Review-Electrode Kinetics and Electrolyte Stability in Vanadium Flow Batteries

Two aspects of vanadium flow batteries are reviewed: electrochemical kinetics on carbon electrodes and positive electrolyte stability. There is poor agreement between reported values of kinetic parameters; however, most authors report that kinetic rates are faster for VIV/VV than for VII/VIII. Cycling the electrode potential increases the rates of both reactions initially due to roughening but when no further roughening is observed, the VII/VIII and VIV/VV reactions are affected oppositely by the pretreatment potential. Anodic pretreatment activates the electrode for the VII/VIII reaction, and deactivates it for VIV/VV. Three states of the carbon surface are suggested: reduced and oxidized states R and O, respectively, both with low electrocatalytic activity, and an intermediate state M with higher activity. The role of surface functional groups and the mechanisms of electron transfer for the VII/VIII and VIV/VV reactions are still not well understood. The induction time for precipitation of V2O5 from positive electrolytes decreases with temperature, showing an Arrhenius-type dependence with an activation energy of 1.79 eV in agreement with DFT calculations based on a VO(OH)3 intermediate. It also decreases exponentially with increasing VV concentration and increases exponentially with increasing sulphate concentration. Both arsenate and phosphate are effective additives for improving thermal stability

Clinical complexity and impact of the ABC (Atrial fibrillation Better Care) pathway in patients with atrial fibrillation: a report from the ESC-EHRA EURObservational Research Programme in AF General Long-Term Registry

Background: Clinical complexity is increasingly prevalent among patients with atrial fibrillation (AF). The ‘Atrial fibrillation Better Care’ (ABC) pathway approach has been proposed to streamline a more holistic and integrated approach to AF care; however, there are limited data on its usefulness among clinically complex patients. We aim to determine the impact of ABC pathway in a contemporary cohort of clinically complex AF patients. Methods: From the ESC-EHRA EORP-AF General Long-Term Registry, we analysed clinically complex AF patients, defined as the presence of frailty, multimorbidity and/or polypharmacy. A K-medoids cluster analysis was performed to identify different groups of clinical complexity. The impact of an ABC-adherent approach on major outcomes was analysed through Cox-regression analyses and delay of event (DoE) analyses. Results: Among 9966 AF patients included, 8289 (83.1%) were clinically complex. Adherence to the ABC pathway in the clinically complex group reduced the risk of all-cause death (adjusted HR [aHR]: 0.72, 95%CI 0.58–0.91), major adverse cardiovascular events (MACEs; aHR: 0.68, 95%CI 0.52–0.87) and composite outcome (aHR: 0.70, 95%CI: 0.58–0.85). Adherence to the ABC pathway was associated with a significant reduction in the risk of death (aHR: 0.74, 95%CI 0.56–0.98) and composite outcome (aHR: 0.76, 95%CI 0.60–0.96) also in the high-complexity cluster; similar trends were observed for MACEs. In DoE analyses, an ABC-adherent approach resulted in significant gains in event-free survival for all the outcomes investigated in clinically complex patients. Based on absolute risk reduction at 1 year of follow-up, the number needed to treat for ABC pathway adherence was 24 for all-cause death, 31 for MACEs and 20 for the composite outcome. Conclusions: An ABC-adherent approach reduces the risk of major outcomes in clinically complex AF patients. Ensuring adherence to the ABC pathway is essential to improve clinical outcomes among clinically complex AF patients

Impact of renal impairment on atrial fibrillation: ESC-EHRA EORP-AF Long-Term General Registry

Background: Atrial fibrillation (AF) and renal impairment share a bidirectional relationship with important pathophysiological interactions. We evaluated the impact of renal impairment in a contemporary cohort of patients with AF. Methods: We utilised the ESC-EHRA EORP-AF Long-Term General Registry. Outcomes were analysed according to renal function by CKD-EPI equation. The primary endpoint was a composite of thromboembolism, major bleeding, acute coronary syndrome and all-cause death. Secondary endpoints were each of these separately including ischaemic stroke, haemorrhagic event, intracranial haemorrhage, cardiovascular death and hospital admission. Results: A total of 9306 patients were included. The distribution of patients with no, mild, moderate and severe renal impairment at baseline were 16.9%, 49.3%, 30% and 3.8%, respectively. AF patients with impaired renal function were older, more likely to be females, had worse cardiac imaging parameters and multiple comorbidities. Among patients with an indication for anticoagulation, prescription of these agents was reduced in those with severe renal impairment, p <.001. Over 24 months, impaired renal function was associated with significantly greater incidence of the primary composite outcome and all secondary outcomes. Multivariable Cox regression analysis demonstrated an inverse relationship between eGFR and the primary outcome (HR 1.07 [95% CI, 1.01–1.14] per 10 ml/min/1.73 m2 decrease), that was most notable in patients with eGFR <30 ml/min/1.73 m2 (HR 2.21 [95% CI, 1.23–3.99] compared to eGFR ≥90 ml/min/1.73 m2). Conclusion: A significant proportion of patients with AF suffer from concomitant renal impairment which impacts their overall management. Furthermore, renal impairment is an independent predictor of major adverse events including thromboembolism, major bleeding, acute coronary syndrome and all-cause death in patients with AF

Impact of clinical phenotypes on management and outcomes in European atrial fibrillation patients: a report from the ESC-EHRA EURObservational Research Programme in AF (EORP-AF) General Long-Term Registry

Background: Epidemiological studies in atrial fibrillation (AF) illustrate that clinical complexity increase the risk of major adverse outcomes. We aimed to describe European AF patients\u2019 clinical phenotypes and analyse the differential clinical course. Methods: We performed a hierarchical cluster analysis based on Ward\u2019s Method and Squared Euclidean Distance using 22 clinical binary variables, identifying the optimal number of clusters. We investigated differences in clinical management, use of healthcare resources and outcomes in a cohort of European AF patients from a Europe-wide observational registry. Results: A total of 9363 were available for this analysis. We identified three clusters: Cluster 1 (n = 3634; 38.8%) characterized by older patients and prevalent non-cardiac comorbidities; Cluster 2 (n = 2774; 29.6%) characterized by younger patients with low prevalence of comorbidities; Cluster 3 (n = 2955;31.6%) characterized by patients\u2019 prevalent cardiovascular risk factors/comorbidities. Over a mean follow-up of 22.5 months, Cluster 3 had the highest rate of cardiovascular events, all-cause death, and the composite outcome (combining the previous two) compared to Cluster 1 and Cluster 2 (all P <.001). An adjusted Cox regression showed that compared to Cluster 2, Cluster 3 (hazard ratio (HR) 2.87, 95% confidence interval (CI) 2.27\u20133.62; HR 3.42, 95%CI 2.72\u20134.31; HR 2.79, 95%CI 2.32\u20133.35), and Cluster 1 (HR 1.88, 95%CI 1.48\u20132.38; HR 2.50, 95%CI 1.98\u20133.15; HR 2.09, 95%CI 1.74\u20132.51) reported a higher risk for the three outcomes respectively. Conclusions: In European AF patients, three main clusters were identified, differentiated by differential presence of comorbidities. Both non-cardiac and cardiac comorbidities clusters were found to be associated with an increased risk of major adverse outcomes

Characterization of β-lactoglobulin fibrillar assemblies

The overall goal of this research was to study the mechanism of heat-induced whey proteins fibrils and to characterise their properties for possible food applications. Experimental parameters such as protein concentration, pH, ionic strength, time and temperature of heating were varied to optimize the process of fibril formation of β- lactoglobulin (β-lg). Fibrillar structures could only be formed at acidic pH; the optimal conditions were pH 2, low ionic strength and 2% (w/w) protein concentration. A two-stage mechanism of β-lg fibril formation was proposed: 1) denaturation, partial unfolding and increase in β-sheets content, with hydrolysis of monomers, followed by 2) the linear aggregation of polypeptide fragments into fibrils via noncovalent interactions, accompanied by hydrolysis and a decrease in β-sheets content and overall secondary structure. In this study, β-lg and whey protein isolate (WPI) – derived fibrils were observed by atomic force microscopy (AFM). Their height was ca. 2 - 3 nm, while their length and periodicity was up to 15 μm and ~ 30 nm, respectively. Various process treatments such as high pressure, heating, shearing and acidification can induce changes in the physicochemical properties of whey proteins and their fibrillar aggregates. The studies on pH stability of β-lg fibrillar structures morphology revealed that the longer fibrils break up in the isoelectric range (pH 4.6 - 6) but were stable starting with pH 7 to 12. High dynamic pressure treatment (microfluidization) produced changes in the general physical dimensions of whey protein fibrils and in the secondary structures of their constituent units. Long fibrils (15 μm) were fractured under high-pressure treatment, the end result being shorter length fibrils (< 350 nm) with the same thickness of 2-3 nm. The study on the foaming properties of whey protein fibrils revealed that foam capacity and stability were related to the protein concentration, pH, whipping time, thermal and/or high pressure treatment of the protein and their assemblies. Results indicated the fibrillization of whey proteins increased foam capacity and stability compared to non-fibrillar whey proteins

Fibrillization of whey proteins improves foaming capacity and foam stability at low protein concentrations

The foaming properties of fibrillar whey proteins were compared with those of native or denatured whey proteins and also with egg white protein. Whey protein foaming capacity and stability were related to protein concentration, pH, time of whipping, pressure and heating treatments. Foams produced from fibrils showed significant improvement in foaming capacity and stability when compared with non-fibrillar whey proteins. Dynamic high shear (microfluidization) or moderate shear (Ultra-Turrax mixing) of fibrillar protein dispersions did not significantly affect their subsequent foaming properties. Furthermore, foams prepared with fibrillar whey protein (0% protein) had comparable capacity and stability to that from egg white protein, which is the traditional foaming ingredient in food industry. Results suggest that fibrillized whey proteins are highly effective foaming agents even at relatively low protein concentrations (1-3% w/w). (C) 2013 Elsevier Ltd. All rights reserved

Modelling and accelerated testing of catholyte stability in vanadium flow batteries

Using our standard methodology, we examined the thermal stability of vanadium flow battery positive electrolytes over a range of temperature from 30 to 70 °C with stable lifetimes from 11 min to 87 days. At higher temperatures (45 °C–70 °C) measurements showed excellent reproducibility but at lower temperatures (30 °C–45 °C) showed some scatter. Measurements at higher temperatures are in good agreement with our (single-slope) model which is based on earlier data but there is some divergence from the model at lower temperatures. Arrhenius plots of the data show two linear regimes: one in the range 45 °C–70 °C and another in the range 30 °C–45 °C, the latter having a higher Arrhenius slope. Based on linear least-squares best fits in these two regimes, we have formulated an improved stability model (two-slope model). We use our models to derive expressions for accelerated testing of thermal stability using increased temperature, increased vanadium concentration and decreased sulfate concentration and estimate values for the acceleration factors over a range of test and use temperatures and concentrations. We analyse the effect of changing concentration to counteract the decrease in electrolyte stability at higher temperatures and derive expressions to calculate the necessary concentrations

Communication—A new additive for increased stabilization of catholytes in vanadium flow batteries (VFBs)

We report a newadditive,monobasic potassium arsenate (KH2AsO4), for improving the thermal stability of VFB catholytes.Using our standard accelerated testing methodology at 30–70°C, we showed that the effect increases continuously with increasing concentration of arsenate over the range investigated (0 – 0.10 mol dm−3). In comparison to similar experiments with phosphate (H3PO4), the magnitude of the effect was greater for arsenate. A combination of arsenate and phosphate was also effective. Based on these results, we speculate that other Group-V elements in the +5 oxidation state may also stabilize VFB catholyte

Measurement and computer simulation of catholyte stability in vanadium flow batteries (VFBs)

Based on careful experimental measurements, a model for the stability of vanadium flow battery (VFB) catholytes was developed which quantifies their precipitation behavior as a function of temperature and composition. The model enables simulation of the induction time for precipitation at a temperature T for any catholyte with concentrations of sulfate and VV within the range of applicability. The results of such simulations are in good agreement with experiment. The model can predict catholyte stability using any of three alternative metrics: the induction time τ, the relative stability parameter ρ and the stability temperature TW. The induction time is a good measure of overall stability; the relative stability parameter compares the stability of any catholyte to a standard in a temperature-independent manner; and the stability temperature estimates the upper temperature limit at which a catholyte is stable for practical purposes. Equations are derived for these parameters and the behavior of each parameter is simulated and plotted under a variety of conditions. Likewise, the effect of state of charge is simulated and plotted. The plots and the associated equations provide detailed stability data that can be useful in the design of practical flow batteries

Communication-observation of arrhenius behavior of catholyte stability in vanadium flow batteries

The stability of typical vanadium flowbattery (VFB) catholytes with respect to precipitation of V2O5 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 VV 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 VV was simulated, and stability diagrams for additive-free VFB catholytes were generated