Search

Zinc-based flow batteries have attracted tremendous attention owing to their outstanding advantages of high theoretical gravimetric capacity, low electrochemical potential, rich abundance, and low cost of metallic zinc. Among which, zinc-iron (Zn/Fe) flow batteries show great promise for grid-scale energy storage. However, they still face challenges associated with the corrosive and environmental pollution of acid and alkaline electrolytes, hydrolysis reactions of iron species, poor reversibility and stability of Zn/Zn2+ redox couples. In this work, bromide ions are used to stabilize zinc ions via complexation interactions in the cost-effective and eco-friendly neutral electrolyte. Cyclic voltammetry results reveal that the redox reversibility between Zn and stabilized Zn2+ is greatly improved. The results of spectrum characterization and density functional theory calculation verify that the formation of Zn[Brn(H2O)6-n]2-n (1≤n≤4, n is integer.) ions accounts for the increased electrochemical reversibility of Zn/Zn2+ pairs. Moreover, to overcome the bottleneck of slow kinetics of the coordination interactions between Zn2+ and Br−, ZnBr2 is judiciously selected as the electrolyte additive to promote the complexation process. Adopting K3Fe(CN)6 as the positive redox species to pair with the zinc anode with ZnBr2 modified electrolyte, the proposed neutral Zn/Fe flow batteries deliver excellent efficiencies and superior cycling stability over 2000 cycles (356 hours), shedding light on their great potential for large scale energy storage.

A novel diamine (FAPDA) bearing rigid planar fluorene and amide groups was successfully synthesized. Using such diamine and pyromellitic dianhydride (PMDA), a high-barrier polyimide (FAPPI) was obtained. FAPPI exhibits an outstanding gas barrier. Its water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) are as low as 0.51 g·m–2·day–1 and 0.43 cm3·m–2·day–1, respectively. Additionally, FAPPI shows excellent thermal stability with a coefficient of thermal expansion (CTE) of 5.8 ppm·K–1 and a glass transition temperature (Tg) of 416 °C. Molecular simulations, positron annihilation, and X-ray diffraction were utilized to gain insight on the microstructures for the enhanced barrier properties. Introducing fluorene moieties and amide groups improves the regularity and rigidity of molecular chains and increases interchain interaction of PI, resulting in low free volumes and decreased movement capacity of the chain. The low free volumes of FAPPI restrain the gas diffusivity and solubility. Meanwhile, the decreased chain movement reduces the diffusivity of gases. Consequently, barrier performances of FAPPI are improved. The polyimide possesses widespread application in the microelectronics packaging fields.

An aqueous all-iron flow battery is a promising alternative for large-scale energy storage applications due to its low cost and high safety. However, the inferior Fe plating/stripping reversibility and hydrolysis of Fe2+ at the anode significantly limit its capacity retention and lifespan. Herein, we propose a coordination strategy to delicately tune the coordination structure of Fe2+, enabling effective suppression of Fe2+ hydrolysis and a highly reversible Fe plating/stripping reaction. Firstly, citrate is screened to feature a strong ligand field with the largest splitting energy among various ligand anions. Subsequently, sodium citrate bearing a high LUMO and large binding energy is identified to be the most suitable additive for the anolyte. By adding sodium citrate into FeCl2, the formation of a highly stable Fe2+–citrate coordination structure is confirmed via carboxyl groups. This effectively alters the intrinsic [Fe(H2O)6]2+ structure and yields remarkably improved Fe deposition during charging, allowing a highly reversible Fe plating/stripping reaction at the anode. Finally, the all-iron flow cell adopting Fe2+–citrate anolyte delivers an averaged 100% CE for 300 charge–discharge cycles without capacity decay, which is the longest cycle-life reported in the open literature.

The vanadium flow battery (VFB) has seen a promising potential for use in large-scale energy storage. However, the sluggish anode redox chemistry still greatly limits the cycling performance of the VFBs. Herein, we realize an enhanced anode redox chemistry for the VFBs by tailoring the oxygen functional groups on carbon felts via a facile ozone-accelerated acid oxidation method, and more importantly uncover the modulation essence of p-band center in activated carbon felts. By introducing oxygen functional groups, the activated carbon felts exhibit both increased specific surface area and improved hydrophilicity over pristine carbon felts. Material and electrochemical characterizations indicate that an increased oxygen content in the carbon felts can substantially facilitate the V2+/V3+ redox kinetics. Benefiting from the enhanced V2+/V3+ kinetics, the VFB full cell delivers a superior energy efficiency of 72.8 % at 300 mA cm−2, and a long-term cycling stability is also achieved over 600 consecutive charge-discharge cycles at 150 mA cm−2 with only a 6.5% decay in energy efficiency. Most importantly, first principle calculations uncover that the oxygen function groups, especially carboxyl, can enhance the adsorption process but meanwhile to a certain extent suppress the charge transfer process for the V2+/V3+ redox reactions, which highlights the significance of delicate modulation of oxygen function groups on carbon felts to enhancing anode redox chemistry and full cell performance for the VFBs.

Nitrogen-doped carbon felt has exhibited great promise in enhancing the cycling performance and lifespan of vanadium flow batteries (VFBs). However, the fabrication of stable and high-performance nitrogen-doped carbon felt is still to a certain extent hindered by existing preparation processes. Herein, a two-step novel in situ interfacial co-polymerization strategy is proposed to construct microvillus-like nitrogen-doped carbon on carbon felt, which features excellent homogeneity, high doping content and controllable nitrogen type conversion. By adding polyethyleneimine into the polymerization reaction, the aggregation effect of polydopamine is corrected and more strongly bonded nitrogen atoms are introduced via covalent interactions, yielding a hierarchical electrode interface with a greatly enhanced pyridinic-N content. Electrochemical characterization studies show that the prepared electrode possesses superior reaction kinetics towards both VO2+/VO2+ and V2+/V3+ redox couples, which can also realize a facile mass-transfer process. First principles calculations at the atomic level further ascribe the promoted V2+/V3+ kinetics to the enhanced vanadium adsorption on pyridinic-N, while attributing the promoted VO2+/VO2+ kinetics to a remarkably reduced activation energy barrier associated with doped N atoms. Adopting the prepared electrodes, the VFB demonstrates a superior energy efficiency of 73.6% at 300 mA cm−2, and achieves an excellent and long-term cycling stability over 600 cycles at 200 mA cm−2 with an extremely low energy efficiency decay of 0.006% per cycle.

Metal-nitrogen-carbon materials are promising catalysts for CO2 electroreduction to CO. Herein, by taking the unique hierarchical carbon nanocages as the support, an advanced nickel-nitrogen-carbon single-site catalyst is conveniently prepared by pyrolyzing the mixture of NiCl2 and phenanthroline, which exhibits a Faradaic efficiency plateau of > 87% in a wide potential window of −0.6–−1.0 V. Further S-doping by adding KSCN into the precursor much enhances the CO specific current density by 68%, up to 37.5 A·g−1 at −0.8 V, along with an improved CO Faradaic efficiency plateau of > 90%. Such an enhancement can be ascribed to the facilitated CO pathway and suppressed hydrogen evolution from thermodynamic viewpoint as well as the increased electroactive surface area and improved charge transfer fromkinetic viewpoint due to the S-doping. This study demonstrates a simple and effective approach to advanced electrocatalysts by synergetic modification of the porous carbon-based support and electronic structure of the active sites.

The mechanical condition in stack assembly can impose a significant influence in performance and reliability of the vanadium flow battery. In order to analyze the influence and optimize the overall performance, the effect of clamping force on electrode morphology, mass transfer and polarizations is investigated in this study by measurement of contact resistance and development of a coupled mechanical-electrochemical model. The experimental results indicate that the contact resistance and ohmic polarization decreases with an increase in clamping force, while the simulation results demonstrate that the clamping force can significantly impact on the electrode morphology and mass transport phenomena, and subsequently affect the distributions of activation and concentration polarizations. Despite the concentration polarization presenting to rise at a large clamping force, the overall polarization is proved to be decreased demonstrating that an increased clamping force can offer high voltage efficiency and power density. By further considering the mechanical failure probability and trading off the cell performance and reliability, an optimal clamping force is successfully determined. Such an analysis focusing on assembling condition is vital for understanding the effect of mechanical condition on the battery performance, while also highlighting the significance of rational mechanical design and assembly in flow battery manufacture.

Stack reliability is of great importance in commercialization of vanadium redox flow battery (VFB) since practical VFB stacks are prone to undergo material failure and electrolyte leakage caused by unreliable stack design and improper assembling conditions. A comprehensive evaluation of mechanical behavior and analysis of stack failure is thus highly valued for material fabrication, stack design and assembly. In this study, mechanical behavior and Weibull statistics based failure analysis of the VFB stacks are investigated. The Weibull parameters of two key components are firstly determined from tensile strength tests, which, in combination with finite element analysis of the stack mechanical behavior, are subsequently used to calculate the stack failure probability at specified clamping forces for two different stack designs that both contains 20 individual cells. The results demonstrate that the stack failure probability can be significantly reduced by properly decreasing the clamping forces for both designs, while adding a thick plate to the middle of the stack can effectively lower the probability of failure thus offering a superior stack mechanical performance and a prolonged stack life cycle. Such an approach to analyze stack failure can be readily accessed by flow battery engineers for design and assembly of commercial VFB stacks.

In order to meet the increasingly stringent requirements for heat resistance and barrier properties in the packaging and electronic device encapsulation field. A high-barrier polyimide (NAPPI) contains naphthalene ring and amide group was prepared by polymerization of a novel diamine (NAPDA) and pyromellitic dianhydride. The structure and properties of diamine monomers and polymers were characterized. Results show that the NAPPI exhibits superior barrier properties with extremely low water vapor and oxygen transmission rate values of 0.14 g·m−2·day−1 and 0.04 cm3·m−2·day−1, respectively. In addition, the NAPPI presents outstanding mechanical properties and thermal stability as well. This article attempts to explore the relationship between NAPPI structure and barrier properties by combining experiment and simulation. Studies on positron annihilation lifetime spectroscopy, Wide angle X-ray diffractograms and molecular dynamics simulations prove that the NAPPI has smaller interplanar spacing and higher chain regularity. In addition, the strong chain rigidity and interchain cohesion of NAPPI due to the presence of the rigid naphthalene ring and a large number of hydrogen bond interactions formed by amide groups result in compact chain packing and smaller free volume, which reduces the solubility and diffusibility of small molecules in the matrix. In general, the simulation results are consistent with the experimental results, which are important for understanding the barrier mechanism of NAPPI.

A novel diamine (3,6-CAPDA) bearing carbazole and amide group was prepared. On the basis of 3,6-CAPDA and pyromellitic dianhydride (PMDA), a high-barrier polyimide (3,6-CAPPI) was obtained through a two-step polymerization method. The 3,6-CAPPI displays excellent barrier performances and thermal stability. Its oxygen permeability (OP) and water vapor permeability (WVP) are low to 2.63 cm3·mil·m−2·day−1 and 3.22 g·mil·m−2·day−1, respectively. The 5% weight-loss temperature (Td5%) and glass transition temperature (Tg) are up to 526 °C and 431 °C, respectively. Through a combination of molecular simulation, X-ray diffraction and positron annihilation test, the effet of polymer structure on the barrier properties are fully explored. The results demonstrate that the introduction of carbazole and amide groups not only improves the chain order and rigidity, but also enhances the interchain force of polyimide, which thereby bring about enhancement of crystallinity and decreases of free volume and chain movement of 3,6-CAPPI. These factors lower the gas diffusivity and solubility in polymer matrix. Simultaneous decreases of gas diffusivity and solubility give rise to the notable enhancement of gas barrier for 3,6-CAPPI.

A high-barrier polyimide (2,7-CPI) was synthesized through the polymerization of pyromellitic dianhydride (PMDA) and a novel diamine (2,7-CDA) containing carbazole moiety. The synthesized diamine and polyimide were fully characterized by elemental analyses, FTIR and NMR. The 2,7-CPI displays very attractive barrier performances, with oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) low to 0.14 cm3&middot, m&minus, 2&middot, day&minus, 1 and 0.05 g&middot, 1, respectively. Meanwhile, 2,7-CPI also exhibits exceptional thermal stability with a glass transition temperature (Tg) of 467 &deg, C, 5% weight-loss temperature (Td5%) of 550 &deg, C under N2 and coefficient of thermal expansion (CTE) of 3.4 ppm/K. The barrier performances of 2,7-CPI are compared with those of a structural analogue (2,7-CPPI) and a typical polyimide (Kapton). Their barrier performances with respect to microstructure were investigated by molecular simulations, wide angle X-ray diffraction (WAXD), and positron annihilation lifetime spectroscopy (PALS). The results show that 2,7-CPI possesses better coplanar structure and more number of intermolecular hydrogen bonds among the three PIs, which result in tight chain packing and thereby high crystallinity, low free volume, and decreased chains mobility. That is, the high crystallinity and low free volume of 2,7-CPI reduce the diffusion and solubility of gases. Meanwhile, the poor chains mobility further decreases the gases diffusion. The reduced diffusion and solubility of gases consequently promote the improvement of barrier properties for 2,7-CPI. The polyimide has a wide application prospect in the field of flexible electronic packaging industries.

In vanadium redox flow batteries, an accumulated imbalance of the states-of-charge between the two half-cell electrolytes caused by vanadium ion crossover and gassing side reactions can result in only one half-cell achieving 100% state-of-charge, which is referred to as capacity loss that needs to be corrected online. In order to implement rebalancing control, online states-of-charge have to be monitored. In this paper, the electrolyte viscosity and its use for online state-of-charge monitoring design are investigated. The study firstly measures the viscosities of both V2+/V3+ and VO2+/VO2+ redox couples in sulfuric acid as the negative and positive half-cell electrolytes at different states-of-charge and temperatures, followed by establishing an empirical neural network model that correlates the state-of-charge to viscosity and temperature. To overcome the limitation in online viscosity measurements, Darcy’s law describing the flow of a fluid through a porous medium is further introduced to link the electrolyte viscosity to the pressure drop across a porous medium where the electrolyte solutions flow through. Together with the neural network model, the state-of-charge can be eventually represented as a function of pressure, temperature and flow rate that are readily measurable online, and accordingly an online state-of-charge monitoring design is developed, which could be readily integrated into the online battery control system for automated electrolyte rebalance. Experimental validation is performed on a 15-cell stack system and the results demonstrate the feasibility of the proposed method.

During the operation of vanadium redox flow battery, the cell stack can suffer from electrolyte leakage and material failure that significantly affect the overall performance of the battery, provided that the stack is improperly designed and assembled. In order to manufacture more reliable battery stacks without undergoing electrolyte leakage and mechanical failure, the stress distributions on all key components of the stack need to be known. In this study, three-dimensional mechanical models are developed to perform simulation analyses on stress distribution for the cell stacks. Stress distributions on key cell components under specified sealing gasket designs, assembling forces and number of cells in a stack are investigated for the single cell and multi-cell stacks, while potential material failure and damage for the stack components are also analyzed in accordance with maximum stress criterion and von Mises yield criterion depending on the material of the components. Simulations results successfully demonstrate the stress distribution and magnitude in specified stack design and assembly condition, and highlight the importance of mechanical analyses in developing flow battery stacks with superior sealing and mechanical performance for long-term use.

Implantable electronic devices (IEDs) are increasingly used in medical treatment and diagnose for physiological monitoring. However, encapsulation of IEDs still faces significant challenges as full prevention of body fluid penetration into the coating remains unsolved. To enable an extended lifecycle for IEDs, the impact of water transport on the failure mechanism of silicone rubber coating was systematically investigated in this study. Water absorption and morphology characterization firstly illustrate the water diffusion model and demonstrate the presence of cracks inside the silicone rubber coating, respectively. Subsequent electrochemical characterizations further verify a three-step water penetration behavior in the coating/substrate system, and meanwhile quantify the crack growth and evolution. By further experimental and finite element studies, it is proved that crack propagation is responsible for coating failure in IEDs, while a comprehensive failure mechanism of medical silicone rubber coating in simulated body fluid is also uncovered in a detailed manner for the first time. Such a clear elucidation of failure mechanism for silicone rubber coating is greatly beneficial for future packaging material design for IEDs.

Zinc-manganese flow batteries have drawn considerable attentions owing to its advantages of low cost, high energy density and environmental friendliness. On the positive carbon electrode, however, unstable MnO2 depositions can be formed during oxidation through disproportionation reaction of Mn3+, which result in poor reversibility of Mn2+/MnO2 and bring instability to Zn–Mn flow battery limiting its performance and further development. To tackle this issue, in this study, we reported a highly reversible Zn–Mn flow battery by employing EDTA-Mn as the positive electrolyte. In aqueous solutions, EDTA exhibits a strong ligand field for Mn2+ from ab initio calculations, which proves to form bonds with Mn2+ through carboxyl/amino groups and replace bonded waters in the solvation structure of Mn2+. Benefiting from the coordination effect of EDTA, both electrochemical and material characterizations demonstrate a highly reversible Mn2+/Mn3+ redox reaction in EDTA-Mn, which effectively inhibits the disproportionation reaction of Mn3+ without forming any deposited MnO2 on carbon electrode. The constructed Zn–Mn flow cell adopting EDTA-Mn not only demonstrates excellent rate performance with a high CE over 95 % operated at 10–50 mA cm−2, but also realizes a superior cycling stability over 300 cycles at 20 mA cm−2 affording 98 % CE and 75 % EE.

4-Amino-N′-(4-aminobenzoyl)benzohydrazide (AAPDA), a diamine monomer that contains two amide groups, was synthesised by amidation and reduction, after which it was polymerised with pyromellitic dianhydride (PMDA) to prepare AAPPI, a novel polyimide. AAPPI exhibited excellent barrier performance, with oxygen- and water-vapor-transmission rates (OTR and WVTR, respectively) of only 1.7 cm3 m−2 d−1 and 1.0 g m−2 d−1, respectively. This polyimide (PI) also exhibits outstanding thermal properties, with a glass transition temperature (Tg) of 423 °C, a 5% weight-loss temperature (Td5%) of 509 °C, and a coefficient of thermal expansion (CTE) of 2.58 ppm K−1 under nitrogen. The barrier performance of AAPPI was also compared to that of DABPI, a structurally similar PI. Molecular simulations, wide-angle x-ray diffractometry (WAXD), and positron annihilation lifetime spectroscopy (PALS) revealed that AAPPI forms many more interchain hydrogen bonds than DABPI due to its additional amide groups. Consequently, AAPPI has very tightly packed polymer chains, a high degree of crystallinity, a small free volume, and poor chain mobility. These factors generally inhibit the permeation of small molecules, which explains why AAPPI has better barrier properties than DABPI. This novel PI has broad applications for the packaging of flexible electronics.

The damage modes in ferrite-martensite dual-phase (DP) steels include ferrite grain boundary (F/F) decohesion, ferrite/martensite interface (F/M) decohesion and martensite cracking. To explore the mesoscopic origin for each damage nucleation mode, we investigated ferrite-martensite dual-phase (DP) steels with different volume fractions of martensite, and characterized mesoscopic strain and stress distributions using microscopic-digital image correlation in SEM (μ-DIC) and finite element (FE) calculations. We performed in-situ tensile testing in a SEM and observed that the dominant damage nucleation mode changed from ferrite grain boundary (F/F) decohesion to ferrite/martensite interface (F/M) decohesion and finally to martensite cracking, with increasing martensite volume fraction (Vm) and varying martensite distribution. Mesoscale stress and strain analysis based on μ-DIC and FE calculations clearly reveal mesoscale origins of these damage modes: 1) F/F decohesion is caused by high strain which promotes accumulation of regular dislocations near the grain boundary and residual dislocations in the grain boundary; 2) F/M decohesion is attributed to high strain gradient which is associated with the accumulation of geometry necessary dislocations; 3) Martensite cracking stems from high stress that is partitioned to martensite. Our work demonstrated the pivot of microstructure engineering to improve the damage resistance of composite-like alloys consisting of soft and hard constituent phases, such as dual-phase steels.

An intrinsic high-barrier polyimide (9-OH-FPPI) was prepared through the polycondensation reaction of pyromellitic dianhydride (PMDA) with a novel diamine (9-OH-FPDA) containing fluorenol moiety. The synthesized polyimide displays superior barrier performances, possessing water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) low to 1.64 g·m−2·day−1 and 0.66 cm3·m−2·day−1, respectively. Meanwhile, 9-OH-FPPI also demonstrates high thermal stability with a glass transition temperature (Tg) of 410 °C, 5% weight-loss temperature (Td5%) of 577 °C under N2 and coefficient of thermal expansion (CTE) of 5.65 ppm/K. A detailed molecular simulation study as well as positron annihilation lifetime spectroscopy (PALS) and wide angle X-ray diffraction (WAXD) analysis have been carried out to reveal the barrier mechanism. The results reveal that the introduction of fluorenol moiety not only enhances the rigidity and regularity of polymer backbone, but also improves the interchain cohesion of PI matrix, which in turn lead to high crystallinity, low free volume and poor chains mobility of 9-OH-FPPI. The high crystallinity and low free volume decrease the diffusion and solubility of gases in polyimide matrix. In addition, the poor chains mobility further suppresses the gases diffusion. Simultaneous reductions of gases diffusion and solubility promote the barrier properties of 9-OH-FPPI. The as-synthesized polyimide exhibits wide application prospects in the flexible electronic packaging industry.

High power output and efficient charge-discharge operation are deemed to be the pivotal for technological development of vanadium flow batteries. Due to large polarizations however, cycling efficiency is still to a great extent limited in high-power commercialized stacks adopting the conventional flow-through design. To facilitate an in-depth understanding of polarizations and realize a high-power and efficient operation, polarization analyses are performed in this study on a flow-through design based vanadium flow cell. Combined experimental and calculated results show that under the investigated testing conditions, the ohmic polarization dominates the cell polarization across 20–250 mA cm−2, while the electrolyte resistance can account for 70% of the cell resistance. To reduce the electrolyte resistance, further experimental results uncover that enhancing the ionic conductivity through adopting a dilute vanadium electrolyte at a high temperature can readily yield an energy efficiency of 80% at 250 mA cm−2. Such an efficiency enhanced operation can aid to reduce the stack cost, and further discussions concerning other electrolyte properties (e.g., viscosity and surface tension) and their associated effects on battery design and operation also manifest that the electrolyte optimization strategy is practically viable and can be considered for certain flow battery application scenarios.

Full commercialization of vanadium flow batteries requires a high current density operation. However, this can be only realized when associated large polarizations of the cell are properly reduced. Of all the cell components, the porous electrode plays a critical role in determining cell polarizations since it directly relates to each of the polarizations. Despite that, an in-depth understanding of electrode compression impact on polarizations of a flow cell is still limited in literature. In this work, a quantitatively experimental study to unveil the electrode compression impact on each of the polarizations as well as the performance of a vanadium flow cell is conducted by employing a symmetric cell configuration. Four different compression ratios are investigated by both ex-situ characterizations and in-situ symmetric cell tests, which successfully reveal its influence on activation, ohmic and concentration polarizations at varied operating current densities. Charge-discharge cycling tests further prove the significance of electrode compression to both efficiency and discharge capacity, while also delivering an optimal compression ratio for the investigated flow cell. Such a quantitative analysis not only promotes a deep understanding of the importance of electrode compression to cell performance, but is also of vital importance for stack design and optimization in practice.

Flow batteries are being increasingly deployed in grid-scale energy storage applications. However, long-term operation of flow batteries still suffers from a different extent of capacity decay. While the effects of ion diffusion and side reactions on capacity degradation have been identified and further minimized by improvement in materials, the mechanism of volumetric transfer and its influence in capacity still receive insufficient attentions that impedes further capacity optimizations for flow batteries. In order to gain an in-depth understanding of volumetric transfer mechanism in flow batteries, six different types of flow batteries are adopted in this study and further classified in accordance with electrolyte viscosities for investigations. Experimental results show that a net volumetric transfer in a conventional flow battery highly depends on viscosity values of the two half-cell electrolytes and is virtually towards the half-cell possessing a smaller electrolyte viscosity. For flow batteries with a mixed electrolyte in both half-cells, moreover, cycling tests further demonstrate a zero net transfer under similar viscosity measurements of both half-cell electrolytes. Unraveling the viscosity impact on volumetric transfer is greatly beneficial to facilitate deeper understandings of transport phenomena in flow batteries, which can contribute to realize long-term flow battery operation with a superior capacity retention.

In vanadium flow batteries, electrolyte transfer across the membrane can lead to a volumetric imbalance between the two half-cell electrolytes and a subsequent loss of available capacity. However, the transfer mechanism has not been comprehensively understood and this lack of knowledge has significantly limited long-term discharge capacity and stability of the vanadium flow battery. To overcome this issue, the electrolyte transfer mechanism is systematically developed in this study by analyzing the pressure drop across the membrane in accordance with Darcy's law and further validated by experiments. The experimental results show that the viscosity difference between the two half-cell electrolytes contributes greatly to the electrolyte transfer from negative half-cell to positive half-cell, while a large flow rate applied to both half-cells may also exacerbate the electrolyte transfer. Moreover, further experiments also demonstrate that the electrolyte transfer in continuous charge-discharge operation can be effectively suppressed by optimizing the flow rates based on viscosity measurements, which subsequently yields a notable improvement in discharge capacity. Revealing the electrolyte transfer mechanism is not only beneficial to enhancing long-term performance and stability of the vanadium flow battery, but also highly valued for understanding the transport phenomena in other flow battery systems.

Binary data in 1T1C or 2T2C non-volatile ferroelectric random access memories, which are represented by the polarization charges of switching and non-switching events, are retrieved when a reading current pulse exceeds the sense amplifier threshold for discrimination of nonswitching pulses, and a reset pulse is required after the destructive readout. Downscaling the dimensions of such memory cells reduces the measurable polarization charge proportional to the capacitor area, and data are no longer detected reliably in high-density memories. The nondestructive readout of the binary information is possible from the high- and low-conductance bipolar switching of a ferroelectric diode under two opposite poling fields, where the direction of the diode effect switches with polarization reversal. Our study of BiFeO3 thin-film capacitors shows measured polarization-modulated diode currents for encoding information within high-density memories. We used two in-plane nano-electrodes fabricated on the film surface in gaps of a few tens of nanometers. As an in-plane field is applied antiparallel to the domain orientation above a coercive field, the partial domains near the film surface layer are switched firstly to form conductive charged walls with respect to the underlying unswitched bulk matrix, so that we can observed an “on” current from current-voltage loops. As the switching field is high enough, the underlying domains throughout the whole film thickness are switched. In this case, there was no charged domain wall, and thus, we observed an “off” current. Both “on” and “off” currents with the ratio of 100 are stable over laboratory time with write cycles larger than 2×105 and write time as short as 10 ns, which provide the proof of ferro-resistive switching and independent adjustments of ferroelectricity and conductivity in a single-phase ferroelectric in promotion of the integration density of the memory with high performance.

The history of partial reversed domains in Pt/SrBi2Ta2O9/Pt thin-film capacitor arouses the splitting of the peak in one branch of butterfly capacitance–voltage (C–V) loops swept in a fast speed of 10 V/s. Nevertheless, the doublet emerges together, once the sweeping speed is slow enough. This is due to time-related imprint effect induced by the opposite trapped charges within the film thickness to compensate for the previous reversed domains. The previous volume fraction of switched domains under various dc voltages can be estimated from the intensity of the double peaks. Besides the memory effect due to the polarization reversal, one additional shoulder can also appear in the C–V loop under a stressing field at position equal to the applied voltage. This reflects the previous charge injection into the film under an arbitrary field. It is believed that the injected charge distribution within the film thickness facilitates the formation of a p–n junction with junction voltage equal to the applied voltage.

A ferroelectric-resistive random access memory consisting of a conductive BiFeO3 epitaxial thin film with a unipolar diode current modulated by electric polarization orientation is reported. This device has a memory that lasts for months, a sufficiently high on current and on/ off ratio to permit ordinary sense amplifiers to measure "1" or " 0", and is fully compatible with complementary metal- oxide semiconductor processing.

A general HSPICE macromodel for the CuxO based resistive random access memory(ReRAM) cell is presented in this paper. It can simulate both the dc and transient behavior of ReRAM cells. The simulation results were compared with the experimental results and exhibited desirable accordance.

Polycrystalline Sr 0.8 La 0.1 Bi 2.1 Ta 2 O 9 (SLBT), Sr 0.8 Bi 2.2 Ta 1.5 Nb 0.5 O 9 (SBTN), Sr 0.8 La 0.1 Bi 2.1 Ta 1.5 Nb 0.5 O 9 (SLBTN) were fabricated on Pt/Ti/SiO 2 /Si substrates by metalorganic decomposition. Well-saturated hysteresis loops with remanent polarization (2 P r ) around 24 μC/cm 2 and coercive field (2 E c ) around 112 kV/cm are obtained on Pt/SLBTN/Pt capacitors. Imprints, shifts of hysteresis loops along the voltage axis, are observed after heat treatment of poled Pt/SLBTN/Pt capacitors. Pt/SLBTN/Pt capacitors show excellent fatigue resistance with no polarization reduction up to 10 9 switches. The dc leakage current density of Pt/SLBTN/Pt capacitors is in the order of 10 −8 A/cm 2 below 100 kV/cm. These results indicate that the La 3+ and Nb 5+ co-modification is an effective way to improve the ferroelectric properties of Sr 0.8 Bi 2.2 Ta 2 O 9 (SBT) thin films.

La modified Sr0.8Bi2.2Ta2O9 (SLBT) thin films were fabricated on Pt/Ti/SiO2/Si substrates by metalorganic decomposition. All the films were annealed at 800°C using a rapid thermal annealing furnace. X-ray diffraction analysis indicated that single-phase layered perovskite SLBT ferroelectric thin films can be obtained and no secondary phase was found. The crystallization and hysteresis behavior of SLBT films showed a dependence on the La content. An increase of Pr and decrease of Ec with increasing La concentration were observed. The fatigue properties were found to be improved when more La was added to SLBT films. The results were discussed with respect to the effects of La3+ and Bi3+ substitution at perovskite A-site.

Samples of phosphorus silicate glass (PSG) layers were deposited in a class 100 clean room in two kinds of industrial type reactors: by plasma enhanced chemical vapour deposition (PECVD) and micro pressure chemical vapour deposition (μPCVD) at working temperatures of 380 °C and 430 °C, respectively. After deposition the samples were subjected to rapid thermal annealing (RTA) in a vacuum at 5×10 −3 Pa and temperatures of 800 °C, 1000 °C, 1200 °C and 1400 °C for 15–180 s. X-Ray photoelectron spectroscopy (XPS) investigations show that phosphorous oxides pass through a phase transition and evaporate, while silicon oxides evaporate and decompose. The rate of etching in ‘p’ etcher of μPCVD-PSG layer before annealing is 1023 A min −1 , after RTA at 800 °C for 15 s it is 909 A min −1 , and after annealing for 3 min it is 690 A min −1 . In the case of RTA at 1000, 1200 and 1400 °C for 3 min the etching rates are 660, 469 and 351 A min −1 , respectively, i.e. RTA results in considerable decrease of rate of etching. The same behaviour shows curves related to PSG layers obtained by PECVD. IR spectra show that PO bond vibration at 1320 cm −1 appears at temperatures of annealing T ≥1000 °C and time interval 60–180 s. A correlation between PSG layers characteristics and conditions of RTA is found.

ZrO2 thin film with suitable dielectric constant for MFIS FET's application was prepared by novel metal-organic-decomposition (MOD) method. The dielectric constants of the thin film laid between 10 and 30 and increased with the development of the crystallinity. The magnitude of the leakage current of the thin film with thickness of 27nm and 35nm was 1E-5 and 1E-7 A/cm2 respectively when 5V bias voltage was applied. The C-V characteristics show a memory window of 2.5V for a sweep voltage from -5V to +5V. It indicates that the thin film could satisfy the requirement of MFIS structure.

PbZr0.52Ti0.48O3 thin film prepared by metal-organic decomposition method was chemically etched by utilizing HF/HNO3 solution. Typical semiconductor processes were used to pattern the film. The dependence of the conformity of pattern transfer on the microstructure of the film was studied. The results showed that the etching rates were different between the islands of the grains and the surrounding areas within the film. The film with small grains is favored for pattern transfer of fidelity. The dimension of the islands of grains contributes greatly to the tolerance of patterned features. Tolerance of 2 μm has been achieved to fulfill the need of usage in microelectromechanical systems.

The critical dimension for reverse domain nucleation in the ferroelectric polarization switching of $\text{Pb}({\text{Zr}}_{0.4}{\text{Ti}}_{0.6}){\text{O}}_{3}$ (PZT) thin film was estimated experimentally from a coercive voltage estimation in $\text{Pt}/{\text{Al}}_{2}{\text{O}}_{3}/\text{PZT}/\text{Ir}$ ferroelectric thin-film capacitors with various ${\text{Al}}_{2}{\text{O}}_{3}$ thicknesses and switching currents. The critical nuclei dimension for reverse domain formation in a 300-nm-thick PZT was only $4.5\ifmmode\pm\else\textpm\fi{}0.4\text{ }\text{nm}$, which is in agreement with theoretical predictions of the critical nucleus size. Almost all the coercive voltage was applied to the nucleation layer thickness during ferroelectric switching. The classical Merz's exponential law for the domain velocity description and Laudauer's paradox of an implausibly large nucleation energy barrier were understood in terms of the charge-injection limited domain motion described by thermionic field emission at the $\text{Pt}/{\text{Al}}_{2}{\text{O}}_{3}$ interface or Fowler-Nordheim tunneling at the Pt/PZT interface.

A novel 2D nanometer edge contact type cell for phase change RAM is manufactured, in which the active area can be controlled mainly by the thickness of both bottom electrode film and the GST film. The high resistive GST is indispensable to minimize the writing current and threshold voltage of PCRAM. The GST resistivity can be increased effectively by doping nitrogen and the nitrogen-doped film is first used in the novel 2D nanometer structure successfully for reducing the threshold voltage application. It is found the phase change from FCC to hexagonal structure is suppressed by nitrogen doping, while 3 stable resistance states is first found in the resistivity-annealling temperature curve for the film by sputtering method, which might be used in multilevel PCRAM.

Generally, the ferroelectric capacitance under a d.c. voltage drops continuously with time, and the shape of capacitance–voltage (C–V) loops within a sweeping time more than 1 s resemble a butterfly, in comparison to the double-butterfly shape of an antiferroelectric. In this work, we developed a measuring technique for shortening sweeping time down to 500 ns for the rapid study of dielectric relaxation in ferroelectric Pb(Zr,Ti)O3 thin films. It is interestingly found that the traditional butterfly loops of a ferroelectric degenerate into double butterfly loops of an antiferroelectric when the sweeping time is sufficiently short, providing evidence of the nonlinear dielectric contribution of reversible domain motion. Reversible domains can align along a field under a voltage, but reverses back immediately into their previous directions under a reduced field strength to release their polarization charges, similarly to antiferroelectric domains. When the voltage stressing time is sufficiently long, the internal field for driving reversible domain motion is temporally screened by the injected charges accumulated in regions with different polarizations, dielectric permittivities, and conductivities (domain pinning), which results in time-dependent dielectric degradation. This charge injection is different from the traditional model of defect motion with a low mobility. Finally, we showed evidence of the charge injection from the imprint profile and reversible domain freezing into irrecoverable domains upon cooling.

The self‐aligned titanium silicide device technology has been studied by using NH3 plasma assisted thermal annealing and ion implant through titanium metal or silicide film. Enhanced surface nitridation of titanium by activated species suppresses lateral silicide growth and oxide contamination. NH3 plasma assisted annealing can be used as an effective method to form TiSi2 and activate implanted dopant. P+N junction and P channel metal–oxide–semiconductor field‐effect transistor can be produced by boron implant through Ti metal or its silicide and the NH3 plasma assisted thermal annealing.