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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Application of electron beam technology to decompose persistent emerging drinking water contaminants: poly- and perfluoroalkyl substances (PFAS) and 1,4-Dioxane

Poly- and perfluoroalkyl substances (PFAS) and 1,4-dioxane are persistent emerging contaminants that are currently under consideration for federal and state-specific regulations in drinking water. Both PFAS and 1,4-dioxane are highly resistant to degradation and are not effectively removed by conventional drinking water treatment systems. Results from the Unregulated Contaminant Monitoring Rule 3 survey showed that >540 sites across the nation are contaminated with both PFAS and 1,4-dioxane. Hence, there is a need to identify technologies that can effectively remove both these contaminants. Water treatment via electron beam (e-beam) has been proven effective at treating a wide range of contaminants, including perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), polychlorinated biphenyls, and trichloroethylene. While the e-beam process is often considered similar to advanced oxidation processes (AOPs), e-beam technology is unique in that it produces both highly oxidizing and reducing species at the same time. The specific objectives of this study were to: (i) determine the effectiveness of 9 MeV electrons provided by the Fermilab’s Accelerator Application Development and Demonstration (A2D2) tool to decompose PFAS and 1,4-dioxane; (ii) assess the formation of byproducts during water treatment; (iii) apply the optimized treatment to field groundwater samples contaminated with PFAS and 1,4-dioxane, and (iv) assess the energy demands for the treatment of these contaminants using e-beam. Results from this study showed that e-beam is effective in treating both 1,4-dioxane and PFAS. Complete degradation of 1,4-dioxane was observed at a dose of 5 kGy for an initial concentration of up to 1 ppm without the need for any sample modification. The electrical energy per order (EEo) for treatment of 1,4-dioxane ranged from 0.46 to 0.72 kWh/m 3 /order and was comparable and even lower, in some cases, than other AOP technologies. Alkaline conditions (pH 13) and low dissolved oxygen concentration (2 mg/L) highly favored the treatment of PFAS by e-beam. Greater than 90% removal of PFOA and PFOS from an initial concentration of 100 to 500 ppb was achieved at a dose of 250 kGy and 500 kGy, respectively, under optimized conditions. The degradation efficiency was not significantly changed when treating other PFAS of fluorinated carbon chain length of 5 to 7 individually at 250 kGy with a removal ranging from 85¬–99% for different compounds. Short chain PFAS (perfluorobutanoate: PFBA and perfluorobutane sulfonate: PFBS) did not degrade under the same conditions at 250 kGy, but 70 to 99% degradation was observed at a higher dose of 1000 kGy. Short chain PFAS (perfluorohexanoate: PFHxA (C5) and perfluoroheptanoate: PFHpA (C6)) were detected after treatment of PFOA, but not after PFOS treatment. Inability to close the mass balance through targeted analysis suggests the presence of other intermediates not detectable by available analytical methods. When treating PFAS mixture containing ten compounds at equimolar concentration of 0.05 µM each, preferential degradation of polyfluorinated compound (6:2 fluorotelomer sulfonate or 6:2 FTS) followed by C8 and C7 compounds was observed as a function of increasing e-beam dose. About 30% degradation of ΣPFAS was observed at 250 kGy and no further removal was observed up to a dose of 1000 kGy. C4 to C6 PFASs showed no degradation, while C3 PFAS (PFBS) showed an increase in concentration by 34% at 1000 kGy due to formation from the breakdown of other long chain PFAS. These results suggested that (a) the reaction kinetics is likely different for different PFAS based on chain length, functional group, and the degree of fluorination of the carbon chain, and (b) there may be intermediates generated from the degradation of 6:2 FTS and C7/C8 compounds that can potentially scavenge hydrated electrons needed for reaction with the untreated PFAS molecules. Treatment of three PFAS-contaminated groundwater samples from two US states showed similar trends as observed in the treatment of equimolar PFAS mixtures. Up to 71% removal of ΣPFAS was achieved in real groundwater samples at 750 kGy and data trend suggested that higher degradation is feasible if higher doses (>1MGy) are applied to treat field samples to overcome matrix effects and competing species. Calculated EEo for PFAS ranged from as low as ~48 to 1081 kWh/m 3 /order depending on the type of PFAS treated. These values are comparable and even lower, in some cases, than other destructive technologies employed for PFAS treatment such as ultrasound, plasma, and photochemical treatment. The results from this study indicate e-beam is a promising approach under favorable conditions and should be explored further as an end-of-train treatment option for PFAS destruction.

1,4-Dioxane↗
DOE OSTI2022

Mild, Electroreductive Lignin Cleavage: Optimizing the Depolymerization of Authentic Lignins

Among candidate strategies to depolymerize lignin, electroreduction has promise as a mild, environmentally friendly, low-cost method to cleave lignin’s most common linkage, the β-O-4 bond. Much of the prior work on lignin electrolysis has focused on anodic (oxidative) approaches, while most available electroreduction studies have studied lignin model compounds rather than authentic lignin. Here, after optimizing with a model system, we investigated the room-temperature electroreductive cleavage of four common lignin samples from different pretreatment approaches, including Kraft, Soda, GVL, and Cu-AHP lignin. This mild electrolysis process resulted in the solubilization of 45% of the GVL lignin and 60% of the Cu-AHP lignin, affording approximately 17.6 and 19.4 wt % of monomeric materials, respectively. Furthermore, the present work is an encouraging first step toward an electroreductive strategy for lignin depolymerization and upgrading.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Systematic investigations on iron cycling in phosphorus/siderophore systems: Synergism or antagonism?

Synergisms between microbial exudates on Fe (hydr)oxide dissolution as an effective Fe acquisition pathway have been recently addressed and vigorously debated. However, Fe liberation mechanisms and where siderophores and phosphorus (P) coexist received little attentions. Current study systematically investigated ferrihydrite dissolution in the presence of desferrioxamine B (DFOB) (a kind of fungally-derived siderophores) and inorganic/organic phosphorus (orthophosphate, Pi; myo-inositol hexaphosphate, IHP), as a function of solute pH, reaction time and reagent content. Reacted solids were characterized by N 2 -BET adsorption, zeta (ζ) potential analysis, sequential extraction analysis (SEDEX), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), micro Raman spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). Our results indicate that upon reaction with P-only or (DFOB + P) systems, interfacial complexation partially switched from monolayer bidentate-binuclear surface complexes to ternary complexes, or laterally transformed into amorphous Fe–P precipitates. The Fe-Pi complex precipitated more readily under acidic conditions, and Fe-IHP complex preferentially nucleated in neutral-alkaline environments. Phosphorus slightly promoted Fe release from minerals and fixation to the leached layer or interfacial liquid zone initially, but subsequently prevented further attacks from protons and DFOB. The co-effects of P and DFOB likely correspond to two successive scenarios: 1) DFOB is preferentially attracted toward ferrihydrite surfaces by negative electrical fields induced by adsorbed phosphorus and can act synergistically with labile P–Fe complexes, resulting in intensive temporal dissolution of Fh; 2) subsequent Fe shuttling to DFOB can be prohibited by stabilized, passive P/Fe–P layers. Finally, our results emphasize the antagonism between P compounds and siderophores (i.e., DFOB here) on ferrihydrite dissolution to improve understanding of the biologically-mediated Fe cycling in natural systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Non-Fouling, Low Cost Electrolytic Coagulation & Disinfection for Treating Flowback and Produced Water for Reuse

Executive Summary This Final Report is composed of two major sections. The first section presents experimental results obtained in the laboratory during Budget Period 1. The second section presents results from the field test conducted during Budget Period 2. Laboratory Results This research investigated a novel electrochemical process for producing a ferric iron coagulant for use in treating flowback and produced water from hydraulic fracturing and oil production operations. The treatment system improves the effectiveness and lowers the cost of coagulation processes using Fe3+ as the coagulant. The electrolytic coagulant generation (ECG) system uses an electrochemical cell to produce acid and base from oilfield brine solutions. The acid is used to dissolve scrap iron to provide a Fe3+ coagulating agent. The base is used to neutralize the treated water. Compared to conventional electrocoagulation (EC), the main advantage of the ECG system is an order of magnitude lower cost for the source of iron. The second advantage over conventional EC is that it can deliver Fe3+ doses greater than 1 mM, since it is not limited by the amount of dissolved oxygen in the water required to oxidize ferrous to ferric iron. The capital costs for conventional EC and the ECG system are similar, but the operational costs for the ECG system are an order of magnitude lower than conventional EC. The combined costs for iron and electrical energy for treating 1 m3 of FPW with 1 mM Fe3+ is estimated to be $0.87 for conventional EC, and $0.087 for the ECG system. The estimated all-in cost for treating FPW with a 2 mM Fe3+ dose is $0.73/m3 ($0.12/bbl). Field Test Results The field test was conducted at the Paul Foster Central Tank Battery (CTB) in Lea County, New Mexico from November 10, 2022 through December 15, 2022. The feed water to the system was produced water from the Tatanka 1H formation. After approximately two weeks of testing, the initial batch of produced water had been treated and no untreated produced water was available. Thus, after this time, the feed water to the system consisted of previously treated water (i.e., recycled water). The recycled water had nearly all colloidal particles removed, and had a much lower alkalinity due to precipitation of carbonate minerals during the first pass through the system. Although the recycled water was not an ideal test solution due to its low particulate concentrations, its lower alkalinity did allow us to identify the main problem with the treatment system. The main problem with the treatment system was caused by the high alkalinity of the initial feed water (5.4 meq/L) that consumed a significant fraction of the electrochemically generated acid. This resulted in pH values exiting the iron contact tank that were too high to dissolve enough iron to effectively treat the produced water. Tests performed with recycled water with lower alkalinity did not have this issue, and dissolved iron concentrations greater than 20 mM could be achieved. One consistent observation was that effluent water from the iron contact tank was always free of particulates, even when fed with circumneutral solutions. This suggests that there is no need to dissolve high concentrations of iron if all the water to be treated is passed through the scrap iron canister. In this case, dissolved O2 and hypochlorous acid can promote sufficient iron corrosion to provide an effective coagulating agent – even in neutral pH water. This solves the problem resulting from highly alkaline produced water. Modifications to the design of the treatment system were made based on the field test results. These modifications will add minimal additional cost, and were tested in bench-scale laboratory experiments. In short-term testing, the modified treatment process was able to remove colloidal FeS particulates to levels below detection. Long-term, steady state testing will be required to determine whether the modified process is suitable for commercial treatment systems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Is Pt dissolution a concern from the counter electrode in electrochemical oxygen evolution reaction?

The Pt metal and its oxides dissolution from the counter electrode (CE, in hydrogen evolution reaction (HER)) has been suspected to affect the non-noble metal catalysts toward oxygen evolution reaction (OER). However, little effort has been devoted to this concern, and this work aims to determine the effect. The influence of electrolytes (H 2 SO 4 and NaOH) and Pt CE (acid-treated and pristine) on the Pt dissolution and membrane separations (Nafion and PiperION) on preventing Pt species migration were evaluated. Here, the results indicate only 11.2 ppb Pt from the cathodic electrolyte with Nafion 211 and 5 M NaOH electrolyte is observed, and no Pt is found from all other samples with acid-treated Pt CE. Regarding pristine Pt CE, 0.4 and 4.4 ppb Pt are observed from 0.5 M H 2 SO 4 and 5 M NaOH electrolytes, respectively. The findings in this work include: (1) Nafion membrane can effectively prevent the migration of Pt species from the cathode to the anode side; (2) a simple acid treatment of Pt could minimize the Pt dissolution into the acid electrolyte while showing an opposite role in the alkaline electrolyte; (3) the Pt dissolution from all experiments is minor, indicating Pt is a suitable CE for OER.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

In-situ polarization modulation IRRAS investigation of ammonia electrooxidation on Pt-Ir and Pt-Ru nanoparticles prepared on engineered catalyst supports

The catalytic activity and surface reactivity of monometallic Pt and bimetallic Pt-Ir and Pt-Ru nanoparticles, supported on two distinct Engineered Catalyst Supports (ECSs), were investigated for the Ammonia Electrooxidation Reaction (AmER) in alkaline media. XRD measurements confirmed alloy formation between Pt-Ir and Pt-Ru nanoparticles, as indicated by the shift of the (111) reflection to higher 2θ values. Cyclic voltammetry, linear sweep voltammetry, and chronoamperometry experiments were conducted to assess the catalytic activity of the Pt, Pt-Ir, and Pt-Ru electrocatalysts. All bimetallic catalysts exhibited lower onset potentials compared to Pt. The differing Tafel slopes between Pt (74 mV dec⁻¹), Pt-Ir (152 mV dec⁻¹), and Pt-Ru (118–197 mV dec⁻¹) suggest that alloying Pt with Ir or Ru alters the reaction mechanisms. Furthermore, the bimetallic Pt-Ir and Pt-Ru catalysts demonstrated greater tolerance for concentrated ammonia solutions relative to Pt. In-situ Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) provided insights into the formation of N-H species, azide anions (N₃⁻), and N-O compounds. For the Pt-Ru catalyst, an additional peak around ~3600 cm⁻¹ was observed, corresponding to OH⁻ species. The PM-IRRAS results align with the Gerischer–Mauerer mechanism, indicating that partially dehydrogenated ammonia adsorbates act as active intermediates in the oxidation of ammonia over Pt-Ir and Pt-Ru catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Modular Solar-to-Fuel Electrolysis at Low Cell Potentials Enabled by Glycerol Electrooxidation and a Bipolar Membrane Separator

Solar fuel generation through water electrolysis or electrochemical CO 2 reduction is thermodynamically limited when paired with the oxygen evolution reaction (OER). The glycerol electrooxidation reaction (GEOR) is an alternative anodic reaction with lower anodic electrochemical potential that utilizes a renewable coproduct produced during biodiesel synthesis. We show that GEOR on a Au-Pt-Bi ternary metal electrocatalyst in a model alkaline crude glycerol solution can provide significant cell potential reductions even when paired to reduction reactions in seawater and acidic catholytes via a bipolar membrane (BPM). We showed that the combination of GEOR electrooxidation and a BPM separator lowers the total cell potential by 1 V at an electrolysis current of 10.0 mA cm -2 versus to an anode performing OER when paired with hydrogen evolution and CO 2 reduction cathodes. The observed voltage reduction was steady for periods of up to 80 hours, with minimal glycerol crossover observed through the membrane. Furthermore, these results motivate new, high-performance cell designs for photoelectrochemical solar fuels integrated systems based on glycerol electrooxidation.

25 ENERGY STORAGE↗
DOE OSTI2023

Electrochemical Reduction of Flue Gas Carbon Dioxide to Commercially Viable C2-C4 Products (Final Report)

This is the final scientific/technical report for a DOE project focused on the electrochemical conversion of CO 2 in non-aqueous solvents to novel products. Electrochemical reduction of CO 2 provides an attractive route to produce valuable fuels and chemicals that can simultaneously lower greenhouse gas emissions when powered by renewable electricity. While recent technological advances have shown the feasibility of industrial CO 2 electroreduction, many challenges remain to improve this technology and expand the list of economically viable products. The vast majority of electrochemical CO 2 reduction research has been conducted in aqueous media under neutral to alkaline conditions, leading to commonly reported products including carbon monoxide, formic acid, methane, methanol, ethylene, acetic acid, and ethanol. In comparison, non-aqueous media for CO 2 reduction has been underexplored but represents a possible avenue to yield new products and improved operating conditions. The aim of the project was to convert waste CO 2 in the form of flue gas to a multicarbon C2 - C4 chemical product in a reactor designed to achieve economically competitive values of current density and selectivity. The project strived to advance the technology readiness of an electrochemical CO 2 reduction process in alcohol solvents from the proof-of-concept stage to a device capable of meeting performance metrics for commercial viability. In the initial plan, the University of Louisville researchers were to focus on investigating the electrochemical process and improving the faradaic efficiency for novel C2 – C4 species, while also working on a parallel effort to build a practical electrolysis reactor to markedly increase the CO 2 reduction current density. The reactor development effort also aimed to engineer a dual-electrolyte feed strategy with non-aqueous catholyte and aqueous anolyte to promote water oxidation as the coupling anodic half-reaction to enable a sustainable and economical overall process. At the outset, the University of North Dakota was to investigate the feasibility of operating directly from coal-derived flue gas without separate capture and purification. The research team sought to determine impurity effects and test mitigation strategies, as well as engineer the gaseous feed system for high reactor tolerance to lower CO 2 concentration. In the last half year of the project, the focus was planned to shift to integrating the advances in the catalysis, electrochemical conditions, reactor design, and flue gas compatibility into a fully functional device and improve it for maximum current density and faradaic efficiency for C2 – C4 species. Knowledge of the full system components, constraints, and maximum performance was then to be used as the basis for a thorough technoeconomic analysis (TEA) and life cycle analysis (LCA) at the end of the project.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2020

Enthalpy and entropy of oxygen electroadsorption on RuO 2 (110) in alkaline media

We report the temperature influence of the OHad and Oad electroadsorption on RuO 2 (110) films grown on TiO 2 (110) crystals in alkaline media. From the temperature effect, we evaluate the enthalpy and entropy of the OH ad and O ad electroadsorption, including the adsorbate–adsorbate interactions that we analyze using the interaction parameters of the Frumkin-isotherm model. We found that the adsorbates repel each other enthalpically but attract each other entropically. Our result suggests that an entropy analysis is necessary to capture the electroadsorption behavior on RuO 2 since the enthalpy–entropy competition strongly influences the electroadsorption behavior. Our observation of an entropic force is consistent with the view that water may be a mediator for adsorbate–adsorbate interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Multiscale Investigation of the Mechanisms Controlling the Corrosion of Borosilicate Glasses in Hyper-Alkaline Media

The overarching goal of the present multiscale investigation is to unearth the kinetics and mechanisms of corrosion of borosilicate glasses in hyper-alkaline (pH = 13) environments as a function of their chemical composition. Accordingly, a series of 3- to 6-component borosilicate glasses have been designed starting from Na 2 O–B 2 O 3 –SiO 2 ternary, wherein the compositional complexity has been added in a systematic tiered approach, finally resulting in the composition of the well-known international simple glass (ISG). Tetramethylammonium hydroxide (TMAH), one of the most widely used alkaline etchant in the glass and electronics industry, has been used as the corrosion media. A series of state-of-the-art characterization techniques including magic angle spinning nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, elastic recoil detection analysis, and high-resolution transmission electron microscopy have been employed to unearth the compositional dependence of glass corrosion in hyper-alkaline environments. The glass compositions underwent congruent corrosion in the forward rate regime, whereas the controlling mechanism of corrosion in the residual rate regime depends on the presence/absence of Ca in the surrounding environment and can be explained on the basis of the dissolution–reprecipitation model. The dependence of corrosion kinetics and the chemistry of alteration products (in the residual rate regime) on the glass composition have been discussed. Here, the results presented in this contribution will ultimately supplement the scientific literature attempting to understand the fundamental science governing the aqueous corrosion of silicate-based glass chemistries and add to the growing database required to develop non-empirical predictive models for designing glasses with controlled dissolution rates.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Carbon sequestration of steel slag and carbonation for activating RO phase

Carbonation of Ca/Mg minerals in industrial alkaline residues is a technology to sequester CO{sub 2} and reduce its emissions to the atmosphere. In this work, BSE-EDS were used to determine the mineral phase in steel slag; compositions of RO phase were identified and simulated. The carbon sequestration of steel slag was studied, and RO phase was activated by carbonation. Result shows that the amount of CO{sub 2} sequestered in steel slag and RO phase increases as carbonation time increases. Under autoclaving condition, the hydration ratio of MgO in RO phase was 20.10%. Through carbonation, up to 58.83% of MgO in RO phase can be converted into MgCO{sub 3}, and the activation of RO phase by carbonation was manifested. The mechanical properties and volume stability of carbonated steel slag were improved, proving that the positive effect of carbonation on steel slag when applied in cement and cementitious materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Hydroxide Exchange Membrane Carbon Capture (HEMCC) Using Nickel Hydroxide Batteries and Flow-through Membranes

Proposed is an electrochemical nickel hydroxide based hydroxide exchange membrane carbon capture (HEMCC) device for Direct Air Capture (DAC) of CO2. DAC has been identified as one of the key net negative carbon technologies to achieve net zero carbon emissions. Net negative carbon technologies are required to offset continued emissions from dilute CO2 sources such as agriculture and construction. The majority of current DAC technologies at scale (>1 KT∙yr-1) are adsorbent based technologies with significant energy cost. The traditional DAC energy cost is primarily driven by the temperature swing required to regenerate the sorbent and has been shown to be 1.8 MWh·ton-1 at the system level. Electrochemical pH swing devices are a growing research area for carbon capture devices with the goal of lowering the energy cost required for DAC. A pH gradient is built by generating OH- at the cathode and consuming OH- at the anode. An acid-base equilibrium with CO2 allows for the capture of CO2 at the cathode and release at the anode. This extends from other electrochemical CO2 capture devices based on pKa shifts of an electrochemically active organic species allowing for the capture and release of CO2. Electrochemical CO2 capture is considered promising based on potentially low energy costs to capture CO2 in comparison with current temperature swing adsorption technologies. This work explores Ni(OH)2 electrodes to produce the pH gradient for CO2 capture and release. At the cathode NiOOH is reduced to Ni(OH)2 while at the anode Ni(OH)2 is oxidized to NiOOH. The symmetrical electrodes allow for a low voltage requirement; the thermodynamic potential difference of standard electrochemical reactions is zero. Most of the voltage observed is to produce the pH gradient with the remainder driving the polarization of the electrodes. There is a resistance component as well, but this is small in comparison due to the low current densities used in the device, nominally 2 mA·cm-1. Two similar devices are presented, a traditional MEA (membrane electrode assembly) and a flow-through MEA. The traditional MEA separates the two Ni(OH)2 electrodes with an 80μm Piperion® membrane. While the flow-through membrane separates the electrodes with a three piece membrane consisting of two 80μm Piperion® membranes with a porous membrane between them. In the traditional MEA system air is passed over the cathode for capture, while the flow-through MEA the air is passed through the porous membrane isolated from the electrodes. The traditional MEA has been used to establish a baseline performance of the device and has been shown to capture CO2 at an energy cost of 1 MWh·ton-1 at the device level. An understanding has been built around the components of that energy cost including the relationship of flux to current density, effect of a regeneration process, transient battery behavior, and gas losses coinciding with changing the polarization of the batteries. The flow-through MEA looks to address of transient battery behavior and gas losses. It allows for denser, higher capacity electrodes, which can lean on traditional Ni-MH battery technology used in alkaline batteries used today. The higher capacities, limit the transient battery effect on flux in the device. Gas losses are addressed by having a continuous inlet air stream to the device and continuous outlet product.

Buchen, James↗
DOE OSTI2024

ZeroCAL: Eliminating Carbon Dioxide Emissions from Limestone’s Decomposition to Decarbonize Cement Production

Limestone (calcite, CaCO 3 ) is an abundant and cost-effective source of calcium oxide (CaO) for cement and lime production. However, the thermochemical decomposition of limestone (~800 °C, 1 bar) to produce lime (CaO) results in substantial carbon dioxide (CO 2(g) ) emissions and energy use, i.e., ~1 tonne [t] of CO 2 and ~1.4 MWh per t of CaO produced. Here, we describe a new pathway to use CaCO 3 as a Ca source to make hydrated lime (portlandite, Ca(OH) 2 ) at ambient conditions (p, T) while nearly eliminating process CO 2(g) emissions (as low as 1.5 mol. % of the CO 2 in the precursor CaCO 3 , equivalent to 9 kg of CO 2(g) per t of Ca(OH) 2 ) within an aqueous flowelectrolysis/ pH-swing process that coproduces hydrogen (H 2(g) ) and oxygen (O 2(g) ). Because Ca(OH) 2 is a zero-carbon precursor for cement and lime production, this approach represents a significant advancement in the production of zero-carbon cement. The Zero CArbon Lime (ZeroCAL) process includes dissolution, separation/recovery, and electrolysis stages according to the following steps: (Step 1) chelator (e.g., ethylenediaminetetraacetic acid, EDTA)-promoted dissolution of CaCO 3 and complexation of Ca 2+ under basic (>pH 9) conditions, (Step 2a) Ca enrichment and separation using nanofiltration (NF), which allows separation of the Ca-EDTA complex from the accompanying bicarbonate (HCO 3 – ) species, (Step 2b) acidity-promoted decomplexation of Ca from EDTA, which allows near-complete chelator recovery and the formation of a Ca-enriched stream, and (Step 3) rapid precipitation of Ca(OH) 2 from the Ca-enriched stream using electrolytically produced alkalinity. These reactions can be conducted in a seawater matrix yielding coproducts including hydrochloric acid (HCl) and sodium bicarbonate (NaHCO 3 ), resulting from electrolysis and limestone dissolution, respectively. Careful analysis of the reaction stoichiometries and energy balances indicates that approximately 1.35 t of CaCO 3 , 1.09 t of water, 0.79 t of sodium chloride (NaCl), and ~2 MWh of electrical energy are required to produce 1 t of Ca(OH) 2 , with significant opportunity for process intensification. This approach has major implications for decarbonizing cement production within a paradigm that emphasizes the use of existing cement plants and electrification of industrial operations, while also creating approaches for alkalinity production that enable cost-effective and scalable CO 2 mineralization via Ca(OH) 2 carbonation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Anolyte Buffering and CO Coverage Effects in the Electrochemical Reduction of CO at Cu Electrocatalysts

Electrolytic CO reduction was investigated at copper electrocatalysts in zero-gap membrane electrode assemblies as a function of buffering agents and cofeeding with CO 2 or Ar. Results show an acetate Faradaic efficiency (FE) of 90% at 300 mA cm −2 using pure CO feeds and phosphate-buffered anolyte near pH 8. When using CO feeds with more alkaline anolytes, the hydrogen evolution reaction becomes the dominant reduction reaction, independent of the buffer. Product distributions of cofeeding experiments with CO and CO 2 show that increasing CO 2 cofeeding results in increased selectivity toward ethylene (42% FE) in near-neutral KHCO 3 anolytes or ethanol (40% FE) in alkaline KOH anolytes. Evaluation of several commercial anion exchange membranes shows similar selectivity trends, suggesting product selectivity is dominated by the local pH and surface coverage of CO. Based on these results, we propose pH buffering and CO coverage behaviors that facilitate high selectivities to acetate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Spatially Mapping the CO 2 Alkaline Sorbent Diffuse Microenvironment Using Operando Raman Spectroscopy

When designing a chemical process, the local balance of transport and kinetics, collectively referred to as the diffuse microenvironment, plays a critical role in performance but is difficult to directly observe. This work demonstrates a method of two-dimensional spatial chemical mapping of the diffuse microenvironment in the context of alkali metal hydroxide direct air capture of carbon dioxide using a custom operando gas-absorption flow cell along with confocal Raman spectroscopy. Notably, we observe the concentration boundary layer near the gas–liquid interface and elucidate the interplay of carbonate and bicarbonate ions within it while inferring local hydroxide depletion through continuum modeling. These first of their kind observations provide a technique to compare the performance of direct air capture solvents based on diffuse microenvironment dynamics while also providing metrics important for air contactor design such as boundary layer thickness. Overall, this work showcases a new experimental platform to study interfacial diffuse microenvironments in and outside of the field of direct air capture of carbon dioxide.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Carbonate Management to Enable Energy- and Carbon-Efficient CO 2 Electrolysis (Final Technical Report)

The rapid growth and plummeting cost of solar energy have spurred growing interest in using CO 2 electrolysis to produce chemicals and fuels as an alternative to conventional petrochemical processes. High-temperature (>800 °C) solid oxide electrolyzers that convert CO 2 into CO and O 2 have recently become commercially available. Low-temperature electrolysis cells offer the prospect of more convenient and flexible operation, which is critical for utilizing intermittent solar energy, and provide access to more valuable C 2+ products such as ethylene, ethanol, and propanol. Over the past 10 years, research in this area has yielded substantial progress in both fundamental understanding of the requisite electrocatalytic reactions and design of prototype devices. Leveraging insights from fuel cells and membrane water electrolyzers, researchers have developed electrolysis cells with gas diffusion electrodes (GDE) that have demonstrated high CO 2 electrolysis current densities (>100 mA cm –2 ) as well as promising selectivity and stability. Despite these advances, the energy efficiency (electrical energy-to-product) and carbon efficiency (CO 2 -to-product) of low-temperature CO 2 electrolysis remain far too low for large-scale deployment. A preponderance of evidence indicates that the principal source of efficiency losses is the rapid and thermodynamically favorable reaction of CO 2 with hydroxide (OH – ) to form carbonate (CO 3 2– ). Carbonate formation imposes steady-state electrolysis conditions that result in large voltage and CO 2 losses for all known (photo)electrochemical CO 2 cells. While much current research remains focused on CO 2 reduction catalyst design, this largely overlooked CO 3 2– problem presents a fundamental scientific barrier to creating a viable electrochemical option for converting solar energy into chemicals and fuels. The project pursues an integrated, multi-PI research effort that establishes a fundamental science of CO 3 2– management. PI Kanan and Co-PI Mani’s contribution to the project is to evaluate strategies to mitigate the CO 3 2– problem by changing the properties of the electrolyte and the environment in which CO 2 reduction catalysis takes place. Experimental studies showed that electrolytes composed of a high concentration of both CO 3 2– and HCO 3 – , which serve as moderately alkaline buffers, improved the cell voltage by compared to all-HCO 3 – electrolytes, but these buffered systems still show substantial CO 2 uptake that reduces pH over time. Computational studies developed a homogenized model of a CO 2 reduction catalyst layer that permits a low-cost exploration of the high-dimensional parameter space associated with catalyst layers on gas diffusion electrodes. The model was validated by accurately reproducing experimental data for the related but simpler reaction of CO reduction and then used to probe the effects of catalyst layer architecture on CO 2 reduction. Minimizing the size of catalyst and hydrophobic domains in the catalyst layer is predicted to mitigate CO 3 2– formation and thereby enable prolonged operation at elevated pH. In support of the CO 2 electrolysis studies, a new method for rapidly prototyping electrochemical cells was developed and validated. The method uses a combination of 3D printing and electroless plating to generate conductive cell components for evaluating new cell designs. The carbonate problem encompasses mass transport processes and acid-base reactions that are relevant to many other electrochemical systems. Investigation of strategies to address the carbonate problem led to an additional line of inquiry into the physicochemical phenomena that determine the efficiency of electrochemical acid-base production, which has numerous applications in the broader field of carbon management. New strategies for using the supporting electrolyte to inhibit H + /OH – recombination in electrochemical acid-base production were evaluated, leading to the development of a novel acid-base producing system that eliminates the need for ion exchange membranes and exhibits promising efficiency and current densities for scalable applications.

25 ENERGY STORAGE↗
DOE OSTI2025

Surface Manipulation on Pt 2.2 Ni(111) Nanocatalysts for Boosting Their ORR Performance in Alkaline Media

We have previously shown that Pt–Ni alloy nano-octahedra with {111} facets exhibit outstanding electrochemical performance in the oxygen reduction reaction (ORR) in acidic media when their surfaces are finely tailored at the atomic level. Here, in this investigation, we further refine the surface structure of Pt 2.2 Ni octahedral nanocatalysts to improve ORR performance in a 0.1 M KOH solution using diverse surface manipulation techniques. Through systematic analysis using electrochemical CO stripping, cyclic voltammetry, and X-ray photoelectron spectroscopy, we examined the surfaces of Pt 2.2 Ni octahedral nanocatalysts pretreated with various methods, including etching in acetic acid or perchloric acid, and subsequent electrochemical activation in an alkaline solution or an acidic solution. Among these treatments, those involving acidic media, particularly electrochemical cycling in acidic electrolytes, demonstrated significantly enhanced ORR activity in 0.1 M KOH. The latter exhibited a mass activity of 2.95 A/mg pt and a specific activity of 8.71 mA/cm 2 at 0.90 V, surpassing state-of-the-art Pt/C by 12-fold and 34-fold, respectively. Furthermore, this identified nanocatalyst displayed robust stability, with negligible activity decay observed after 10,000 cycles. This study suggests that the improved ORR activity can be attributed to the Pt-rich surfaces with well-preserved {111} lattices on the surface-modified Pt–Ni nano-octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2025

From Micro-environments to Macroscopic Effects: How the Alkaline Hydrogen Evolution Reaction Drives Cu Cathodic Corrosion

Cathodic corrosion of copper (Cu) has posed a significant challenge for over a century, impeding various technological progresses such as electrochemical conversion of CO 2 (eCO 2 RR) into fuels and other value-added carbon products. Here, in this study, employing a combined Density Functional Theory (DFT) and kinetic Monte Carlo (kMC) simulation approach, we delve into the atomistic level mechanism driving this phenomenon in Cu. Our hypothesis posits the pivotal role of alkaline hydrogen evolution reaction (HER) in facilitating cathodic corrosion in Cu. We rigorously develop a pH-dependent hydroxide (OH) adsorption mechanism and calculate the equilibrium OH coverage (𝜃 OH ) at varying pH levels, the thermodynamic stability of subsurface oxygen (O sub ), as well as the Cu-vacancy mediated diffusion of subsurface oxygens (O sub ). Through comprehensive analysis, we establish correlation among various microenvironments, including oxygen diffusion in subsurface layers, pH-dependent OH adsorption, and Cu dissolution into the electrolyte as (Cu-OH) complexes. Furthermore, our investigation explores the correlation between surface coordination environment of active sites and cathodic corrosion of Cu. Finally, by integrating DFT-derived thermodynamic data into a kMC model, we successfully predict the formation of experimentally observed corrosion pits on Cu-surfaces. This combined approach not only advances our fundamental understanding of Cu cathodic corrosion but also offers insights crucial for developing effective corrosion mitigation strategies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗