The aggregation process of beta-lactoglobulin (beta-lg) from 0 min to 20 h was studied using atomic force microscopy (AFM), scanning transmission electron microscopy (STEM), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and in situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). Fibril assembly was monitored in real time using AFM up to 20 h. From 0 to 85 min, beta-lg monomers deformed and expanded with some aggregation. After 85 min, fibrillar structures were formed, exceeding 10 mum in length. Fibrillar structures were confirmed by STEM. Secondary structural changes occurring during fibril formation were monitored by ATR-FTIR at 80 degrees C and indicated a decrease in alpha-helix content and an increase in beta-sheet content. SDS-PAGE indicated that fibrils were composed of polypeptides and not intact monomers. In this study, beta-lg and whey protein isolate (WPI)-derived fibrils, including some double helices, in water were observed by AFM under ambient conditions and in their native aqueous environment.

The stability of typical vanadium flow battery (VFB) catholytes was investigated at temperatures in the range 30-60 • C for V V concentrations of 1.4-2.2 mol dm −3 and sulfate concentrations of 3.6-5.4 mol dm −3 . In all cases, V 2 O 5 precipitates after an induction time, which decreases with increasing temperature. Plots of the logarithm of induction time versus the inverse of temperature (equivalent to Arrhenius plots) show excellent linearity and all have similar slopes. The logarithm of induction time also increases linearly with sulfate concentration and decreases linearly with V V concentration. The slopes of these plots give values of concentration coefficients β S and β V5 which were used to normalize induction times to reference concentrations of sulfate and V V . An Arrhenius plot of the normalized induction times gives a good straight line, the slope of which yields a value of 1.791 ± 0.020 eV for the activation energy. Combining the Arrhenius equation with the observed variation with sulfate and V V concentrations, an equation was derived for the induction time for any catholyte at any temperature in the range investigated. Although the mechanism of precipitation of V V from catholytes is not yet well understood, a precise activation energy can now be assigned to the induction process. The rapid growth of renewable electricity generation from intermittent sources such as solar photovoltaic and wind is driving a need for advanced, cost-effective, electrical energy storage (EES) technologies.1-3 Redox flow batteries 4-11 (RFBs) have attracted much interest for large-scale energy storage due to advantages over other EES technologies, and research activities in this area have grown exponentially in recent years.12,13 The energy storage capability and power output of a flow battery, unlike conventional batteries, can be scaled independently to suit the desired application. 7 Other advantages 14 include a high degree of safety, long lifetime, potentially low capital costs, high reliability and relatively high energy efficiency.Among the numerous systems that have been studied, the vanadium flow battery (VFB), also known as the vanadium redox flow battery (VRFB), is commonly regarded as one of the most promising. [5][6][7][15][16][17] The chemistry of this system is perhaps the most thoroughly characterized and the cell design has been considerably optimized. 2,18,19 It has seen the widest commercial deployment 17 and systems as large as 250-1000 kWh have been demonstrated. 20 Compared to other flow battery systems, VFBs have the additional advantage that crosscontamination due to transport through the separating membrane is effectively eliminated because the anolyte and catholyte differ only in the oxidation state of the vanadium. 21 As a result, electrolyte maintenance issues are reduced; in theory, the electrolyte is indefinitely reuseable. Furthermore, if rebalancing of the system is required the electrolytes in the two reservoirs can be mixed with each other. Since aqueous vanadium species are highly ...

The ultraviolet-visible spectra of catholytes for vanadium flow batteries (VFBs) were measured and analyzed for a range of V IV :V V ratios and vanadium concentrations. Using a model of V 2 O 3 3+ in equilibrium with VO 2+ and VO 2 + , the spectra were characterized in terms of an excess absorbance parameter p and the molar extinction coefficients ε 4 and ε 5 of VO 2+ and VO 2 + , respectively. The results showed that p varies weakly with the vanadium concentration C and this variation was quantified relative to a reference concentration C r by means of a concentration coefficient φ r . Experimental data showed that plots of φ r versus Cφ r and plots of 1/φ r versus C are linear and, based on this linearity, φ r was expressed as a simple function of C in terms of its reference concentration C r and a single parameter M that is independent of the choice of C r . Standard spectra of p at a concentration C 0 = 1 mol dm −3 and of ε 4 and ε 5 were generated from which the spectrum of any catholyte may be simulated using the measured value of M in a governing equation. This enables determination of the state of charge for any VFB catholyte using absorbance measurements at a small number of wavelengths. The use of non-dispatchable power sources such as solar, wind and ocean energy is increasing.1 Due to the intermittency of these sources, their use is restricted unless there is a means of storing the energy they produce in periods of high availability for utilization in periods of limited availability. 2,3 There is considerable interest in flow batteries for storing energy from such sources and for other large and medium scale energy storage applications. 4,5 Vanadium flow batteries (VFB), 5-13 also known as vanadium redox flow batteries (VRFB or VRB), are particularly attractive because, in addition to having long cycle life, they are essentially immune to cross-contamination problems due to mass transfer across the membrane that can limit the service life of the electrolyte in other systems. 3,4,7,[14][15][16][17][18][19] This is because both the positive and negative sides of a VFB are based on vanadium species, eliminating the need for costly re-purification processes. 1,12 Typical cells have carbon felt electrodes; both cell design and the electrochemical behavior of electrodes are active areas of research. 20-31The cells can operate at coulombic efficiencies of over 90% 32,33 and their carbon electrodes have very good stability as long as the positive half-cell is not overcharged. 34,35 Accurate monitoring of state of charge (SoC) is intrinsically important for the reliability of energy storage systems, particularly large systems in critical applications. Furthermore, independent monitoring of the SoC of both electrolytes is important for effective operation of flow battery technology. For example in a VFB, transfer of vanadium ions across the membrane [36][37][38] and side reactions such as hydrogen formation 12,39-44 at the negative electrode can cause the battery to become unbalanced (e.g. more V V on the posi...

The stability of typical vanadium flow battery (VFB) catholytes with respect to precipitation of V 2 O 5 was investigated at temperatures in the range 30-60 • C. In all cases a precipitate formed after an induction time, which decreased with increasing temperature and concentration of V V and increased with concentration of sulfate. Arrhenius-type plots are shown for two typical solutions. These have excellent linearity and have similar slopes which yield an apparent activation energy of 1.79 eV (172 kJ mol −1 ). The variation of induction time with temperature for various concentrations of V V was simulated, and stability diagrams for additive-free VFB catholytes were generated. Vanadium flow batteries 1,2 (VFBs), also known as vanadium redox flow batteries (VRFBs), are currently the subject of much interest and recent research 3-7 because they are attractive for a variety of largescale energy storage applications. 8 An important advantage of a flow battery is that its energy storage capacity and its power capability can be scaled independently.2 VFBs have the additional advantage that cross-contamination due to transport through the membrane is effectively eliminated because the anolyte and catholyte differ only in the oxidation state of the vanadium.9 Also, since aqueous vanadium species are highly colored, the state-of-charge may be precisely monitored using ultraviolet-visible spectroscopy. 10,11The energy density of VFBs is limited by the solubility of V II , V III , V IV and V V in the electrolyte. In the anolyte, the solubility of V 2+ and V 3+ generally increases with temperature and decreases with increasing concentration of H 2 SO 4 and this is also true for the solubility of the V IV species, VO 2+ , in the catholyte. 12 The predominant V V species 13 present in strongly acidic solutions such as typical VFB catholytes is the pervanadyl ion VO 2 + . The solubility of vanadium (V) oxide, V 2 O 5 , in this region of pH is ∼0.1 mol dm −3 or less. 14 Thus, at the concentrations typically encountered in VFB catholytes, V V is expected to be thermodynamically unstable in solution with respect to precipitation as V 2 O 5 . However, precipitation is usually found to be very slow and, in practice, supersaturated solutions of V V in sulfuric acid can persist for very long periods of time. The stability of these metastable solutions (VFB catholytes) decreases, as expected, as the concentration of V V increases. 15 This is reflected in a lowering of stability at a particular vanadium concentration as the state-of-charge (i.e. the fraction of vanadium present as V V ) of the catholyte increases. 16Stability improves with increasing concentration of sulfate 17 and in the presence of certain additives 1 such as H 3 PO 4 . Thus, there have been several studies 7,[15][16][17][18][19] of the stability of V V in the catholyte of VFBs, and several mechanisms of precipitation have been proposed. 7,18 However, there is an absence in the literature of detailed kinetic studies of the precipitation process and the variation w...