The reactivity of cobalt(II) complexes with molecular oxygen is a heavily studied and extremely important catalytic system. These interactions result in the formation of metal-dioxygen adducts that are responsible for numerous cobalt-catalyzed oxidations. In the case of 4-coordinate cobalt salen [Co(salen)] complexes, the formation of catalytically active, mononuclear, superoxo adducts in the presence of a secondary, N-donor ligand has been demonstrated [Co(salen)pyr-O 2 ]. In batch reactions, these adducts are known to readily oxidize certain para-substituted phenolic compounds resulting in benzoquinones in high yield. Para-phenolic model compounds have been used to demonstrate the potential use of cobalt Schiff base complexes in the oxidation of lignin biomass. This work investigates the redox behavior of the Co(salen)pyr-O 2 adduct as a potential recyclable electrocatalyst. Using traditional electrochemical techniques, the activity of the Co(salen)pyr-O 2 adduct is evaluated as it applies to the oxidation of the substrate syringyl alcohol (4-(hydroxymethyl)-2,6-dimethoxy-phenol) in acetonitrile. Typical EC′ electrochemical behavior is reported showing a near linear relationship between substrate concentration and peak current density (J p ) up to 200 mV s −1 . Electrochemical titration of catalytic amounts of Co(salen) with pyridine in the presence of excess oxygen and substrate indicate that the one-electron oxidation of Co(salen)pyr-O 2 H is reversible up to 2:1 pyridine to cobalt. However EPR characterization of electrolysis experiments with Co(salen)pyr-O 2 in the presence of excess substrate show evidence for the deactivation of the catalyst system after two hours, indicating possible poor ligand stability or the occurrence of an inhibiting side reaction under reaction conditions.

Currently most mobile consumer electronics and battery powered electric vehicles are based on lithium ion technology, which require little maintenance and boast a much higher energy density than most battery types. However, there is a dire need to develop a new generation of energy storage devices which show a higher energy density and improved safety over current technology. The former need is more evident in electric vehicles which currently suffer from short ranges and long recharge times while the latter is of great concern for all applications. Metal air batteries have received increased attention in recent years as a potential replacement technology1. Metal air batteries utilize oxygen from the air as an input to the positive electrode; this significantly limits the size and weight of the cell. Among the potential candidates for use in these batteries zinc stands out due to its all-aqueous design and low cost with acceptable energy density1. The use of a polymer electrolyte membrane in a zinc air cell would reduce the amount of liquid electrolyte equired, increasing the energy density. Zn-air batteries may also benefit from the use of an exchange membrane by diminishing zinc crossover and carbonate precipitation. In this work membranes were synthesized using a poly(phenylene oxide) (PPO) based backbone structure. PPO was chosen because it is known to be relatively stable to basic environments2 and has been well studied as an anion exchange membrane for fuel cells3. Anion exchange membranes were crafted by functionalizing brominated PPO with quaternary ammonium and imidazolium moieties. Both cross-linked and uncross-linked membranes were investigated. In this contribution, we will report primarily on the detailed behavior of PPO membranes modified with benzyl trimethyl ammonium (BTMA) cations. An initial characterization was conducted on each membrane in order characterize the physical, mechanical, chemical, and conductive properties. The physical and mechanical properties measured included glass transition temperature, tensile strength, swelling ratio, and base and water uptake in different concentrations of KOH. Chemical properties such as ion exchange capacity were measured. The conductivity of membranes saturated in hydroxide solutions and equilibrated water vapor activities was measured. In order to characterize the degradation of the AEMs, changes in the physical, mechanical, chemical, and conductive properties mentioned above were monitored for membranes in several concentrations of potassium hydroxide solutions. It was found that the PPO backbone slowly degraded under accelerated test conditions, though the polymer electrolytes were stable at room temperature for long periods in battery tests. Typical data are shown in Figure 1. As we find for most ion exchange membranes in contact with concentrated solutions of acids, bases and salts, the conductivity exhibits a maximum with increasing electrolyte bath concentration. Note also that the conductivity of the samples degrades over a period of weeks. Chromatographic analysis of the bathing solution were used to explore the breakdown products of the reaction. That analysis is ongoing. A complete set of data correlating the water, KOH and carbonate uptake of the membrane, conductivity and other properties as functions of polymer and solution compositions will be presented and discussed. Extensive durability tests will also be described and a comparison between our methods and literature approaches to testing durability and analyzing reaction pathways will be presented. Implications for device applications will be inferred. Acknowledgement; The authors would like to thank ZAF Energy Systems for providing funding for this work. References: 1) Md. A. Rahman, W. Wang, C. Wen. J. Electrochemical Soc. 160 (10) A1759-A1771. 2) S. A. Nunez, M. A. Hickner, ACS Macro Letters 2013, 2(1), 49–52. 3) N. Li, Y. Leng, M. A. Hickner, C.-Y. Wang, J. Am. Chem. Soc. 2013, 135 (27), 10124–10133.

The reactivity of cobalt(II) complexes with molecular oxygen has long been a known and is a much-studied chemical mechanism. These interactions result in the formation of metal-dioxygen adducts that are responsible for numerous cobalt-catalyzed oxidations. In the case of 4-coordinate cobalt salen [Co(salen)] complexes, the formation of catalytically active, mononuclear, superoxo adducts in the presence of a secondary, N-donor ligands has been demonstrated [Co(salen)pyr-O2]. In batch reactions, these adducts are known to readily oxidize para-substituted phenolic compounds resulting in benzoquinone in high yield. Para-phenolic model compounds have been used to demonstrate the potential use of cobalt Schiff base complexes in the oxidation of lignin biomass. This work investigates the redox behavior of the Co(salen)pyr-O2­­ adduct as a potential recyclable electrocatalyst. Using traditional electrochemical techniques, the activity of the Co(salen)pyr-O2 adduct is evaluated as it applies to the oxidation of the substrate syringyl alcohol (4-(hydroxymethyl)-2,6-dimethoxy-phenol) in acetonitrile. Typical EC’ electrochemical behavior is reported showing a near linear relationship between substrate concentration and peak current density (Jp) up to 200 mV s-1. Electrochemical titration of catalytic amounts of Co(salen) with pyridine in the presence of excess oxygen and substrate indicate that the one-electron oxidation of Co(salen)pyr-O2H is reversible up to 2:1 pyridine to cobalt. However, both FTIR and EPR characterization of electrolysis experiments with Co(salen)pyr-O2 in the presence of excess substrate show evidence for the deactivation and/or degradation of the catalyst system after the two-hour mark indicating possible poor ligand stability under reaction conditions. Acknowledgements We gratefully acknowledge the NSF EPSCoR program, TN-SCORE, for support of this work.