Showing papers by "Wuhan University of Technology published in 2017"

Nanostructured Metal Oxides and Sulfides for Lithium-Sulfur Batteries

Abstract: Lithium-sulfur (Li-S) batteries with high energy density and long cycle life are considered to be one of the most promising next-generation energy-storage systems beyond routine lithium-ion batteries. Various approaches have been proposed to break down technical barriers in Li-S battery systems. The use of nanostructured metal oxides and sulfides for high sulfur utilization and long life span of Li-S batteries is reviewed here. The relationships between the intrinsic properties of metal oxide/sulfide hosts and electrochemical performances of Li-S batteries are discussed. Nanostructured metal oxides/sulfides hosts used in solid sulfur cathodes, separators/interlayers, lithium-metal-anode protection, and lithium polysulfides batteries are discussed respectively. Prospects for the future developments of Li-S batteries with nanostructured metal oxides/sulfides are also discussed.

Battery-Supercapacitor Hybrid Devices: Recent Progress and Future Prospects.

Abstract: Design and fabrication of electrochemical energy storage systems with both high energy and power densities as well as long cycling life is of great importance. As one of these systems, Battery-supercapacitor hybrid device (BSH) is typically constructed with a high-capacity battery-type electrode and a high-rate capacitive electrode, which has attracted enormous attention due to its potential applications in future electric vehicles, smart electric grids, and even miniaturized electronic/optoelectronic devices, etc. With proper design, BSH will provide unique advantages such as high performance, cheapness, safety, and environmental friendliness. This review first addresses the fundamental scientific principle, structure, and possible classification of BSHs, and then reviews the recent advances on various existing and emerging BSHs such as Li-/Na-ion BSHs, acidic/alkaline BSHs, BSH with redox electrolytes, and BSH with pseudocapacitive electrode, with the focus on materials and electrochemical performances. Furthermore, recent progresses in BSH devices with specific functionalities of flexibility and transparency, etc. will be highlighted. Finally, the future developing trends and directions as well as the challenges will also be discussed; especially, two conceptual BSHs with aqueous high voltage window and integrated 3D electrode/electrolyte architecture will be proposed.

Design of N-Coordinated Dual-Metal Sites: A Stable and Active Pt-Free Catalyst for Acidic Oxygen Reduction Reaction

Abstract: We develop a host-guest strategy to construct an electrocatalyst with Fe-Co dual sites embedded on N-doped porous carbon and demonstrate its activity for oxygen reduction reaction in acidic electrolyte. Our catalyst exhibits superior oxygen reduction reaction performance, with comparable onset potential (Eonset, 1.06 vs 1.03 V) and half-wave potential (E1/2, 0.863 vs 0.858 V) than commercial Pt/C. The fuel cell test reveals (Fe,Co)/N-C outperforms most reported Pt-free catalysts in H2/O2 and H2/air. In addition, this cathode catalyst with dual metal sites is stable in a long-term operation with 50 000 cycles for electrode measurement and 100 h for H2/air single cell operation. Density functional theory calculations reveal the dual sites is favored for activation of O-O, crucial for four-electron oxygen reduction.

Hierarchical Porous O-doped g-C3N4 with Enhanced Photocatalytic CO2 Reduction Activity

Abstract: Artificial photosynthesis of hydrocarbon fuels by utilizing solar energy and CO2 is considered as a potential route for solving ever-increasing energy crisis and greenhouse effect. Herein, hierarchical porous O-doped graphitic carbon nitride (g-C3 N4 ) nanotubes (OCN-Tube) are prepared via successive thermal oxidation exfoliation and curling-condensation of bulk g-C3 N4 . The as-prepared OCN-Tube exhibits hierarchically porous structures, which consist of interconnected multiwalled nanotubes with uniform diameters of 20-30 nm. The hierarchical OCN-Tube shows excellent photocatalytic CO2 reduction performance under visible light, with methanol evolution rate of 0.88 µmol g-1 h-1 , which is five times higher than bulk g-C3 N4 (0.17 µmol g-1 h-1 ). The enhanced photocatalytic activity of OCN-Tube is ascribed to the hierarchical nanotube structure and O-doping effect. The hierarchical nanotube structure endows OCN-Tube with higher specific surface area, greater light utilization efficiency, and improved molecular diffusion kinetics, due to the more exposed active edges and multiple light reflection/scattering channels. The O-doping optimizes the band structure of g-C3 N4 , resulting in narrower bandgap, greater CO2 affinity, and uptake capacity as well as higher separation efficiency of photogenerated charge carriers. This work provides a novel strategy to design hierarchical g-C3 N4 nanostructures, which can be used as promising photocatalyst for solar energy conversion.

Hierarchically porous materials: synthesis strategies and structure design

Abstract: Owing to their immense potential in energy conversion and storage, catalysis, photocatalysis, adsorption, separation and life science applications, significant interest has been devoted to the design and synthesis of hierarchically porous materials. The hierarchy of materials on porosity, structural, morphological, and component levels is key for high performance in all kinds of applications. Synthesis and applications of hierarchically structured porous materials have become a rapidly evolving field of current interest. A large series of synthesis methods have been developed. This review addresses recent advances made in studies of this topic. After identifying the advantages and problems of natural hierarchically porous materials, synthetic hierarchically porous materials are presented. The synthesis strategies used to prepare hierarchically porous materials are first introduced and the features of synthesis and the resulting structures are presented using a series of examples. These involve templating methods (surfactant templating, nanocasting, macroporous polymer templating, colloidal crystal templating and bioinspired process, i.e. biotemplating), conventional techniques (supercritical fluids, emulsion, freeze-drying, breath figures, selective leaching, phase separation, zeolitization process, and replication) and basic methods (sol–gel controlling and post-treatment), as well as self-formation phenomenon of porous hierarchy. A series of detailed examples are given to show methods for the synthesis of hierarchically porous structures with various chemical compositions (dual porosities: micro–micropores, micro–mesopores, micro–macropores, meso–mesopores, meso–macropores, multiple porosities: micro–meso–macropores and meso–meso–macropores). We hope that this review will be helpful for those entering the field and also for those in the field who want quick access to helpful reference information about the synthesis of new hierarchically porous materials and methods to control their structure and morphology.

A Review of Direct Z-Scheme Photocatalysts

Abstract: Recently, great attention has been paid to fabricating direct Z-scheme photocatalysts for solar-energy conversion due to their effectiveness for spatially separating photogenerated electron–hole pairs and optimizing the reduction and oxidation ability of the photocatalytic system. Here, the historical development of the Z-scheme photocatalytic system is summarized, from its first generation (liquid-phase Z-scheme photocatalytic system) to its current third generation (direct Z-scheme photocatalyst). The advantages of direct Z-scheme photocatalysts are also discussed against their predecessors, including conventional heterojunction, liquid-phase Z-scheme, and all-solid-state (ASS) Z-scheme photocatalytic systems. Furthermore, characterization methods and applications of direct Z-scheme photocatalysts are also summarized. Finally, conclusions and perspectives on the challenges of this emerging research direction are presented. Insights and up-to-date information are provided to give the scientific community the ability to fully explore the potential of direct Z-scheme photocatalysts in renewable energy production and environmental remediation.

Layered VS2 Nanosheet‐Based Aqueous Zn Ion Battery Cathode

Abstract: DOI: 10.1002/aenm.201601920 class of materials show great potential for the insertion/extraction of multivalent ions (Zn2+, Mg2+, Al3+) owing to the characteristic of large layer spacing and high conductivity. Among all the TMDs, VS2 is a typical family member of TMDs with hexagonal system, which shows similar crystal structure to that of graphite lamellar with an interlayer spacing of 5.76 Å.[25,30] There is a vanadium layer between two sulfur layers to form a kind of sandwich structure. In VS2 crystal structure, each V atom is arranged around six S atoms and connected with S atoms with covalent bonds. The interlayer spacing of VS2 is so large that enables the convenient insertion/extraction of lithium ions (0.69 Å), sodium ions (1.02 Å), zinc ions (0.74 Å) or their solvation sheath in electrolyte. However, to the best of our knowledge, there is no report about VS2 as the electrode materials for ZIBs. Herein, the VS2 nanosheets are synthesized via a facile hydrothermal reaction (Supporting Information), which deliver a high capacity of 190.3 mA h g−1 at a current density of 0.05 A g−1 and exhibit long-term cyclic stability as the cathode for ZIBs. The electrochemical reaction mechanism of such VS2 electrodes is further investigated systematically through a series of measurements including ex situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), in situ Raman, ex situ transmission electron microscopy (TEM). A reversible insertion/extraction process can be observed from all aspects. Both the ex situ TEM and ex situ XRD results demonstrate that the interlayer space of VS2 can self adapt to the intercalation of Zn2+ with an expansion along the c-axis (only 1.73%) and a slightly shrink along the aand b-axes, which plays a key role in the realization of long-life ZIBs. All the above evidences reveal that the VS2 is a promising cathode material with high capacity and good cyclic stability for ZIBs. The crystal structure of the as-prepared VS2 is tested by XRD. All characteristic peaks are in accordance with the standard card of VS2 (JCPDS NO. 01-089-1640) (Figure 1a). The Raman spectrum of the VS2 in the range of 100–1100 cm−1 is shown in Figure 1b. Six peaks located at 140.4, 192.0, 282.0, 406.6, 687.8, and 993.2 cm−1 are observed, which correspond to the rocking and stretching vibrations of V–S bonds or their combination.[25] The morphology and microstructures of as-prepared VS2 are investigated by field emission scanning electron microscopy (SEM) and high-resolution TEM (HRTEM). As shown in Figure 1c, The VS2 flowers are assembled by nanosheets with a diameter of 5–8 μm and a thickness of 50–100 nm. The d-spacing calculated from selected area electron diffraction (SAED) patterns are 2.89 and 1.64 Å (Figure 2f), which match the d-spacing values of (002) and (110) crystal planes of VS2, respectively. TEM and corresponding HRTEM images in Figure 2e show VS2 nanosheets with a d-spacing of ≈5.76 Å, The continuous researches of energy-storage devices have gained considerable attention in our world which results from the increased development of new-type energy caused by energy crisis and environmental pollution.[1–3] In the past several decades, lithium ion batteries have been widely explored and applied to various fields as they deliver higher energy density compared to other secondary batteries.[4,5] Nevertheless, the processing cost, complicated issues of safety, the limited lithium resources as well as some environmental issues lead to an urgent challenge for exploring new energy storage system.[6,7] The rechargeable aqueous batteries, such as aqueous sodiumion batteries and aqueous Zn ion batteries (ZIBs) have received incremental attention because of cost effectiveness and material abundance.[8–16] There is interest in aqueous ZIBs due to the safety, low cost, abundance of Zn source, and utilizing divalent cations to increase charge-storage capabilities. However, existing aqueous ZIBs are far from achieving the goals of excellent performances demanded by the ever increasing energy consumption. It’s hard to find cathode materials suitable for the reversible intercalation/deintercalation of Zn ions (or their solvation sheath in electrolyte), which limits the developmen of ZIBs.[16] The previous explorations of the cathode material mostly focus on manganese dioxide (MnO2) and Prussian blue analogues, whereas, the former suffers a poor rate performance and a rapid capacity fading, while the latter delivers limited capacities (about 50 mA h g−1).[17–22] Recently, Nazar and co-workers reported a high-capacity and long-life aqueous rechargeable zinc battery, composing of a Zn0.25V2O5⋅nH2O nanobelts cathode, 1 m ZnSO4 electrolyte, and a zinc anode.[23] The work indicates that the layered structure materials show great potential for the cathode of ZIBs. During the past decades, layered transition-metal dichalcogenides (TMDs), such as MoS2, WS2, and VS2 have received significant attentions in a variety of fields for their outstanding characteristic (graphene-like layered structure, direct bandgap, and fast ion diffusion).[24–26] These properties make TMDs potential candidates for battery electrode materials. When applied as the electrode materials for lithium/sodium ion battery, some excellent studies have been reported.[27–29] Also, this

Homogeneous/Inhomogeneous-Structured Dielectrics and their Energy-Storage Performances.

Abstract: The demand for dielectric capacitors with higher energy-storage capability is increasing for power electronic devices due to the rapid development of electronic industry. Existing dielectrics for high-energy-storage capacitors and potential new capacitor technologies are reviewed toward realizing these goals. Various dielectric materials with desirable permittivity and dielectric breakdown strength potentially meeting the device requirements are discussed. However, some significant limitations for current dielectrics can be ascribed to their low permittivity, low breakdown strength, and high hysteresis loss, which will decrease their energy density and efficiency. Thus, the implementation of dielectric materials for high-energy-density applications requires the comprehensive understanding of both the materials design and processing. The optimization of high-energy-storage dielectrics will have far-reaching impacts on the sustainable energy and will be an important research topic in the near future.

General Oriented Formation of Carbon Nanotubes from Metal–Organic Frameworks

Abstract: Carbon nanotubes (CNTs) are of great interest for many potential applications because of their extraordinary electronic, mechanical and structural properties. However, issues of chaotic staking, high cost and high energy dissipation in the synthesis of CNTs remain to be resolved. Here we develop a facile, general and high-yield strategy for the oriented formation of CNTs from metal–organic frameworks (MOFs) through a low-temperature (as low as 430 °C) pyrolysis process. The selected MOF crystals act as a single precursor for both nanocatalysts and carbon sources. The key to the formation of CNTs is obtaining small nanocatalysts with high activity during the pyrolysis process. This method is successfully extended to obtain various oriented CNT-assembled architectures by modulating the corresponding MOFs, which further homogeneously incorporate heteroatoms into the CNTs. Specifically, nitrogen-doped CNT-assembled hollow structures exhibit excellent performances in both energy conversion and storage. On the ...

Multifunctional Mo–N/C@MoS2 Electrocatalysts for HER, OER, ORR, and Zn–Air Batteries

Abstract: Replacement of noble-metal platinum catalysts with cheaper, operationally stable, and highly efficient electrocatalysts holds huge potential for large-scale implementation of clean energy devices Metal–organic frameworks (MOFs) and metal dichalcogenides (MDs) offer rich platforms for design of highly active electrocatalysts owing to their flexibility, ultrahigh surface area, hierarchical pore structures, and high catalytic activity Herein, an advanced electrocatalyst based on a vertically aligned MoS2 nanosheet encapsulated Mo–N/C framework with interfacial Mo–N coupling centers is reported The hybrid structure exhibits robust multifunctional electrocatalytic activity and stability toward the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction Interestingly, it further displays high-performance of Zn–air batteries as a cathode electrocatalyst with a high power density of ≈1964 mW cm−2 and a voltaic efficiency of ≈63 % at 5 mA cm−2, as well as excellent cycling stability even after 48 h at 25 mA cm−2 Such outstanding electrocatalytic properties stem from the synergistic effect of the distinct chemical composition, the unique three-phase active sites, and the hierarchical pore framework for fast mass transport This work is expected to inspire the design of advanced and performance-oriented MOF/MD hybrid-based electrocatalysts for wider application in electrochemical energy devices

Ultra-thin nanosheet assemblies of graphitic carbon nitride for enhanced photocatalytic CO2 reduction

Abstract: A two-dimensional layered polymeric photocatalyst, graphitic carbon nitride (g-C3N4), is becoming the rising star in the field of solar-to-fuel conversion. However, the performance of commonly prepared g-C3N4 is usually very weak because of the high recombination rate of photogenerated charge carriers and a small amount of surface active sites. Here we demonstrate simultaneous texture modification and surface functionalization of g-C3N4via a stepwise NH3-mediated thermal exfoliation approach. The resulting g-C3N4 photocatalyst possesses a hierarchical structure obtained by the assembly of amine-functionalized ultrathin nanosheets and thus exhibits remarkably enhanced light harvesting, a high redox ability of charge carriers, increased CO2 adsorption and a larger amount of surface active sites, as well as improved charge carrier transfer and separation. Therefore the aforementioned hierarchical g-C3N4 consisting of amine-functionalized ultra-thin nanosheets shows much better performance for photocatalytic CO2 reduction than unmodified conventional g-C3N4 photocatalysts.

Manipulating Adsorption–Insertion Mechanisms in Nanostructured Carbon Materials for High‐Efficiency Sodium Ion Storage

Abstract: Hard carbon is one of the most promising anode materials for sodium-ion batteries, but the low Coulombic efficiency is still a key barrier. In this paper, a series of nanostructured hard carbon materials with controlled architectures is synthesized. Using a combination of in situ X-ray diffraction mapping, ex situ nuclear magnetic resonance (NMR), electron paramagnetic resonance, electrochemical techniques, and simulations, an “adsorption–intercalation” mechanism is established for Na ion storage. During the initial stages of Na insertion, Na ions adsorb on the defect sites of hard carbon with a wide adsorption energy distribution, producing a sloping voltage profile. In the second stage, Na ions intercalate into graphitic layers with suitable spacing to form NaC x compounds similar to the Li ion intercalation process in graphite, producing a flat low voltage plateau. The cation intercalation with a flat voltage plateau should be enhanced and the sloping region should be avoided. Guided by this knowledge, nonporous hard carbon material has been developed which has achieved high reversible capacity and Coulombic efficiency to fulfill practical application.

Low-crystalline iron oxide hydroxide nanoparticle anode for high-performance supercapacitors.

Abstract: Carbon materials are generally preferred as anodes in supercapacitors; however, their low capacitance limits the attained energy density of supercapacitor devices with aqueous electrolytes. Here, we report a low-crystalline iron oxide hydroxide nanoparticle anode with comprehensive electrochemical performance at a wide potential window. The iron oxide hydroxide nanoparticles present capacitances of 1,066 and 716 F g−1 at mass loadings of 1.6 and 9.1 mg cm−2, respectively, a rate capability with 74.6% of capacitance retention at 30 A g−1, and cycling stability retaining 91% of capacitance after 10,000 cycles. The performance is attributed to a dominant capacitive charge-storage mechanism. An aqueous hybrid supercapacitor based on the iron oxide hydroxide anode shows stability during float voltage test for 450 h and an energy density of 104 Wh kg−1 at a power density of 1.27 kW kg−1. A packaged device delivers gravimetric and volumetric energy densities of 33.14 Wh kg−1 and 17.24 Wh l−1, respectively. Carbons dominate anode materials for supercapacitors, however the attained energy density remains low. Here the authors fabricate low-crystalline iron oxide-hydroxide nanoparticle anodes with good electrochemical characteristics, exhibiting high stability and energy/power densities in a hybrid supercapacitor.

RuP2 -Based Catalysts with Platinum-like Activity and Higher Durability for the Hydrogen Evolution Reaction at All pH Values.

Abstract: Highly active, stable and cheap Pt-free catalysts toward hydrogen evolution reaction (HER) are under increasing demand for future energy conversion systems. However, developing pH-universal HER electrocatalysts with Pt-like activity that can function at all pH values still remains as a great challenge. Herein, based on our theoretical predictions, we first design and synthesize a novel N,P dual-doped carbon-encapsulated ruthenium diphosphide (RuP2@NPC) nanoparticle electrocatalyst for HER. Electrochemical tests reveal that, compared with the Pt/C catalyst, RuP2@NPC not only possesses Pt-like HER activity with small overpotentials at 10 mA cm-2 (38 mV in 0.5 M H2SO4, 57 mV in 1.0 M PBS and 52 mV in 1.0 M KOH), but demonstrates superior stability at all pH values, as well as 100 % Faradaic yields. Therefore, this work represents an important addition to the growing family of transition metal phosphides/heteroatom-doped carbon heterostructures with advanced performance in HER and beyond.

Intricate Hollow Structures: Controlled Synthesis and Applications in Energy Storage and Conversion

Abstract: Intricate hollow structures garner tremendous interest due to their aesthetic beauty, unique structural features, fascinating physicochemical properties, and widespread applications. Here, the recent advances in the controlled synthesis are discussed, as well as applications of intricate hollow structures with regard to energy storage and conversion. The synthetic strategies toward complex multishelled hollow structures are classified into six categories, including well-established hard- and soft-templating methods, as well as newly emerging approaches based on selective etching of “soft@hard” particles, Ostwald ripening, ion exchange, and thermally induced mass relocation. Strategies for constructing structures beyond multishelled hollow structures, such as bubble-within-bubble, tube-in-tube, and wire-in-tube structures, are also covered. Niche applications of intricate hollow structures in lithium-ion batteries, Li–S batteries, supercapacitors, Li–O2 batteries, dye-sensitized solar cells, photocatalysis, and fuel cells are discussed in detail. Some perspectives on the future research and development of intricate hollow structures are also provided.

Characterization and properties of Zn/Co zeolitic imidazolate frameworks vs. ZIF-8 and ZIF-67

Abstract: A novel Zn/Co zeolitic imidazolate framework (ZIF) has been constructed by an easy and straightforward room temperature technique Several characterization techniques such as SEM, TEM-EDX, single-crystal XRD and ICP have been applied to confirm that the structure formed is a sodalite (SOD) cage type structure The Zn/Co-ZIF possesses a high nano-crystallinity and porosity with a large surface area By tuning the amount of Co and Zn in the Zn/Co zeolitic imidazolate framework, the physical and chemical properties have been improved compared with those of the single metal frameworks (ZIF-8 and ZIF-67) Consequently, the Zn/Co-ZIF was investigated for two different applications; gas adsorption (CO2, CH4 and N2) and catalysis (CO2 conversion to cyclic carbonates) and the obtained results were compared with the performance of previously reported single metal frameworks (ZIF-8 and ZIF-67) Additionally, hydrolytic stability tests under ambient conditions and immersed in water at 75 °C were performed and pointed out that Zn/Co-ZIF exhibits a higher stability Moreover, based on these results, the Zn/Co-ZIF demonstrates better properties compared with ZIF-8 and ZIF-67

High‐Performance Aqueous Zinc–Ion Battery Based on Layered H2V3O8 Nanowire Cathode

Abstract: Rechargeable aqueous zinc-ion batteries have offered an alternative for large-scale energy storage owing to their low cost and material abundance. However, developing suitable cathode materials with excellent performance remains great challenges, resulting from the high polarization of zinc ion. In this work, an aqueous zinc-ion battery is designed and constructed based on H2 V3 O8 nanowire cathode, Zn(CF3 SO3 )2 aqueous electrolyte, and zinc anode, which exhibits the capacity of 423.8 mA h g-1 at 0.1 A g-1 , and excellent cycling stability with a capacity retention of 94.3% over 1000 cycles. The remarkable electrochemical performance is attributed to the layered structure of H2 V3 O8 with large interlayer spacing, which enables the intercalation/de-intercalation of zinc ions with a slight change of the structure. The results demonstrate that exploration of the materials with large interlayer spacing is an effective strategy for improving electrochemical stability of electrodes for aqueous Zn ion batteries.

Superparamagnetic enhancement of thermoelectric performance

Abstract: The ability to control chemical and physical structuring at the nanometre scale is important for developing high-performance thermoelectric materials. Progress in this area has been achieved mainly by enhancing phonon scattering and consequently decreasing the thermal conductivity of the lattice through the design of either interface structures at nanometre or mesoscopic length scales or multiscale hierarchical architectures. A nanostructuring approach that enables electron transport as well as phonon transport to be manipulated could potentially lead to further enhancements in thermoelectric performance. Here we show that by embedding nanoparticles of a soft magnetic material in a thermoelectric matrix we achieve dual control of phonon- and electron-transport properties. The properties of the nanoparticles-in particular, their superparamagnetic behaviour (in which the nanoparticles can be magnetized similarly to a paramagnet under an external magnetic field)-lead to three kinds of thermoelectromagnetic effect: charge transfer from the magnetic inclusions to the matrix; multiple scattering of electrons by superparamagnetic fluctuations; and enhanced phonon scattering as a result of both the magnetic fluctuations and the nanostructures themselves. We show that together these effects can effectively manipulate electron and phonon transport at nanometre and mesoscopic length scales and thereby improve the thermoelectric performance of the resulting nanocomposites.

Whale Optimization Algorithm and Moth-Flame Optimization for multilevel thresholding image segmentation

Abstract: Two metaheuristic algorithms (WOA and MFO) are used.These algorithms are applied to multilevel thresholding image segmentation.MFO and WOA are better than compared algorithms.MFO is better than WOA for higher number of thresholds. Determining the optimal thresholding for image segmentation has got more attention in recent years since it has many applications. There are several methods used to find the optimal thresholding values such as Otsu and Kapur based methods. These methods are suitable for bi-level thresholding case and they can be easily extended to the multilevel case, however, the process of determining the optimal thresholds in the case of multilevel thresholding is time-consuming. To avoid this problem, this paper examines the ability of two nature inspired algorithms namely: Whale Optimization Algorithm (WOA) and Moth-Flame Optimization (MFO) to determine the optimal multilevel thresholding for image segmentation. The MFO algorithm is inspired from the natural behavior of moths which have a special navigation style at night since they fly using the moonlight, whereas, the WOA algorithm emulates the natural cooperative behaviors of whales. The candidate solutions in the adapted algorithms were created using the image histogram, and then they were updated based on the characteristics of each algorithm. The solutions are assessed using the Otsus fitness function during the optimization operation. The performance of the proposed algorithms has been evaluated using several of benchmark images and has been compared with five different swarm algorithms. The results have been analyzed based on the best fitness values, PSNR, and SSIM measures, as well as time complexity and the ANOVA test. The experimental results showed that the proposed methods outperformed the other swarm algorithms; in addition, the MFO showed better results than WOA, as well as provided a good balance between exploration and exploitation in all images at small and high threshold numbers.

A novel quadruple-cation absorber for universal hysteresis elimination for high efficiency and stable perovskite solar cells

Abstract: Organic–inorganic metal halide perovskite solar cells (PSCs) have made a striking breakthrough with a power conversion efficiency (PCE) over 22%. However, before moving to commercialization, the hysteresis of PSCs, characterized as an inconsistent photovoltaic conversion property at varied electric fields, should be eliminated for stable performance. Herein, we present a novel quadruple-cation perovskite absorber, KxCs0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 (labeled as KCsFAMA), with which the hysteresis in PSCs can be fully eliminated irrespective of the electron transportation layers. The incorporation of potassium intensively promotes the crystallization of the perovskite film with a grain size up to ∼1 μm, doubled compared to the K free counterparts. Further characterization revealed that a lower interface defect density, longer carrier lifetime and fast charge transportation have all made contributions to the hysteresis-free, stable and high PCE (20.56%) of the KCsFAMA devices. Moreover, we present a 6 × 6 cm2 sub-module with the KCsFAMA composition achieving a high efficiency of 15.76% without hysteresis. This result suggests that the quadruple-cation perovskite is a highly attractive candidate for future developments of efficient and stable PSC modules.