Low Energy Density Research Articles

Giant Capacitive Energy‐Storage in BaTiO3‐Based Fine‐Grained Relaxors via Local Polarization Enhancement

AbstractPb‐free dielectric energy storage capacitors are core components in advanced pulse‐power electronic systems and devices. However, the relatively low energy density (Wrec) for the industrial pillar BaTiO3 (BT)‐based capacitors remains a significant obstacle for their cutting‐edge applications, due to their low intrinsic polarization and breakdown strength (EB). Herein, through chemical composition and local structure design, a giant Wrec of 15.1 J cm−3 along with a high efficiency (η) of 85% is demonstrated in a BT‐based relaxor bulk ceramic. This is achieved by introducing rare A‐site polarization enhancement substitution (Bi0.5Na0.5)2+ ions in combination with B‐site fastest relaxation alternative (Zn1/3Nb2/3)4+ ions to enhance local polarization and refine grain structure. Atomic‐level local structure analysis has revealed that the diversified atomic polar displacement vectors, characterized by largely extended magnitude and heterogeneous directions, assemble into highly polarizable clusters at several unit‐cells scale. Consequently, it exerts a large polarization difference (ΔP) of 49 µC cm−2 and a high EB of 90 kV mm−1. Moreover, a giant power density (677 MW cm−3), high discharge energy density (3.9 J cm−3), and excellent stability are achieved. This study overcomes the current Wrec bottleneck of ≈10 J cm−3 in BT‐based bulk ceramics, presenting an approach to optimize the energy storage performance of Pb‐free relaxors.

Review: Overview of Organic Cathode Materials in Lithium-Ion Batteries and Supercapacitors

Organic materials have emerged as promising candidates for cathode materials in lithium-ion batteries and supercapacitors, offering unique properties and advantages over traditional inorganic counterparts. This review investigates the use of organic compounds as cathode materials in energy storage devices, focusing on their application in lithium-ion batteries and supercapacitors. The review covers various types of organic materials, organosulfur compounds, organic free radical compounds, organic carbonyl compounds, conducting polymers, and imine compounds. The advantages, challenges, and ongoing developments in this area are examined and the potential of organic cathode materials to achieve higher energy density, improved cycling stability, and environmental sustainability is highlighted. The comprehensive analysis of organic cathode materials provides insights into their electrochemical performance, electrode reaction mechanisms, and design strategies such as molecular structure modification, hybridization with inorganic components, porous architectures, conductive additives, electrolyte optimization, binder selection, and electrode architecture to improve their efficiency and performance. In addition, future research in the field of organic cathode materials should focus on addressing current limitations such as low energy density, cycling stability, poor discharge capability, potential safety concerns and improving their performance. To do this, it will be necessary to improve structural stability, conductivity, cycle life, and capacity fading, explore new redox-active organic compounds, and pave the way for the next generation of high-performance energy storage devices. For organic cathode materials to be commercially viable, it is also essential to develop scalable and economical manufacturing processes.

Effect of Volumetric Energy Density on the Evolution of the Microstructure and the Degradation Behavior of 3D-Printed Fe-Mn-C Alloys from Water-Atomized Powders

Additive manufacturing of metals opens new doors for innovation in custom-based productions in a wide range of fields, including medicine, even if it introduces new challenges that need to be addressed to guarantee the properties are equal to or superior to those of conventional fabrication processes. In this research, porous, biodegradable Fe-Mn-C alloys were fabricated using a 3D printing technique with four different printing energy densities ranging from 62.5 to 125.0 J/mm3. The effect of printing energy density on the microstructure and degradation behavior was investigated. Lower energy densities resulted in higher pore density and the presence of unmelted powder particles, while the alloy printed at 104.2 J/mm3 exhibited the lowest pore density and the smallest grain size. Degradation tests revealed that the highest pore density in the sample printed at 62.5 J/mm3, and the lowest grain size in the sample printed at 104.2 J/mm3 contributed to faster degradation rates. The alloy printed at the highest energy density, 125.0 J/mm3, demonstrated the largest grain size and the slowest degradation rate. Energy-dispersive spectroscopy and Fourier transform infrared spectroscopy analyses identified manganese carbonate as the primary degradation product, with calcium phosphate forming as a secondary product. These findings provide a significant understanding of the relationship between printing parameters, microstructure, and degradation behavior, which are essential for optimizing the performance of Fe-Mn-C alloys in biodegradable material applications.

Building a Better All-Solid-State Lithium-Ion Battery with Halide Solid-State Electrolyte.

Since the electrochemical potential of lithium metal was systematically elaborated and measured in the early 19th century, lithium-ion batteries with liquid organic electrolyte have been a key energy storage device and successfully commercialized at the end of the 20th century. Although lithium-ion battery technology has progressed enormously in recent years, it still suffers from two core issues, intrinsic safety hazard and low energy density. Within approaches to address the core challenges, the development of all-solid-state lithium-ion batteries (ASSLBs) based on halide solid-state electrolytes (SSEs) has displayed potential for application in stationary energy storage devices and may eventually become an essential component of a future smart grid. In this Review, we categorize and summarize the current research status of halide SSEs based on different halogen anions from the perspective of halogen chemistry, upon which we summarize the different synthetic routes of halide SSEs possessing high room-temperature ionic conductivity, and compare in detail the performance of halide SSEs based on different halogen anions in terms of ionic conductivity, activation energy, electronic conductivity, interfacial contact stability, and electrochemical window and summarize the corresponding optimization strategies for each of the above-mentioned electrochemical indicators. Finally, we provide an outlook on the unresolved challenges and future opportunities of ASSLBs.

High-entropy engineered BaTiO3-based ceramic capacitors with greatly enhanced high-temperature energy storage performance

Ceramic capacitors with ultrahigh power density are crucial in modern electrical applications, especially under high-temperature conditions. However, the relatively low energy density limits their application scope and hinders device miniaturization and integration. In this work, we present a high-entropy BaTiO3-based relaxor ceramic with outstanding energy storage properties, achieving a substantial recoverable energy density of 10.9 J/cm3 and a superior energy efficiency of 93% at applied electric field of 720 kV/cm. Of particular importance is that the studied high-entropy composition exhibits excellent energy storage performance across a wide temperature range of −50 to 260 °C, with variation below 9%, additionally, it demonstrates great cycling reliability at 450 kV/cm and 200 °C up to 106 cycles. Electrical and in-situ structural characterizations revealed that the high-entropy engineered local structures are highly stable under varying temperature and electric fields, leading to superior energy storage performance. This study provides a good paradigm of the efficacy of the high-entropy engineering for developing high-performance dielectric capacitors.

Tilt–Roll Heliostats and Non-Flat Heliostat Field Topographies for Compact, Energy-Dense Rooftop-Scale and Urban Central Receiver Solar Thermal Systems for Sustainable Industrial Process Heat

Industrial process heat typically requires large amounts of fossil fuels. Solar energy, while abundant and free, has low energy density, and so large collector areas are needed to meet thermal needs. Land costs in developed areas are often prohibitively high, making rooftop-based concentrating solar power (CSP) attractive. However, limited rooftop space and the low energy density of solar power are usually insufficient to meet a facility’s demands. Maximizing annual CSP energy generation within a bounded rooftop space is necessary to mitigate fossil fuel consumption. This is a different optimization objective than minimizing the Levelized Cost of Energy (LCOE) in typical open-land, utility-scale heliostat layout optimization. Innovative designs are necessary, such as compact, energy-dense central receiver systems with non-flat heliostat field topographies that use spatially efficient Tilt–Roll heliostats or multi-rooftop and multi-height distributed urban systems. A novel ray-tracing simulation tool was developed to evaluate these unique scenarios. For compact systems, optimized annual energy production occurred with maximum heliostat spatial density, and the best non-flat heliostat field topography found is a shallow section of a parabolic cylinder with an East–West focal axis, yielding a 10% optical energy improvement. Tightly packed Tilt–Roll heliostats showed a double improvement in optical energy at the receiver compared to Azimuth–Elevation heliostats.

Exploring the role of volume energy density in altering microstructure and corrosion behavior of nitinol alloys produced by laser powder bed fusion

In the realm of materials science and engineering, the pursuit of advanced materials with tailored properties has been a driving goal behind technological progress. Scientific interest in laser powder bed fusion (L-PBF) fabricated NiTi alloy has in recent times seen an upsurge of activity. In this study, we investigate the impact of varying volume energy density (VED) during L-PBF on the microstructure and corrosion behaviour of NiTi alloys in both scan (XY) and built (XZ) planes. The microstructural evolution in both planes was characterized by electron backscatter diffraction and phase change temperatures were characterized using differential scanning calorimeter measurements. Electrochemical experiments were carried out to compare the specimens produced at high laser energy density and low laser energy density. The results indicate that employing high laser energy density in the production of NiTi alloy induces discontinuous dynamic recrystallization, contributing to grain refinement. This in turn enhances the corrosion resistance of the specimen. X-ray photoelectron spectroscopy was employed to examine the type of oxide layer that developed on the samples. The increased resistance to corrosion in a high laser energy density sample can be associated with the formation of a stable and homogeneous passive layer with enriched TiO2 as opposed to Ti2O3. This exploration has unravelled the intricate relationship between VED, the microstructure, and the corrosion properties of L-PBF fabricated NiTi alloys, offering valuable insights into their performance for diverse applications.

Fabrication and Analysis of BaTiO3-Nb2O5 Ceramics for Advanced Energy Storage Applications

As the demand for high-performance energy storage systems surges, dielectric materials have emerged as frontrunners due to their exceptional power density. Yet, their relatively low energy density has long been a bottleneck for practical deployment. This study breaks new ground by addressing this limitation, focusing on the enhancement of Barium Titanate-based ceramics for energy storage through the strategic incorporation of Niobium Oxide (Nb2O5). By investigating the effects of Nb2O5 on 0.98BT-0.02BMC ceramics, we unlock unprecedented improvements in both dielectric and energy storage properties. X-ray diffraction (XRD) analysis reveals the stability of a single perovskite phase across all compositions, paving the way for reliable performance. Most strikingly, the x = 4 composition delivers a groundbreaking dielectric constant (~2200) alongside a remarkable energy density of 1.40 J/cm3 and a recoverable energy density of 1.10 J/cm3, achieving an efficiency of 78.8%. These extraordinary results propel the material to the forefront of next-generation energy storage technologies, making it a powerhouse for high-demand applications such as power pulse systems. With its unparalleled combination of high energy density, exceptional efficiency, and long-term stability, this material holds the promise to redefine energy storage solutions, setting new benchmarks in both performance and reliability.

Triphenylphosphine Oxide-Derived Anolyte for Application in Nonaqueous Redox Flow Battery.

Recent advances in redox flow batteries have made them a viable option for grid-scale energy storage, however they exhibit low energy density. One way to boost energy density is by increasing the cell potential using a nonaqueous system. Molecular engineering has proven to be an effective strategy to develop redox-active compounds with extreme potentials but these are usually challenged by resource sustainability of the newly developed redox materials. Here, we investigate the utility of phosphine oxides as anolytes with extremely negative potentials. Specifically, we found that cyclic triphenylphosphine oxide (CPO), has a highly negative potential (-2.4 V vs Fc/Fc+). Importantly, CPO is synthesized from triphenylphosphine oxide, a common industrial chemical waste with no commercial value. Structural and electrochemical characterization of the reduced radical anion showed that enhanced stability is due to cyclization or extended pi-conjugation. Importantly, mechanistic investigation into the decomposition of CPO under various solvents and electrochemical conditions allowed us to utilize an acetonitrile/DMF binary solvent system to enable a long-lived anolyte which exhibited no fade over 350 cycles. In summary, this work led to the development of a waste-derived cyclic phosphine oxide that exhibits excellent cycling stability making it an ideal anolyte toward the development of energy-dense RFBs.

Energy density, nutrient density and nutrient-to-price ratio of Indonesian foods

Understanding the concepts of energy density (ED), nutrient density (ND), and nutrient-to -price ratio (NPR) in foods is crucial in making food selections to overcome the triple burden of malnutrition in Indonesia. This study aimed to examine the ED, ND and NPR values of Indonesian foods. A cross-sectional study was conducted to collect mostly consumed food in Malang, Indonesia. This study used nutrient density score (NDS) as a means of measuring and conveying the nutritional density of the foods examined. The ED of snacks (278.90 kcal/100 g), meat and fish (248.90 kcal/100 g), legumes, nuts and seeds (129.55 kcal/100 g), and starchy staples (125.45 kcal/100 g), were significantly higher than the energy density of dark green leafy vegetables (DGLVs) (37.00 kcal/100 g); other fruits and vegetables (34.90 kcal/100 g), and other vitamin A-rich foods (23.40 kcal/100 g). The nutrient density score (NDS) of organ meat (143.3%DV/100 kcal); other vitamin A-rich foods (67.77%DV/100 kcal); DGLVs (61.70%DV/100 kcal); other fruits and vegetables (17.78%DV/100 kcal), were significantly higher than the NDS of starchy staples and snacks. DGLVs (380.50%DV/USD); organ meat (312.5%DV/USD); other vitamin A-rich foods (224.85%DV/USD); legumes, nuts and seeds (118.14%DV/USD) provided significantly higher nutrient contents in lower price compared to snacks. In conclusion, snack has the highest ED but lowest NPR, and in contrary DGLV has lowest ED but highest NPR. The finding of this study was important to support nutritional education and information on food labels, reducing the risk of nutritional problems and diseases.

Advanced Alkali Metal Batteries Based on MOFs and Their Composites.

The integration of metal-organic frameworks (MOFs) with functional materials has established a versatile platform for a wide range of energy storage applications. Due to their large specific surface area, high porosity, and tunable structural properties, MOFs hold significant promise as components in energy storage systems, including electrodes, electrolytes, and separators for alkali metal-ion batteries (AIBs). Although lithium-ion batteries (LIBs) are widely used, their commercial graphite anode materials are nearing their theoretical capacity limits, and the scarcity of lithium and cobalt resources increases costs. Although zinc-ion batteries (ZIBs) suffer from limited cycling stability, they are attractive for their low cost, high capacity, and excellent safety. Meanwhile, potassium-ion (PIBs) and sodium-ion batteries (SIBs) show promise due to their affordability and abundant resources, but they encounter issues such as short cycle life and low energy density. This review outlines the applications of MOF composites in LIBs, SIBs, and ZIBs, introduces common synthesis methods, and forecasts future development directions and challenges in energy storage applications. We emphasize how the understanding can lay the foundation for developing MOF composites with enhanced functionalities.

Theoretical insights and design of MXene for aqueous batteries and supercapacitors: status, challenges, and perspectives.

Aqueous batteries and supercapacitors are promising electrochemical energy storage systems (EESSs) due to their low cost, environmental friendliness, and high safety. However, aqueous EESS development faces challenges like narrow electrochemical windows, irreversible dendrite growth, corrosion, and low energy density. Recently, two-dimensional (2D) transition metal carbide and nitride (MXene) have attracted more attention due to their excellent physicochemical properties and potential applications in aqueous EESSs. Understanding the atomic-level working mechanism of MXene in energy storage through theoretical calculations is necessary to advance aqueous EESS development. This review comprehensively summarizes the theoretical insights into MXene in aqueous batteries and supercapacitors. First, the basic properties of MXene, including structural composition, experimental and theoretical synthesis, and advantages in EESSs are introduced. Then, the energy storage mechanism of MXene in aqueous batteries and supercapacitors is summarized from a theoretical calculation perspective. Additionally, the theoretical insights into the side reactions and stability issues of MXene in aqueous EESSs are emphasized. Finally, the prospects of designing MXene for aqueous EESSs through computational methods are given.

Revealing a new mechanism of stable intersolubility of methanol-n-heptane blended fuel assisted by co-solvents at the microscopic molecular level: Insights and validation from quantum chemical simulation

Methanol, a promising green alternative to traditional fossil fuels, requires blending with high-energy fuels or additives due to its low energy density and cetane number. However, methanol’s high polarity often causes phase separation with other fuels, hindering its widespread use. Adding suitable co-solvents is a known method to address phase separation in fuel blends. For the first time, this study aims to reveal the microscopic molecular mechanism by which butanol, as a co-solvent, can improve the miscibility stability of methanol-gasoline blends. To simplify the analysis in this study, n-heptane, which is a single-component fuel was used as a representative of the multi-component gasoline. Firstly, experimental tests were conducted to investigate the miscibility of different blend ratios of methanol-n-heptane under the influence of different butanol isomers. Secondly, molecular simulation research through the Gaussian and Multiwfn software. Next, through Fourier transform infrared spectroscopy, the mutual solubility of ternary blends was studied. The results showed that the addition of butanol, particularly n-butanol (in comparison to isobutanol), could effectively stabilize the miscibility of anhydrous methanol and n-heptane. Molecular conformation simulations and infrared spectroscopy experiments revealed that the presence of butanol restructures the electrostatic interactions (hydrogen bonding) on the surface of methanol molecules, shielding their polarity. This allows the butanol and methanol molecules to associate more like non-polar species, enhancing their interaction with n-heptane through van der Waals forces, thereby improving the overall miscibility stability of the methanol and n-heptane. These findings offer new insights into the micro-molecular miscibility mechanism of methanol-gasoline blends, which is essential for the successful application of methanol as an alternative fuel.

Comparative analysis of ternary lithium batteries and lithium iron phosphate

Ternary lithium batteries (TLB) and lithium iron phosphate batteries (LIPB) are two popular battery types in the current battery market. They have their own advantages and disadvantages in performance and application areas. Through the analysis of the structure, performance and application of the two types of batteries, it can be seen that the anode of TLB is an octahedral structure with high energy density, strong fast charging ability and excellent low temperature discharge performance. The different ratios of nickel, cobalt and manganese in the anode material are suitable for a variety of unused occasions. However, the high-temperature stability of TLB is poor, and thermal runaway is easy to occur at high temperatures, and their cycle life is relatively short. LIPB are known for their high safety, long cycle life and relatively low cost. Its unique olivine crystal structure and stable P-O covalent bonds give it excellent thermal stability, even at high temperatures, the battery will not easily decompose. The disadvantages of LIPB are mainly reflected in their lower energy density and low-temperature discharge performance. Combining the advantages of the two materials to develop a new battery material with both high energy density and high safety will be an important research direction in the future.

Diet quality components and gut microbiota of patients on peritoneal dialysis.

To evaluate the associations between the quality of the diet and its components and microbial diversity and composition in peritoneal dialysis (PD) patients. This crossectional study included PD patients for at least 3 months, aged 18-75 years and clinically stable. The Diet Quality Index (DQI), validated for the Brazilian population, is based on the energy density of 11 components ("sugar and sweets"; "beef, pork and processed meat"; "refined grains and breads"; "animal fat"; "poultry, fish and eggs"; "whole cereals, tubers and roots"; "fruits"; "non-starch vegetables"; "legumes and nuts"; "milk and dairy products"; "vegetable oil"). A proportional score - based on the adequacy of the intake to Brazilian dietary guidelines - is calculated, and a final score ranged from 0 (worse) to 100 (better) is obtained. Fecal samples were collected at home, in a sterile material, kept refrigerated and delivered to the clinic within 12h. α-diversity indices (Observed OTUs, Chao-1, Shannon', Gini-Simpsons', Pielou eveness and faith phylogenetics) and microbial profile were determined by 16S ribosomal DNA with PCR-amplification and sequenced on an Illumina MiSeq platform. Forty-three participants were included (53.5% men, 52.4±14.1 years, BMI:25.9±4.1 kg/m2, 30.2% had diabetes mellitus). DQI score was 50.5 (41.9 - 54.9). The lowest energy density was for the components "animal fat" and "whole cereals and breads, tubers, and roots", and the highest were for "refined grains and bread" and "beef, pork and processed meat". Diversity indices and Enterorhabdus genus were directly associated with the energy density of the components "whole cereals and breads, tubers, and roots" and inversely with "refined grains and bread", after adjustments for age and diabetes. Even low, the intake of whole cereals, tubers and roots has the potential of positively influence the microbiota profile in peritoneal dialysis patients.

P2-Na0.67Mn0.7Ni0.2Co0.1O2 stabilized by optimal active facets for sodium-ion batteries.

Considering factors such as crustal reserves, atomic mass, redox potential and energy density, sodium-ion batteries (SIBs) are regarded as the most promising alternative to lithium-ion batteries (LIBs). Transition metal-based layered oxides, especially typical NaxMnO2, stand out among cathode materials due to their low cost and high energy density. However, NaxMnO2 cathodes face several challenges, including Jahn-Teller distortion, manganese dissolution, structural collapse, irreversible phase transition and significant capacity loss. In addition, the significant changes in lattice parameters can lead to the formation of cracks and nanovoids. It has been reported that optimizing the assembly of surface facets can be beneficial to electrochemical properties. In this work, Na0.67MnO2 (NMO) with a multilayered structure featuring (distinct {010} active facets and Na0.67Mn0.7Ni0.2Co0.1O2 (NMNCO) with a homogeneous polyhedra structure featuring distinct {001} active facets were synthesized. The initial charge capacity of NMNCO reached 110.1mA h g-1 at a current density of 10mA g-1. After 100 cycles at 100mA g-1, it displayed a good cycling retention rate of 82.1%. The distribution of relaxation times (DRT) reveals the facile transfer of Na+ ions in the NMNCO cathode. In addition, the effects of Ni and Co are revealed, and the mechanism underlying the relationship between distinct surface facet and crack formation is studied.

Energy storage performance and dielectric tunability of AgNbO3 ferroelectric films

AgNbO3 ceramics have attracted significant attention as environmentally friendly energy storage materials; however, their low energy densities limit further development. In this study, a 400- nm AgNbO3 films with a dense microstructure and flat surface is prepared by pulsed laser deposition. The dielectric tenability and hysteresis loops of the film reveal its ferroelectric nature. The dielectric tunability of the AgNbO3 film was 63.6% at 600kV/cm. The breakdown strength reached 1500kV/cm, resulting in a high recoverable energy density of 13.3J/cm3. The recoverable energy storage density of AgNbO3 films indicates good temperature stability with a variation of < 10% between 30 ℃ and 150 ℃ and good frequency stability with a variation of < 10% between 103Hz and 105 Hz. These results suggest that AgNbO3 dielectric films are promising energy storage materials.

Nickel-oxide embedded laser-induced graphene for high-performance supercapacitors.

This study explores the fabrication of nickel-oxide-embedded laser-induced graphene and its application in high-performance supercapacitors. Supercapacitors are critical for various applications due to their high power density and long cycle life. Nevertheless, they suffer from lower energy density compared to batteries. By embedding redox-active nickel oxide (NiO) nanoparticles into graphene electrodes, we enhance the energy density of these supercapacitors while maintaining high power. The NiO nanoparticles were synthesized at the nanoscale and embedded into graphene oxide (GO) using a one-step laser processing technique, resulting in a composite material with improved electrochemical properties. High specific capacitance for a discharge current density of 0.25 A g-1 is 1420 F g-1 in 6 M KOH. Moreover, by tracking the crystallographic X-ray diffraction (XRD) pattern of the composite electrodes upon electrochemical cycling, we identified the phase transition from NiO to Ni(OH)2. Our results verify the advantages of laser processing to incorporating highly-dispersed NiO nanoparticles into graphene films, which significantly enhances the electrochemical performance of supercapacitors, offering a promising approach for developing high-energy and high-power energy storage devices.

Research on the Integrated Converter and Its Control for Fuel Cell Hybrid Electric Vehicles with Three Power Sources

Separate DC-DC converters for each energy source are typically configured in fuel-cell hybrid vehicles. This results in a complex control structure of the powertrain system, low energy density of the converter, and high cost due to the large number of components. Conducting research on DC-DC converters with good energy flow management and high integration is a trend to solve such problems. Based on the analysis of the basic functional structure of the converter, this paper designs a buffering unit circuit with energy collection and distribution functions and appropriately connects it with the pulse unit circuit of the converter. Through device optimization reuse and power transmission path integration, a class of non-isolated four-port DC-DC converters is constructed, which consists of an auxiliary energy charging module, input energy source control module, braking energy feedback module and forward bootstrap boost circuit. This converter has two bi-directional ports, a uni-directional input and a bi-directional output, for separate connection to the power batteries, supercapacitors, fuel cells and DC bus. It can adapt to the fluctuation of the vehicle’s driving condition while achieving dynamic and flexible regulation of power flow and can flexibly allocate power according to the load current and voltage level of energy. It can realize a total of 14 operation modes, including six output power supply operation modes, five auxiliary power charging operation modes, and three braking energy regeneration operation modes. Furthermore, the mathematical model of this converter is constructed using the state-average method and the small-signal modeling method in order to achieve the responsiveness and stability of switching multiple operating modalities. The PI control parameters are optimized using the particle swarm optimization algorithm to achieve optimized control of the converter. The simulation system is set up using MATLAB R2024a to verify that the proposed converter topology and algorithm can dynamically allocate appropriate current paths to manipulate the power flow under various operating conditions, effectively improving the utilization rate and efficiency of energy. The converter has the characteristics of high gain and high power density, which is suitable for three-energy fuel cell hybrid electric vehicles.

Effects of Co/Fe doping on the optical limiting behaviors of copper-based sulfides under low energy densities

Abstract Copper-based sulfides have demonstrated excellent potential in optical fields due to their unique optical properties. In this work, heteroatom doping is conducted in copper-based sulfides to regulate their photo-physical properties. The average grain size of CuCo2S4/CuFeS2 is about 15 nm, whereas the average grain sizes of CuCo2S4 and CuFeS2 are 69 and 73 nm, respectively. The as-obtained derivations of CuCo2S4, CuFeS2, and the coprecipitated CuCo2S4/CuFeS2 are systematically characterized, and the nonlinear optical properties (NLO) of the copper-based sulfides are investigated via the Z-scan technique in the low-laser intensity range of 1–4 µJ to avoid the contribution of solvent scattering in nonlinear optical results. All copper-based sulfides exhibit optical limiting effects, and the open aperture Z-scan results suggested the coexistence of both nonlinear absorption and nonlinear refraction in the sulfides. Co or Fe doping can enhance the optical limiting effects of copper sulfides to some extent, and the normalized transmittances in CuCo2S4 and CuFeS2 are reduced to about 72% from the pristine Cu1.8S (85%) at the input energy of 4 µJ. Interestingly, the optical limiting performances of the coprecipitated CuCo2S4/CuFeS2 are enhanced significantly, and the normalized transmittance in CuCo2S4/CuFeS2 is reduced to about 59% at an input energy of 4 µJ, much lower than the counterpart of the physical mixture of CuCo2S4 and CuFeS2. The highest nonlinear absorption coefficient (β) value is achieved in CuCo2S4/CuFeS2, consistent with the Z-scan results. The NLO enhancement in CuCo2S4/CuFeS2 may derive from the more efficient interfacial charge transfer between coprecipitated CuCo2S4 and CuFeS2, which give a higher efficiency in the carrier mobility.