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In this study, we explored the extent to which hydrotropes can be used to increase the aqueous solubilities of redox-active compounds previously used in flow batteries. We measured how five hydrotropes influenced the solubilities of five redox-active compounds already soluble in aqueous electrolytes (≥0.5 M). The solubilities of the compounds varied as a function of hydrotrope type and concentration, with larger solubility changes observed at higher hydrotrope concentrations. 4-OH-TEMPO underwent the largest solubility increase (1.18 ± 0.04 to 1.99 ± 0.12 M) in 20 weight percent sodium xylene sulfonate. The presence of a hydrotrope in solution decreased the diffusion coefficients of 4-OH-TEMPO and 4,5-dihydroxy-1,3-benzenedisulfonate, which was likely due to the increased solution viscosity as opposed to a specific hydrotrope–solute interaction because the hydrotropes did not alter their molecules’ hydraulic radii. The standard rate constants and formal potentials of both 4-OH-TEMPO and 4,5-dihydroxy-1,3-benzenedisulfonate remained largely unchanged in the presence of a hydrotrope. The results suggest that using hydrotropes may be a feasible strategy for increasing the solubilities of redox-active compounds in aqueous flow batteries without substantially altering their electrochemical properties.

A major goal of developing electrochemical CO 2 capture technologies is to minimize the energy demand. One strategy for decreasing energy demands of electrochemical capture technologies is increasing the ratio of CO 2 molecules captured per transferred electron. Here, we examined an electrochemical capture approach that has the potential to capture up to two CO 2 molecules per electron, which is higher than many existing approaches. We used the Cu(II)/Cu(I) redox couple to control the aqueous availability of a CO 2 sorbent, 1,2-dimethylimidazole (Me 2 Im), by transitioning between Cu(Me 2 Im) 4(aq) 2+ and Cu-(Me 2 Im) 2(aq) + . As expected from equilibrium calculations, a solution containing reduced Cu(I) had a greater CO 2 capacity than the oxidized Cu(II) state. In a bench-scale test, the energy demand for CO 2 capture was 27 ± 6 kJ e /mol C, despite operating at 7−11% energy efficiency due to a high experimentally-set cell voltage. We estimate that under market-ready concentration conditions and the same low energy efficiency, the energy demand will be approximately 65 ± 14 kJ e /mol C, although it can only remove 60% of the CO 2 from coal power plant flue gas (P CO 2 = 0.15 atm) at equilibrium. To address this issue, we used an equilibrium model of the relevant chemical reactions to identify how altering the substituent groups on imidazole will influence the CO 2 capture capacity and energy demand.

Electrokinetically controlled microinjection is reported as an effective transport mechanism for microinjection into the wild-type strain of the widely studied model microalga Chlamydomonas reinhardtii. A microinjection system using glass capillary pipettes was developed to capture and impale the motile cells. To apply an electric field and induce electrokinetic flow (e.g., electrophoresis and electroosmosis), an electrode was inserted directly into the solution inside the impaling injection pipette and another electrode was inserted into the external cell media. The viability of the impaled cells was confirmed for more than an hour under 0.01 V using the fluorescein diacetate/propidium iodide dual fluorescent dye based assay. The viability was also found to increase almost logarithmically with decreasing voltage and to depend strongly on the solution within the injection pipette. Successful electrokinetic microinjection into cells was confirmed by both an increase in cell volume under an applied voltage and electric field dependent delivery of fluorescent fluorescein molecules into an impaled cell. Our study offers novel opportunities for quantitative delivery of biomolecules into microalgae and advancing the research and development of these organisms as biosynthetic factories.

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