We report aircraft observations of extreme levels of HCl and the dihalogens Cl 2 , Br 2 , and BrCl in an industrial plume near the Great Salt Lake, Utah. Complete depletion of O 3 was observed concurrently with halogen enhancements as a direct result of photochemically produced halogen radicals. Observed fluxes for Cl 2 , HCl, and NO x agreed with facility-reported emissions inventories. Bromine emissions are not required to be reported in the inventory, but are estimated as 173 Mg year −1 Br 2 and 949 Mg year −1 BrCl, representing a major uncounted oxidant source. A zero-dimensional photochemical box model reproduced the observed O 3 depletions and demonstrated that bromine radical cycling was principally responsible for the rapid O 3 depletion. Inclusion of observed halogen emissions in both the box model and a 3D chemical model showed significant increases in oxidants and particulate matter (PM 2.5 ) in the populated regions of the Great Salt Lake Basin, where winter PM 2.5 is among the most severe air quality issues in the U.S. The model shows regional PM 2.5 increases of 10%−25% attributable to this single industrial halogen source, demonstrating the impact of underreported industrial bromine emissions on oxidation sources and air quality within a major urban area of the western U.S.

The VO2+/VO2+ redox couple commonly employed on the positive terminal of the all-vanadium redox flow battery was investigated at various states of charge (SOC) and H2SO4 supporting electrolyte concentrations. Electron paramagnetic resonance was used to investigate the VO2+ concentration and translational and rotational diffusion coefficient (DT, DR) in both bulk solution and Nafion membranes. Values of DT and DR were relatively unaffected by SOC and on the order of 10−10 m2s−1. Cyclic voltammetry measurements revealed that no significant changes to the redox mechanism were observed as the state of charge increased; however, the mechanism does appear to be affected by H2SO4 concentration. Electron transfer rate (k0) increased by an order of magnitude (10−6 ms−1 to 10−8 ms−1) for each H2SO4 concentrations investigated (1, 3 and 5 M). Analysis of cyclic voltammetry switching currents suggests that the technique might be suitable for fast determination of state of charge if the system is well calibrated. Membrane uptake and permeability measurements show that vanadium absorption and crossover is more dependent on both acid and vanadium concentration than state of charge. Vanadium diffusion in the membrane is about an order of magnitude slower (~10−11 m2s−1) than in solution (~10−10 m2s−1).

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.

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