in water as anionic arsenate (As(V)) or arsenite (As(III)), with the latter being acutely toxic and difficult to remove. [3] Commonly employed techniques to remove arsenic are coagulation-flocculation or chemical adsorption, both which require significant chemical input, and extensive pretreatment steps for As(III) to As(V) conversion. [3c] Thus, novel removal technologies that integrate removal and conversion of arsenic are critical for sustainable environmental management.The development of advanced materials for water purification, selective contaminant removal, and improved energy efficiency is critical to tackling water-energy nexus challenges, including through the design of more effective membranes and field-assisted adsorbents. [4] Electrochemical methods for water treatment such as capacitive deionization (CDI) have garnered increased attention as a desalination technology, and also as a heavy metal removal platform, due to their efficiency and low environmental footprint compared to typical methods. [5] Electrosorption systems benefit from inherent modularity and scalability, which opens the door to point of source remediation systems. Electrochemical conversion of As(III) to As(V) on carbon electrode has been investigated previously for CDI-based arsenic remediation. [5l,6] However, low arsenic selectivity in the presence of competing ions has limited the total uptake capacity of carbon-based CDI, [5c,h-l] as most arsenic contaminated water sources are composed of 10 to 1000-fold excess salts. [7] Thus, the design of molecularly selective functional adsorbents is necessary to address these materials chemistry limitations.Recent work has shown redox-active/Faradaic materials as an attractive platform for selective water contaminant removal. [8] Redox-active metallopolymers have demonstrated remarkable uptake of anions with significant selectivity, both of organic anions and heavy metal oxyanions. [8b,9] At the same time, asymmetric electrochemical systems have traditionally been proposed in energy-storage applications to enhance capacitance and electrochemical properties. [10] Here, we leverage this electrochemical design for the first time to integrate both the separation and the reactions step electrochemically at functionalized electrodes. We seek to combine two redox-active polymer Advanced redox-polymer materials offer a powerful platform for integrating electroseparations and electrocatalysis, especially for water purification and environmental remediation applications. The selective capture and remediation of trivalent arsenic (As(III)) is a central challenge for water purification due to its high toxicity and difficulty to remove at ultra-dilute concentrations. Current methods present low ion selectivity, and require multistep processes to transform arsenic to the less harmful As(V) state. The tandem selective capture and conversion of As(III) to As(V) is achieved using an asymmetric design of two redox-active polymers, poly(vinyl)ferrocene (PVF) and poly-TEMPO-methacrylate (PTMA). D...

Selection of an appropriate electrolyte medium is essential for successful NH 3 electro-synthesis at low temperature and pressure. In this study, 2-propanol was employed as an electrolyte medium and its effectiveness in the electro-reduction of N 2 to NH 3 under ambient conditions was evaluated. NH 3 synthesis and faradaic efficiency using a mixture of 2-propanol/water (9:1, v/v) surpassed those when electrosynthesis was carried out using solely water. The concentration of H 2 SO 4 and the applied current density influenced NH 3 synthesis in this 2-propanol-based system, and the optimal conditions led to maximized N 2 reduction, indicating that the competing and electron-losing reaction of H 2 evolution was relatively well suppressed.

In this study, a novel electrolysis cell based on ethylenediamine (EDA) as a cathodic solvent was developed for NH 3 electro-synthesis. The NH 3 -generating cathode chamber was filled with 0.1 M LiCl/EDA and separated by a cation exchange membrane from the anodic compartment, which was filled with 0.05 M H 2 SO 4 aqueous solution. It appeared that EDA was cathodically stable, and thus electron-stealing medium destruction was substantially avoided. The faradaic efficiency for NH 3 synthesis was 17.2%, producing 7.73 × 10 −7 mol NH 3 for 1 h electrolysis at a cell voltage of 1.8 V with the charge consumption of 1.3 C.

Lithium-mediated reduction of dinitrogen is ap romising methodt oe vade electron-stealing hydrogen evolution, ac ritical challenge which limits faradaic efficiency (FE) and thus hinders the success of traditional protic-solvent-based ammonia electro-synthesis. Av iable implementation of the lithium-mediated pathway using lithium-ion conducting glass ceramics involves i) lithium deposition, ii)nitridation,a nd iii)ammonia formation. Ammonia was successfully synthesized from molecular nitrogen and water,y ielding am aximum FE of 52.3 %. Witha n ammonia synthesis rate comparable to previously reported approaches, the fairly high FE demonstrates the possibility of using this nitrogen fixation strategya sasubstitute for firmly established, yet exceedingly complicated and expensivet echnology,a nd in so doing represents an ext-generation energy storagesystem.The Haber-Bosch process is aw ell-established ammonia (NH 3 ) synthesis technology that converts more than 120 million tons of N 2 into NH 3 annually. [1,2] However,this process is exceedingly energy intensiveo wing to harsh operating conditions, and exhibits extensive carbon emission. [1] Therefore, the development of more environmentally benign alternatives is crucial.Electrochemical synthesisi sa na ttractive candidatef or N 2 fixation ase nergy consumption, if optimized (i.e. with low overvoltage and high faradaic efficiency), could potentially be reduced as compared to the Haber-Bosch process while avoiding CO 2 emission. [3,4] If the required electricity for the process is supplied from renewable sources, this approach offers a meanstostore excess renewable energy in agreen energy carrier with an energy density comparable to fossil fuels. [5] True sustainability,h owever,w ill only be realized if the electrons required for the N 2 reduction originate from water rather than H 2 .Over the last three decades, such electrochemical processes have been developed, with state-of-the art technologiess ummarized in Ta ble S1 in the Supporting Information. [6][7][8][9][10][11][12][13][14][15][16] Unfortunately,t he faradaic efficiencies (FEs) in most cases were unbearably low (< 5%)a st he competing hydrogen evolution from water or ap rotonw as preferred over the intended N 2 reduction, which was particularly sluggish owing to the strong triple bond of N 2 (941 kJ mol À1 ). [3,17,18] Innovative strategies are thus indispensable to overcome such obstacles and achieve excellent selectivity in the N 2 reduction.One promisingw ay is to employ Li as amediator in the electro-synthesis. In contact with N 2 ,m etallicL i, on accounto fi ts strong reducing power,c auses dissociation to form lithium nitride (Li 3 N) even under ambient conditions. Thus-formed Li 3 N is ah igh-energyi ntermediate for NH 3 synthesis that is readily transformed into NH 3 upon reaction with protons or water. [17] This so-called "Li-mediated pathway" was firstly applied to synthesizing NH 3 in studies by Ts unetoe tal.,w hich reported an impressively high maximum FE of 59 %a t5 0atm of N 2 (1 atm = 0....

Molecular design of redox-materials provides a promising technique for tuning physicochemical properties which are critical for selective separations and environmental remediation. Here, the structural tuning of redox-copolymers, 4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TMA) and 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine (TMPMA), denoted as P(TMA x-co-TMPMA 1−x), is investigated for the selective separation of anion contaminants ranging from perfluorinated substances to halogenated aromatic compounds. The amine functional groups provide high affinity toward anionic functionalities, while the redox-active nitroxyl radical groups promote electrochemically-controlled capture and release. Controlling the ratio of amines to nitroxyl radicals provides a pathway for tuning the redox-activity, hydrophobicity, and binding affinity of the copolymer, to synergistically enhance adsorption and regeneration. P(TMA x-co-TMPMA 1−x) removes a model perfluorinated compound (perfluorooctanoic acid (PFOA)) with a high uptake capacity (>1000 mg g −1) and separation factors (500 vs chloride), and demonstrates exceptional removal efficiencies in diverse perand polyfluoroalkyl substances (PFAS) and halogenated aromatic compounds, in various water matrices. Integration with a boron-doped diamond electrode allows for tandem separation and destruction of pollutants within the same electrochemical cell, enabling the energy integration of the separation step with the catalytic degradation step. The study demonstrates for the first time the tuning of redox-copolymers for selective remediation of organic anions, and integration with an advanced electrochemical oxidation process for energy-efficient water purification.

Nitrate is a ubiquitous aqueous pollutant from agricultural and industrial activities. At the same time, conversion of nitrate to ammonia provides an attractive solution for the coupled environmental and energy challenge underlying the nitrogen cycle, by valorizing a pollutant to a carbon-free energy carrier and essential chemical feedstock. Mass transport limitations are a key obstacle to the efficient conversion of nitrate to ammonia from water streams, due to the dilute concentration of nitrate. Here, we develop bifunctional electrodes that couple a nitrate-selective redox-electrosorbent (polyaniline) with an electrocatalyst (cobalt oxide) for nitrate to ammonium conversion. We demonstrate the synergistic reactive separation of nitrate through solely electrochemical control. Electrochemically-reversible nitrate uptake greater than 70 mg/g can be achieved, with electronic structure calculations and spectroscopic measurements providing insight into the underlying role of hydrogen bonding for nitrate selectivity. Using agricultural tile drainage water containing dilute nitrate (0.27 mM), we demonstrate that the bifunctional electrode can achieve a 8-fold up-concentration of nitrate, a 24-fold enhancement of ammonium production rate (108.1 ug h−1 cm−2), and a >10-fold enhancement in energy efficiency when compared to direct electrocatalysis in the dilute stream. Our study provides a generalized strategy for a fully electrified reaction-separation pathway for modular nitrate remediation and ammonia production.

Summary Critical minerals are essential for the ever-increasing urban and industrial activities in modern society. The shift to cost-efficient and ecofriendly urban mining can be an avenue to replace the traditional linear flow of virgin-mined materials. Electrochemical separation technologies provide a sustainable approach to metal recovery, through possible integration with renewable energy, the minimization of external chemical input, as well as reducing secondary pollution. In this review, recent advances in electrochemically mediated technologies for metal recovery are discussed, with a focus on rare earth elements and other key critical materials for the modern circular economy. Given the extreme heterogeneity of hydrometallurgically-derived media of complex feedstocks, we focus on the nature of molecular selectivity in various electrochemically assisted recovery techniques. Finally, we provide a perspective on the challenges and opportunities for process intensification in critical materials recycling, especially through combining electrochemical and hydrometallurgical separation steps.

Molecularly-selective metal separations are key to sustainable recycling of Li-ion battery electrodes. However, metals with close reduction potentials present a fundamental challenge for selective electrodeposition, especially for critical elements such as cobalt and nickel. Here, we demonstrate the synergistic combination of electrolyte control and interfacial design to achieve molecular selectivity for cobalt and nickel during potential-dependent electrodeposition. Concentrated chloride allows for the speciation control via distinct formation of anionic cobalt chloride complex (CoCl42-), while maintaining nickel in the cationic form ([Ni(H2O)5Cl]+). Furthermore, functionalizing electrodes with a positively charged polyelectrolyte (i.e., poly(diallyldimethylammonium) chloride) changes the mobility of CoCl42- by electrostatic stabilization, which tunes cobalt selectivity depending on the polyelectrolyte loading. This strategy is applied for the multicomponent metal recovery from commercially-sourced lithium nickel manganese cobalt oxide electrodes. We report a final purity of 96.4 ± 3.1% and 94.1 ± 2.3% for cobalt and nickel, respectively. Based on a technoeconomic analysis, we identify the limiting costs arising from the background electrolyte, and provide a promising outlook of selective electrodeposition as an efficient separation approach for battery recycling.