Boron, a ubiquitous element in seawater, is an essential micronutrient for plants but becomes toxic at elevated concentrations. Its narrow beneficial range necessitates efficient removal from water intended for potable use and irrigation. Conventional boron removal methods, such as multi-stage reverse osmosis and ion exchange, are both chemical- and energy-intensive, underscoring the need for more sustainable alternatives. Here, we present an energy-efficient electrosorption approach using electrodes functionalized with boron-selective polymeric films. Specifically, we fabricated a series of electrodes functionalized with polymeric films incorporating diolcontaining functional groups. This electrode functionalization significantly enhanced boron selectivity over competing chloride ions, from 0.19 f 0.02 in pristine electrodes to 2.02 f 0.09 in polyvinyl alcohol (PVA) (1 wt %, 10 k)-functionalized electrodes, and increased electrosorption capacity by facilitating borate transport from the bulk solution into the electrode micropores in our previously developed bipolar membrane-assisted electrosorption system. The specific energy consumption was reduced by over 80%, from 0.260 f 0.010 (i.e., pristine electrode) to 0.040 f 0.003 kWh g-B- 1 with PVA (5 wt%, 10 k)-functionalized electrodes. Density functional theory (DFT) calculations revealed that the binding energy between boron and functional groups within the polymeric films plays a critical role in controlling boron transport and, consequently, electrosorption performance. These findings demonstrate a versatile platform for energy-efficient and selective contaminant removal, offering a scalable alternative to conventional boron removal methods.

As the gap between lithium supply and demand continues to widen, the need to develop ion-selective technologies, which can efficiently extract lithium from unconventional water sources, grows increasingly crucial. In this study, we investigated the fundamentals of applying a solid-state electrolyte (SSE), typically used in battery technologies, as a membrane material for aqueous lithium extraction. We find that the anhydrous hopping of lithium ions through the ordered and confined SSE lattice is highly distinct from ion migration through the hydrated free volumes of conventional nanoporous membranes, thus culminating in unique membrane transport properties. Notably, we reveal that the SSE provides unparalleled performance with respect to ion-ion selectivity, consistently demonstrating lithium ion selectivity values that are immeasurable by even the part-per-billion detection limit of mass spectrometry. Such exceptional selectivity is shown to be the result of the characteristic size and charge exclusion mechanisms of solid-state ion transport, which may be leveraged in the design of next-generation membranes for resource recovery.

Lithium-ion batteries are becoming more ubiquitous, increasing lithium demand. Lithium carbonate, the most common form of industrial lithium, is primarily produced from lithium-rich brines concentrated using solar evaporation ponds. This extraction method is environmentally damaging and slow, taking a year or more to sufficiently concentrate. To meet the increasing demand, new technologies are being developed which can facilitate lithium recovery and shorten production timelines. This work examines two promising separations technologies, ion exchange resins due to their low cost and intercalation electrodes due to their high selectivity, and applies them to two potential alternative lithium sources - seawater reverse osmosis concentrate, and oil and gas produced water - to evaluate their efficacy. We develop process trains for each technology and analyze them using technoeconomic analysis and lifecycle assessment to determine economic and environmental feasibility. Further, technical improvements and process train modifications are examined to determine the impact on lithium carbonate cost. Our results show that currently ion exchange resins are the cheaper technology for recovering lithium, and that oil and gas produced water can produce lithium carbonate for as little as $14.96 kgLi(2)CO(3)(-1) while recovering 34.3 % of lithium in solution, making it economically viable as a recovery option. Given sufficient technical improvements, intercalation electrode production costs for lithium carbonate may also be competitive. The preferred technology for minimizing the environmental impact is dependent on water source, but the ion exchange resin paired with oil and gas produced water has the lowest environmental impact overall, producing only 17.7 kgCO(2)-eq kgLi(2)CO(3)(-1).

Selective removal of trace contaminants from water remains a crucial challenge in water treatment. Boron is a trace contaminant that is ubiquitous in seawater and has been widely detected in groundwater. Current boron removal methods, such as multi-stage reverse osmosis and ion-exchange adsorption, are chemical and energy intensive, necessitating the development of more sustainable technologies. Here we address this challenge by developing surface functionalized microporous electrodes that enable boron-selective bipolar membrane-assisted electrosorption. Our study demonstrates that micropore functionalization with oxygen-containing (hydroxyl, lactone and carboxyl) and boron-selective (dopamine, 3-methylamino-1,2-propanediol and N-methyl-d-glucamine) functional groups substantially improves electrode performance for boron removal and selectivity. The functionalized electrodes exhibit a boron removal selectivity that is an order of magnitude higher than that of the pristine electrode, facilitating energy efficient boron electrosorption. We identify hydroxyl groups as the key factor in enhancing boron removal performance and selectivity during electrosorption. Molecular dynamics simulations demonstrate the underlying mechanisms of boron selectivity, highlighting the role of hydrogen bonding between hydroxyl groups and boron in governing the boron-selective electrosorption process. Boron removal is a persistent challenge in traditional desalination approaches. The functionalized microporous electrodes enable efficient boron removal with high selectivity in the electrosorption process.

Securing decarbonized economies for energy and commodities will require abundant and widely available green H2. Ubiquitous wastewaters and nontraditional water sources could potentially feed water electrolyzers to produce this green hydrogen without competing with drinking water sources. Herein, we show that the energy and costs of treating nontraditional water sources such as municipal wastewater, industrial and resource extraction wastewater, and seawater are negligible with respect to those for water electrolysis. We also illustrate that the potential hydrogen energy that could be mined from these sources is vast. Based on these findings, we evaluate the implications of small-scale, distributed water electrolysis using disperse nontraditional water sources. Techno-economic analysis and life cycle analysis reveal that the significant contribution of H2 transportation to costs and CO2 emissions results in an optimal levelized cost of hydrogen at small- to moderate-scale water electrolyzer size. The implications of utilizing nontraditional water sources and decentralized or stranded renewable energy for distributed water electrolysis are highlighted for several hydrogen energy storage and chemical feedstock applications. Finally, we discuss challenges and opportunities for mining H2 from nontraditional water sources to achieve resilient and sustainable economies for water and energy.

Modern technology relies on an undisrupted supply of metals, yet many metals have limited geological deposits. Recovering metals from wastewater and brine could augment metal stocks, but there is little guidance on which metals to prioritize for recovery or on the techno-economic viability of extraction processes. Here we critically assess the potential for recovering metals from wastewater and brine. We first look at which metals are critical for recovery on the basis of their supply risks and the impacts of those supply restrictions. We then assess the feasibility of recovering these metals from various water sources by estimating the required operational costs to match market prices. Next we discuss the limitations of established separation technologies that may inhibit the practicality and scalability of metal recovery from water. We conclude by highlighting materials and processes that could serve as more sustainable alternatives to metal recovery with further research and development. Recovering metals from wastewater and brine could augment metal stocks that are fundamental to modern technology. This Perspective assesses the potential of, and provides guidance for, recovering metals from wastewater and brine.

Effective removal of hexavalent chromium (Cr(VI)) from water is challenging due to the need for a highly selective process. Efficient chromium removal may potentially be achieved through the use of redox-assisted flowthrough electrosorption. In this study, graphitized nanodiamonds (NDs) were annealed under various conditions and the ND with the lowest internal resistance was applied to an activated carbon cloth electrode. The NDmodified electrode was then used as the cathode in a flow-through electrode cell with pristine carbon cloth as the anode. Effective chromium removal was found through a dual pathway mechanism, whereby Cr(VI) is directly electrosorbed at the anode while Cr(VI) is reduced to Cr(III) at the cathode, and subsequently precipitated as Cr(OH)(3 )under the locally high cathodic pH conditions. The effects of flow rate and charging/discharging voltage on Cr(VI) removal were further investigated, revealing that sufficiently low flow rates (i.e., <= 1 mL min(-1)) are required for effective Cr(OH)(3) precipitation and sufficiently high (i.e., >1.4 V) reverse voltages are needed during the discharging period to enable full desorption. Overall, the system displayed high Cr removal capacity (i.e., up to 39.51 mu mol g-1) and favorable redox of Cr(VI) to trivalent chromium Cr(III) and Cr(III) to Cr (VI). These results suggest that the ND-modified electrode is a promising tool for the removal of toxic metal ions from wastewater.

Boron removal from aqueous solutions has long persisted as a technological challenge, accounting for a disproportionately large fraction of the chemical and energy usage in seawater desalination and other industrial processes like lithium recovery. Here, we introduce a novel electrosorption-based boron removal technology with the capability to overcome the limitations of current state-of-the-art methods. Specifically, we incorporate a bipolar membrane (BPM) between a pair of porous carbon electrodes, demonstrating a synergized BPM-electrosorption process for the first time. The ion transport and charge transfer mechanisms of the BPM-electrosorption system are thoroughly investigated, confirming that water dissociation in the BPM is highly coupled with electrosorption of anions at the anode. We then demonstrate effective boron removal by the BPM-electrosorption system and verify that the mechanism for boron removal is electrosorption, as opposed to adsorption on the carbon electrodes or in the BPM. The effect of applied voltage on the boron removal performance is then evaluated, revealing that applied potentials above ∼1.0 V result in a decline in process efficiency due to the increased prevalence of detrimental Faradaic reactions at the anode. The BPM-electrosorption system is then directly compared with flow-through electrosorption, highlighting key advantages of the process with regard to boron sorption capacity and energy consumption. Overall, the BPM-electrosorption shows promising boron removal capability, with a sorption capacity >4.5 μmol g-C-1 and a corresponding specific energy consumption of <2.5 kWh g-B-1.

Bipolar membranes (BPMs), a special class of ion exchange membranes with the unique ability to electrochemically induce either water dissociation or recombination, are of growing interest for environmental applications including eliminating chemical dosage for pH adjustment, resource recovery, valorization of brines, and carbon capture. However, ion transport within BPMs, and particularly at its junction, has remained poorly understood. This work aims to theoretically and experimentally investigate ion transport in BPMs under both reverse and forward bias operation modes, taking into account the production or recombination of H+ and OH-, as well as the transport of salt ions (e.g., Na+, Cl-) inside the membrane. We adopt a model based on the Nernst-Planck theory, that requires only three input parameters─membrane thickness, its charge density, and pK of proton adsorption─to predict the concentration profiles of four ions (H+, OH-, Na+, and Cl-) inside the membrane and the resulting current-voltage curve. The model can predict most of the experimental results measured with a commercial BPM, including the observation of limiting and overlimiting currents, which emerge due to particular concentration profiles that develop inside the BPM. This work provides new insights into the physical phenomena in BPMs and helps identify optimal operating conditions for future environmental applications.

The unavoidable and detrimental formation of silica scale in engineered processes necessitates the urgent development of effective, economic, and sustainable strategies for dissolved silica removal from water. Herein, we demonstrate a rapid, chemical-free, and selective silica removal method using electrosorption. Specifically, we confirm the feasibility of exploiting local pH dynamics at the electrodes in flow-through electrosorption, achieved through a counterintuitive cell configuration design, to induce ionization and concomitant electrosorption of dissolved silica. In addition, to improve the feasibility of silica electrosorption under high-salinity solutions, we developed a silica-selective anode by functionalizing porous activated carbon cloths with aluminum hydroxide nanoparticles (Al(OH)(3)-p-ACC). The modification markedly enhances silica sorption capacity (2.8 vs 1.1 mg(silica) g(anode)(-1)) and reduces the specific energy consumption (13.3 vs 19.8 kWh kg(silica)(-1)). Notably, the modified electrode retains remarkable silica sorption capacity even in the presence of high concentrations of co-occurring ions (up to 100 mM NaCl). The mechanisms underlying the superior silica removal stability and selectivity with the Al(OH)(3)-p-ACC electrode are also elucidated, revealing a synergistic interaction involving outer-sphere and inner-sphere complexation between dissolved silica and Al(OH)(3) nanoparticles on the electrodes. Moreover, we find that effective regeneration of the electrodes may be achieved by applying a reverse potential during discharge, although complete regeneration of the modified electrodes may necessitate alternative materials or process optimization. We recommend the adoption of feedwater-specific designs for the development of future silica-selective electrodes in electrosorption capable of meeting silica removal demands across a wide range of engineered systems.

While electrodialysis (ED) demonstrates lower energy consumption than reverse osmosis (RO) in the desalination of low salinity waters, RO continues to be the predominant technology for brackish water desalination. In this study, we probe this skewed market share and project the potential for future disruption by ED through systematic assessment of the levelized cost of water (LCOW). Using rigorous process- and economic-models, we minimize the LCOW of RO and ED systems, highlighting important tradeoffs between capital and operating expenditure for each technology. With optimized current state-of-the-art systems, we find that ED is more economical than RO for feed salinities ≤ 3 g L-1, albeit to a minor extent. Considering that RO is a highly mature technology, we focus on predicting the future potential of ED by evaluating plausible avenues for capital and operating cost reduction. Specifically, we find that reduction in the price of ion-exchange membranes (i.e., < 60 USD m-2) can ensure competitiveness with RO for feed salinities up to 5 g L-1. For higher feed salinities (≥ 5 g L-1) we reveal that the LCOW of ED may effectively be reduced by decreasing ion-exchange membrane resistance, while preserving high current efficiency. Through extensive assessment of structure-property-performance relationships, we precisely identify target membrane charge densities and diffusion coefficients which optimize the LCOW of ED, thus providing novel guidance for future membrane material development. Overall, we emphasize that with a unified approach - whereby ion-exchange membrane price is reduced and performance is enhanced - ED can become the economically preferable technology compared to RO across the entire brackish water salinity range.

In recent years, the development of nanopore-based membranes has revitalized the prospect of harvesting salinity gradient (blue) energy. In this study, we systematically analyze the energetic performance of nanopore-based power generation (NPG) at various process scales, beginning with a single nanopore, followed by a multipore membrane coupon, and ending with a full-scale system. We confirm the high power densities attainable by a single nanopore and demonstrate that, at the coupon scale and above, concentration polarization severely hinders the power density of NPG, revealing the common, yet significant, error in linearly extrapolating single-pore performance to multipore membranes. Through our consideration of concentration polarization, we also importantly show that the development of materials with exceptional nanopore properties provides limited enhancement of practical process performance. For a full-scale NPG membrane module, we find an inherent tradeoff between power density and thermodynamic energy efficiency, whereby achieving a high power density sacrifices the energy efficiency. Furthermore, we derive a simple expression for the theoretical maximum energy efficiency of NPG, showing it is solely related to the membrane selectivity (i.e., S2/2). Through this relation, it is apparent that the energy efficiency of NPG is limited to only 50% (for a completely selective membrane, i.e., S = 1), reinforcing our optimistic full-scale simulations which result in a (practical) maximum energy efficiency of 42%. Finally, we assess the net extractable energy of a full-scale NPG system which mixes river water and seawater by including the energy losses from pretreatment and pumping, revealing that the NPG process-both in its current state of development and in the case of highly optimistic performance with minimized external energy losses-is not viable for power generation.

We discuss a recent publication in Energy & Environmental Science that presented a techno-economic analysis of electrochemical water desalination technologies.

Electrodialysis (ED) is an electro-driven desalination technology that relies on the selective transport of ions through ion exchange membranes. Though several approaches have been developed to model and evaluate the performance of ED, mechanistic ion-transport models, which rigorously solve the fundamental Nernst-Planck equation, remain some of the most reliable and utilized. However, complexity of the involved transport phenomena prevents analytical solutions of such models, and numerical solutions can be prohibitively intensive. Here, we use an equivalent circuit analogue to derive a simple correlation equation that predicts the energetic performance of ED for brackish water desalination. Specifically, our correlation equation predicts the specific energy consumption of ED for a given productivity, set of desalination parameters (i.e., feed salinity, salt removal, water recovery), and system properties. The correlation equation demonstrates robustness in predicting the specific energy consumption across a wide range of operational parameters, showing excellent agreement with a Nernst-Planck ion-transport model and literature-reported experimental data. Furthermore, we use the developed correlation equation to show the dependence of the specific energy consumption on the productivity, highlighting the tradeoff between the thermodynamic energy efficiency and desalination rate of the ED process. Overall, our developed correlation equation provides a convenient alternative to computationally intensive mechanistic models for performance analysis of the ED process.

Though electrodialysis (ED) and reverse osmosis (RO) are both mature, proven technologies for brackish water desalination, RO is currently utilized to desalinate over an order of magnitude more brackish water than ED. This large discrepancy in the adoption of each technology has yet to be thoroughly justified in the literature, particularly from the perspective of energy consumption. Hence, in this study, we performed a direct and systematic comparison of the energy consumption of RO and ED for brackish water desalination, precisely mapping out the ideal operational space of each technology for the first time. Using rigorous system-scale models for RO and ED, we determine the specific energy consumption and energy efficiency of each process over a wide range of brackish water conditions. Specifically, we investigate the effects of varying feed salinity, extent of salt removal, water recovery, and productivity to ultimately identify the operational sweet spots of each technology. By maintaining the same separation parameters (i.e., feed salinity, salt removal, water recovery) and productivity between RO and ED throughout the study, we ensure that our comparison of the technologies is valid and fair. Our results indicate that both RO and ED are capable of operating with high energy efficiency (>30%) for brackish water desalination, though for differing conditions. Particularly, we show that whereas ED excels for low feed salinities (<3 gL(-1)) and extents of salt removal, RO operates optimally for high salinity feeds (>5 gL(-1)), which require more extensive desalination. Through our in-depth energetic analysis, we provide guidance for future applications of RO and ED, emphasizing that increased implementation of ED will require significant reduction in the cost of ion-exchange membranes.

Electro-driven technologies are viewed as a potential alternative to the current state-of-the-art technology, reverse osmosis, for the desalination of brackish waters. Capacitive deionization (CDI), based on the principle of electrosorption, has been intensively researched under the premise of being energy efficient. However, electrodialysis (ED), despite being a more mature electro-driven technology, has yet to be extensively compared to CDI in terms of energetic performance. In this study, we utilize Nernst-Planck based models for continuous flow ED and constant-current membrane capacitive deionization (MCDI) to systematically evaluate the energy consumption of the two processes. By ensuring equivalently sized ED and MCDI systems-in addition to using the same feed salinity, salt removal, water recovery, and productivity across the two technologies-energy consumption is appropriately compared. We find that ED consumes less energy (has higher energy efficiency) than MCDI for all investigated conditions. Notably, our results indicate that the performance gap between ED and MCDI is substantial for typical brackish water desalination conditions (e.g., 3 g L-1 feed salinity, 0.5 g L-1 product water, 80% water recovery, and 15 L m-2 h-1 productivity), with the energy efficiency of ED often exceeding 30% and being nearly an order of magnitude greater than MCDI. We provide further insights into the inherent limitations of each technology by comparing their respective components of energy consumption, and explain why MCDI is unable to attain the performance of ED, even with ideal and optimized operation.

We reveal the insignificance of advanced materials in further enhancing the energy efficiency of desalination and suggest more impactful approaches.

Capacitive deionization (CDI), which is based on the electrosorption of ions by porous electrodes, is an emerging technology for brackish water desalination. Understanding the key drivers of energy consumption in CDI and benchmarking CDI with reverse osmosis (RO), the current state-of-the-art for brackish and seawater desalination, is crucial to guide the future development of desalination technologies. In this study, we develop system-scale models to analyze the energy consumption and energy efficiency of CDI and RO over a wide range of material properties and operating conditions. Using our models, we explore how the energetic performance of CDI and RO compare as a function of feed salinity, water recovery, salt rejection, and average water flux, which is normalized by electrode and membrane area in CDI and RO, respectively. Our analysis shows that RO is significantly more energy efficient than CDI, particularly when targeting higher salinity feed streams and higher salt rejection values. For brackish water with a salt concentration of 2000 mg L-1, achieving 50% water recovery and 75% salt rejection, with an average water flux of 10 L m(-2) h(-1) using CDI requires a specific energy consumption of 0.85 kWh m(-3), more than eight times that of RO (0.09 kWh m(-3)). Importantly, our results also indicate that current efforts to improve electrode materials can only marginally reduce the energy consumption of CDI. We conclude with a discussion highlighting other important factors, such as capital cost, electrode stability, and membrane fouling, which affect the efficacy of CDI and RO for low-salinity desalination.