Hydrophobicity Tuned Polymeric Redox Materials with Solution-Specific Electroactive Properties for Selective Electrochemical Metal Ion Recovery in Aqueous Environments.

Adaptable redox-active materials hold great potential for electrochemically mediated separation processes via targeted molecular recognition and reduced energy requirements. This work presents molecularly tunable vinylferrocene metallopolymers (P(VFc-co-X)) with modifiable operating potentials, charge storage capacities, capacity retentions, and analyte affinities in various electrolyte environments based on the hydrophobicity of X. The styrene (St) co-monomer impedes hydrophobic anions from ferrocene access, providing P(VFc-co-St) with specific response capabilities for and greatly improved cyclabilities in hydrophilic anions.

Electrochemically Mediated Direct CO Capture by a Stackable Bipolar Cell.

The unprecedented increase in atmospheric CO concentration calls for effective carbon capture technologies. With distributed sources contributing to about half of the overall emission, CO capture from the atmosphere [direct air capture, (DAC)] is more relevant than ever. Herein, an electrochemically mediated DAC system is reported which utilizes affinity of redox-active quinone moieties towards CO molecules, and unlike incumbent chemisorption technologies which require temperature or pH swing, relies solely on the electrochemical voltage for CO capture and release.

Selective adsorption of organic anions in a flow cell with asymmetric redox active electrodes.

Electrochemically mediated adsorption is an emerging technology that utilizes redox active (or Faradaic) materials and has exhibited high salt adsorption capacity and superb ion selectivity. Here, we use a redox polymer polyvinylferrocene (PVFc) as the anode and a conducting polymer polypyrrole doped with a large anionic surfactant (pPy-DBS) as the cathode for selective electrochemical removal of inorganic and organic components. We fabricated a flow system with alternating adsorption/desorption steps incorporating an electrosorption cell and inline probes (ultraviolet-visible spectroscopy, conductivity and pH sensors) to demonstrate on-the-fly quantification of the ion adsorption performance.

Electrochemical Selective Recovery of Heavy Metal Vanadium Oxyanion from Continuously Flowing Aqueous Streams.

An electrochemical flow cell with redox-active electrodes was used for selective removal and recovery of vanadium(V) oxyanions from aqueous streams. The cell relies on intrinsic affinity of the redox-active polymer poly(vinyl)ferrocene (PVFc) and demonstrates selectivity of >10 towards vanadium compared to a background electrolyte in 40-fold abundance. We demonstrate highly selective vanadium removal in the presence of various competing anions (i.

Ion selectivity in capacitive deionization with functionalized electrode: Theory and experimental validation.

Capacitive deionization (CDI) is a promising technique for salt removal and may have potential for highly selective removal of ion species. In this work, we take advantage of functional groups usually used with ionic exchange resins and apply these to CDI. To this end, we functionalize activated carbon with a quaternary amines surfactant and use this surface to selectively and passively (no applied field) trap nitrate ions.

Thermodynamics of Ion Separation by Electrosorption.

We present a simple, top-down approach for the calculation of minimum energy consumption of electrosorptive ion separation using variational form of the (Gibbs) free energy. We focus and expand on the case of electrostatic capacitive deionization (CDI). The theoretical framework is independent of details of the double-layer charge distribution and is applicable to any thermodynamically consistent model, such as the Gouy-Chapman-Stern and modified Donnan models.

Self-Cleaning Porous Surfaces for Dry Condensation.

Efficient water removal from a cool surface during condensation is critically important to the enhancement of a variety of heat transfer applications. Previous work has focused on the fabrication of superhydrophobic surfaces which promote water droplets and removal via droplet shedding or jumping. Here, we report a novel strategy with a droplet self-cleaning surface which spontaneously transports all of the droplets from the condensation surface to the back side.

Self similarities in desalination dynamics and performance using capacitive deionization.

Charge transfer and mass transport are two underlying mechanisms which are coupled in desalination dynamics using capacitive deionization (CDI). We developed simple reduced-order models based on a mixed reactor volume principle which capture the coupled dynamics of CDI operation using closed-form semi-analytical and analytical solutions. We use the models to identify and explore self-similarities in the dynamics among flow rate, current, and voltage for CDI cell operation including both charging and discharging cycles.

Charging and Transport Dynamics of a Flow-Through Electrode Capacitive Deionization System.

We present a study of the interplay among electric charging rate, capacitance, salt removal, and mass transport in "flow-through electrode" capacitive deionization (CDI) systems. We develop two models describing coupled transport and electro-adsorption/desorption which capture salt removal dynamics. The first model is a simplified, unsteady zero-dimensional volume-averaged model which identifies dimensionless parameters and figures of merits associated with cell performance.

Equilibria model for pH variations and ion adsorption in capacitive deionization electrodes.

Ion adsorption and equilibrium between electrolyte and microstructure of porous electrodes are at the heart of capacitive deionization (CDI) research. Surface functional groups are among the factors which fundamentally affect adsorption characteristics of the material and hence CDI system performance in general. Current CDI-based models for surface charge are mainly based on a fixed (constant) charge density, and do not treat acid-base equilibria of electrode microstructure including so-called micropores.

Energy breakdown in capacitive deionization.

We explored the energy loss mechanisms in capacitive deionization (CDI). We hypothesize that resistive and parasitic losses are two main sources of energy losses. We measured contribution from each loss mechanism in water desalination with constant current (CC) charge/discharge cycling.