We evaluate the efficiency and capacity of electrochemically reversible insertion electrodes for use in targeted ion removal applications in aqueous solutions. The relative attributes of insertion material chemistry are evaluated by comparing the performance of two different sodium insertion materials, NaTi(PO) and NaMnO, in different electrolyte environments. We performed experiments over a range of solution compositions containing both sodium and other non-inserting ions, and we then developed mechanistic insight into the effects of solution concentration and composition on overpotential losses and round trip Coulombic efficiency. In dilute aqueous streams, performance was limited by the rate of ion transport from the bulk electrolyte region to the electrode interface. This leads to slow rates of ion removal, large overpotentials for ion insertion, parasitic charge loss due to water electrolysis, and lower round trip Coulombic efficiencies. This effect is particularly large for insertion electrodes with redox potentials exceeding the water stability window. In solutions with high background concentrations of non-inserting ions, the accumulation of non-inserting ions at the electrode interface limits inserting ion flux and leads to low ion removal capacity and round trip Coulombic efficiency.

Hybrid solid electrolytes are promising alternatives for high energy density metallic lithium batteries. Scalable manufacturing of multi-material electrolytes with tailored transport pathways can provide an avenue toward controlling Li stripping and deposition mechanisms in all-solid-state devices. A novel roll-to-roll compatible coextrusion device is demonstrated to investigate mesostructural control during manufacturing. Solid electrolytes with 25 and 75 wt % PEO-LLZO compositions are investigated. The coextrusion head is demonstrated to effectively process multimaterial films with strict compositional gradients in a single pass. An average manufacturing variability of 5.75 ± 1.2 μm is observed in the thickness across all the electrolytes manufactured. Coextruded membranes with 1 mm stripes show the highest room temperature conductivity of 8.8 × 10–6 S cm–1 compared to the conductivity of single-material films (25 wt %, 1.2 × 10–6 S cm–1; 75 wt %, 1.8 × 10–6 S cm–1). Distribution of relaxation times and effective mean field theory calculations suggest that the interface generated between the two materials possesses high ion-conducting properties. Computational simulations are used to further substantiate the influence of macroscale interfaces on ion transport.

A continuum of water populations can exist in nanoscale layered materials, which impacts transport phenomena relevant for separation, adsorption, and charge storage processes. Quantification and direct interrogation of water structure and organization are important in order to design materials with molecular-level control for emerging energy and water applications. Through combining molecular simulations with ambient-pressure X-ray photoelectron spectroscopy, X-ray diffraction, and diffuse reflectance infrared Fourier transform spectroscopy, we directly probe hydration mechanisms at confined and nonconfined regions in nanolayered transition-metal carbide materials. Hydrophobic (K+) cations decrease water mobility within the confined interlayer and accelerate water removal at nonconfined surfaces. Hydrophilic cations (Li+) increase water mobility within the confined interlayer and decrease water-removal rates at nonconfined surfaces. Solutes, rather than the surface terminating groups, are shown to be more impactful on the kinetics of water adsorption and desorption. Calculations from grand canonical molecular dynamics demonstrate that hydrophilic cations (Li+) actively aid in water adsorption at MXene interfaces. In contrast, hydrophobic cations (K+) weakly interact with water, leading to higher degrees of water ordering (orientation) and faster removal at elevated temperatures.

Here we investigate the competitive electrosorption of mono-and divalent phosphate anions through electrochemical desalination-and dilatometry-based experiments. Through in situ dilatometry, we monitor the strain at the electrode surface as anions and cations are electrosorbed. Strain measurements show that the presence of divalent ions promotes a greater than anticipated electrode expansion during cation (Na + ) electrosorption. The expansion observed with Na + equaled the expansion observed with HPO 4 2− . Because the ionic radius of Na + is smaller than that of HPO 4 2− , the symmetric expansion suggests that divalent anions do not completely desorb during electrode regeneration, causing the adverse interactions with the cation during co-ion expulsion. This results in a decrease in desalination performance, indicated by a decreased salt adsorption capacity. Conversely, an expected asymmetric expansion during anion and cation electrosorption occurs with monovalent phosphate anions (H 2 PO 4 − ), indicating that monovalent ions can be effectively replaced by the cation at the electrode surface.

We evaluate the effectiveness of an aluminum-based electrocoagulation pretreatment system to remove dissolved silica and hardness. Silica and hardness limit water recovery during membrane-based desalination applications when silica and hardness exceed the solubility limit and generate scale on the membrane surface. We show that simultaneous removal of nearly all silica (95 ± 4%) and a significant amount of hardness (40–60%) occurs with a hydraulic residence time of 2 h and a charge loading between 0 and 1200 C/L. Increasing the residence time maximized the hardness removal (58 ± 8%) via the formation of larger flocs, which allowed for more constituent removal by gravity settling. We highlight the trade-offs between improved energy efficiency at lower charge loadings and an improved removal rate at a higher charge loading. We further compare the percente of silica and hardness removed in multicomponent solutions and compare this to single component feed solution. We discuss the implications that operational considerations have in terms of cost and treatment capacity. Finally, a cost–benefit analysis comparing chemical coagulation with electrocoagulation indicates that electrocoagulation could be half the cost of chemical coagulation and could produce more stable effluent pH and conductivity.