Vanadium Transport Research Articles

Distinguishing contributions of diverse sediment components to vanadium transport, immobilization and transformation in aquifer

Vanadium (V) occurs in environment naturally and anthropogenically, but little has been understood about its environmental behavior in groundwater aquifer with sediments. This study investigated the pentavalent V [V(V)] transport and transformation under the influence of different sediment components (minerals, organic matter, and microorganisms) through column experiments. All these components played pivotal roles in V immobilization. The synergistic effects of sediment components enhanced V retention compared to individual component. Mineral components, particularly those containing carbonates and metal oxides, predominantly influenced V(V) transport as indicated by XRD analysis. Organic matter, especially under low pH conditions, induced particle aggregation, thereby inhibiting the transport of V(V). The V K-edge X-ray absorption near-edge structure spectroscopy revealed the formation of tetravalent V[V(IV)] in treatments involving organic matter and microorganisms. Notably, organic matter exhibited the capability to directly reduce V(V). The introduction of microorganisms restricted V(V) transfer. V(V) reducing genera (e.g., Brevundimonas, Arenimonas, Xanthobacter) were detected, achieving V(V) reduction to insoluble V(IV). V(V) bioreduction was improved by minerals that promote microbial metabolism with enhanced electron transfer, or by organic matter that increases levels of intracellular nicotinamide adenine dinucleotide and extracellular polymeric substances. This study specifies the contributions of different sediment components to the transportation and transformation of V, deepening our understanding of V biogeochemistry in groundwater aquifer.

Improving the Selectivity of Commercial Membranes in Vanadium Redox Flow Batteries through the Direct Deposition of an Additional Selective Layer

The evolution of both energy demand and energy supply requires large energy storage systems to face the challenges related to the not-programmable nature of renewable energy source. Vanadium Redox Flow Batteries (VRFB) is a promising solution for these challenges due to its decoupled energy and power, high flexibility, fast response time and long cycle life [1]. However, some technological issues limit the competitiveness of the technology by increasing the cost of the system. One of these issues is vanadium cross-over, which is the undesired transport of vanadium ions through the not-ideally selective membrane, causing battery self-discharge, capacity loss and electrolyte imbalance [1]. Relatively thick membranes (>50 µm) are usually employed in the commercial applications to mitigate cross-over losses, leading to increased voltage ohmic losses and high system costs. Indeed, the membrane is one of the main cost items of the technology as it may contribute up to 50% of total stack costs [2]. Therefore, the development of a low-cost and selective separator will improve the technology. As demonstrated by the authors [3], an effective strategy to reduce system costs and cross-over losses is to improve the selectivity of NafionTM membranes with an additional selective layer, allowing to reduce the thickness, thus the costs and the ohmic losses. The additional selective layer, referred as “the barrier”, proposed by the authors is a layer of controlled morphological properties directly deposited on the membrane that introduces a tortuous path for the ion transport, successfully mitigating vanadium fluxes through the separator [3]. In previous works the barrier was deposited by Reactive Spray Deposition Technology (RSDT) [3], but in this work the barrier was manufactured via Ultrasonic Spray Coating (USC), a commercial and easily scalable technique. Exploiting the USC for the manufacturing of the barrier accelerates the scale-up of the barrier to a scale closer to the commercial applications (100 cm2). Moreover, the barrier is composed by only commercially available materials (NafionTM ionomer, Vulcan® XC-72R and silica nanoparticles) and deposited on commercial membranes, thus facilitating a future industrial production.In this work, further developments of the barrier with respect to previous works [4] are discussed. In particular, the deposition process is further investigated by evaluating the influence of the heat-plate temperature and the ink flow rate on the evaporation process of the solvent and its impact on the performance of the barrier. Regarding barrier composition, different commercial polymers (AquivionTM and NafionTM ) were employed both as ionomer in the barrier layer and as supporting membrane to analyse the influence of different equivalent weight and the coupling of different materials on the selectivity of the barrier. Moreover, the barrier was also deposited on thin membranes (<25 µm) to enable their use in commercial applications, reducing system costs and ohmic losses.The barrier layers were characterized combining morphological and electrochemical characterization. SEM analysis was conducted to relate the morphology of the layer with the ink composition and the deposition parameters. Instead, charge-discharge cycles with voltage cut-offs were performed to evaluate the influence of the different barrier layers on the capacity loss and the efficiency of the battery. A commercial electrolyte was used for the cycling test to assess the ability of the barriers in operating conditions closer to the ones of real applications. In these operating conditions the capacity loss due to cross-over was reduced by nearly 20%, as reported in Figure 1, while the net vanadium transport by 30% with respect the bare membrane, as resulted from ICP-OES analysis of electrolytes at the end of the test. The barrier effectiveness is further improved adopting different electrolyte composition.Finally, the combination of ink and deposition parameters that ensured the highest selectivity were used to deposit a barrier with an active area of 100 cm2. The barrier was able to mitigate cross-over losses and reduced the capacity decay due to cross-over, confirming its effectiveness also at higher cell area.Figure 1 – Comparison of the discharged capacity with NafionTM N212 and the barrier during charge-discharge cycles with cut-off voltages at 100 mA cm-2. Cycles at different current densities were performed at beginning and end of test to evaluate battery performance in different conditions.

A comprehensive experimental and modelling approach for the evaluation of cross-over fluxes in Vanadium Redox Flow Battery

Vanadium cross-over is a critical issue in Vanadium Redox Flow Battery consisting in a complex interplay of different mechanisms of which a complete comprehension has not been reached yet. Due to the complexity of the involved phenomena, several models have been developed in literature to investigate vanadium cross-over. However, the conventional approaches for model calibration present a limited set of experiments for the validation preventing a complete understanding of cross-over phenomena. In this work a new and comprehensive approach is proposed. It is based on charge-discharge cycles with fixed exchanged capacity, able to isolate the capacity loss induced by cross-over fluxes, and on the measure of the self-discharge of the single electrolyte solutions by exploiting through-plate reference electrodes. Moreover, a 1D physically-based model of the operation of the battery is developed and calibrated on the data of electrolyte imbalance during charge-discharge cycles at three different current densities to obtain model parameters able to accurately describe the involved physics in different operating conditions. The model is then exploited to investigate the main vanadium transport mechanisms through the membrane and to evaluate the influence of the current density on the vanadium cross-over fluxes, net vanadium transport and self-discharge rate of the electrolyte.

In situ and in operando detection of redox reactions with integrated potential probes during vanadium transport in ion exchange membranes

The vanadium crossover is the primary source of capacity fade in vanadium flow batteries (VFB). Available transport models for the vanadium crossover use significantly different diffusion coefficients for the vanadium species. Previously, we demonstrated that redox reactions between V3+ and VO2+ occur within cation exchange membranes. Therefore, it seems very likely that the neglect of redox reactions inside the membrane may lead to these inconsistencies. To investigate the reactions inside the membrane, a time-resolved in situ and in operando method based on potential probes, which have already been successfully used to measure potentials on and in electrodes, was developed. The probes were integrated into firmly pressed layers of several membranes. This work reports the new experimental design and presents the first results which give valuable insights into the transport processes and redox reactions inside the membrane.

Determination of the through-plane profile of vanadium species in hydrated Nafion studied with micro X-ray absorption near-edge structure spectroscopy - proof of concept.

Vanadium-ion transport through the polymer membrane results in a significant decrease in the capacity of vanadium redox flow batteries. It is assumed that five vanadium species are involved in this process. Micro X-ray absorption near-edge structure spectroscopy (micro-XANES) is a potent method to study chemical reactions during vanadium transport inside the membrane. In this work, protocols for micro-XANES measurements were developed to enable through-plane characterization of the vanadium species in Nafion 117 on beamline P06 of the PETRA III synchrotron radiation facility (DESY, Hamburg, Germany). A Kapton tube diffusion cell with a diameter of 3 mm was constructed. The tube diameter was chosen in order to accommodate laminar flow for cryogenic cooling while allowing easy handling of the cell components by hand. A vertical step size of 2.5 µm and a horizontal step size of 5 µm provided sufficient resolution to resolve the profile and good statistics after summing up horizontal rows of scan points. The beam was confined in the horizontal plane to account for the waviness of the membrane. The diffusion of vanadium ions during measurement was inhibited by the cryogenic cooling. Vanadium oxidation, e.g. by water radiolysis (water percentage in the hydrated membrane ∼23 wt%), was mitigated by the cryogenic cooling and by minimizing the dwell time per pixel to 5 ms. Thus, the photo-induced oxidation of V3+ in the focused beam could be limited to 10%. In diffusion experiments, Nafion inside the diffusion cell was exposed on one side to V3+ electrolyte and on the other side to VO2+. The ions were allowed to diffuse across the through-plane orientation of the membrane during one of two short defrost times (200 s and 600 s). Subsequent micro-XANES measurements showed the formation of VO2+ from V3+ and VO2+ inside the water body of Nafion. This result proves the suitability of the experimental setup as a powerful tool for the determination of the profile of vanadium species in Nafion and other ionomeric membranes.

Dynamics of vertical vanadium migration in soil and interactions with indigenous microorganisms adjacent to tailing reservoir

Severe vanadium pollution in deep soil through surface infiltration during mining activities has been particularly concerned, but little is known about vanadium migration dynamics in vertical soil profile. Indigenous microorganisms widely exist in soil, however, their functions and suffered impacts during vertical vanadium migration have rarely been investigated. In this study, 100 cm height columns were constructed with undisturbed soil around vanadium tailing reservoir were constructed to describe vertical vanadium transport process and corresponding interactions between vanadium and indigenous microorganisms. 91 d continuous leaching with pentavalent vanadium [V(V)] showed that V(V) gradually downward migrated. Soil microorganisms slowed down vertical V(V) migration rate by transferring V(V) to insoluble tetravalent vanadium. Enriched Gemmatimonadaceae and Actinobacteria were identified to contribute to microbial V(V) transformation. Co-existing nitrate weakened the soil’s ability to intercept V(V) via electron competition. Microbial communities were reshaped by vanadium during leaching, while enzyme activities increased slightly due to vanadium stimulation. This work advances the understanding of vertical vanadium migration characteristics in soil, which is essential to risk management and effective remediation of vanadium-polluted sites.

Characterization of Dimeric Vanadium Uptake and Species in Nafion™ and Novel Membranes from Vanadium Redox Flow Batteries Electrolytes

A core component of energy storage systems like vanadium redox flow batteries (VRFB) is the polymer electrolyte membrane (PEM). In this work, the frequently used perfluorosulfonic-acid (PFSA) membrane Nafion™ 117 and a novel poly (vinylidene difluoride) (PVDF)-based membrane are investigated. A well-known problem in VRFBs is the vanadium permeation through the membrane. The consequence of this so-called vanadium crossover is a severe loss of capacity. For a better understanding of vanadium transport in membranes, the uptake of vanadium ions from electrolytes containing Vdimer(IV–V) and for comparison also V(II), V(III), V(IV), and V(V) by both membranes was studied. UV/VIS spectroscopy, X-ray absorption near edge structure spectroscopy (XANES), total reflection X-ray fluorescence spectroscopy (TXRF), inductively coupled plasma optical emission spectrometry (ICP-OES), and micro X-ray fluorescence spectroscopy (microXRF) were used to determine the vanadium concentrations and the species inside the membrane. The results strongly support that Vdimer(IV–V), a dimer formed from V(IV) and V(V), enters the nanoscopic water-body of Nafion™ 117 as such. This is interesting, because as of now, only the individual ions V(IV) and V(V) were considered to be transported through the membrane. Additionally, it was found that the Vdimer(IV–V) dimer partly dissociates to the individual ions in the novel PVDF-based membrane. The Vdimer(IV–V) dimer concentration in Nafion™ was determined and compared to those of the other species. After three days of equilibration time, the concentration of the dimer is the lowest compared to the monomeric vanadium species. The concentration of vanadium in terms of the relative uptake λ = n(V)/n(SO3) are as follows: V(II) [λ = 0.155] > V(III) [λ = 0.137] > V(IV) [λ = 0.124] > V(V) [λ = 0.053] > Vdimer(IV–V) [λ = 0.039]. The results show that the Vdimer(IV–V) dimer needs to be considered in addition to the other monomeric species to properly describe the transport of vanadium through Nafion™ in VRFBs.

In Situ and in Operando Detection of Redox Reactions with Integrated Potential Probes During Vanadium Transport in Ion Exchange Membranes

In Situ and in Operando Detection of Redox Reactions with Integrated Potential Probes During Vanadium Transport in Ion Exchange Membranes

Vanadium Transport through Cation and Anion Exchange Membranes

Transport of vanadium ions (V2+ plus V3+) and water through Nafion® and the anion exchange membrane Fumasep FAPQ-330 were measured as functions of current density in a triple membrane cell. The amount of vanadium moving through FAPQ was an order of magnitude less than through Nafion® at all current densities. A large amount of water, -1.5 moles per mole of univalent positively charged ions, was transferred through FAPQ in the direction opposite to vanadium and current. Relatively little water moved through Nafion® at the same operating conditions.

State of Charge Effects on Vanadium Crossover in Vanadium Redox Flow Batteries

Large-scale energy storage technologies play a pivotal role in the global clean energy transition, enabling intermittent renewable energy sources such as solar and wind to serve as feasible replacements for fossil fuels. The vanadium redox flow battery (VRFB) is a promising candidate for renewable energy storage applications due to its high energy efficiency, low toxicity, and long lifespan. [1] The half-cells of the battery are separated by a membrane through which ions migrate in order to maintain charge balance. Nafion, a perfluorinated polymer with sulfuric acid functional groups that facilitate proton transport, is the most widely used cation-exchange membrane due to its high proton conductivity and chemical and thermal stability. However, the low ion selectivity of Nafion permits positively charged vanadium ions to also cross through the membrane into the opposite electrolyte resulting in self-discharge of the battery, reducing efficiency.The characterization of vanadium crossover should consider the correlation between electrolyte composition and membrane properties. Vanadium concentration, sulfuric acid concentration, and state of charge are the three main factors that determine electrolyte composition. Electrolyte solutions with higher H2SO4 concentration corresponded to lower VO2+ membrane permeability.[2] A higher initial VO2+ concentration also corresponded to lower VO2+ membrane permeability. The low permeability at high H2SO4 and VO2+ concentrations could only be partially attributed to increased viscosity; other contributing factors may include dehydration of the membrane from interactions with sulfuric acid.In previous crossover-diffusion experiments,[3] the permeability of VO2+ with respect to the counter ion followed the trend H+ > VO2 + > VO2+, while the permeability of V3+ with respect to the counter ion was found to be VO2 + > VO2+. Uptake of vanadium species in the membrane followed the order V3+ ≈ VO2+> VO2 + at all concentrations of H2SO4 (0.5 M to 5 M), suggesting that permeability behavior of each vanadium species depends on the presence or absence of competitive partitioning resulting from particular vanadium counter ions. For all vanadium species, increased acid concentration decreased both the permeability and uptake of vanadium ions, likely due to the dehydration of the membrane in more acidic conditions (Lawton, JES, 2017).The state of charge (SOC) of the electrolyte, expressed as a percentage from 0% to 100%, describes the extent of oxidation that has occurred in each electrolyte. In the catholyte, for example, a 0% SOC solution consists of entirely VO2+, while a 100% SOC solution is entirely VO2 +. The characterization of mass transfer in the operating VRFB has yet to fully investigate the role of SOC on electrolyte properties. Here, we study the relationship between SOC and physical constants of the catholyte using electron paramagnetic resonance spectroscopy.[4,5][6] Our work seeks to elucidate some of the questions that remain in characterizing Nafion membrane permeability in the VRFB catholyte, in particular: how vanadium ion permeability varies with SOC; how the presence of VO2+ and VO2 + together in the catholyte influences each ion’s permeability; and how H2SO4 concentration affects all of these factors. 1. Skyllas-Kazacos, M.; Rychcik, M.; Robins, R. G.; Fane, A. G. New All-Vanadium Redox Flow Cell. J. Electrochem. Soc. 1986, 133, 1057–1058, doi:10.1149/1.2108706.2. Lawton, J. S.; Jones, A.; Zawodzinski, T. Concentration dependence of VO2+ crossover of nafion for vanadium redox flow batteries. J. Electrochem. Soc. 2013, 160, 697–702, doi:10.1149/2.004306jes.3. Lawton, J. S.; Jones, A. M.; Tang, Z.; Lindsey, M.; Zawodzinski, T. Ion effects on vanadium transport in Nafion membranes for vanadium redox flow batteries. J. Electrochem. Soc. 2017, 164, A2987–A2991.4. Lawton, J. S.; Smotkin, E. S.; Budil, D. E. Electron spin resonance investigation of microscopic viscosity, ordering, and polarity in nafion membranes containing methanol-water mixtures. J. Phys. Chem. B 2008, 112, 8549–8557, doi:10.1021/jp800222c.5. Lawton, J. S.; Budil, D. E. Investigation of water and methanol sorption in monovalent- and multivalent-ion-exchanged nafion membranes using electron spin resonance. J. Phys. Chem. B 2009, 113, 10679–10685, doi:10.1021/jp902750j.6. Lawton, J. S.; Budil, D. E. Spin Probe ESR Study of Cation Effects on Methanol and DMMP Solvation in Sulfonated Poly (styrene− isobutylene− styrene) Triblock Copolymers at High Ion-Exchange Capacities. Macromolecules 2009, 43, 652–661.

Vanadium Transport through Cation and Anion Exchange Membranes

Transport of redox active molecules across the separator in a flow battery represents an important source of inefficiency and electrolyte-imbalance-induced capacity fade [1]. This transport can occur by diffusion, migration, and convection, with driving forces that change as cells are charged and discharged. The negative electrolyte in a vanadium redox flow battery, for example, contains V2+ and V3+ in proportions that depend on state of charge, but these species are absent from the positive side, leading to ever present concentration driving forces for diffusion across the separator. Migration alternately enhances and diminishes crossover since the electric field in the membrane orients in opposite directions during charge and discharge. Finally, hydraulic and osmotic pressure differences between the positive and negative electrolytes cause solvent flow that carries redox ions.Rigorous theoretical treatment of transport across membranes in flow batteries with concentrated-solution theory is complicated by the large number of species. For example, Nafion in a vanadium redox flow battery may contain: V2+, V3+, VO2+, VO2 +, H+, HSO4 -, SO4 2-, H2O, and fixed SO3 - anions (8). The number of multicomponent diffusion coefficients required to characterize a systems is , where n is the number of species present (after accounting for species coupled by rapid chemical equilibrium). The n multicomponent diffusion coefficients define one conductivity, transference numbers or ratios, , and diffusion coefficients of neutral combinations of species. The experimental and theoretical complexities associated with the multicomponent framework when many species are present motivates exploration of the applicability of the simpler, but less generally valid dilute-solution framework. In particular, we seek to understand how well do the relationships between diffusion coefficients, transference numbers, and conductivity predicted by dilute solution theory hold in practical membranes exposed to application-relevant electrolyte solutions? Do transference numbers predicted from conductivity and permeability measurements agree with independently measured values?Figure 1 shows measured transference numbers for the four vanadium ions relevant to flow batteries in N211 and N212 as blue and red squares, respectively. The measurements were made using a cell with three membranes and four flow compartments [2, 3]. Good agreement between the two data sets is apparent. The averages of the N211 and N212 values are plotted as crosses and reported in boxes to the right of the symbols. Transference numbers for V(IV) and V(V) are approximately an order of magnitude lower than transference numbers for V(II) and V(III). The grey squares with blue and red perimeters are the transference numbers calculated from the formula using measured conductivities and permeabilities. The average calculated values are given to the left of the data symbols, to facilitate comparison with the measured values. The measured and calculated transference numbers agree in magnitude, and no systemic differences are evident. The calculated transference number for V(III) appears to be off the experimental trend with one exception: a relatively large transference number is calculated for V(III) because it has a charge number of 3. The disagreement between the measured and calculated transference numbers for V(III) could arise from ion pairing effectively lowering the charge number. The calculated transference numbers are higher for V(II) and V(III) than V(IV) and V(V) because their permeabilities are higher while their conductivity is lower. All these results indicate the value of the study: dilute solution theory accurately predicts transference numbers for all species except perhaps V(III) in Nafion, and this deviation from the model for V(III) may inform the solvated behavior of V(III) ions.AcknowledgementsThis work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

Unravelling the Contribution of Kinetics and Mass Transport Phenomena to Impedance Spectra in Vanadium Redox Flow Batteries: Development and Validation of a 1D Physics-Based Analytical Model

Vanadium redox flow battery technology can support the spread of energy storage in stationary applications and allow higher penetration of renewables in the electric grid. Currently, its market competitiveness is hindered by low power density, which stems from complex interplay between kinetic and mass transport losses. The quantitative interpretation of experimental observations should rely on physics-based models, which allow a consistent comparison of different operative conditions. In this work, a fast analytical physics-based 1D model of the impedance of vanadium flow battery is presented and validated with respect to experimental data. The model, made available online at http://mrtfuelcell.polimi.it, employs a macro-homogeneous approach and considers losses due to kinetics, reactant distribution within the electrode (Sigracet® SGL 39 AA carbon paper), convection in flow channel and vanadium transport to electrode surface. Additionally, analytical expressions of contributions to impedance of single physical phenomena are derived through an asymptotical analysis. The results show that, at negative electrode, transport of ions to active surface is the limiting phenomenon at lower flow rates, while at higher flow rates depletion of reactants within electrode becomes critical together with charge transfer processes. At positive electrode, the main contribution to performance loss is the vanadium transport to electrode surface.

Ion Effects on Vanadium Transport in Nafion Membranes for Vanadium Redox Flow Batteries

Vanadium diffusion through Nafion membranes was investigated under conditions applicable to vanadium redox flow batteries (VRFBs). In this case, we examine the effects of interdiffusion of VO2+ with protons, V3+ and VO2+ by a ‘cross-diffusion’ experiment in which VO2+ and the other ion diffuse from opposite sides of the membrane. Vanadium concentrations in reservoirs designed to flow solution over both sides of the membrane were monitored using UV/vis and EPR spectroscopies. The permeability of each ion was determined and diffusion coefficients determined from permeability and measurements of ion uptake by the membrane. The VO2+ permeability is highest when H+ is the only ion on the counter side, and decreases in the following order: H+ > VO2+ > V3+.

Block Copolymer Sdapp Membranes for Vanadium Redox Flow Batteries-Strategy to Address Transport and Durability

The electrolyte separator (membrane) is a key component in vanadium redox flow batteries (VRFB) for large scale electrical energy storage. In the VRFB cell, the separator serves to physically separate positive and negative electrolyte solutions while establishing ionic conduction to pass current between two half cells. High ionic conductivity, low vanadium permeability, chemical stability and low cost are desired properties of RFB separators. To serve as a separator, the membrane should deter unwanted redox species transport while maintaining excellent ionic transport properties to minimize ohmic resistance. In the harsh electrolyte environment, the membrane must be stable enough to withstand chemical attacks in the electrolyte environment for a long lifespan. Moreover, the cost of the separator must be kept low enough to be integrated into large-scale battery system. Generally, ion exchange membranes are used as electrolyte separator in VRFBs. Sulfonated Diels Alder poly(phenylene) (SDAPP) cation exchange membranes have emerged as a good membrane candidate for both proton exchange membrane fuel cell and VRFB. The first generation SDAPP is a partially sulfonated poly(phenylene) random polymer. The random SDAPP membrane has shown comparable performance to Nafion in transport study and battery testing.1 From the perspective transport properties, SDAPP is satisfactory as anelectrolyte separator in VRFBs. However, random SDAPP is not chemically stable enough in the electrolyte environment to serve for a targeted lifespan because the unfunctionalized benzene ring in SDAPP is vulnerable to attack from V5+ (VO2 +) ion, a strong oxidant. Sulfonated polyphenylene/polysulfone block copolymer SDAPP membranes show significantly improved resistance to V5+ attack and excellent cell performance.2 The SDAPP block copolymer consists of a hydrophilic segment of fully sulfonated polyphenylene and hydrophobic segment of polysulfone. The block-SDAPP membrane provides an extended lifespan within VRFB environment in comparison to random SDAPP. Chemical stability of block-SDAPP is enhanced by full sulfonation of poly(phenylene) in the hydrophilic segment. Ionic conductivity is not sacrificed by block copolymerization. In the battery, the performance of block-SDAPP can be better than state of art Nafion 212. As is shown in the figure, at 500 mA/cm2cycling current density, cells equipped with three different block-SDAPP membranes can reach 76% energy efficiency, compared to 70% with Nafion 212, with the same electrode and electrolyte conditions. About 80% voltage efficiency was achieved with block-SDAPP membranes, because of the lowered internal resistance. Moreover, the coulombic efficiency reached by the three block SDAPPs is respectively 97%, 95% and 93%, compared to 95% of Nafion. Vanadium crossover across block SDAPP membranes is similar to that in Nafion 212. Considering that block-SDAPPs have lower ASR in the battery, the ionic selectivity of block SDAPP is essentially better than Nafion. To further optimize the structure of block-SDAPP for VRFB application, we are investigating the correlation between structure and performance of block-SDAPP. Under battery electrolyte conditions, ionic equilibrium, ionic transport and membrane morphology will be studied via the protocol established in previous studies.3Sulfuric acid, water uptake and vanadium ion partitioning in membrane will be determined after being equilibrated in electrolyte of various acid and vanadium composition to simulate battery environment. Conductivity and vanadium permeability of block SDAPP will also be measured after the same equilibration. Since water is a critical mediator for proton and cation transport in aqueous media, pulsed field gradient nuclear magnetic resonance (PFG-NMR) will be performed to investigate proton and vanadium transport mechanisms in equilibrated membranes. Membrane morphology will be studied by transmission electron microscopy and small angle X-ray scattering will be used to establish the geometry of ionic cluster channel. Acknowledgement This work is supported by Dr. Imre Gyuk, Office of Electricity Delivery and Energy Reliability, US Department of Energy.

Processing and Pretreatment Effects on Vanadium Transport in Nafion Membranes

This work describes how manufacturing processes and pretreatments affect the proton conductivity and vanadyl permeability of Nafion® and how these properties are altered by running in a cell. Five Nafion membranes were examined: reinforced XL100, dispersion cast NR211 and NR212, and extruded N115 and N117. The membranes were subjected to pretreatments that included annealing at 120°C and immersing in ambient temperature and boiling water and sulfuric acid. Vanadyl permeability varied by ∼15X with pretreatment and ∼3X with manufacturing process. Variations in ionic conductivity were comparatively modest: ∼1.5X with pretreatment and ∼1.2X with processing. Differences in permeability can be eliminated by annealing the extruded membranes above their glass-transition temperature or by immersing in boiling sulfuric acid. The differences induced by processing and pretreatments were largely absent from membranes removed from vanadium redox cells subjected to repeated charge/discharge cycles.

ChemInform Abstract: Water Vapor‐Mediated Volatilization of High‐Temperature Materials

Volatilization in water vapor–containing atmospheres is an important and often unexpected mechanism of degradation of high-temperature materials during processing and in service. Thermodynamic properties data sets for key (oxy)hydroxide vapor product species that are responsible for material transport and damage are often uncertain or unavailable. Estimation, quantum chemistry calculation, and measurement methods for thermodynamic properties of these species are reviewed, and data judged to be reliable are tabulated and referenced. Applications of water vapor–mediated volatilization include component and coating recession in turbine engines, oxidation/volatilization of ferritic steels in steam boilers, chromium poisoning in solid-oxide fuel cells, vanadium transport in hot corrosion and degradation of hydrocracking catalysts, Na loss from Na β″-Al2O3 tubes, and environmental release of radioactive isotopes in a nuclear reactor accident or waste incineration. The significance of water vapor–mediated volati...

Water Vapor–Mediated Volatilization of High-Temperature Materials

Volatilization in water vapor–containing atmospheres is an important and often unexpected mechanism of degradation of high-temperature materials during processing and in service. Thermodynamic properties data sets for key (oxy)hydroxide vapor product species that are responsible for material transport and damage are often uncertain or unavailable. Estimation, quantum chemistry calculation, and measurement methods for thermodynamic properties of these species are reviewed, and data judged to be reliable are tabulated and referenced. Applications of water vapor–mediated volatilization include component and coating recession in turbine engines, oxidation/volatilization of ferritic steels in steam boilers, chromium poisoning in solid-oxide fuel cells, vanadium transport in hot corrosion and degradation of hydrocracking catalysts, Na loss from Na β″-Al2O3tubes, and environmental release of radioactive isotopes in a nuclear reactor accident or waste incineration. The significance of water vapor–mediated volatilization in these applications is described.

Species transport mechanisms governing capacity loss in vanadium flow batteries: Comparing Nafion® and sulfonated Radel membranes

In this study, a 2-D, transient vanadium redox flow battery (VRFB) model was used to investigate and compare the ion transport mechanisms responsible for vanadium crossover in Nafion® 117 and sulfonated Radel (s-Radel) membranes. Specifically, the model was used to distinguish the relative contribution of diffusion, migration, osmotic and electro-osmotic convection to the net vanadium crossover in Nafion® and s-Radel. Model simulations indicate that diffusion is the dominant mode of vanadium transport in Nafion®, whereas convection dominates the vanadium transport through s-Radel due to the lower vanadium permeability, and thus diffusivity of s-Radel. Among the convective transport modes, electro-osmotic convection (i.e., electro-osmotic drag) is found to govern the species crossover in s-Radel due to its higher fixed acid concentration and corresponding free ions in the membrane. Simulations also show that vanadium crossover in s-Radel changes direction during charge and discharge due to the change in the direction of electro-osmotic convection. This reversal in the direction of crossover during charge and discharge is found to result in significantly lower “net” crossover for s-Radel when compared to Nafion®. Comparison of these two membranes also provides guidance for minimizing crossover in VRFB systems and underscores the importance of measuring the hydraulic and the electro-kinetic permeability of a membrane in addition to vanadium diffusion characteristics, when evaluating new membranes for VRFB applications.

Performance evaluation of vanadium (IV) transport through supported ionic liquid membrane

Increasing use of vanadium in different industries including alloys and steel manufacturing, electrochemical coating and catalysts causes environmental concern about the toxic effluents. In the present research, the extraction of vanadium in supported ionic liquid membrane was studied. The effect of operational conditions on the process performance such as initial feed phase concentration, pH of the feed solution, pore size of the membrane support, type of ionic liquid charged on the support and stripping agent solution was investigated. Vanadium was effectively transported from the feed phase to the stripping phase of ammonia solution using the room temperature ionic liquid, tri-n-octyl methyl ammonium chloride (TOMAC) embedded in the support membrane. Selective transport of vanadium from its mixture with chromium ions was carried out applying TOMAC as carrier. It was also observed that addition of a slight amount of a second room temperature ionic liquid, 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide [BMIM][NTF2], improved the vanadium extraction process considerably.

A bulk liquid membrane–flow injection (BLM–FI) coupled system for the preconcentration and determination of vanadium in saline waters

A bulk liquid membrane–flow injection (BLM–FI) system has been developed for the preconcentration and spectrophotometric determination of vanadium in saline waters. The preconcentration step was based on a bulk liquid membrane containing Aliquat 336 (acting as a carrier) dissolved in dodecane/dodecanol. Vanadium species were chemically pumped due to the pH gradient between the sample (pH 3.2) and the receiving solution (pH 9.8). Vanadium transport through the membrane was monitored by a new and sensitive spectrophotometric method based on its reaction with di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an acidic medium. As a consequence of membrane transport, vanadium was recovered in an ammonium solution, where total vanadium concentration was spectrophotometrically determined at 375nm, as the pentavalent species, by using a flow injection analysis (FIA) system. Under optimal conditions, this FIA system provided a detection limit of 4.7μgL−1 (3sblank/m) and RSD 2.72%, for vanadium determination in saline samples. Both preconcentration and determination steps were previously optimized by modified simplex methodologies.The proposed coupled method was successfully applied to the determination of vanadium in a certified reference material (TMDA-62) and in two seawater samples.