Carbon capture in polymer-based electrolytes.

Nanoparticle organic hybrid materials (NOHMs) have been proposed as excellent electrolytes for combined CO2 capture and electrochemical conversion due to their conductive nature and chemical tunability. However, CO2 capture behavior and transport properties of these electrolytes after CO2 capture have not yet been studied. Here, we use a variety of nuclear magnetic resonance (NMR) techniques to explore the carbon speciation and transport properties of branched polyethylenimine (PEI) and PEI-grafted silica nanoparticles (denoted as NOHM-I-PEI) after CO2 capture. Quantitative 13C NMR spectra collected at variable temperatures reveal that absorbed CO2 exists as carbamates (RHNCOO- or RR'NCOO-) and carbonate/bicarbonate (CO32-/HCO3-). The transport properties of PEI and NOHM-I-PEI studied using 1H pulsed-field-gradient NMR, combined with molecular dynamics simulations, demonstrate that coulombic interactions between negatively and positively charged chains dominate in PEI, while the self-diffusion in NOHM-I-PEI is dominated by silica nanoparticles. These results provide strategies for selecting adsorbed forms of carbon for electrochemical reduction.

Elucidating the assembly of nanoparticle organic hybrid materials (NOHMs) near an electrode interface with varying potential using neutron reflectivity.

A critical concern regarding electrolyte formulation in an electrochemical environment is the impact of the interaction of the multiple components (i.e., supporting electrolyte or additive) with the electrode surface. Recently, liquid-like neat Nanoparticle Organic Hybrid Materials (NOHMs) have been considered as an electrolyte component to improve the transport of redox-active species to the electrode surface. However, the structure and assembly of the NOHMs near the electrode surface is unknown and could significantly impact the electrode-electrolyte interface. Hence, we have investigated the depth profile of polyetheramine (HPE) polymer and NOHM-I-HPE (nanoparticles with ionically bonded HPE polymer) in deuterated water (D2O) in the presence of two different salts (KHCO3 and ZnCl2) near two different electrode surfaces using neutron reflectometry. Moreover, the depth profile of the NOHM-I-HPE near the electrode surface in a potential has also been studied with in situ reflectivity experiments. Our results indicate that a change in the chemical structure/hydrophilicity of the electrode surface does not significantly impact the ordering of HPE polymer or NOHM-I-HPE near the surface. This study also indicates that the NOHM-I-HPE particles form a clear layer near the electrode surface immediately above an adsorbed layer of free polymer on the electrode surface. The addition of salt does not impact the layering of NOHM-I-HPE, though it does alter the conformation of the polymer grafted to the nanoparticle surface and free polymer sequestered near the surface. Finally, the application of negative potential results in an increased amount of free polymer near the electrode surface. Correlating the depth profile of free polymer and NOHM-I-HPE particles with the electrochemical performance indicates that this assembly of free polymer near the electrode surface in NOHM-I-HPE solutions contributes to the higher current density of the system. Therefore, this holistic study offers insight into the importance of the assembly of NOHM-I-HPE electrolyte and free polymer near the electrode surface in an electrochemical milieu on its performance.

Introduction to CO2 capture and conversion.

An introduction to the Nanoscale themed collection on CO2 capture and conversion, featuring exciting research on advanced nanoscale materials and reactions.

Wet flue gas CO2 capture and utilization using one-dimensional metal-organic chains.

Herein, we describe the use of an ultramicroporous metal-organic framework (MOF) with a composition of [Ni3(pzdc)2(ade)2(H2O)1.5]·(H2O)1.3 (pzdc: 3,5-pyrazole dicarboxylic acid; ade: adenine), for the selective capture of carbon dioxide (CO2) from wet flue gas followed by its conversion to value-added products. This MOF is comprised of one-dimensional Ni(II)-pyrazole dicarboxylate-adenine chains; through pi-pi stacking and H-bonding interactions, these one-dimensional chains stack into a three-dimensional supramolecular structure with a one-dimensional pore network. Upon heating, our MOF undergoes a color change from light blue to lavender, indicating a change in the coordination geometry of Ni(II). Variable temperature ultraviolet-visible (UV/vis) spectroscopy data revealed a blue shift of the d-d transitions, suggesting a change in the Ni-coordination geometry from octahedral to a mixture of square planar and square pyramidal. The removal of the water molecules coordinated to Ni(II) leads to the generation of a MOF with open Ni(II) sites. Nitrogen isotherms collected at 77 K and 1 bar revealed that this MOF is microporous with a pore volume of 0.130 cm3 g-1. Carbon dioxide isotherms show a step in the uptake at low pressure, after which the CO2 uptake is saturated. The step in the CO2 uptake is likely attributable to the rearrangement of the three-dimensional supramolecular structure to accommodate CO2 within its pores. The affinity of this MOF for CO2 is 35.5 kJ mol-1 at low loadings, and it increases to 41.9 kJ mol-1 at high loadings. While our MOF is porous to CO2 and water (H2O) at 298 K, it is not porous to N2, and the CO2/N2 selectivity increases from 28.5 to 31.5 as a function of pressure. Breakthrough experiments reveal that this MOF can capture CO2 from dry and wet flue gas with uptake capacities of 1.48 ± 0.01 and 1.14 ± 0.06 mmol g-1, respectively. The MOF can be regenerated and reused at least three times, demonstrating consistent CO2 uptake capacities. Upon understanding the sorption behavior of this MOF, catalysis experiments show that the MOF is catalytically active in the fixation of CO2 into an epoxide ring for the formation of a cyclic carbonate. The turnover frequency for this reaction is 21.95 ± 0.03 h-1. The MOF showed no catalytic deterioration after two cycles and maintained comparable catalytic activity when dry and wet CO2/N2 mixtures were used. This highlights that both N2 and H2O do not dramatically affect the catalytic activity of our MOF toward CO2 fixation.

Mechanistic Study of Controlled Zinc Electrodeposition Behaviors Facilitated by Nanoscale Electrolyte Additives at the Electrode Interface.

Nanoparticle organic hybrid materials (NOHMs) are liquid-like materials composed of an inorganic core to which a polymeric canopy is ionically tethered. NOHMs have unique properties including negligible vapor pressure, high oxidative thermal stability, and the ability to bind to reactive species of interest due to the tunability of their polymeric canopy. This makes them promising multifunctional materials for a wide range of energy and environmental technologies, including electrolyte additives for electrochemical energy storage (e.g., flow batteries) and the electrochemical conversion of CO2 to chemicals and fuels. Due to their unique transport behaviors in fluid systems, an understanding of the near-electrode surface behavior of NOHMs in electrolyte solutions and their effect on electrochemical reactions is still lacking. In this work, the complexation of zinc (Zn) by NOHMs with an ionically tethered polyetheramine canopy (HPE) (NOHM-I-HPE) was studied using attenuated total reflectance Fourier transform infrared and Carbon-13 nuclear magnetic resonance spectroscopy. Additionally, various electrochemical techniques were employed to discern the role of NOHM-I-HPE during zinc electrodeposition, and the results were compared to those of the electrochemical system containing untethered HPE polymers. Our findings confirmed that NOHM-I-HPE and HPE reversibly complex zinc in the aqueous electrolyte. NOHM-I-HPE and HPE were found to block some of the electrode active sites, reducing the overall current density during electrodeposition, while facilitating the formation of smooth zinc deposits, as revealed by surface imaging and diffraction techniques. Observed variations in the current density responses and the degree of passivation created by the NOHM-I-HPE and HPE adsorbed on the electrode surface revealed that their different packing behaviors at the electrode-electrolyte interface influence the zinc deposition mechanism. The presence of the nanoparticle and ordering offered by the NOHMs as well as the structured conformation of the polymeric canopy allowed the formation of void spaces and free volumes for enhanced transport behaviors. These findings provided insights into how structured electrolyte additives such as NOHMs can allow for advancements in electrolyte design for controlled deposition of metal species from energy-dense electrolytes or for other electrochemical reactions.

Nanoscale Hybrid Electrolytes with Viscosity Controlled Using Ionic Stimulus for Electrochemical Energy Conversion and Storage.

As renewable energy is rapidly integrated into the grid, the challenge has become storing intermittent renewable electricity. Technologies including flow batteries and CO2 conversion to dense energy carriers are promising storage options for renewable electricity. To achieve this technological advancement, the development of next generation electrolyte materials that can increase the energy density of flow batteries and combine CO2 capture and conversion is desired. Liquid-like nanoparticle organic hybrid materials (NOHMs) composed of an inorganic core with a tethered polymeric canopy (e.g., polyetheramine (HPE)) have a capability to bind chemical species of interest including CO2 and redox-active species. In this study, the unique response of NOHM-I-HPE-based electrolytes to salt addition was investigated, including the effects on solution viscosity and structural configurations of the polymeric canopy, impacting transport behaviors. The addition of 0.1 M NaCl drastically lowered the viscosity of NOHM-based electrolytes by up to 90%, reduced the hydrodynamic diameter of NOHM-I-HPE, and increased its self-diffusion coefficient, while the ionic strength did not alter the behaviors of untethered HPE. This study is the first to fundamentally discern the changes in polymer configurations of NOHMs induced by salt addition and provides a comprehensive understanding of the effect of ionic stimulus on their bulk transport properties and local dynamics. These insights could be ultimately employed to tailor transport properties for a range of electrochemical applications.

Electrochemical CO2 Reduction Reaction over Cu Nanoparticles with Tunable Activity and Selectivity Mediated by Functional Groups in Polymeric Binder.

The electrochemical carbon dioxide reduction reaction (CO2RR) using copper (Cu)-based catalysts has received significant attention mainly because Cu is an element capable of producing hydrocarbons and oxygenates. One possible way to control the CO2RR performance at the electrode interface is by modifying catalysts with specific functional groups of different polymeric binders, which are necessary components in the process of electrode fabrication. However, the modification effect of the key functional groups on the CO2RR activity and selectivity is poorly understood over Cu-based catalysts. In this work, the role of functional groups (e.g., -COOH and -CF2 groups) in hydrophilic and hydrophobic polymeric binders on the CO2RR of Cu-based catalysts is investigated using a combination of electrochemical measurements, in situ characterization, and density functional theory (DFT) calculations. DFT results reveal that functional groups influence the binding energies of key intermediates involved in both CO2RR and the competing hydrogen evolution reaction, consistent with experimental observation of binder-dependent product distributions among formic acid, CO, CH4, and H2. This study provides a fundamental understanding that the selection of desired polymeric binders is a useful strategy for tuning the CO2RR activity and selectivity.

Dynamic Mixing Behaviors of Ionically Tethered Polymer Canopy of Nanoscale Hybrid Materials in Fluids of Varying Physical and Chemical Properties.

An emerging area of sustainable energy and environmental research is focused on the development of novel electrolytes that can increase the solubility of target species and improve subsequent reaction performance. Electrolytes with chemical and structural tunability have allowed for significant advancements in flow batteries and CO2 conversion integrated with CO2 capture. Liquid-like nanoparticle organic hybrid materials (NOHMs) are nanoscale fluids that are composed of inorganic nanocores and an ionically tethered polymeric canopy. NOHMs have been shown to exhibit enhanced conductivity making them promising for electrolyte applications, though they are often challenged by high viscosity in the neat state. In this study, a series of binary mixtures of NOHM-I-HPE with five different secondary fluids, water, chloroform, toluene, acetonitrile, and ethyl acetate, were prepared to reduce the fluid viscosity and investigate the effects of secondary fluid properties (e.g., hydrogen bonding ability, polarity, and molar volume) on their transport behaviors, including viscosity and diffusivity. Our results revealed that the molecular ratio of secondary fluid to the ether groups of Jeffamine M2070 (λSF) was able to describe the effect that secondary fluid has on transport properties. Our findings also suggest that in solution, the Jeffamine M2070 molecules exist in different nanoscale environments, where some are more strongly associated with the nanoparticle surface than others, and the conformation of the polymer canopy was dependent on the secondary fluid. This understanding of the polymer conformation in NOHMs can allow for the better design of an electrolyte capable of capturing and releasing small gaseous or ionic species.

Electrochemical approaches for selective recovery of critical elements in hydrometallurgical processes of complex feedstocks.

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.

CO2 utilization in built environment via the PCO2 swing carbonation of alkaline solid wastes with different mineralogy.

Carbon mineralization to solid carbonates is one of the reaction pathways that can not only utilize captured CO2 but also potentially store it in the long term. In this study, the dissolution and carbonation behaviors of alkaline solid wastes (i.e., waste concrete) was investigated. Concrete is one of the main contributors to a large carbon emission in the built environment. Thus, the upcycling of waste concrete via CO2 utilization has multifaceted environmental benefits including CO2 emission reduction, waste management and reduced mining. Unlike natural silicate minerals such as olivine and serpentine, alkaline solid wastes including waste concrete are highly reactive, and thus, their dissolution and carbonation behaviors vary significantly. Here, both conventional acid (e.g., hydrochloric acid) and less studied carbonic acid (i.e., CO2 saturated water) solvent systems were explored to extract Ca from concrete. Non-stoichiometric dissolution behaviors between Ca and Si were confirmed under far-from-equilibrium conditions (0.1 wt% slurry density), and the re-precipitation of the extracted Si was observed at near-equilibrium conditions (5 wt% slurry density), when the Ca extraction was performed at a controlled pH of 3. These experiments, with a wide range of slurry densities, provided valuable insight into Si re-precipitation phenomena and its effect on the mass transfer limitation during concrete dissolution. Next, the use of the partial pressure of CO2 for the pH swing carbon mineralization process was investigated for concrete, and the results were compared to those of Mg-bearing silicate minerals. In the PCO2 swing process, the extraction of Ca was significantly limited by the precipitation of the carbonate phase (i.e., calcite), since CO2 bubbling could not provide a low enough pH condition for concrete-water-CO2 systems. Thus, this study showed that the two-step carbon mineralization via PCO2 swing, that has been developed for Mg-bearing silicate minerals, may not be viable for highly reactive Ca-bearing silicate materials (e.g., concrete). The precipitated calcium carbonate (PCC) derived from waste concrete via a pH swing process showed very promising results with a high CO2 utilization potential as an upcycled construction material.

Alkaline thermal treatment of seaweed for high-purity hydrogen production with carbon capture and storage potential.

Current thermochemical methods to generate H2 include gasification and steam reforming of coal and natural gas, in which anthropogenic CO2 emission is inevitable. If biomass is used as a source of H2, the process can be considered carbon-neutral. Seaweeds are among the less studied types of biomass with great potential because they do not require freshwater. Unfortunately, reaction pathways to thermochemically convert salty and wet biomass into H2 are limited. In this study, a catalytic alkaline thermal treatment of brown seaweed is investigated to produce high purity H2 with substantially suppressed CO2 formation making the overall biomass conversion not only carbon-neutral but also potentially carbon-negative. High-purity 69.69 mmol-H2/(dry-ash-free)g-brown seaweed is produced with a conversion as high as 71%. The hydroxide is involved in both H2 production and in situ CO2 capture, while the Ni/ZrO2 catalyst enhanced the secondary H2 formation via steam methane reforming and water-gas shift reactions.

Review of liquid nano-absorbents for enhanced CO2 capture.

Liquid nano-absorbents have become a topic of interest as a result of their enhanced mass-transfer performance for CO2 capture. They are believed to have revolutionized the conventional CO2 chemisorption process by largely improving CO2 capture kinetics and reducing the energy requirement for solvent regeneration. Two classes of nanomaterial-based CO2 capture absorbents, amine-based nanoparticle suspensions (nanofluids) and nanoparticle organic hybrid materials (NOHMs), have been developed, with significant progress achieved in recent decades. This review addresses two key questions for these two state-of-the-art nanomaterials: how are the physical and chemical properties of the prepared liquid nano-absorbents transformed relative to those of the base fluids? And how does the transformation of the properties affect the CO2 capture behavior? While the current synthesis procedure for liquid nano-absorbents is quite straightforward, more advanced synthesis methods for long-term nanoparticle stability have been suggested for the future. Nanofluids have been shown to increase the CO2 uptake by over 20% and the CO2 capture rate by 2-93% compared with the values observed with neat amine solvents. Nanoparticles with catalytic effects on CO2 capture can significantly increase the CO2 desorption rate by as high as 4000%. NOHMs exhibit the interesting feature of enhanced mass transfer in CO2 capture because of the unique pathway network that is created in them for CO2 to reach specific functional groups. NOHMs promise an effect of combined CO2 capture and conversion, and can be used especially as electrolytes for CO2 electro-reduction. However, there are still some challenges for the application of these materials in real life, such as poor stability and high viscosity. Therefore, efficient CO2 capture processes using these solvents need to be urgently developed and studied in the future.

Directed precipitation of hydrated and anhydrous magnesium carbonates for carbon storage.

Magnesite is the most desirable phase within the magnesium carbonate family for carbon storage for a number of reasons: magnesium efficiency, omission of additional crystal waters and thermodynamic stability. For large-scale carbonation to be a viable industrial process, magnesite precipitation must be made to occur rapidly and reliably. Unfortunately, the formation of metastable hydrated magnesium carbonate phases (e.g. MgCO3·3H2O and Mg5(CO3)4(OH)2·4H2O) interferes with the production of anhydrous magnesite under a variety of reaction conditions because magnesite crystals are slower to both nucleate and grow compared to the hydrated carbonate phases. Furthermore, the reaction conditions required for the formation of each magnesium carbonate phases have not been well understood with conflicting literature data. In this study, the effects of both magnesite (MgCO3) and inert (Al2O3) seed particles on the precipitation of magnesium carbonates from a Mg(OH)2 slurry were explored. It was interesting that MgCO3 seeding was shown to accelerate anhydrous magnesite growth at temperatures (80-150 °C), where it would normally not form in short time scale. Since the specific surface areas of MgCO3 and Al2O3 seeding particles were similar, this phenomenon was due to the difference in the surface chemistry of two seeding particles. By providing a template with similar chemistry for the growth of magnesite, the precipitation of anhydrous magnesite was demonstrated. The effect of temperature on seeded carbonation was also investigated. A comparison with published MgCO3 precipitation rate laws indicated that the precipitation of magnesite was limited by either CO2 adsorption from the gas phase or the dissolution rate of Mg(OH)2.

Genetic manipulation of outer membrane permeability: generating porous heterogeneous catalyst analogs in Escherichia coli.

The limited permeability of the E. coli outer membrane can significantly hinder whole-cell biocatalyst performance. In this study, the SARS coronavirus small envelope protein (SCVE) was expressed in E. coli cells previously engineered for periplasmic expression of carbonic anhydrase (CA) activity. This maneuver increased small molecule uptake by the cells, resulting in increased apparent CA activity of the biocatalysts. The enhancements in activity were quantified using methods developed for traditional heterogeneous catalysis. The expression of the SCVE protein was found to significantly reduce the Thiele moduli (ϕ), as well as increase the effectiveness factors (η), effective diffusivities (De), and permeabilities (P) of the biocatalysts. These catalytic improvements translated into superior performance of the biocatalysts for the precipitation of calcium carbonate from solution which is an attractive strategy for long-term sequestration of captured carbon dioxide. Overall, these results demonstrate that synthetic biology approaches can be used to enhance heterogeneous catalysts incorporated into microbial whole-cell scaffolds.

Morphological changes during enhanced carbonation of asbestos containing material and its comparison to magnesium silicate minerals.

The disintegration of asbestos containing materials (ACM) over time can result in the mobilization of toxic chrysotile ((Mg, Fe)3Si2O5(OH)4)) fibers. Therefore, carbonation of these materials can be used to alter the fibrous morphology of asbestos and help mitigate anthropogenic CO2 emissions, depending on the amount of available alkaline metal in the materials. A series of high pressure carbonation experiments were performed in a batch reactor at PCO2 of 139atm using solvents containing different ligands (i.e., oxalate and acetate). The results of ACM carbonation were compared to those of magnesium silicate minerals which have been proposed to permanently store CO2 via mineral carbonation. The study revealed that oxalate even at a low concentration of 0.1M was effective in enhancing the extent of ACM carbonation and higher reaction temperatures also resulted in increased ACM carbonation. Formation of phases such as dolomite ((Ca, Mg)(CO3)2), whewellite (CaC2O4·H2O) and glushinskite (MgC2O4·2H2O) and a reduction in the chrysotile content was noted. Significant changes in the particle size and surface morphologies of ACM and magnesium silicate minerals toward non-fibrous structures were observed after their carbonation.

Surface Display of Small Peptides on Escherichia coli for Enhanced Calcite Precipitation Rates.

Mineralization has emerged as a promising strategy for long-term carbon sequestration. These processes involve carbon dioxide hydration followed by mineral precipitation. We have explored the production of whole-cell biocatalysts engineered with carbonic anhydrase (CA) activity to accelerate the CO2 hydration reaction. In this study, short polypeptides were displayed on the surface of E. coli cells and whole-cell biocatalysts containing periplasmically expressed CAs in an attempt to enhance calcite mineral formation. It was found that cells coexpressing recombinant periplasmic CA and surface-displayed GPA peptide (PEVPEGAFDTAI) outperformed other peptide-expressing biocatalysts evaluated in terms of the amount of precipitate formed, as well as the overall formation rate of solids. Cells expressing the Cab CA isoform (BLR-pCab) and Cam isoform (BLR-pCam) with the surface-displayed GPA peptide exhibited 36 and 59% improvements in precipitation amounts, as well as 18 and 60% improvements in overall formation rates, respectively, over similar biocatalysts without GPA expression. The biocatalyst with the best performance was BLR-pCam/GPA, which generated 0.15 g of CaCO3, while BLR cells generated only 0.08 g of CaCO3 under the same small batch reaction conditions. The BLR-pCam/GPA cells also exhibited the fastest formation rates, achieving the maximum change in solution turbidity after only 2.2 min, as opposed to 6.3 min for BLR cells. These results demonstrate that synthetic biology approaches can be used to create novel biocatalysts with the ability to enhance both catalysis and precipitation activities.

Tuning the dissolution kinetics of wollastonite via chelating agents for CO2 sequestration with integrated synthesis of precipitated calcium carbonates.

Carbon mineralization has recently received much attention as one of the most promising options for CO2 sequestration. The engineered weathering of silicate minerals as a means of permanent carbon storage has unique advantages such as the abundance of naturally occurring calcium and magnesium-bearing minerals and the formation of environmentally-benign and geologically stable solids via a thermodynamically favored carbonation reaction. However, several challenges need to be overcome to successfully deploy carbon mineralization on a large scale. In particular, the acceleration of the rate-limiting mineral dissolution step along with process optimization is essential to ensure the economic feasibility of the proposed carbon storage technology. In this study, the effect of various types of chelating agents on the dissolution rate of calcium-bearing silicate mineral, wollastonite, was explored to accelerate its weathering rate. It was found that chelating agents such as acetic acid and gluconic acid significantly improved the dissolution kinetics of wollastonite even at a much diluted concentration of 0.006 M by complexing with calcium in the mineral matrix. Calcium extracted from wollastonite was then reacted with a carbonate solution to form precipitated calcium carbonate (PCC), while tuning the particle size and the morphological structure of PCC to mimic commercially available PCC-based filler materials.