications. [ABSTRACT FROM AUTHOR]

The design and development of the next-generation power-efficient CIGS solar cells are at the research forefront due to their potential applications in renewable energy. Due to rich fundamental properties such as chemical and physical structures of the CIGS layer, cell scaffolding, and its promising applications like low cost, easy integration, and high efficiency, the CIGS-based solar cell systems are of considerable interest and received tremendous attention. In this article, we review the CIGS solar cells from the point of view of structural engineering. We explain the intrinsic parts of crystalline, optical, and electronic structures of the CIGS absorber layer up to the extrinsic part of the cell multilayer structure. For intrinsic structure, we primarily review the modification of the crystallinity or chemical composition of the CIGS and the effects that these modifications have on the physical properties such as the adjustment of the bandgap grading, effect of impurity or doping, selenization, oxidation processes, and the surface morphology and structure orientation. For extrinsic structure, the effect of substrates, electrical back contact, windows, n -buffer, grid, and antireflection layers will be discussed further, as well as the possibility of their tandem use with other solar cell thin films. [ABSTRACT FROM AUTHOR]