Electrochemical Reduction Of CO2 Research Articles

Electrochemical CO2 Reduction in the Presence of Flue Gas Impurities: Effect of NOx, SOx and O2

Electrochemically converting CO2 to valuable chemical products using renewable energy sources may present solutions to alter current increasing CO2 emission trends. Currently, electrolyzer research is almost exclusively done with pure CO2 streams that - in practice - would originate from carbon capture units that prevent CO2 release to the atmosphere [1]. The capture and purification steps are cost intensive processes which is why direct usage of flue gases that contain impurities is a highly interesting approach. For this reason, the performance of CO2 electrolyzers equipped with state-of-the-art Bi2O3 or Ag catalysts is investigated in this work with an impure CO2 feed stream containing SO2, NO or O2. The short-term effect of highly concentrated SO2 (10 000 ppm) and NO (8 300 ppm) impurities during CO2 electrolysis was previously described [2,3]. Our work [4] elaborates further on this matter through 20 h experiments with flue gas-like concentrations of 200 ppm SO2 or NO. The results show a stable operation without severe FE losses (remains >90%) and structural adaptations to neither Ag nor Bi2O3 by these impurities. The presence of oxygen in flue gas streams at concentrations of several percent is common and causes a major decrease in FE to the target products (CO or HCOO-) during electrolysis. This is a result of the competition between the ORR and CO2RR with the former occurring more preferentially. To overcome this, we have discovered two possible strategies, which allow high FE’s to CO2RR products even in the presence of oxygen. (1) By operating the electrolyzer at a sufficiently high overall current density, all of the O2 entering and reaching the electrode surface gets reduced, allowing the CO2RR to become the dominant reaction. Although this approach has a higher electricity penalty, the extra cost is negligible compared to the cost otherwise associated with the CO2 purification for CO2 streams with an O2 content below 3%. (2) Given that the ORR is mostly occurring at the carbon-based gas diffusion layers another approach to improve CO2RR efficiency in the presence of oxygen is to replace this conventional support with ultra hydrophobic PTFE membrane filters. Since they are inefficient oxygen reduction catalysts, CO2RR again takes up the major fraction of the applied current density. A downside of using PTFE is that an additional conductive layer is required in case the catalyst itself (e.g. for bismuth oxide) is not conductive enough. These results thus not only offer new insights into the impact of gaseous impurities during CO2 electrolysis, but also suggest a strategy to improve electrolyzer performance with O2-containing feed streams. Bibliography [1] Lee M.Y., Environ. Sci. and Technol.; DOI: 10.1080/10643389.2019.1631991[2] Luc W.; JACS, DOI: 10.1021/jacs.9b03215[3] Ko B., Nature Comm. DOI : 10.1038/s41467-020-19731-8[4] Van Daele S ., J. Appl. Catal. B, Environ.; DOI: 10.1016/J.APCATB.2023.123345 Figure 1

Measuring the Electrolyte Distribution in Silver Gas Diffusion Electrodes during CO2 Electroreduction Using Operando Synchrotron Tomography

Electrochemical CO2 reduction (eCO2R) has emerged as a promising technology to support the shift away from fossil fuels in the chemical industry. When coupled with renewable energies it allows for an overall carbon-negative process, while enabling CO2 as a carbon source for the production of commodity chemicals. Efficient eCO2R requires gas diffusion electrodes (GDEs) that provide a large wetted surface area inside the porous system, while also preserving gaseous diffusion pathways for CO2 mass transport through their hydrophobicity. Under the high cathodic overpotential in eCO2R, electrowetting diminishes the hydrophobicity of the GDE and can lead to excessive flooding of the porous system [1]. This severely hinders the CO2 mass transport and thus gives rise to the competing hydrogen evolution reaction (HER), lowering the Faradaic efficiency of the process. Therefore, understanding the flooding behavior of GDEs is of major interest for further development of the process.Mathematic models can be applied here to describe the flooding state under the influence of electrowetting and elucidate its influence on the gas transport through the GDE. The validation of such models requires direct experimental measurements of the electrolyte saturation during eCO2R, which can be accomplished with the use of synchrotron radiation [2].In this work, experimental results for the direct measurement of the electrolyte saturation during eCO2R in sprayed silver GDEs are presented. In a first, these measurements were obtained in operando synchrotron tomography experiments, utilizing a high beam energy to penetrate through the 3 mm diameter GDE in the in-plane direction. The results indicate a higher beam absorption towards the gas side of the GDE, as well as higher absorption at increased current density. Key to the interpretation of these results is the disentanglement of the effects of concentration increase due to migration in the electric field and the actual increase in electrolyte saturation. The experimental results are used to validate a continuum model for a sprayed silver GDE in eCO2R which includes the effect of electrowetting on flooding behavior by introducing capillary pressure – saturation and contact angle – potential correlations [3]. A good agreement between model and tomography results is reached, showing an interplay between concentration increase and flooding effects.[1] Bienen, F., Paulisch, M. C., Mager, T., Osiewacz, J., Nazari, M., Osenberg, M., Ellendorff, B., Turek, T., Nieken, U., Manke, I., & Friedrich, K. A., Investigating the electrowetting of silver‐based gas‐diffusion electrodes during oxygen reduction reaction with electrochemical and optical methods. Electrochemical Science Advances (2022) e2100158.[2] Hoffmann, H., Paulisch, M. C., Gebhard, M., Osiewacz, J., Kutter, M., Hilger, A., Arlt, T., Kardjilov, N., Ellendorff, B., Beckmann, F., Markötter, H., Luik, M., Turek, T., Manke, I., & Roth, C., Development of a Modular Operando Cell for X-ray Imaging of Strongly Absorbing Silver-Based Gas Diffusion Electrodes. Journal of The Electrochemical Society 169 (2022) 044508.[3] Osiewacz, J., Löffelholz, M., Turek, T., Modeling the Influence of Electrolyte Distribution in Silver Gas Diffusion Electrodes for CO2 Electroreduction. ECS Meeting s 01 (2023) 1727. Figure 1

Developing Online ICP-MS Methodology for Examining Catalyst Degradation Dynamics during Electrochemical CO2 Reduction

The electrochemical CO2 reduction reaction (CO2RR) provides a path towards sustainable production of carbon-based fuels and chemicals, using renewable electricity to drive the conversion of CO2 into products such as ethylene, ethanol, and methane. A challenge limiting the implementation of CO2RR is catalyst stability during operation, and greater fundamental understanding is needed to uncover the governing physical, chemical, and electrochemical factors, as well as degradation mechanisms, operative under reducing conditions. One tool that can be used for conducting such fundamental studies is online inductively coupled plasma mass spectrometry (ICP-MS). In this study, an experimental framework was developed for using online ICP-MS for time-resolved degradation studies during CO2RR conditions. Using a customized flow cell setup, we coupled an ICP-MS to a potentiostat to simultaneously apply a potential or current while evaluating dynamics and degradation for both Au and Cu catalysts. Both ionic dissolution and degradation in the form of nanoparticle detachment can be detected and analyzed. The presence of nanoparticles is indicated by spikes in ICP-MS data. The intensity of the spikes is directly related to particle size. We used ICP-MS to determine particle mass, size distribution, and cumulative mass loss over time. We found the use of ICP-MS to obtain particle size distribution gave comparable results to transmission electron microscopy (TEM) determination of particle size distribution.Au foil as the CO2 reduction catalyst was used as a model system for detecting and quantifying degradation in situ using ICP-MS. We found Au degradation to occur in the form of nanoparticle detachment, with increasingly negative applied potential (0 V vs RHE to -1 V vs. RHE) in the presence of CO2 leading to increased number of nanoparticles in the electrolyte; however, no ionic dissolution was observed. In comparison, when the electrolyte was saturated with N2, nanoparticles detached from the electrode at a lower rate than in CO2-saturated conditions. We also examined Cu degradation under the same conditions as the Au system. Cu degradation occurs as both ionic dissolution and nanoparticle detachment, but under all conditions, Cu has less nanoparticle detachment and cumulative mass loss due to nanoparticles than Au. The developed experimental framework in this study would be translatable to a variety of electrocatalytic reactions and environments. Examination of catalyst degradation behavior in situ, including non-traditional degradation mechanisms such as nanoparticle detachment from bulk materials, can be used to obtain greater fundamental understanding of degradation mechanisms and rational design of materials with improved stability.

Scaling-up a Photo-Electrocatalytic Reactor for CO2 Capture and Conversion to Syngas

The most challenging deal we face today is the need to lower greenhouse gas (GHG) emissions and tackle climate change. Though calls to reduce them are growing louder yearly, emissions remain unsustainably high. CO2 is the key contributor to global climate change in the atmosphere. Electrochemical CO2 reduction (EC CO2R) into chemicals or fuels holds great research interest as a promising approach to mitigate CO2 emissions and reach a carbon-neutral future.1 In this regard, an extraordinary effort has been made to discover new efficient and sustainable catalysts at the laboratory level over recent years. High-performance electrocatalysts in aqueous electrolytes often rely on noble metals, which may hinder their industrial applications. Herein, we successfully synthesized core-shell Cu2O/SnO2 nanoparticles2–4 functionalized with a silane group, using a simple and versatile methodology based on a three-step scalable synthesis method involving wet precipitation followed by salinization and, finally, a rhenium-based complex has been assembled by electro-polymerization.5 The carbon paper-supported Cu2O/SnO2-Re electrocatalyst was characterized at 10 cm2 scale achieving a CO:H2 ratio from 3 to 9, and demonstrating an stable syngas production up to 24 hours at -20 mA·cm-2. To translate those developments from the laboratory level to a higher TRL towards the practical application of CO2 capture and utilization6, an additional chamber was added to the system for the continuous CO2 capture and electrochemical conversion, increasing the electrode area from 10 cm2 to 100 cm2. Captured CO2 co-electrolysis to syngas (H2:CO ratio of 5) in one step was demonstrated with a high CO2 conversion at a current up to -2 A, indicating the scale-up potential of this intensified system. The technology is currently under validation in a TRL4 reactor composed of an array of 5 modules (i.e., 4 x 5 cells x 100 cm2) with a total active area of or 0.2m2 for direct CO2 conversion from simulated anthropogenic sources. The design integrates low-cost photovoltaic (PV) cells to provide any required additional bias to drive the reaction, thus, Perovskite PV panels with a cost of up to 5 times lower (10 €/m2) than Si PV cells were used. The TRL5 demonstration of the developed technology will be done with real flue gas emissions the first semester of 2024. Acknowledgements The financial support of the SUNCOCHEM project (Grant Agreement No 862192) of the European Union’s Horizon 2020 Research and Innovation Action programme is acknowledged. References Guzmán, H., Russo, N. & Hernández, S. CO2 valorisation towards alcohols by Cu-based electrocatalysts: challenges and perspectives. Green Chemistry vol. 23 1896–1920 Preprint at https://doi.org/10.1039/d0gc03334k (2021).Cuatto, G. et al. Standardization of Cu2O nanocubes synthesis: Role of precipitation process parameters on physico-chemical and photo-electrocatalytic properties. Chemical Engineering Research and Design 199, 384–398 (2023).Zoli, M., Guzmán, H., Sacco, A., Russo, N. & Hernández, S. Cu2O/SnO2 Heterostructures: Role of the Synthesis Procedure on PEC CO2 Conversion. Materials 16, (2023).Zoli, M. et al. Facile and scalable synthesis of Cu2O-SnO2 catalyst for the photoelectrochemical CO2 conversion. Catal Today 413–415, 113985 (2023).Miró, R. et al. Solar-driven CO2 reduction catalysed by hybrid supramolecular photocathodes and enhanced by ionic liquids. Catal Sci Technol 13, 1708–1717 (2023).Sullivan, I. et al. Coupling electrochemical CO2 conversion with CO2 capture. Nat Catal 4, 952–958 (2021). Figure 1

Coupling Microkinetics with Continuum Transport Models to Understand CO2R on Planar and Optimized Patterned Electrodes

Electrochemical CO2 reduction has emerged as an attractive technique to sustainably produce valuable fuels and chemicals, while reducing CO2 emissions. In addition to the specific electrode material, the microenvironment local to the electrode interface – e.g., the electrolyte pH, CO2 concentration, buffer concentration – plays a significant role in determining the selectivity and activity of the electrolyzer. In this work, we demonstrate a multi-scale approach, where microkinetic simulations of Au are coupled to a two-dimensional continuum transport model in a flow reactor configuration. Specifically, concentrations and potentials solved for in the continuum model are fed into microkinetic models along the planar electrode surface, which return concentration fluxes that are used to update the continuum model. We find that local quantities at the electrode interface, such as the CO2 concentration and pH, vary not only with the applied potential and flow rate, but also with position on the electrode. We investigate two ways to increase CO2 availability at the interface: (1) increasing the applied flow rate, thus reducing the boundary layer thickness, and (2) introducing an inert defect in the middle of the electrode, allowing CO2 to partially replenish within the depletion boundary layer. Inspired by the effect of a single inert defect, we explore electrodes patterned with inert defects and multiple catalyst materials, i.e. a generalized tandem system. We show how the specific pattern of the electrode can be optimized in order to target a specific desired product. The different parts of the electrode have different goals that work together: converting CO2 to CO, converting CO to C2+ products, and allowing concentrations to replenish through the boundary layer. Overall, our aim is to demonstrate the need for multi-dimensional, multi-scale approaches to simulating CO2 reduction to elucidate the reaction environment near the electrode.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL release number: LLNL-ABS-857537.

Revealing the Path-Dependence of Catalyst Degradation in Polymer Electrolyte Fuel Cells

Electro-catalyst plays a central role in many clean energy technology applications including water electrolysis for green hydrogen generation, emission free fuel cells for transportation, electrochemical CO2 reduction and combine heat and power generation. Electro-catalysts degrade via multiple mechanisms, depending on the exact operating conditions in its life cycles. In this presentation, we demonstrate the dependance of the electro-catalyst degradation in polymer electrolyte fuel cell (PEFC) on the specific “paths” that the fuel cell takes to age. Specifically, differently ordered aging protocols with the same total number of accelerated stress tests (ASTs) cycles (i.e., 31,000 total cycles including 30,000 cycles of square-wave load/unload ASTs and 1000 cycles of triangular-wave carbon corrosion ASTs) were used to degrade membrane electrode assemblies (MEAs). At the end-of-life, performances were distinct, indicating that depending on the specific aging route taken, the fuel cell catalyst layer degrades differently after same number of total AST cycles. The load/unload aging protocol led to more severe losses of performance when preceding after the carbon corrosion aging ASTs

Electrochemical and Photoelectrochemical Reduction of Carbon Dioxide on Ruthenium-Cultured Bacterial Biofilms

Most of the bacterial species form biofilms, in which microorganisms are attached to a surface and they are held together by extracellular polymeric substances that they produce. They tend to grow almost everywhere both on living or non-living surfaces. Biofilms are able to propagate charge within their structures and to transfer effectively electrons at interfaces, as well as they could exhibit electrocatalytic properties (e.g. in Microbial Fuels Cells). The application of microbes provides better flexibility: experiments with fuel cells can be operated at normal conditions (temperatures and pressures). Wide variety of microbial metabolic pathways gives the possibility to use aggregates of bacteria in diverse processes. Proposed electrochemical studies using bacterial biofilms (in the form of thin coatings on the glassy carbon electrodes) can be considered as an attempt to find efficient methods of using the energy produced by microorganisms and converting it to electricity.The ultimate goal of the present research has been to determine whether it is possible under laboratory conditions to perform electrocatalytic processes using the hybrid (composite) layers composed of aggregates of bacteria in pristine or modified forms. A biofilm formed by a strain of Yersinia enterocolitica (Y. enterocolitica) is characterized by a high physicochemical stability over a wide pH range (4-10) and temperatures (0-40°C).The subject of interest is a fairly complex reaction, electroreduction of carbon dioxide. There has been growing interest in the search of electrocatalytic anf photoelectrochemical systems capable of efficient conversion of carbon dioxide into fuels and utility chemicals. Our previously performed studies have clearly shown that the Y. enterocolitica biofilm itself has no activity with respect to reduction of CO2, however it acts as a good matrix for the catalytic (e.g. noble metal or metaloorganic) centers, because it affects the reaction mechanism and appears to decrease overpotential of the electroreduction processes. The conducted research shows that the composite materials containing bacterial biofilms can be successfully used to construct systems that have an electrocatalytic reactivity in the reduction of carbon dioxide. We will also address the possibility of dispersing the organometallic ruthenium (II) complex in the biological layer (biofilm). Indeed, the ruthenium (II) complex has been immobilized in the biofilm matrix by successive modification of the liquid medium (Luria-Bertani medium) for culturing bacteria with a solution of the complex compound. In addition, the biological matrix was used (along with the ruthenium (II) complex molecules dispersed in its layer) as a protective coating, stabilizing the unstable p-type semiconductor - copper (I) oxide. The proposed hybrid co-catalytic system showed activity during the photoelectrochemical reduction of carbon dioxide and stability under semi-neutral experimental conditions. Finally, we are going to address the design of the above-mentioned catalytically active systems emphasizing the need to control the structure of the studied hybrid materials (in addition to their stability). Among important issues is the viability of bacteria in the biological membrane as well as elucidation of the role of the bacterial biofilm during the carbon dioxide reduction.

Electron Reservoir Effect of Adjacent Fe Nanoclusters Boosts Atomic Fe Active Sites on Porous Carbon for the Both Electrocatalytic Oxygen Reduction and CO2 Reduction Reaction.

Electrochemical oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR) are greatly significant in renewable energy-related devices and carbon-neutral closed cycle, while the development of robust and highly efficient electrocatalysts has remained challenges. Herein, a hybrid electrocatalyst, featuring axial N-coordinated Fe single atom sites on hierarchically N, P-codoped porous carbon support and Fe nanoclusters as electron reservoir (FeNCs/FeSAs-NPC), is fabricated via in situ thermal transformation of the precursor of a supramolecular polymer initiated by intermolecular hydrogen bonds co-assembly. The FeNCs/FeSAs-NPC catalyst manifests superior oxygen reduction activity with a half-wave potential of 0.91V in alkaline solution, as well as high CO2 to CO Faraday efficiency (FE) of surpassing 90% in a wide potential window from -0.40 to -0.85V, along with excellent electrochemical durability. Theoretical calculations indicate that the electron reservoir effect of Fe nanoclusters can trigger the electron redistribution of the atomic Fe moieties, facilitating the activation of O2 and CO2 molecules, lowering the energy barriers for rate-determining step, and thus contributing to the accelerated ORR and CO2RR kinetics. This work offers an effective design of electron coupling catalysts that have advanced single atoms coexisting with nanoclusters for efficient ORR and CO2RR.

Theoretical Investigation of the Adsorbate and Potential-Induced Stability of Cu Facets during Electrochemical CO2 and CO Reduction

The activity and product selectivity of electrocatalysts for reactions like the carbon dioxide and carbon monoxide reduction reactions (CO2RR and CORR) are intimately dependent on the catalyst’s structure and composition. While engineering catalytic surfaces can improve performance, discovering the key sets of rational design principles remains challenging due to limitations in modeling catalyst stability under operating conditions. Herein, we perform first-principles density functional calculations adopting implicit solvation methods with potential control to study the influence of adsorbates and applied potential on the stability of different facets of model Cu electrocatalysts. Using coverage dependencies extracted from microkinetic models, we describe an approach for calculating potential and adsorbate-dependent contributions to surface energies under reaction conditions, where Wulff constructions are used to understand the morphological evolution of Cu electrocatalysts under CO2RR and CORR conditions. We identify that CO*, a key reaction intermediate, exhibits higher kinetically and thermodynamically accessible coverages on (100) relative to (111) facets, which can translate into an increased relative stabilization of the (100) facet during CO2RR. Our results support the known tendency for increased (111) faceting of Cu nanoparticles under more reducing conditions and that the relative increase in (100) faceting observed under CO2RR conditions is likely attributed to differences in CO* coverage between these facets.This work was partially performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 and partially supported by the U.S. DOE, Office of Energy Efficiency and Renewable Energy, Advanced Materials & Manufacturing Office.

Influence of Carbon Nanotube Support on Electrochemical Nitrate Reduction Catalyzed by a Cobalt Complex

Access to clean water is a pressing environmental and public health concern. Excess nitrate (NO3 -) from the overuse of fertilizer finds its way into our surface water and groundwater, which leads to adverse health effects such as cancer and causes significant damage to ecosystems.1-4 The electrochemical nitrate reduction reaction (NO3RR) has emerged as a promising water treatment approach to address this issue. The NO3RR involves the transformation of waste NO3 - into value-added nitrogen species, such as ammonia (NH3), via reduction. NH3 serves as a valuable chemical in various applications, including its use as a fertilizer, chemical precursor, fuel, and a potential hydrogen (H2) carrier for energy storage and transportation.5-7 Leveraging renewable energy, the NO3RR provides a sustainable approach to distributed NH3 production, which stands in stark contrast to the energy-intensive Haber-Bosch process.8-10 As a result, there is growing interest in designing catalysts for the selective reduction of NO3 - to NH3. However, this requires that we obtain a clear understanding of the role of each component in the catalyst structure.Molecular catalysts have unique advantages over other electrocatalytic materials due to their well-defined structures, which can be tailored through the choice of the metal center and ligands.11,12 Moreover, molecular catalysts can be immobilized on substrates to create heterogeneous electrocatalysts capable of achieving a high current density.13,14 In previous investigations, we showcased the efficacy of multi-walled carbon nanotubes (CNTs) as a catalyst support for electrochemical carbon dioxide reduction reactions.13,15 In heterogenized molecular catalysts, CNTs are generally believed to provide high surface area and electron conduction. However, our recent investigation reveals that CNTs can serve as catalysts themselves for the NO3RR,16 which expands our understanding of the diverse roles CNTs play in NO3 - reduction electrocatalysis.A major challenge in the field of electrocatalysis is the development of catalyst design strategies to control the reaction selectivity. We report on an underexplored approach to overcome this challenge by tuning the CNT support for a cobalt complex. With pristine CNTs as the support, the cobalt complex/CNT hybrid catalyst is selective for NO3 - reduction to NH3 with a maximum Faradaic efficiency of 70%. In contrast, the cobalt complex supported on oxidized CNTs (OCNTs) generates mostly H2 under the same conditions. On the basis of kinetic measurements which reveal that the rate-determining step of NO3 – reduction is limited by the first electron transfer without involving a proton, we propose that the oxygen functional groups on the OCNT support help deliver protons and steer the supported cobalt complexes from catalyzing NO3 - reduction to H2 evolution. The performance of both of these hybrid catalysts is compared with the controls of bare CNTs and OCNTs. Additional control experiments include tests conducted in the absence of NO3 -. These control experiments together with the rest of the experimental data provide strong evidence to support the notion that the product selectivity of the NO3RR catalyzed by cobalt complexes can be controlled via the CNT support. This study demonstrates the importance of tailoring the catalyst support to advance reactivity in catalysis for environmental remediation.

Selectivity and Durability in the Electrochemical Reduction of CO2 to C2 Products Using Cu-P, Cu-Sn and Cu-Se Electrocatalysts

Ethylene is typically reported as the primary product from CO2 reduction at copper electrocatalysts in MEA-type cell configurations with alkaline anolytes. In this work, we evaluate CO2 reduction selectivity at Cu-P, Cu-Sn, and Cu2Se electrocatalysts that were synthesized via a common one-pot approach. Electron microscopy, X-ray diffraction and inductively coupled plasma optical emission spectrometry show 100-110 nm nanoparticles with uniform distributions of P, Sn, or Se. When using neutral (0.1 M KHCO3) anolytes, electrocatalysts with P-doping yield increases in ethylene Faradaic efficiency (up to 52 % at 150 mA cm-2) while Cu-Sn and Cu-Se electrocatalysts result in increased oxygenate selectivity. Cu-Sn electrocatalysts yield an FE of 24 % ethanol at 150 mAcm-2 and Cu2Se electrocatalysts yield an FE of 32 % to acetate at 150 mAcm-2. More alkaline anolytes (1 M KOH) further increased oxygenate formation, with 48 % ethanol Faradaic efficiency on Cu-Sn and 40 % acetate Faradaic efficiency on Cu2Se at 350 mA cm-2. Galvanostatic experiments were conducted at 150 mA cm-2 in 0.1 M KHCO3 electrolyte for over 200 h for the three electrocatalysts. Figure 1 shows the slow losses in FEs to C2 products (0.02 % per h) and increasing cell potentials (1 mV per h). In this talk, we consider the mechanisms for selectivity and the nature of durability improvements. Figure 1

Continuous Direct Air Capture and Electrochemical Conversion of CO2 and H2O into Ethylene and Oxygen in Solid Electrolyte Reactor

Chemelectronics LLC has developed economical approach to use solar energy to convert CO2 directly captured from air using carbon dioxide capture conductive sorbent materials coated on carbon foam electrodes into chemical products (ethylene) and oxygen from nick foam electrodes separated with solid polyelectrolytes. We take advantage of commercial off-the-shelf solar panels as electricity to supply the electrochemical reduction of CO2 directly captured from air into chemical products with zero carbon emission.Based on the life cycle analysis, there is no CO2 emission from CO2 capture and conversion. The energy will be produced from solar panels.

Understanding the Role of Entropy in Promoting Electrocatalytic CO2 Reduction

A global push towards increased sustainability requires technologies that enable the long-term storage of renewable electricity and the sustainable synthesis of chemicals. The electrochemical reduction of CO2 to fuels and chemicals represents a promising avenue to meet these goals. Yet, despite extensive research, many fundamental aspects of the interfacial interactions that enable this reaction remain unclear. One simple question that has not been addressed to date is the mechanism through which the applied potential controls the rate of CO2 reduction. To provide insight, we measured CO2 reduction activation energies on Ag electrodes in the presence of different cations. Building on our earlier work (J. Am. Chem. Soc. 2016, 138, 25, 7820–7823), where some of us demonstrated the important role of structural modifications to imidazolium cations in controlling the rate of CO2 reduction reactions, we expected that these structural modifications impact the reaction rate through changes to the activation energy. However, our findings revealed a much more fascinating picture of the impact of imidazolium cations on CO2 reduction rates.By measuring the activation energy in the presence of imidazolium cations with different structural features, we find that introducing 1-ethly-3-methylimidazolium (EMIM) results in an apparent activation energy of zero. Under these conditions, the applied potential modifies the reaction rate solely through changes to the pre-exponential factor of the Arrhenius equation.Based on literature on homogeneous catalysis, we suggest that our finding indicates that the rate of CO2 reduction in the presence of EMIM is entirely controlled by the formation entropy of the CO2 reduction transition state, with the potential likely influencing the rate by modifying the degree of ordering of imidazolium cations at the electrode surface. We further show that proton abstraction from EMIM forms a neutral compound, resulting in the elimination of the rate enhancement. Our results provide important new insight into the mechanism through which the applied potential controls the rate of electrocatalytic reactions and we expect them to be of broad importance to a better understanding of the connection between interface structure and electrocatalytic rates.

Electrochemical CO2 Reduction to Methane with Remarkably High Faradaic Efficiency in the Presence of a Proton Permeable Membrane

The combustion of fossil fuels is a major contributor to rising levels of anthropogenic carbon dioxide (CO2) in the atmosphere. Due to the adverse effects of climate change caused in large part by CO2, new technologies must be developed that contribute to a global renewable energy supply. Electrochemical reduction of CO2 offers a viable pathway to generating value-added products and synthetic fuels to meet our future energy demands while decreasing greenhouse gas emissions. By constructing electrocatalysts capable of modulating proton transfer, we are able to tune product selectivity. Previous studies have demonstrated that two-electron products (CO and HCOOH) can be produced with high selectivity, but multiple-electron transfer products (CH4, CH3OH, and C2+ products) typically are produced at much lower Faradaic efficiencies. In this work, we construct polymer-modified Cu electrodes that exhibit extraordinarily high CH4 production (88% Faradaic efficiency). These electrodes afford a new strategy for increasing the selectivity of CO2 reduction electrocatalysts, an attribute that is key in developing industrially-relevant CO2 conversion devices. Nafion is a widely used fluoropolymer that is often mixed with electrocatalysts to facilitate proton transport. In contrast to these Nafion-catalyst composites, this work studies electrodes covered by Nafion overlayers for the CO2 reduction reaction. By varying the thickness, substrates, and voltage, we perform a detailed study of the effect of Nafion overlayers on metal and carbon mesh electrodes for CO2 reduction. Depending on the thickness of the Nafion membrane, CO2 reduction occurs at either the polymer–electrolyte interface or electrode–polymer interface. A Nafion overlayer of 15 μm on a Cu electrode enables an extraordinarily high yield of CH4 production (88% Faradaic efficiency) at a low overpotential (540 mV) via the stabilization of metal-bound CO intermediates. To the best of our knowledge, this yield is the highest for electrocatalytic CO2 reduction to CH4 production at room temperature reported.

Diagnosing Copper-Palladium Bimetallic Cathode Capability in CO2 Electrolyzers through Surface Enhanced Raman Spectroscopy

The electrochemical reduction of CO2 offers potential for utilizing CO2 as a carbon feedstock and storing intermittent renewable energy. Presently, copper stands out as the only electrocatalyst capable of reducing CO2 into multiple hydrocarbon products. However, the performance of Cu catalysts is hindered due to poor selectivity, stability and high overpotential. In addressing these bottlenecks, our research focuses on the synthesis and characterization of Pd doped Cu bimetallic catalysts, for improving the selectivity and stability of Cu catalysts during CO2 reduction. We leverage cutting-edge In-situ Shell-Isolated Nanoparticles Enhanced Raman Spectroscopy (SHINERS) to investigate structural and compositional changes on the catalyst surface during electrochemical processes within a CO2 electrolyzer. Our preliminary in-situ Raman findings indicate a strong link between the selectivity of the bimetallic electrocatalyst in CO2 electrolysis and the surface oxide phases of the catalysts. This investigation provides crucial insights for designing an efficient electrocatalyst for CO2 reduction.

Rational Design and Synthesis of CO2 Reduction Reaction Catalysts of High Faradaic Efficiency Toward C2 + Chemical Conversions

Carbon dioxide emission from fossil fuel combustion poses a major threat to global environment and ecological systems.Carbon capture, sequestration and conversion technologies are widely pursued as possible solutions to mitigate negative impact by CO2. The electrochemical CO2 reduction reaction (CO2RR) to fuels and chemicals using renewable electricity offers attractive “carbon-neutral” and “carbon-negative” mitigation strategies. Various catalysts have been investigated as the electrocatalysts for CO2RR. Key challenges facing the current catalyst and electrolyzer designs include insufficient energy efficiency and low single product selectivity.CO2RR to C2+ chemicals represent a highly important area for CO2 reduction and utilization. For example, ethanol, ethylene, propanol, etc. are among the most produced chemicals by the industry and are widely used for various applications. Using CO2 as raw material for chemical production through electrocatalysis not only improves the carbon cycling, but also reduces the overall emissions from chemical production. While CO2RR via two proton-electron pairs (PEPs), such as the conversion of CO2 to CO or formate, have been proven high selective with fast kinetics, conversions to C2+ chemicals are significantly more difficult due to the rapid escalation of required PEPs to much higher numbers (for example, 12 for ethanol and 18 for propanol), in addition to C-C bond coupling. The increased PEPs substantially complicate the conversion by required multiple steps along the electrochemical coordinate, leading to a high probability of branching reactions and low single product Faradaic efficiency (FE).To address these challenges, the design criteria for CO2RR to C2+ chemicals should be based on high uniformity of active center for directing identical catalytic path and suppressing competing reactions, strong catalyst-reactant binding in capturing the transient species through multiple PEP transfers, and microenvironment with nanoconfinement for retaining reaction intermediates during extended catalytic processes.Recently, we developed a new amalgamated lithium metal (ALM) synthesis method of preparing highly selective and active CO2RR catalyst and achieved > 90% FE for conversion of CO2 to ethanol [1]. Our have since expanded the approach to other C2 + chemicals including acetate, acetone, glycerol, isopropanol, etc., all with FE at or higher than 80%. To better formulate our catalyst design strategy, we not only measured the CO2RR performance over a variety of electrocatalysts, but also investigated their activity-structure relationship through advanced material characterizations, combined with the first-principle computation. We found many interesting properties uniquely associated to CO2RR mechanism and kinetics, such as catalyst-size and electro-potential modulated single selectivity. In this presentation, we will share our recent discoveries and future perspective on the development of highly selective CO2RR catalysts for C2+ chemical conversions. Acknowledgement: This work is supported by U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy - Industrial Efficiency & Decarbonization Office and by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.[1] “Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically dispersed copper” Haiping Xu, Dominic Rebollar, Haiying He, Lina Chong, Yuzi Liu, Cong Liu, Cheng-Jun Sun, Tao Li, John V. Muntean, Randall E. Winans, Di-Jia Liu and Tao Xu, (2020) Nature Energy, 5, 623–632

Aggregation of Homogeneous Porphyrin Catalysts in Organic Electrolyte Broadly Inhibits Electrochemical CO2 Reduction Performance

Metalloporphyrins are widely used as homogeneous electrocatalysts for the production of renewable fuels from abundant feedstocks and sustainable energy. The modularity of porphyrin catalysts has led to the establishment of structure‐function correlations that aid in predicting and optimizing catalytic activity. Although metalloporphyrins are widely known to aggregate due to their planar structure that promotes π–π stacking, it is surprising that the influence of metalloporphyrin aggregation on electrocatalytic performance has not been previously investigated. Herein, we will document the relative aggregation and electrocatalytic activity for CO2 reduction to CO with three structurally related iron meso-phenylporphyrins in commonly used N,N-dimethylformamide (DMF) electrolyte. An inverse dependence of kinetics on catalyst concentration is observed for all three porphyrins based on cyclic voltammetry data. Furthermore, this inhibition extends to bulk electrolysis performance, where up to 75% of the catalyst in a 1 mM solution is inactive compared to in a 0.25 mM solution. This talk will additionally discuss how aggregation is influenced by organic additives, axial ligands, redox state, metal identity, and porphyrin substituents. Overall, this work emphasizes that metalloporphyrins can aggregate severely (even in well-solubilizing organic electrolytes) and that aggregation effects must be considered for optimization of performance and for meaningful catalytic activity comparisons.

Sulfur Modified Copper Nitride for Electrochemical CO2 Reduction Reaction

Metallic copper has been attracted attention as efficient catalyst for electrochemical CO2 reduction reaction (CO2RR). However, the activity of the catalyst with a single adsorption site is limited by the imbalance of the intermediate binding energy, so-called “scaling relationship”. [1] Therefore, it is crucial to break the scaling relationship between reaction intermediates in order to increase product selectivity and lower overpotential. One of the candidates to overcome this scaling relationship is metal sulfide. According to the computational study, since sulfur atoms work as an adsorption site, metal sulfide is expected to be a suitable catalyst for CO2RR with multiple adsorption sites.[2] In addition, surface modification by sulfur is also effective approach to enhance product selectivity in CO2RR. Increase of formate (HCOO-) selectivity by sulfur introduction on Cu has been reported in some previous reports.[3]-[5] On the other hand, the repulsion between the oxygen lone pair electrons of the CO2 molecule and the electronic clouds of the surface sulfur atoms become an obstacle on CO2RR.[6] A potential solution to this problem is the construction of sulfide-nitride composite. Because of the difference in electronegativity between nitrogen and metal or sulfur, it is considered that the electronic structure of the metal sulfide is altered to reduce the repulsion between oxygen and sulfur.[7] Based on these backgrounds, it is expected that the CO2RR activity of copper nitride (Cu3N) will be enhanced by sulfur introduction.Here, sulfur modified Cu3N with different amount of sulfur were synthesized by reflux method with some modification of previously reported method.[8] X-ray diffraction pattern and SEM-EDX elemental analysis result indicate that the sulfur ratio increases and copper sulfide (Cu2S) crystal phase appears with the amount of sulfur source precursor. CO2RR activity was evaluated in 0.1M KHCO3 electrolyte, and volcano trend was identified between the amount of sulfur and methane selectivity. Among all the catalysts including pure Cu3N and Cu2S which were synthesized by the same method, 4.2 mol% sulfur containing Cu3N showed the highest methane faradaic efficiency (41.4 %). This faradaic efficiency is more than 10 times higher than that of Cu3N (0.48 %) and Cu2S (1.3 %). This finding offers valuable insights into the sulfur role on the modified catalyst.

In-Situ Investigation of Surface Modifiers Dithiocarbamates on Au Electrodes for Electrochemical CO2 Reduction

Molecular functionalization of metal electrodes via self-assembled monolayers (SAMs) can introduce synthetically tunable properties to metal surfaces and has exhibited great potential in electrocatalysis. Alkanethiols are commonly used organic ligands because of their strong affinity to Au but they are prone to desorption at negative potentials. Alternatively, dithiocarbamates (DTC) show superior electrochemical stability. In this study, a series of DTCs, differing in hydrophobicity, size, and steric bulk, were synthesized to prepare SAM-functionalized Au electrodes. The properties of the resulting surfaces (e.g. wettability, surface coverage, and reductive stability) were investigated by analytical and electrochemical techniques. Particularly, in-situ approaches such as surface-enhanced infrared absorption spectroscopy (SEIRAS) are employed to characterize the molecularly modified interface. The novel catalyst platforms were explored for electrochemical CO2 reduction.

(Invited) Insights from the Interplay of the Electrode Structure and the Microenvironment for Electrochemical CO2 Conversion

The electrochemical CO2 reduction reaction (CO2RR) represents a critical approach toward the carbon-neutral generation of hydrocarbons. However, despite intense research efforts, the need remains to increase the selectivity and activity of electrocatalysts for CO2RR. Thus, there has been increasing interest in optimizing the microenvironment to boost the activity and selectivity of electrocatalytic sites for CO2 conversion.This presentation discusses several strategies that are being pursued in my research group to optimize the microenvironment for CO2 conversion based on a detailed understanding of model systems for electrochemical CO2 conversion to C2+ products on Cu. Here, microenvironment-level insights from two model systems will be discussed: The effect of localization of Ag co-catalysts in Cu nanowire arraysThe impact of the 3D interface on the microenvironment within model Cu nanowire array cathodes to boost C2 product activity Overall, these insights can aid in the rational design of electrodes for electrochemical CO2 conversion. Figure 1