Open Voltage Research Articles

Advanced K3V2(PO4)2O2F cathode for rechargeable potassium-ion batteries with high energy density

Potassium-ion batteries (PIBs) have emerged as promising candidates for cost-effective and sustainable energy-storage systems. Nevertheless, limited by the large K+ radius, PIBs have great difficulty in figuring out and designing suitable host materials. Herein, a suitable cathode material K3V2(PO4)2O2F (KVPOF) for PIBs has been carefully prepared. It exhibits a high specific capacity close to the theoretical value, 116.3 mAh/g at 20 mA/g within the voltage window of 2.0–4.5 V vs K+/K, corresponding to a de-/intercalation process of ∼2 mol K+ per formula unit. In addition, it presents an average operating voltage plateau of about 3.5 V, resulting in an energy density of about 410 Wh/kg. The crystal structure and phase transition are revealed by in situ x-ray diffraction, and the structure is found to be fully reversible during the de-/intercalation of K+. Furthermore, the potential of KVPOF cathode for applications at low temperatures was explored, and the full cell matched with graphite anode demonstrated fair electrochemical performance. The experimental results suggest the feasibility of using KVPOF as cathode material for rechargeable PIBs.

Porous carbon-MnO2 heterostructures for high energy density aqueous ammonium-ion asymmetric supercapacitors

Aqueous ammonium-ion (NH4+) is gaining attention as a viable energy storage option due to the use of NH4+ as the charge carrier, offering advantages of resource abundance, safety, fast diffusion, and a unique storage mechanism. Despite these benefits, the development of storage devices with NH4+ as the charge carrier are still in the early stages, highlighting the crucial need to explore suitable electrode materials for the production of high-performance devices. In this study, broken porous carbon nanocages (BPCs) serve as the support structure to form a heterostructure with δ-MnO2 nanosheets (MnO2-BPCs) grown onto them, building aqueous NH4+ asymmetric supercapacitors (ASCs). Both MnO2-BPCs and BPCs act as host materials for storing aqueous NH4+, exhibiting high specific capacitance and long cycling durability. The assembled NH4+ ASCs present good capacitive performance, with a large specific capacitance of 223 F g−1 and capacitance preservation of 91.4 % over 10,000 cycles. The high energy density achieved by NH4+ ASCs is crucial for advanced energy storage thanks to their elevated specific capacitance and broad operating voltage. The balanced capacitive performance of the positive and negative electrodes is essential in enhancing the energy storage capabilities of NH4+ ASCs. This work provides a straightforward method for creating porous carbon-MnO2 heterostructures for NH4+ storage and paves the way for designing aqueous NH4+-based sustainable energy storage systems (SESSs) for capacitive energy storage.

Three modes of electrochemical impedance spectroscopy measurements performed on vanadium redox flow battery

This article presents an innovative approach to monitor working redox flow batteries using dynamic electrochemical impedance spectroscopy, diverging from the commonly sequential impedance methods carried out under potentiostatic or galvanostatic conditions close to the open circle voltage. The authors introduce a fresh variation of dynamic impedance measurement that leverages an amplitude-modulated multi-frequency alternating current perturbation signal. This technique leads to a reduction in measurement time, making it possible to monitor impedance in real-time under typical operational conditions. Consequently, it effectively addresses the limitations stemming from the absence of stationary conditions during impedance measurements. There is no doubt that measurement techniques enabling the study of processes during the operational life of a battery provide the most valuable insights into the properties of these systems. The potential of this proposed approach is exemplified through the examination of a full vanadium redox flow battery as a case study. Classical impedance measurements were also conducted under potentiostatic and galvanostatic conditions with sequential frequency signal change, which requires stopping the battery operation, resulting in electrode potential changes of over 200 mV compared to the working system. Spectra for all modes of measurements were compared. In the case of dynamic measurements, such significant differences in spectra during charging and discharging are not observed, which is characteristic of classical measurements. The authors deliberately and consciously refrain from analyzing the results by fitting equivalent circuits.

Artificial Funnel Nanochannel Device Emulates Synaptic Behavior.

Creating artificial synapses that can interact with biological neural systems is critical for developing advanced intelligent systems. However, there are still many difficulties, including device morphology and fluid selection. Based on Micro-Electro-Mechanical System technologies, we utilized two immiscible electrolytes to form a liquid/liquid interface at the tip of a funnel nanochannel, effectively enabling a wafer-level fabrication, interactions between multiple information carriers, and electron-to-chemical signal transitions. The distinctive ionic transport properties successfully achieved a hysteresis in ionic transport, resulting in adjustable multistage conductance gradient and synaptic functions. Notably, the device is similar to biological systems in terms of structure and signal carriers, especially for the low operating voltage (200 mV), which matches the biological neural potential (∼110 mV). This work lays the foundation for realizing the function of iontronics neuromorphic computing at ultralow operating voltages and in-memory computing, which can break the limits of information barriers for brain-machine interfaces.

Comprehensive modeling and characterization of the General-Purpose Heat Source Radioisotope Thermoelectric Generator for solar system missions

The radioisotope thermoelectric generator relies solely on radioactive decay for its energy and generates power through the thermoelectric effect. The General-Purpose Heat Source Radioisotope Thermoelectric Generator (GPHS-RTG) represents the RTG with the largest power and highest conversion efficiency ever built, and its energy supply supported four daring interplanetary missions (Galileo, Ulysses, Cassini, New Horizons). To explore the use potential of the GPHS-RTG in the solar system, its conservative application range and performance should be determined. In this work, a comprehensive model of the GPHS-RTG was developed, and its calculated results agreed well with Lockheed Martin’s test report (temperature relative error < 1 %). The study demonstrates that within the Earth orbit, the distance of the mission area from the sun and the angle of incidence sunlight significantly affect the thermoelectric performance and hot-junctions’ temperature. Moreover, conservative application ranges and their extending methods (changing coating material, thermal loading, and operational voltage) for GPHS-RTG at different attitudes in the solar system were determined for the first time by comparing the proportion of the hot-junction over-temperature area. The temperature distribution and its cause of formation in the axial and circumferential directions of the GPHS-RTG during solar system missions were revealed in the end. This work is valuable for future RTG design and mission planning.

Multi-objective optimization strategy for multipolar magnesium electrolysis cell based on thermal-electric model

In the operation of industrial multipolar magnesium electrolysis cell, cell voltage and current density are important indicators of the production performance of the cell, while thermal balance is a key factor for normal operation. This paper utilizes the finite element method to establish a three-dimensional full cell thermal-electric model, studying the thermal field distribution and current density distribution in a 165kA multipolar magnesium electrolysis cell. Based on the heat balance of the multipolar cell, the influence of structural parameters on current intensity, average current density at the anode surface and resistance voltage is assessed. Dimensionless analysis yielded optimization criteria, and the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was employed for multi-objective optimization problems. When stringent optimization is executed, significant performance improvements can be achieved in terms of the electrolysis cell's resistance voltage and current density. Moreover, under the optimization criteria, the relative error of the 265kA multipolar magnesium electrolysis cell model is less than 1 %. The results indicate that the workflow combining the finite element method with multi-objective optimization algorithms can be applied to the optimization and scale-up design of high-current multipolar magnesium electrolysis cell.

Bias-stress-stable sub-1.5V oxide thin-film transistors via synergistic composition of sol-gel quaternary high-k oxide dielectrics

A rising demand in reliable, energy-efficient, and large-area electronics, particularly in the realm of sol-gel oxide thin-film transistors (TFTs), has steered research focus away from semiconductor towards dielectrics. However, achieving both bias stability and low-voltage operation remains a significant hurdle. While typical oxide TFTs employ high-dielectric-constant (high-k) dielectrics with lowered film thickness to acquire low-voltage operation, they inevitably suffer from undesired defects at both bulk and interfacial trap sites in dielectric layer. In this study, bias-stress-stable all solution-processed oxide TFTs were demonstrated with operation voltage under 1.5 V via sol-gel quaternary high-k oxide dielectric (Al-Hf-Zr-O, AHZO). In-depth understanding of their individual contributions to dielectric performance leads to the acquisition of optimized composition ratios of AHZO with amorphous feature and outstanding dielectric performance, marked by dielectric constant (k) over 11, leakage current density (Jleak) below 10−5.5 A cm−2, and sturdy breakdown strength (EB) exceeding 5 MV cm−1. By integrating the AHZO with In-Ga-Zn-O (IGZO) layer, we achieved sub 1.5 V TFTs while maintaining excellent bias stability with threshold voltage (VTH) shift lower than 0.20 V for 3600 s. Our findings offer a detailed insight into the realm of multi-component oxide dielectrics, paving the way for miniaturization and reliability in functional devices and sensors.

PVP-assisted preparation of high-performance LiMn0.6Fe0.4PO4/C cathode materials

LiMnXFe1-XPO4 (X = 0.6) has excellent energy density and thermal stability, combining the excellent multiplicity performance of LiFePO4 and the high operating voltage of LiMnPO4. However, lower electronic conductivity and lithium ion diffusion rate are the main problems faced. We successfully synthesized LiMn0.6Fe0.4PO4 with uniform particles by a solvothermal method using surfactant PVP as an anti-agglomeration agent. At the same time, we found that the concentration of PVP in the reaction mixture plays a crucial role in the controllable structure and morphology of LiMn0.6Fe0.4PO4, thus accelerating the de-embedding of lithium ions reached 145.2 mAh g−1 under 1 C test. Therefore, the high-performance LiMn0.6Fe0.4PO4/C nanomaterials synthesized by the solvothermal method are significant for developing and applying lithium-ion batteries.

Li Promoting Long Afterglow Organic Light-Emitting Transistor for Memory Optocoupler Module.

The artificial brain is conceived as advanced intelligence technology, capable to emulate in-memory processes occurring in the human brain by integrating synaptic devices. Within this context, improving the functionality of synaptic transistors to increase information processing density in neuromorphic chips is a major challenge in this field. In this article, Li-ion migration promoting long afterglow organic light-emitting transistors, which display exceptional postsynaptic brightness of 7000cdm-2 under low operational voltages of 10V is presented. The postsynaptic current of 0.1mA operating as a built-in threshold switch is implemented as a firing point in these devices. The setting-condition-triggered long afterglow is employed to drive the photoisomerization process of photochromic molecules that mimic neurotransmitter transfer in the human brain for realizing a key memory rule, that is, the transition from long-term memory to permanent memory. The combination of setting-condition-triggered long afterglow with photodiode amplifiers is also processed to emulate the human responding action after the setting-training process. Overall, the successful integration in neuromorphic computing comprising stimulus judgment, photon emission, transition, and encoding, to emulate the complicated decision tree of the human brain is demonstrated.

Suppressed phase separation in high-voltage LiNi0.5Mn1.5O4 cathode via Co-doping

Spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode material with high operating voltage and energy density. However, the poor rate performance caused by the two-phase reaction during charging and discharging limits its large-scale application. In this work, Co3+ doped LNMO cathode materials are prepared by co-precipitation method, and the effect of Co3+ doping replacing Mn4+, as well as the amount of Co3+ doping (LiNi0.5CoxMn1.5-xO4) are explored. Co3+ doping increases the content of Mn3+, thus improving the electronic conductivity of LNMO. Co3+ doping suppresses the phase transition of LNMO during discharging, which results in a smaller volume change and improves cycling stability. The presence of a solid solution intermediate allows for more uniform changes within the particles during the discharge process, thus increasing the diffusion rate of Li+ ion. LiNi0.5Co0.05Mn1.45O4 exhibits the best electrochemical performance compared to other samples, with a discharge specific capacity of 111.1 mAh g−1 after 500 cycles at 1 C and a capacity retention of 92.4%. At 10 C high rate, the specific discharge capacity is 106.8 mAh g−1. Our research reveals that Co3+ doping can improve the electrochemical performance of LNMO and provide a deeper insight into Co3+ doping of other cathode materials.

Sustainable, low-cost, high-contrast electrochromic displays via host–guest interactions

Electrochromic (EC) displays with electronically regulating the transmittance of solar radiation offer the opportunity to increase the energy efficiency of the building and electronic products and improve the comfort and lifestyle of people. Despite the unique merit and vast application potential of EC technologies, long-awaited EC windows and related visual content displays have not been fully commercialized due to unsatisfactory production cost, durability, color, and complex fabrication processes. Here we develop a unique EC strategy and system based on the natural host and guest interactions to address the above issues. A completely reusable and sustainable EC device has been fabricated with potential advantages of extremely low cost, ideal user-/environment friendly property, and excellent optical modulation, which is benefited from the extracted biomass EC materials and reusable transparent electrodes involved in the system. The as-prepared EC window and nonemissive transparent display also show comprehensively excellent properties: high transmittance change (>85%), broad spectra modulation covering Ultraviolet (UV), Visible (Vis) to Infrared (IR) ranges, high durability (no attenuation under UV radiation for more than 1.5 mo), low open voltage (0.9 V), excellent reusability (>1,200 cycles) of the device's key components and reversibility (>4,000 cycles) with a large transmittance change, and pleasant multicolor. It is anticipated that unconventional exploration and design principles of dynamic host-guest interactions can provide unique insight into different energy-saving and sustainable optoelectronic applications.

Electrochemical processes for simultaneous sulfur and energy recoveries from sulfide-containing wastewater

Hydrogen sulfide and dissolved sulfide are notorious and lethal contaminants. The electrochemical process adopting the two-electron sulfide anodic oxidation reaction is an attractive strategy, which can simultaneously recycle and convert the chemical energy and sulfur resources into valued products. Sulfide pollutants are promising electron donors to reduce the electrochemical production cost, which is demonstrated in a sulfide/air fuel cell and a sulfide depolarized electrolyser. Sulfide oxidation behaviors are investigated on the developed IrxRu1-xO2 catalyst. A sulfide/air fuel cell is applied to evaluate the self-driven abilities of sulfur recovery and electricity generation. The sulfide/air fuel cell exhibits a notable discharge current density of > 120 mA cm−2 for 1.0 mol/L Na2S solution and 42.43 ± 1.94 mA cm−2 for the sulfide spent caustic stream. The potentials of sulfide anodic depolarization for electrochemical cost reduction are evaluated in a sulfide depolarized electrolyser for hydrogen production. Its open cell voltage is −0.33 V. For sulfur recovery, the cell can achieve about 20 mA cm−2 at 1.0 V, where the average energy cost of hydrogen production is about 2.39 kWh Nm−3. The sulfide removal rate is 0.26 ± 0.04 kgS m-2h−1, with an average current efficiency of 152.47 ± 28.59 %. This work may shed light on the potential of the incorporation of sulfide contaminants abatement and electrochemical productions.

Effect of substrate temperature on growth mechanism and properties of PEALD-MgO dielectric films for amorphous-IGZO TFTs

Magnesium oxide (MgO) films have been prepared by plasma enhanced atomic layer deposition with bis(cyclopentadienyl)magnesium precursor and oxygen plasma reactant at substrate temperature between 150 °C and 450 °C. The structural, morphological, optical, and chemical properties of the prepared MgO films were studied by spectroscopic ellipsometer, grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS). The electrical property of MgO film was obtained by performing capacitance-voltage measurement on the Al/MgO/Si structures. The experiment result shows that growth rate of MgO film decreases with the deposition temperature increased. GIXRD analysis presented that MgO films are cubic with predominantly (220) crystal orientation. XPS analysis shows that ratio of Mg/O is highest in MgO film prepared at 350 °C. To illustrate the possible applications of MgO film as a gate dielectric in thin film transistor (TFT), indium‑gallium‑zinc oxide (IGZO) was used as channel layer. The optimized IGZO/MgO TFT showed an electron mobility of 1.63 cm2/Vs, an on/off current ratio of 106, and a subthreshold swing of 0.50 V/decade at a low operation voltage of −0.11 V.

Side chain-engineered pseudocapacitive semiconducting polymer electrodes for symmetrical supercapacitors operable at wide potentials

Pseudocapacitive electrodes based on inorganic metal oxides exhibit superior capacitance. However, they suffer from limited operational voltage, resulting in low energy and power densities. To address these issues, redox semiconducting polymer (SP)-based pseudocapacitive electrodes, integrating electron donor and acceptor functionalities, offer a promising solution. In this study, we introduce two novel pseudocapacitive SP electrodes composed of highly planar electron-donating building blocks 4,8-bis ((5-octylthiophen-2-yl)ethynyl)benzo[1,2-b:4,5-b'] dithiophene (TBDT) with an electron-accepting building blocks benzo[c][1,2,5]thiadiazole (BT) and its side chain manipulated counterpart, i.e., OBT, denoted as SP1 and SP2, respectively. Among them, SP2 demonstrates a maximum specific capacitance of 117 F/g at 1 A/g. Furthermore, a symmetric supercapacitor fabricated for full-cell applications exhibits a significant energy density, reaching 29.1 Wh kg−1, and a maximum power density of 12.4 kW kg−1 within the wide operating potential window of 2.5 V. The exceptional performance of the pseudocapacitive electrode can be attributed to its highly planar backbone, nanoporous morphology, low crystallinity, and low lowest unoccupied molecular orbital levels. Overall, this new class of pseudocapacitive polymer electrode holds great potential for diverse sustainable energy storage technologies, addressing the limitations of traditional inorganic metal oxide-based electrodes by offering wide potentials window.

Controllable Meshing of Distribution Grids through a Multi-Leg Smart Charging Infrastructure (MLSCI)

The paper provides a novel approach for controllably meshing traditional medium-voltage networks by means of a fast-charging parking station with multiple points of delivery connected to different radial feeders. Regulating power flows at each point of delivery while the charging service is being provided, which means actively controlling power exchanges between radial distribution feeders can significantly increase the hosting capacity of the power system. Remarkable benefits are expected when the distribution networks to which the charging infrastructure is connected differ in terms of main characteristics, e.g., rated voltage level, end-user type and operating profiles, and the number and type of renewable plants. The paper focuses on technical targets, such as loss reduction and power quality in terms of admitted voltage deviation from the rated value. The power exchanges between distribution feeders are made possible by a controlled DC link, where bi-directional DC/DC converters are connected so as to charge or discharge vehicles according to the Vehicle-To-Grid approach. A multiplexer topology in which several vehicles can be alternatively connected to the same DC/DC converter is modeled. The proposed concept can contribute to network flexibility by controllably meshing distribution feeders and, jointly, by modulating charging processes according to assigned charging constraints.

Recent development in addressing challenges and implementing strategies for manganese dioxide cathodes in aqueous zinc ion batteries

Safety issues of energy storage devices in daily life are receiving growing attention, together with resources and environmental concerns. Aqueous zinc ion batteries (AZIBs) have emerged as promising alternatives for extensive energy storage due to their ultra-high capacity, safety, and eco-friendliness. Manganese-based compounds are key to the functioning of AZIBs as the cathode materials thanks to their high operating voltage, substantial charge storage capacity, and eco-friendly characteristics. Despite these advantages, the development of high-performance Mn-based cathodes still faces the critical challenges of structural instability, manganese dissolution, and the relatively low conductivity. Primarily, the charge storage mechanism of manganese-based AZIBs is complex and subject to debate. In view of the above, this review focuses on the mostly investigated MnO2-based cathodes and comprehensively outlines the charge storage mechanisms of MnO2-based AZIBs. Current optimization strategies are systematically summarized and discussed. At last, the perspectives on elucidating advancing MnO2 cathodes are provided from the mechanistic, synthetic, and application-oriented aspects.

Tunable THz absorbers based on LC-tuned Yagi-Uda antennas

ABSTRACT This study examines the structural configuration of Yagi-Uda micro-antenna arrays, the resonant properties of which are tunable through nematic liquid crystals in the terahertz spectral region. Reorienting liquid crystals by varying the voltage applied to the liquid crystal cell allows for control of the reflectance and absorbance amplitudes within the 7–12 THz operational frequency range. The reflectance and absorbance control ranges are around 50–60% across most of the frequency range, notably reaching approximately 90% at 11.1 THz. The optimal operational voltage ranges for the presented structure were approximately 1.1–1.9 V at the lower frequencies and 1.4–2.5 V at higher frequencies. This research highlights the potential of such metamaterial designs for efficient and adaptable applications in the THz spectrum.

J-MISFET Hybrid Dual-Gate Switching Device for Multifunctional Optoelectronic Logic Gate Applications.

High-performance and low operating voltage are becoming increasingly significant device parameters to meet the needs of future integrated circuit (IC) processors and ensure their energy-efficient use in upcoming mobile devices. In this study, we suggest a hybrid dual-gate switching device consisting of the vertically stacked junction and metal-insulator-semiconductor (MIS) gate structure, named J-MISFET. It shows excellent device performances of low operating voltage (<0.5 V), drain current ON/OFF ratio (∼4.7 × 105), negligible hysteresis window (<0.5 mV), and near-ideal subthreshold slope (SS) (60 mV/dec), making it suitable for low-power switching operation. Furthermore, we investigated the switchable NAND/NOR logic gate operations and the photoresponse characteristics of the J-MISFET under the small supply voltage (0.5 V). To advance the applications further, we successfully demonstrated an integrated optoelectronic security logic system comprising 2-electric inputs (for encrypted data) and 1-photonic input signal (for password key) as a hardware security device for data protection. Thus, we believe that our J-MISFET, with its heterogeneous hybrid gate structures, will illuminate the path toward future device configurations for next-generation low-power electronics and multifunctional security logic systems in a data-driven society.

Atomic layer annealing for spatial tailoring in sub-4 nm AlN RRAM devices with low-voltage operation

This article investigates the spatial tailoring of nitrogen vacancies by atomic layer annealing (ALA) on resistive random access memory (RRAM) devices with an AlN resistive switching layer. The ALA technique involves the in-situ layer-by-layer He/Ar plasma treatment in the cycle of atomic layer deposition for AlN. The AlN RRAM devices prepared with the ALA treatment near the TiN electrode have significantly superior uniformity of the operation voltages and the switching resistances, along with a lower cycle-to-cycle variation in endurance. This enhancement could be attributed to the relatively stable location of rupture and formation of conductive filaments, as a result of the film densification and the suppression of nitrogen vacancies in the AlN region treated with the ALA process. The AlN RRAM devices also demonstrate excellent retention of more than 106 seconds at 125°C. In addition, the ultra-thin 3.3 nm AlN switching layer contributes to low operation voltages of AlN RRAM. The outcomes manifest that the ALA technique could effectively improve the properties of nanoscale materials through precise spatial tailoring, with an accuracy up to atomic scale.

Accurate 2-D analytical model for cylindrical gate-junctionless ferroelectric-nanowire (CG-JFe-NW) MOSFET with scaled channel length

In this article, we propose a 2D analytical-model of a cylindrical gate-junctionless ferroelectric-nanowire (CG-JFe-NW) MOSFET for evaluating central potential, electric field, threshold voltage, mobility and current voltage characteristics. Central potential, threshold voltage, and current in the linear and saturation regions are derived by solving the 2D Poisson’s equation employing the parabolic-potential- approximation (PPA) profile. The recommended model is appropriate for compact modelling as it includes the phenomenon of bulk conduction, surface conduction and ferroelectric negative capacitance in all the regions of the device operation. Ferroelectric properties are introduced by combining Silicon doped hafnium oxide (ferroelectric layer) with HfO2 and SiO2 (dielectric layers), and an extensive study has been performed to determine the effects of interfacial-layer thickness and variation of channel length on device performance. For all relevant device characteristics and for all the operational voltage ranges, it is demonstrated that the analytical model entirely corresponds with the numerical simulations. For simulations, the Atlas 3-D simulator has been taken into consideration.