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Journal of synchrotron radiation 28(6), 1865 - 1873 (2021). doi:10.1107/S160057752100905X, 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 ��m and a horizontal step size of 5 ��m 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 V$^{3+}$ in the focused beam could be limited to 10%. In diffusion experiments, Nafion inside the diffusion cell was exposed on one side to V$^{3+}$ electrolyte and on the other side to VO$_2$$^{+}$. The ions were allowed to diffuse across the through-plane orientation of the membrane during one of two short defrost times (200 s and 600 s). Subsequent micro-XANES measurements showed the formation of VO$^{2+}$ from V$^{3+}$ and VO$_2$$^{+}$ 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., Published by Wiley-Blackwell, [S.l.]

In 2012, the European Bioanalysis Forum published a recommendation on biomarker method development and the bioanalysis of biomarkers in support of drug development. Since then, there has been significant discussion on how to bring the topic of context of use of biomarker assays to the forefront so that the purpose of the assay, the use of the data and the decisions being made with the data are well defined and clearly understood, not just by the bioanalytical scientist, but across all stakeholders. Therefore, it is imperative that discussions between the bioanalytical laboratory and the end users of the data happen early (and regularly) in the drug development process to enable the right assays to be developed and appropriately validated to generate the correct data and allow suitable decisions to be made. This updated refinement to the previous European Bioanalysis Forum recommendation will highlight the items to consider when discussing context of use for biomarker assay development and validation, thus enabling the correct conversations to occur and the move away from the misapplication of PK assay validation criteria to biomarker assays.

The influence of process parameters on the H2O2 yield of gas diffusion electrodes (GDE) are investigated. The investigated GDEs consist of Vulcan XC72 carbon black and PTFE on gold‐plated nickel wire cloth. An electrolysis cell is used to evaluate the influence of various process parameters, such as temperature, pH value, oxygen pressure and stoichiometric factor, electrolyte flow regime, current density and separator material at steady‐state conditions. It is found that the investigated GDE enables current efficiencies greater than 90 % at up to 2 kA m−2, whereby lower electrolyte temperatures and higher pH values contribute to higher H2O2 yields above 90 % current efficiency.

To enable the evaluation of water treatment efficiency of electrochemical advanced oxidation processes (EAOPs), an approach to remove H2O2 as a catalytic pretreatment was investigated to av...

A system of boron-doped diamond (BDD) anode combined with a gas diffusion electrode (GDE) as a cathode is an attractive kind of electrolysis system to treat wastewater to remove organic pollutants. Depending on the operating parameters and water matrix, the kinetics of the electrochemical reaction must be defined to calculate the reaction rate constant, which enables designing the treatment reactor in a continuous process. In this work, synthetic wastewater simulating the vacuum toilet sewage on trains was treated via a BDD-GDE reactor, where the kinetics was presented as the abatement of chemical oxygen demand (COD) over time. By investigating three different initial COD concentrations (C0,1 ≈ 2 × C0,2 ≈ 4 × C0,3), the kinetics was presented and the observed reaction rate constant kobs. was derived at different current densities (20, 50, 100 mA/cm2). Accordingly, a mathematical model has derived kobs. as a function of the cell potential Ecell. Ranging from 1 × 10−5 to 7.4 × 10−5 s−1, the kobs. is readily calculated when Ecell varies in a range of 2.5–21 V. Furthermore, it was experimentally stated that the highest economic removal of COD was achieved at 20 mA/cm2 demanding the lowest specific charge (~7 Ah/gCOD) and acquiring the highest current efficiency (up to ~48%).

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] &gt, V(III) [λ = 0.137] &gt, V(IV) [λ = 0.124] &gt, V(V) [λ = 0.053] &gt, 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.

The kinetics of zinc dissolution in concentrated potassium hydroxide solution were determined as a function of KOH concentration, amount of added ZnO, and temperature through linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The measurements were evaluated with a simplified reaction scheme in which an intermediate ZnI species is formed on the electrode surface that subsequently reacts to a soluble ZnII species. Analysis of the LSV data with a two-step Butler–Volmer kinetics showed that the transfer coefficients and the surface coverage of the intermediate are approximately constant in the entire range of operation conditions, whereas the exchange current density for the first reaction step is about five times larger than for the second step. Analysis of the dynamic EIS measurements resulted in very similar current densities than obtained from the quasi-stationary LSV method. For the first time, activation energies describing the temperature dependence of the exchange current density were also determined.

Regarding the treatment of (waste)water, electrochemical processes have various advantages over other methods. They are robust, easy to operate and flexible in case of fluctuating wastewater streams. In addition, a relatively broad spectrum of organic and inorganic impurities can be removed. This contribution provides an overview of electrochemical reactors for water, process water, and wastewater treatment, which are already in technical‐scale operation or subject of research. Some essential basics of electrochemical processes for the treatment of water are presented and examples for applications are given. This is followed by a description of the reactors.

Over the last several years, the removal of more than 150 micropollutants was investigated. Many pharmaceuticals are persistent and pass the conventional wastewater treatment plants (WWTP). According to literature, the removal efficiency of various pharmaceuticals is between 0 and 50 % in activated sludge processes. For a standard analgesic such as Diclofenac, the removal efficiency is approx. 30 %. Therefore, additional treatment such as 4th treatment step is necessary, which is already implemented in some WWTPs in Europe, to save water bodies as much as possible. Options for the 4th treatment step are, for example, activated carbon adsorption, nanofiltration and advanced oxidation processes (AOP). By far one of the most cost efficient AOP is the ozonation. However, it is not able to remove X-ray contrast media sufficiently. For this purpose, electrochemical oxidation processes (EAOP) based on boron-doped diamond electrodes are much more effective. Keeping in mind that AOPs are still an emerging technology, especially for water reuse options and also might cause even toxic intermediates, one of the biggest disadvantages are the relatively high operational costs due to the electrical energy demand. Especially electrochemical reactors, which are based on two boron-doped diamond (BDD) electrodes are very cost-intensive, particularly in comparison to ozonation or perozone (ozone plus peroxide) processes. For that reason, a new electrochemical reactor concept, which promises lower CAPEX and OPEX costs, was investigated. This reactor concept consists mainly of one BDD electrode as anode and a gas diffusion electrode (GDE) as cathode. The innovative reactor concept combines the generation of highly reactive hydroxyl radicals on the anode surface and simultaneously hydrogen peroxide on the cathode surface, which is very efficient as there is a double use of the same applied power. Both electrodes are mounted in a membrane-less flow-through reactor in pilot-scale for direct treatment of wastewater. Due to the direct contact between the surfaces of both electrodes, the wastewater gets treated specifically, which leads to a high energy efficiency. First results already prove the more energy efficient removal of COD in an artificial wastewater with the new reactor concept. For a detailed evaluation, a defined artificial wastewater with compounds and concentration equal to vacuum toilet wastewater was treated by the new reactor concept as well as by ozonation and perozone process (ozone plus peroxide). COD removal as well as the associated energy demand were measured after defined intervals in each step of the treatment to determine the performance of the different processes. A comparison was made between the different kind of treatments (EAOP, ozonation, perozone) concerning COD degradation and the power demand. The evaluation is based on electrical energy per order (EEO) conception as well as degradation for given reaction kinetics.

Redox flow batteries such as the all-vanadium redox flow battery (VRFB) are a technical solution for storing fluctuating renewable energies on a large scale. The optimization of cells regarding performance, cycle stability as well as cost reduction are the main areas of research which aim to enable more environmentally friendly energy conversion, especially for stationary applications. As a critical component of the electrochemical cell, the membrane influences battery performance, cycle stability, initial investment and maintenance costs. This review provides an overview about flow-battery targeted membranes in the past years (1995–2020). More than 200 membrane samples are sorted into fluoro-carbons, hydro-carbons or N-heterocycles according to the basic polymer used. Furthermore, the common description in membrane technology regarding the membrane structure is applied, whereby the samples are categorized as dense homogeneous, dense heterogeneous, symmetrical or asymmetrically porous. Moreover, these properties as well as the efficiencies achieved from VRFB cycling tests are discussed, e.g., membrane samples of fluoro-carbons, hydro-carbons and N-heterocycles as a function of current density. Membrane properties taken into consideration include membrane thickness, ion-exchange capacity, water uptake and vanadium-ion diffusion. The data on cycle stability and costs of commercial membranes, as well as membrane developments, are compared. Overall, this investigation shows that dense anion-exchange membranes (AEM) and N-heterocycle-based membranes, especially poly(benzimidazole) (PBI) membranes, are suitable for VRFB requiring low self-discharge. Symmetric and asymmetric porous membranes, as well as cation-exchange membranes (CEM) enable VRFB operation at high current densities. Amphoteric ion-exchange membranes (AIEM) and dense heterogeneous CEM are the choice for operation mode with the highest energy efficiency.

Elektrochemische Reaktoren sind Reaktionsapparate, in denen eine Wandlung zwischen chemischer und elektrischer Energie stattfindet. Sie werden haufig und in vielfaltiger Gestalt in der Chemischen Industrie, zur Metallgewinnung und in der Energietechnik eingesetzt. Im vorliegenden Beitrag werden die fur elektrochemische Reaktoren spezifischen Aspekte vorgestellt und die Konsequenzen fur Auslegung und Betrieb diskutiert. Der aktuelle Stand der Entwicklungen wird anhand der technisch bedeutsamen Beispiele Chlor-Alkali-Elektrolyse, PEM-Brennstoffzelle und Redox-Flow-Batterie verdeutlicht.

Porous glass (PG) offers the ability to vary pore sizes and modify surfaces, allowing membranes to be tailored for a given electrochemical application. In this contribution, the application of PG in all-vanadium redox-flow batteries (VFB) and the effect of surface modification with sulfonic acid groups were investigated, and the results were compared with those from well-known polymeric membranes. The performance of native and surface-modified PG membranes with pore sizes ranging from 2 to 20 nm and thicknesses of 300 and 500 µm was investigated by examining their self-discharge behavior, polarization curves and area resistance. A maximum power density of 77 mW cm−2 at a current density of 110 mA cm−2 was observed with the modified membrane 505FDS, and this density is approximately half the power density achieved with Nafion™ 117. The results can be related to the small vanadium crossover, high conductivity and chemical stability. Therefore, the great potential of PG membranes as separators in VFBs was shown.

Zinc-air batteries have a great potential to be the next generation of secondary batteries. They exhibit a high volume and mass specific power density due to the use of oxygen, which can be taken directly from air. Compared to other anodes used in rechargeable batteries, zinc offers many advantages including low cost and environmental friendliness. Unfortunately, morphological changes occur in the zinc electrode after a few charge and discharge cycles which lead to formation of needle-shaped zinc structures (dendrites). Despite many studies about suppressing dendrites by using additives in the electrolyte, no technically feasible solution could be found until today. In this contribution the influence of zinc ion concentrations in the electrolyte at the electrode surface on the dendrite formation is investigated. It is shown that dendritic zinc crystals only occur if the surface concentration of zinc ions falls below a critical value. With the knowledge of this critical surface concentration the time before growth of dendritic zinc starts can be prolonged by pulsed deposition of zinc. Moreover, dendrite growth can be completely avoided in a flow system at an appropriate flow rate in combination with a pulsed current charging procedure. With this approach the favored boulder structures were obtained with current densities up to 80 mA cm−2 and for deposition times up to 1800 s.

The improvement of redox-flow batteries requires the development of chemically stable and highly conductive separators. Porous glass membranes can be an attractive alternative to the nowadays most common polymeric membranes. Flat porous glass membranes with a pore size in the range from 2 to 50 nm and a thickness of 300 and 500 μm have been used for that purpose. Maximum values for voltage efficiency of 85.1%, coulombic efficiency of 97.9% and energy efficiency of 76.3% at current densities in the range from 20 to 60 mA cm−2 have been achieved. Furthermore, a maximum power density of 95.2 mW cm−2 at a current density of 140 mA cm−2 was gained. These results can be related to small vanadium crossover, high conductivity and chemical stability, confirming the great potential of porous glass membranes for vanadium redox-flow applications.

Electrochemical advanced oxidation processes (EAOP®) are promising technologies for the decentralized treatment of water and will be important elements in achieving a circular economy. To overcome the drawback of the high operational expenses of EAOP® systems, two novel reactors based on a next-generation boron-doped diamond (BDD) anode and a stainless steel cathode or a hydrogen-peroxide-generating gas diffusion electrode (GDE) are presented. This reactor design ensures the long-term stability of BDD anodes. The application potential of the novel reactors is evaluated with artificial wastewater containing phenol (COD of 2000 mg L−1), the reactors are compared to each other and to ozone and peroxone systems. The investigations show that the BDD anode can be optimized for a service life of up to 18 years, reducing the costs for EAOP® significantly. The process comparison shows a degradation efficiency for the BDD–GDE system of up to 135% in comparison to the BDD–stainless steel electrode combination, showing only 75%, 14%, and 8% of the energy consumption of the BDD–stainless steel, ozonation, and peroxonation systems, respectively. Treatment efficiencies of nearly 100% are achieved with both novel electrolysis reactors. Due to the current density adaptation and the GDE integration, which result in energy savings as well as the improvements that significantly extend the lifetime of the BDD electrode, less resources and raw materials are consumed for the power generation and electrode manufacturing processes.

The electron paramagnetic resonance (EPR) spectra of poly (vinylidene fluoride) (PVDF) films were studied in order to identify type and intensity of trapped radicals after an electron treatment with 150 kGy in air at room temperature. The observed EPR spectra consist of superimposed spectra of eight different radicals. The individual spectra were simulated by first derivatives of normalized Gaussian functions including intensity, linewidth, g value, and hyperfine splitting constants of the unpaired electron with hydrogen or fluorine atoms in α or β positions. In addition, the number of trapped radicals was estimated using a standard sample of known spin concentrations. Although initially generated radicals tend to be converted to peroxy radicals in the presence of oxygen, the predominant radical is the CH-based mid-chain radical (–CF2–C*H-CF2-) with a relative intensity of 62.3%. This is attributed to CH-based radicals in the crystalline domains with low molecular mobility leading to an enhancement in its linewidth (ΔHpp ⁓ 3.6 mT). A fraction of 20.7% of all radicals are peroxy radicals with anisotropic g values, g ∥ = 2.0210 and g ⊥ = 2.0095. The relative intensity of allyl, dienyl and polyenyl radicals amounts to 4.9%.

The analysis of biomarkers by ligand-binding assays offers significant challenges compared with the bioanalysis of small and large molecule drugs. The presence of endogenous analyte is a commonly cited issue. Also the sourcing and application of appropriate calibration or reference standards can present many issues. One of the main challenges is ensuring the continuity and validity of biomarker data when the source or lot number of calibration standard changes within or between studies. Several strategies exist in attempting to deal with this and standardize the biomarker data through the assay life or looking for ways to compare and normalize biomarker data. In this manuscript, the European Bioanalysis Forum view on dealing with calibration standards in biomarker assays is described.

The vanadium redox flow battery (VRFB) is a promising electrochemical storage system for stationary megawatt-class applications. The currently limited cell area determined by the bipolar plate (BPP) could be enlarged significantly with a novel extruded large-area plate. For the first time a techno-economic assessment of VRFB in a power range of 1 MW–20 MW and energy capacities of up to 160 MWh is presented on the basis of the production cost model of large-area BPP. The economic model is based on the configuration of a 250 kW stack and the overall system including stacks, power electronics, electrolyte and auxiliaries. Final results include a simple function for the calculation of system costs within the above described scope. In addition, the impact of cost reduction potentials for key components (membrane, electrode, BPP, vanadium electrolyte) on stack and system costs is quantified and validated.

Effective methods for graphite felt (GF) treatment based on Fenton’s reagent treatment and thermal modification have been used to improve microbial fuel cell (MFC) performance. The effects of the H2O2 content in Fenton’s reagent on the performances of MFCs with two different GFs (GFD and ACN-211) have been investigated. For GFD, a maximum performance of 190 mW/m2 was achieved with H2O2 volume of 100 ml, while for ACN-211, the maximum performance of 450 mW/m2 is reached with H2O2 volume of 150 ml. MFCs with both treated and untreated ACN-211 consistently showed higher power densities and greater durabilities than those with treated and untreated GFD. The degree of fouling on the surface of ACN-211 was much less than that on the surface of GFD. The higher surface area and better anti-fouling performance of ACN-211 are responsible for its relatively high power density during long-term operation. Thermal modification of ACN-211 was performed at different temperatures and for different durations, and the effects of treatment conditions on the performances of MFCs were studied. Results showed that an MFC fabricated with ACN-211 treated under 400 °C for 2 h exhibited the highest power density, with a maximum value of 470 mW/m2, which is higher than that of an MFC fabricated with ACN-211 treated by Fenton’s reagent. A Coulombic efficiency of 35% and an energy efficiency of 10% were achieved for an MFC fabricated with ACN-211.

Passivation of zinc electrodes caused by formation of oxy-products with low electrical conductivity is one of the most important phenomena which limits the current density during discharge and contributes to the poor cyclability of zinc-based batteries. The present review critically discusses the existing experimental findings related to passivation of zinc in alkaline electrolyte as well as the state of the mathematical modelling of this process. Despite numerous investigations over several decades, no general consensus about the underlying mechanisms and the strategies to prevent passivation could be achieved. Main reason for this uncertainty is that different processes can lead to passivation. On the one hand, precipitation of so-called type 1 films occurs above a critical zincate concentration while on the other hand the direct oxidation of the zinc surface takes place below a certain potential, leading to type 2 passive films. As long as formed films remain porous, passivation does not necessarily lead to complete breakdown of the electrode activity. It is therefore recommended to conduct further measurements employing a combination of techniques in which both the potential and the concentration of zincates at the electrode surface can be precisely controlled. It is also proposed to carry out systematic studies on the influence of temperature, electrolyte flow, and electrolyte composition – including additives – on the passivation time and the structure of the passive film. Finally, the purity and the structure of the zinc electrode may also have an influence on the passivation processes and should be considered during future studies.

European Bioanalysis Forum Focus Workshop, Lisbon, Portugal, 9–10 June 2016 At the recent European Bioanalysis Forum's Focus Workshop ‘Bringing Assay Validation and Analysis of Biomarkers into Practice’, the discussion on best practice for biomarker assay validation continued. Both the presentations and the adjacent panel discussions yielded valuable food for thought for the broader bioanalytical community. The present conference report summarizes the essence from these discussions and from the proposals or conclusions made by all delegates on how to increase the necessary connectivity of the stakeholders involved in the bioanalysis of biomarkers.

Carbon felt electrodes belong to the key components of redox flow batteries. The purpose of this techno-economic assessment is to uncover the production costs of PAN- and rayon-based carbon felt electrodes. Raw material costs, energy demand and the impact of processability of fiber and felt are considered. This innovative, interdisciplinary approach combines deep insights into technical, ecologic and economic aspects of carbon felt and carbon fiber production. Main results of the calculation model are mass balances, cumulative energy demands (CED) and the production costs of conventional and biogenic carbon felts supplemented by market assessments considering textile and carbon fibers.

The application of grafted membranes based on modified poly(ethylene-alt-tetrafluoroethylene) (ETFE) in redox flow-batteries is reported. In analogy to commercial Nafion® 117 based membranes ETFE backbone material provides chemical, thermal, and mechanical stability. Side chains composed of 2-hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) grafted to ETFE were sulfonated to achieve the required proton exchange capacity. Application in a vanadium based redox flow-battery demonstrates the applicability of this kind of membranes for energy storage systems. The degree of grafting was identified as the key parameter to tune the membrane properties.

This contribution describes the effect of the quality of the catalyst coating of cathodes for wastewater treatment by microbial fuel cells (MFC). The increase in coating quality led to a strong increase in MFC performance in terms of peak power density and long-term stability. This more uniform coating was realized by an airbrush coating method for applying a self-developed polymeric solution containing different catalysts (MnO2, MoS2, Co3O4). In addition to the possible automation of the presented coating, this method did not require a calcination step. A cathode coated with catalysts, for instance, MnO2/MoS2 (weight ratio 2:1), by airbrush method reached a peak and long-term power density of 320 and 200&ndash, 240 mW/m2, respectively, in a two-chamber MFC. The long-term performance was approximately three times higher than a cathode with the same catalyst system but coated with the former paintbrush method on a smaller cathode surface area. This extraordinary increase in MFC performance confirmed the high impact of catalyst coating quality, which could be stronger than variations in catalyst concentration and composition, as well as in cathode surface area.

The development of a powerful, cyclically stable and electrically rechargeable zinc-oxygen battery with a three-electrode configuration is reported. A copper foam was used as stable substrate for zinc deposition in flowing potassium hydroxide electrolyte, while oxygen reduction and evolution were accomplished by a commercial silver electrode and a nickel foam, respectively. The cell could be charged and discharged with up to 600 mA cm−2, delivered a peak power density of 270 mW cm−2, and performed for more than 600 cycles, although short circuits by dendrite formation could not yet be completely avoided. At a current density of 50 mA cm−2 and a temperature of 30 °C, a promising energy efficiency of 54% was achieved. Keywords: Secondary zinc–air battery, Three-electrode configuration, Metal foam, Oxygen depolarized cathode, Oxygen evolution catalyst, Alkaline electrolyte

A major source of capacity fade of the common vanadium redox flow battery (VRFB) is the vanadium ion transport through the separator. However, different transport models disagree significantly in the diffusion coefficient for the different V species and the influence of different transport mechanisms. The underlying hypothesis of this work is that reactions inside the membrane are partly responsible for these discrepancies. Accordingly, it was investigated if redox reactions inside the nanoscopic water body of Nafion 117 can occur. X-ray absorption near edge structure spectroscopy (XANES) was used to distinguish between the different V species inside hydrated Nafion 117 and novel PVDF-based membranes. It was validated that the speciation of vanadium can be performed using the pre-edge peak energy and intensity. The experiments were performed as follows: strips of the membrane were exposed from one site to a V3+ solution (green) and from the other site to a VO2+ solution (yellow). The ions could diffuse into the membrane from both sides. A change of color of the membrane strip was observed. The blue color in the middle of the strip indicated that VO2+ was formed where V3+ and VO2+ got in contact. Using XANES this reaction inside Nafion was proven.