16 Search Results

The electrochemical reduction of CO₂ (CO₂RR) is a potentially scalable approach for converting captured carbon dioxide into value-added products. Conventional gas-phase electrolysis systems can suffer from carbonate crossover, which limits the efficiency of the system. Liquid-phase (bi)carbonate electrolysis using bipolar membrane electrode assemblies (BPMMEA) has emerged as a promising alternative. The interposer layer, a porous mass-transport material between the BPM and the catalyst, is an essential component of the MEA, as it allows evolved CO₂ to reach the catalyst surface for reaction. In the absence of this layer, evolved CO₂ generated by the pH swing process at the BPM canmore » be converted back into (bi)carbonate (CO₂ recapture) due to the high bulk pH. Thus, clear design guidelines are needed to maximize CO₂ conversion, minimize CO₂ recapture in the catholyte, and improve energy efficiency. Here, the transport properties of the interposer are systematically characterized by X-ray tomography and symmetric-cell impedance spectroscopy to quantify porosity, tortuosity, and the resulting MacMullin number. We then examine the correlation between these material properties and the electrolyzer performance. We focus on characterizing two commercial porous membrane filters, mixed cellulose ester (MCE) and poly(ether sulfone) (PES).« less

Blowdown water from various industries and cooling facilities contains high concentrations of calcium (Ca), magnesium (Mg), silica, and corrosion inhibitors, which render the water unsuitable for discharge into surface water and wastewater treatment plants. Electrocoagulation (EC) is effective at removing Ca and silica. Here, in this study, Mg-alloy electrodes EC resulted in ∼91% silica removal at a 5400 C/L charge loading. Ca removal, however, was only 31%. To enhance Ca removal, carbon dioxide (CO₂) containing gas was introduced. CO₂ addition formed carbonate ions, which reacted with Ca/Mg ions to generate carbonate precipitates. Introducing 5% and 14% CO₂, simulating natural gas-firedmore » and coal-fired flue gas, enhanced Ca removal to 38% and 47%, respectively. Pure CO₂ facilitated 70% Ca removal, more than two times higher than that without CO₂, while maintaining high silica removal. FTIR, XRD, and SEM-EDS analyses confirmed enhanced Ca/Mg carbonate formation upon CO₂. In situ Raman spectroscopy was employed to monitor carbonate-ions formation. The results demonstrated carbonate-ions removal through Ca-carbonate formation after CO₂ addition. A techno-economic assessment showed that recycled electrode materials and flue gas lead to ∼3 times lower cost compared with conventional silica/Ca removal through chemical coagulation, softening, or membrane filtration. The study demonstrated that CO₂ addition removes high concentrations of Ca and silica ions from wastewaters at a competitive cost.« less

Electrocoagulation (EC), an electrochemical water treatment process, is commonly used to remove particulate and colloidal matter from water. Here, in this study, we demonstrate that EC, when coupled with membrane filtration, is also capable of removing dissolved species, such as Ca⁺, Mg²⁺, and SiO_x. The removal of such species is important for downstream membrane-based desalination treatment of the water that can suffer from reduced performance due to membrane scaling. Here, we describe how EC can be combined with a low-pressure membrane (LPM) system to offer efficient (and potentially universal) pretreatment for downstream membrane desalination. Synthetic water, simulating cooling tower blowdownmore » (CTBD) with elevated concentrations of hardness and silicates (Ca: 418 ppm, Mg: 63 ppm, SiO₂: 50 ppm) is treated using EC coupled to ultrafiltration (UF) to remove Mg up to 30 ± 1%, Ca up to 29 ± 1%, and silica up to 99 ± 1%. We evaluated the effectiveness of the EC-UF pretreatment system in reducing downstream RO scaling using thermodynamic modeling to predict the saturation index (SI) at the RO membrane/water interface. An SI value below zero (SI < 0) indicates under-saturated conditions (with respect to a particular mineral) where mineral scaling does not take place, which correlates with improved water recovery. Our findings suggest that the EC-UF pretreatment system was able to increase water recovery by up to 30%, compared to 0% recovery without pretreatment, under optimal conditions (feed solution pH of 7 and an EC charge loading of 1800 C/L). Finally, we conducted an economic analysis showing that implementing an EC-UF system for CTBD water could yield a cost benefit of up to $$\$$$$14.13 per m³ compared to direct brine disposal.« less

An aluminum (Al)-based electrocoagulation (EC) system can effectively remove dissolved silica and hardness in groundwater. The effectiveness of Al-EC in terms of pollutant removal, Faradaic efficiency, and energy consumption depends on the interfacial electrolysis or passivation of the electrode in water. Thus, understanding the electrolysis reaction at the liquid/electrode interface during operation is important for sustainable EC deployment. Here, a continuous flow-through Al-EC system was tested with various groundwater simulants, i.e., chloride (Cl^–)-based, sulfate (SO₄^2–)-based, and mixed solutions. High pollutant removal with low energy consumption was observed in Cl^–-based groundwater treatment, while low pollutant removal with high energy consumption wasmore » observed in SO₄^2–-based groundwater. For example, the required energy per unit mass of Al dosing in SO₄^2–-based groundwater is three times higher than that in Cl^–-based groundwater at 10 mA/cm². However, increasing the Cl^– concentration significantly reduces this energy demand. In SO₄^2–-based groundwater, the silicate removal efficiency drops from 85.1% to 24.0% compared to that for Cl^–-based groundwater, while Mg²⁺ and Ca²⁺ removal efficiencies decrease to 0.6% from 15.8% and 5.7% from 44.8%, respectively. To better understand this EC performance, we used in situ neutron reflectometry (NR) to examine the interfacial dynamics of Al dissolution and passivation at a 100 nm scale occurring on the surface of the sacrificial Al electrodes during EC. Ex situ X-ray reflectometry (XRR) was also used to support the in situ NR results. Both NR and XRR results revealed that Al dissolution is influenced by the presence of Cl^– in the simulants, while a passivating layer forms on the electrode in a SO₄^2–-based solution. In the Cl^–-based solution, anodic Al dissolution occurred locally and inhomogeneously across the surface of the Al anode film, resulting in a localized thickness reduction over time. In the SO₄^2–-based solution, no apparent dissolution of the Al anode was identified. Instead, Al underwent oxidation, forming an amorphous Al₂O₃ surface layer within the Al electrode film that increased in thickness over time. In the mixed solution, both anodic Al dissolution and surface Al₂O₃ layer formation occurred, indicating that Al dissolution and surface Al₂O₃ layer formation are attributable to the Cl^– and SO₄^2– ions, respectively.« less

This work demonstrates the mechanocatalytic hydrogenolysis of the ether bond in the lignin model compound benzyl phenyl ether (BPE) and hardwood lignin isolated by hydrolysis with supercritical water. Pd catalysts with 4 wt % loading on Al₂O₃ and SiO₂ supports achieve 100% conversion of BPE with a toluene production rate of (2.6–2.9) × 10^–5 mol·min^–1. The formation of palladium hydrides under H₂ gas flow contributes to an increase in the turnover frequency by a factor of up to 300 compared to Ni on silica–alumina. While a near-quantitative toluene yield is obtained, some of the phenolic products remain adsorbed on themore » catalyst.« less

Electrocoagulation (EC) of synthetic groundwater was conducted using a sacrificial aluminum electrode in a flow-through EC reactor with short retention times (<1 min) under varying hydrodynamic and electrochemical conditions. The treated water was allowed to settle for 24 h and achieved silicate removal of up to 50 ± 4%, and hardness removal of 11 ± 1%. Physical, chemical, and electrochemical characterization was performed to explore changes in electrode surface morphology and composition. Electrochemical impedance spectroscopy (EIS) showed that chemical reactions at the electrode/water interface are sensitive to changes in the immediate chemical environment. We demonstrate that the most energy-intensive stepmore » in EC is aluminum dissolution at the anode, which remained fairly constant due to the continuous renewal of the anode’s surface, a result of aluminum dissolution. At the cathode, a structural change in the oxide layer, from γ-Al₂O₃ to gibbsite, was detected by grazing-incidence X-ray diffraction, which decreased the resistance to charge transfer at the cathode surface, resulting in decreased electrode resistance. The high flow rate in the system minimized the accumulation of aluminum hydroxide solids and aluminum ions at the electrode/water interface, which minimized the formation of thick scalants and amorphous Al(OH)₃ on the cathode and anode, respectively. In conclusion, it was further demonstrated by EIS that under these conditions the resistance to charge transfer was constant throughout the duration of the experiment.« less

Electrochemical nitrate reduction (NO₃ RR) has attracted attention as an emerging approach to mitigate nitrate pollution in groundwater. Here, we report that a highly ordered PdCu alloy-based electrocatalyst exhibits selective (91% N₂), stable (480 h), and near complete (94%) removal of nitrate without loss of catalyst. In situ and ex situ XAS provide evidence that structural ordering between Pd and Cu improves long-term catalyst stability during NO₃RR. In contrast, we also report that a disordered PdCu alloy-based electrocatalyst exhibits non-selective (44% N₂ and 49% NH₄⁺), unstable, and incomplete removal of nitrate. The copper within disordered PdCu alloy is vulnerable tomore » accepting electrons from hydrogenated neighboring Pd atoms. This resulted in copper catalyst losses which were 10× greater than that of the ordered catalyst. The design of stable catalysts is imperative for water treatment because loss of the catalyst adds to the system cost and environmental impacts.« less

Decarbonizing desalination systems requires combining renewable energy technologies with desalination systems. Solar thermal desalination, which combines a thermal desalination system (e.g., distillation, multistage flash, etc.) with a concentrated solar system is attractive in geographic regions with an abundance of saline water and solar energy. However, the high economic cost and low efficiency limits its adoption. This review provides an overview of the techno-economic, materials, and performance challenges that need to be overcome to realize solar-desalination. The review describes the four most prominent pathways for overcoming thermodynamic and cost limitations present in current systems. Specifically, methodologies and approaches such as directmore » solar evaporation structures, low-cost thermal energy storage, solar cogeneration schemes for power and desalination, and solar hybrid desalination are discussed. Furthermore, these strategies can enable solar thermal desalination technologies that are resilient to intermittent solar energy.« less