This report details the properties of anion-conducting membranes synthesized by halomethylation and quaternization of benzylmethyl-containing poly(sulfone)s. The benzylmethyl moieties, which serve as precursors to cationic sites, are introduced during polymer synthesis, thereby circumventing postmodification of the polymer by chloromethylation. By directing the distribution of ionic groups, the anion conductivity and water uptake of the membranes could be tuned over a wide range. For homogeneously distributed cationic groups, the water uptake and anionic conductivity were high relative to the material's ion exchange capacity. When an unfunctionalizable comonomer was added, the water uptake decreased for a given ion content. A strong correlation between the water uptake and anion conductivity was observed for all materials. Interestingly, as the cation concentration in the membrane decreased due to an increase in water uptake, the anion conductivity increased. This unexpected relationship between the volumetric density of fixed charged sites and the anion conductivity underscores the importance of water uptake in these materials to promote fast anion transport.

A microbial desalination cell (MDC) is a new method to reduce the salinity of one solution while generating electrical power from organic matter and bacteria in another (anode) solution. Substantial reductions in the salinity can require much larger volumes of the anode solution than the saline water, but any reduction of salinity will benefit the energy efficiency of a downstream reverse osmosis (RO) desalination system. We investigated here the use of an MDC as an RO pre-treatment method using a new type of air-cathode MDC containing three equally sized chambers. A single cycle of operation using a 1 g L À1 acetate solution reduced the conductivity of salt water (5 g L À1 NaCl) by 43 AE 6%, and produced a maximum power density of 480 mW m À2 with a coulombic efficiency of 68 AE 11%. A higher concentration of acetate (2 g L À1 ) reduced solution conductivity by 60 AE 7%, and a higher salt concentration (20 g L À1 NaCl) reduced solution conductivity by 50 AE 7%. The use of membranes with increased ion exchange capacities further decreased the solution conductivity by 63 AE 2% (20 g L À1 NaCl). These results demonstrate substantial (43-67%) desalination of water is possible using equal volumes of anode solution and salt water. These results show that MDC treatment could be used to substantially reduce salt concentrations and thus energy demands for downstream RO processing, while at the same time producing electrical power.

A sulfonated poly(sulfone) (S-Radel Ò ) membrane with high proton conductivity and low vanadium ion permeability showed high initial performance in a vanadium redox flow battery (VRFB) but suffered mechanical and chemical degradation during charge/discharge cycling. The S-Radel membrane showed different degradation behavior in flow cell cycling and ex-situ vanadium ion immersion tests. When the membrane was immersed in aqueous V 5? solution, the sample cracked into small pieces, but did not degrade to any measurable extent in V 4? solution. During charge/discharge cycling in the VRFB cell, the membrane underwent internal delamination, preferentially on the side of the membrane that faced the positive electrode. A vanadium-rich region was observed near the membrane surface that experienced delamination and Raman spectroscopic analysis of the degraded surface indicated a slightly depressed 1026 cm -1 band corresponding to a loss in the sulfonate SO 2 stretch intensity. Even though the S-Radel membrane underwent severe mechanical damage during the flow cell cycling, significant chemical degradation was not obvious from the spectroscopic analyses. For the VRFB containing an S-Radel membrane, an increase in membrane resistance caused an abnormal voltage depression during the discharge cycle. The reversible increase in membrane resistance and severe mechanical degradation of the membrane during cycling may be attributed to repeated formation and dissolution of particles inside the membrane. The mechanical stresses imposed by the particles coupled with a small amount of chemical degradation of the polymer by V 5? ions, are likely degradation mechanisms of the S-Radel membrane in VRFBs under high state-of-charge conditions.

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