Carbon Dioxide Electroreduction Research Articles

Theoretical Study on the Electro-Reduction of Carbon Dioxide to Methanol Catalyzed by Cobalt Phthalocyanine.

Density functional theory (DFT) calculations have been conducted to investigate the mechanism of cobalt(II) tetraamino phthalocyanine (CoPc-NH2) catalyzed electro-reduction of CO2. Computational results show that the catalytically active species 1 (4[CoII(H4L)]0) is formed by a four-electron-four-proton reduction of the initial catalyst CoPc-NH2. Complex 1 can attack CO2 after a one-electron reduction to give a [CoIII-CO22-]- intermediate, followed by a protonation and a one-electron reduction to give intermediate [CoII-COOH]- (4). Complex 4 is then protonated on its hydroxyl group by a carbonic acid to generate the critical species 6 (CoIII-L•--CO), which can release the carbon monoxide as an intermediate (and also as a product). In parallel, complex 6 can go through a successive four-electron-four-proton reduction to produce the targeted product methanol without forming formaldehyde as an intermediate product. The high-lying π orbital and the low-lying π* orbital of the phthalocyanine endow the redox noninnocent nature of the ligand, which could be a dianion, a radical monoanion, or a radical trianion during the catalysis. The calculated results for the hydrogen evolution reaction indicate a higher energy barrier than the carbon dioxide reduction. This is consistent with the product distribution in the experiments. Additionally, the amino group on the phthalocyanine ligand was found to have a minor effect on the barriers of critical steps, and this accounts for the experimentally observed similar activity for these two catalysts, namely, CoPc-NH2 and CoPc.

CO2 Electroreduction to Fuels Using Solid Oxide Electrodes: Beyond Ni-YSZ

Ni-YSZ electrodes form the benchmark in Carbon Dioxide electroreduction to CO. Ni-YSZ due its popular use in Solid Oxide Fuel Cells forms the basis of various process steps. Unfortunately, this material remains active only if a certain amount of hydrogen is supplied along side CO2 to the inlet of the reaction. Consequently, the Ni-YSZ results in CO production via reverse water gas shift (RWGS) reaction when H2 is supplied at the inlet. The currents for the electrode originate from electrolysis of H2O which is formed as a result of reverse water has shift. We have quantified the amount of CO produced from RWGS vs direct CO2 electrolysis in such a system using online mass spectrometry (MS). Electrochemical impedance spectroscopy measurements where analysed using distribution of relaxation times analysis. Under low concentration of H2 the overall impedance is dominated by H2 mass transfer. Effects of concentration of various reactants were measured using online MS. The process of pretreatment of the electrodes and catalyst surface development during reaction were tracked using in situ Raman Spectroscopy and optical spectrocopy. Electrodes were structurally characterised using SEM, TEM, XPS and ICP-OES measurememts. Various new combination of mixed metal oxide electrodes Ni(M)-YSZ were tested and compared with the performance of pure Ni-YSZ. Ni-YSZ electrode when used under pure CO2 results in catastrophic failure of the electrode performance. We have investigated this failure using in situ Raman and Mass spectrometry. The mechanism of CO2 production in pure CO2 stream was found to be drastically different from when a small amount of H2 is used. Figure 1

The Critical Role of Initial/Operando Oxygen Loading in General Bismuth-Based Catalysts for Electroreduction of Carbon Dioxide.

Operando reconstruction of solid catalyst into a distinct active state frequently occurs during electrocatalytic processes. The correlation between initial and operando states, if ever existing, is critical for the understanding and precise design of a catalytic system. Inspired by recently established intermediate metallic state of Bi-based catalysts during electrocatalytic carbon dioxide reduction (CO2RR), here we investigate a series of Bi oxide catalysts (Bi, Bi2O3, BiO2) and demonstrate that the operando surface/subsurface oxygen loading, positively correlated to the initial oxygen content, plays a critical role in determining Bi-based CO2RR performance. Higher initial oxygen loading indicates a better electrocatalytic efficiency. Further analysis shows that this conclusion generally applies to all Bi-based electrocatalysts reported up to date. Following this principle, cost-effective BiO2 nanocrystals demonstrated the highest formate Faradaic efficiency (FE) and current density compared to Bi/Bi2O3, further allowing a pair-electrolysis system with 800 mA/cm2 current density and an overall 175% FE for formate production.

Solar reduction of carbon dioxide on copper-tin electrocatalysts with energy conversion efficiency near 20%

Copper catalysts modified with tin have been demonstrated to be selective for the electroreduction of carbon dioxide to carbon monoxide. However, such catalysts require the precise control of tin loading amount. Here, we develop a copper/tin-oxide catalyst with dominant tin oxide surface being formed via a spontaneous exchange reaction between sputtered tin and copper oxide. Even though the surface of this catalyst is tin-rich, it achieves an excellent performance towards carbon monoxide production in a flow cell. This contrasts with copper/tin-oxide prepared via atomic layer deposition since it yields selectivity towards carbon monoxide only on a copper-rich surface. Mechanism studies reveal that the tin sites on the tin-rich copper/tin-oxide surface achieve a suitable binding with adsorbed carbon monoxide under the presence of copper. Powered by a triple-junction solar cell, the copper/tin-oxide based electrolyzer sets a new benchmark solar-to-chemical energy conversion efficiency of 19.9 percent with a Faradaic efficiency of 98.9 percent towards carbon monoxide under simulated standard air mass 1.5 global illumination.

Heteroatoms Induce Localization of the Electric Field and Promote a Wide Potential-Window Selectivity Towards CO in the CO2 Electroreduction.

Carbon dioxide electroreduction (CO2 RR) is a sustainable way of producing carbon-neutral fuels. Product selectivity in CO2 RR is regulated by the adsorption energy of reaction-intermediates. Here, we employ differential phase contrast-scanning transmission electron microscopy (DPC-STEM) to demonstrate that Sn heteroatoms on a Ag catalyst generate very strong and atomically localized electric fields. In situ attenuated total reflection infrared spectroscopy (ATR-IR) results verified that the localized electric field enhances the adsorption of *COOH, thus favoring the production of CO during CO2 RR. The Ag/Sn catalyst exhibits an approximately 100 % CO selectivity at a very wide range of potentials (from -0.5 to -1.1 V, versus reversible hydrogen electrode), and with a remarkably high energy efficiency (EE) of 76.1 %.

Toward abiotic sugar synthesis from CO2 electrolysis

Toward abiotic sugar synthesis from CO2 electrolysis

Chem-bio interface design for rapid conversion of CO2 to bioplastics in an integrated system

Chem-bio interface design for rapid conversion of CO2 to bioplastics in an integrated system

Atomically Thin, Ionic-Covalent Organic Nanosheets for Stable, High-Performance Carbon Dioxide Electroreduction.

The incorporation of charged functional groups is effective to modulate the activity of molecular complexes for the CO2 reduction reaction (CO2 RR), yet long-term heterogeneous electrolysis is often hampered by catalyst leaching. Herein, an electrocatalyst of atomically thin, cobalt-porphyrin-based, ionic-covalent organic nanosheets (CoTAP-iCONs) is synthesized via a post-synthetic modification strategy for high-performance CO2 -to-CO conversion. The cationic quaternary ammonium groups not only enable the formation of monolayer nanosheets due to steric hindrance and electrostatic repulsion, but also facilitate the formation of a *COOH intermediate, as suggested by theoretical calculations. Consequently, CoTAP-iCONs exhibit higher CO2 RR activity than other cobalt-porphyrin-based structures: an 870% and 480% improvement of CO current densities compared to the monomer and neutral nanosheets, respectively. Additionally, the iCONs structure can accommodate the cationic moieties. In a flow cell, CoTAP-iCONs attain a very small onset overpotential of 40mV and a stable total current density of 212mAcm-2 with CO Faradaic efficiency of >95% at -0.6V for 11h. Further coupling the flow electrolyzer with commercial solar cells yields a solar-to-CO conversion efficiency of 13.89%. This work indicates that atom-thin, ionic nanosheets represent a promising structure for achieving both tailored activity and high stability.

High performance carbon dioxide electroreduction in ionic liquids with in situ shell-isolated nanoparticle-enhanced Raman spectroscopy

Electrochemical CO2 reduction (ECR) has received significant attention with the rising emphasis on renewable energy. However, high Faradaic efficiency (FE) and large current density are still the challenge for ECR. Selecting ionic liquids (ILs) as electrolytes for ECR has advantages of enhancing the FE and improving the current density. Herein, in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is employed to study the ECR process on nickel foam (NF) in imidazolium ILs. Results show that the IL 1-Butyl-3-methylimidazolium chloride (BmimCl) presents the best performance towards ECR. The FE of CO is as high as 94.6 %, with a considerable current density of 72 mA cm−2. Particularly, the FE of CO can keep around 82 % after 15 h continuous electrolysis, indicating the good stability. Structural details of the BmimCl-NF electrode interface are obtained by in situ SHINERS along with density functional theory (DFT) calculations, indicating that the adsorption configuration change of imidazolium cations of BmimCl on NF electrode is favorable for ECR. Moreover, the strong interaction between Cl anions of BmimCl and CO2 could bend and activate the CO2 molecules. The reaction intermediate CO32– confirmed by in situ SHINERS helps to determine the reaction pathway. Particularly, the DFT calculations show the priority of the ECR reaction on Ni surface for CO product. This work presents a promising method for in situ studies of the CO2 electroreduction mechanism in ionic liquids.

Theoretical Investigation of Cu-Au Alloy for Carbon Dioxide Electroreduction: Cu/Au Ratio Determining C1/C2 Selectivity.

Copper-gold alloy exhibits excellent catalytic performance for the carbon dioxide electroreduction (CO2ER) reaction, but the mechanism of the effect of the Cu/Au ratio on the selectivity of C1/C2 products has not been carefully investigated. In this work, (100) and (111) surfaces of three CuAu alloys with different Cu/Au (3:1, 1:1, 1:3) ratios are constructed. The properties of CuAu surfaces like density of states, Bader charge, and the whole CO2ER to C2H4 and C2H5OH mechanisms are investigated. Our calculation reveals that the adsorption capacity of the catalyst surface for the intermediates *COOH and *CO is enhanced with the increase of the Au ratio. The calculation results show that the Cu1Au1(100) surface has the highest activity for CO2ER to CO (UL = -0.32 V). Furthermore, the Cu3Au1(100) surface exhibits the best coupling performance, and ethanol is the dominant product for CO2ER to C2 products. Our work provides a useful guideline for further developing CO2ER electrocatalysts.

Progress of transition metal chalcogenides as efficient electrocatalysts for energy conversion

The continuous excessive usage of fossil fuels has resulted in its fast depletion, leading to an escalating energy crisis as well as several environmental issues leading to increased research towards sustainable energy conversion. Electrocatalysts play crucial role in the development of numerous novel energy conversion devices, including fuel cells and solar fuel generators. In particular, high-efficiency and cost-effective catalysts are required for large-scale implementation of these new devices. Over the last few years, transition metal chalcogenides have emerged as highly efficient electrocatalysts for several electrochemical devices such as water splitting, carbon dioxide electroreduction, and, solar energy converters. These transition metal chalcogenides exhibit high electrochemical tunability, abundant active sites, and superior electrical conductivity. Hence, they have been actively explored for various electrocatalytic activities. Herein, we have provided comprehensive review of transition-metal chalcogenide electrocatalysts for hydrogen evolution, oxygen evolution, and carbon dioxide reduction and illustrated structure–property correlation that increases their catalytic activity.

Cover Picture: A Stable and Conductive Covalent Organic Framework with Isolated Active Sites for Highly Selective Electroreduction of Carbon Dioxide to Acetate (Angew. Chem. Int. Ed. 36/2022)

Electroreduction of CO2 to acetate provides a promising strategy to reduce CO2 emissions and store renewable energy, but acetate is usually a by-product. A covalent organic framework with isolated active sites for highly selective electroreduction of CO2 to acetate was revealed by Pei-Qin Liao and co-wokers in their Communication (DOI: 10.1002/anie.202206470). The copper-phthalocyanine active site with high electron density is conducive to the key step of C−C coupling of *CH3 with CO2 to produce acetate, and can avoid the coupling of *CO with *CO or *CHO to produce ethylene and ethanol.

Titelbild: A Stable and Conductive Covalent Organic Framework with Isolated Active Sites for Highly Selective Electroreduction of Carbon Dioxide to Acetate (Angew. Chem. 36/2022)

Die Elektroreduktion von CO2 zu Acetat ist eine vielversprechende Strategie zur Speicherung erneuerbarer Energie, jedoch fällt Acetat normalerweise als Nebenprodukt an. Pei-Qin Liao und Mitarbeiter berichten in ihrer Zuschrift (e202206470) über ein kovalentes organisches Gerüst mit isolierten aktiven Zentren für die hochselektive Elektroreduktion von CO2 zu Acetat. Das aktive Kupfer-Phthalocyanin-Zentrum mit hoher Elektronendichte begünstigt den Schlüsselschritt der C-C-Kupplung von *CH3 mit CO2 zur Bildung von Acetat und unterdrückt die Kupplung von *CO mit *CO oder *CHO zur Bildung von Ethylen und Ethanol.

Strained Lattice Gold-Copper Alloy Nanoparticles for Efficient Carbon Dioxide Electroreduction.

Electrocatalytic conversion of carbon dioxide (CO2) into specific renewable fuels is an attractive way to mitigate the greenhouse effect and solve the energy crisis. AunCu100-n/C alloy nanoparticles (AunCu100−n/C NPs) with tunable compositions, a highly active crystal plane and a strained lattice were synthesized by the thermal solvent co-reduction method. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) results show that AunCu100−n/C catalysts display a subtle lattice strain and dominant (111) crystal plane, which can be adjusted by the alloy composition. Electrochemical results show that AunCu100−n/C alloy catalysts for CO2 reduction display high catalytic activity; in particular, the Faradaic efficiency of Au75Cu25/C is up to 92.6% for CO at −0.7 V (vs. the reversible hydrogen electrode), which is related to lattice shrinkage and the active facet. This research provides a new strategy with which to design strong and active nanoalloy catalysts with lattice mismatch and main active surfaces for CO2 reduction reaction.

Metal-Organic Framework-Derived BiIn Bimetallic Oxide Nanoparticles Embedded in Carbon Networks for Efficient Electrochemical Reduction of CO2 to Formate.

Bismuth-based catalysts exhibit excellent activity and selectivity for the electroreduction of carbon dioxide (CO2). However, single-component bismuth-based catalysts are not satisfactory for the electrochemical reduction of CO2 to formic acid, mainly due to their high hydrogen production, low electrical conductivity, and small catalytic current density. Herein, we used a coordination strategy to recombine Bi and In at the molecular level to form Bi/In bimetallic metal-organic frameworks (MOFs), which were then calcined to obtain MOF-derived Bi/In bimetallic oxide nanoparticles embedded in carbon networks. Thanks to the synergistic effect of bimetallic components, high specific surface area, suitable pore size distribution, and high electrical conductivity of the carbon network, the material exhibits excellent activity and selectivity for electroreduction of CO2 to formate. In H-type electrolyzers, the formate Faradaic efficiency reaches 91% at -0.9 V (vs RHE) and does not decrease significantly within 48 h. In situ Fourier transform infrared spectroscopy confirms the reaction intermediates and reveals that CO2 electroreduction is dominant by the *OCHO pathway.

CoN5 Sites Constructed by Anchoring Co Porphyrins on Vinylene-Linked Covalent Organic Frameworks for Electroreduction of Carbon Dioxide.

Developing effective electrocatalysts for CO2 reduction (CO2 RR) is of critical importance for producing carbon-neutral fuels. Covalent organic frameworks (COFs) are an ideal platform for constructing catalysts toward CO2 RR, because of their controllable skeletons and ordered pores. However, most of these COFs are synthesized from Co-porphyrins or phthalocyanines-based monomers, and the available building units and resulting catalytic centers in COFs are still limited. Herein, Co-N5 sites are first developed through anchoring Co porphyrins on an olefin-linked COF, where the Co active sites are uniformly distributed in the hexagonal networks. The strong electronic coupling between Co porphyrins and COF is disclosed by various characterizations such as X-ray absorption spectroscopy (XAS) and density functional theory calculation (DFT). Thanks to the CoN5 sites, the catalytic COF shows remarkable catalytic activity with Faraday efficiencies (FECO ) of 84.2-94.3% at applied potentials between -0.50 and -0.80 V (vs RHE), and achieves a turnover frequency of 4578 h-1 at -1.0 V. Moreover, the theoretical calculation further reveals that the CoN5 sites enable adecrease in the overpotential for the formation COOH*. This work provides a design strategy to employ COFs as scaffold for fabricating efficient CO2 electrocatalysts.

A Stable and Conductive Covalent Organic Framework with Isolated Active Sites for Highly Selective Electroreduction of Carbon Dioxide to Acetate.

Electroreduction of CO2 to acetate provides a promising strategy to reduce CO2 emissions and store renewable energy, but acetate is usually a by-product. Here, we show a stable and conductive two-dimensional phthalocyanine-based covalent-organic framework (COF) as an electrocatalyst for reduction of CO2 to acetate with a single-product Faradaic efficiency (FE) of 90.3(2)% at -0.8 V (vs. RHE) and a current density of 12.5 mA cm-2 in 0.1 M KHCO3 solution. No obvious degradation was observed over 80 hours of continuous operation. Combined with the comparison of the properties of other catalysts with isolated metal active sites, theoretical calculations and in situ infrared spectroscopy revealed that the isolated copper-phthalocyanine active site with high electron density is conducive to the key step of C-C coupling of *CH3 with CO2 to produce acetate, and can avoid the coupling of *CO with *CO or *CHO to produce ethylene and ethanol.

A Stable and Conductive Covalent Organic Framework with Isolated Active Sites for Highly Selective Electroreduction of Carbon Dioxide to Acetate

AbstractElectroreduction of CO2to acetate provides a promising strategy to reduce CO2emissions and store renewable energy, but acetate is usually a by‐product. Here, we show a stable and conductive two‐dimensional phthalocyanine‐based covalent‐organic framework (COF) as an electrocatalyst for reduction of CO2to acetate with a single‐product Faradaic efficiency (FE) of 90.3(2)% at −0.8 V (vs. RHE) and a current density of 12.5 mA cm−2in 0.1 M KHCO3solution. No obvious degradation was observed over 80 hours of continuous operation. Combined with the comparison of the properties of other catalysts with isolated metal active sites, theoretical calculations and in situ infrared spectroscopy revealed that the isolated copper‐phthalocyanine active site with high electron density is conducive to the key step of C−C coupling of *CH3with CO2to produce acetate, and can avoid the coupling of *CO with *CO or *CHO to produce ethylene and ethanol.

(Invited) Bacterial Biofilms As Active Components of Electrocatalytic and Photoelectrochemical Systems for Reduction of Carbon Dioxide

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 [1,2], 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. In particular, the influence of the biological matrix on the catalytic activity of different transition metal nanoparticles (Pd, Pt, Ru, PtRu) in the carbon dioxide conversion process will be compared. Here, the successful system based on platinum nanoparticles deposited on the biological carrier, Y. enterocolitica biofilm, supported onto conductive polymer (polyaniline) and utilizing multi-walled carbon nanotubes should be mentioned. 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.[1] Seta E., Lotowska W., Rutkowska I.A., Wadas A., Raczkowska A., Nieckarz. M., Brzostek K., Kulesza P.J., Australian Journal of Chemistry 69 (2016) 411-418.[2] Lotowska W., Rutkowska I.A., Seta E., Szaniawska E., Wadas A., Raczkowska A., Brzostek K., Kulesza P.J., Electrochimica Acta 213 (2016) 314-323.

(Invited) N-Doped Carbon Catalysts in Carbon-Dioxide Electroreduction: Effect of the Chemical Composition and Morphology

N-doped carbon (N-C) materials are increasingly popular in different electrochemical and catalytic applications. Due to the structural and stoichiometric diversity of these materials, the role of different functional moieties is still controversial. We have synthesized a set of N-C catalysts, with identical morphology (~27 nm pore size). By systematically changing the precursors, we have varied the amount and chemical nature of N-functions on the catalyst surface. The CO2 reduction (CO2R) properties of these catalysts were tested in electrochemical experiments, where CO was the major product in all cases, while CH4 appeared as minor product. Importantly, the CO2R activity changed with the chemical composition. The activity was correlated with the amount of different N-functions, and correlation was found only for the -NOx species. Interestingly, the amount of this species decreased radically during CO2R, which was coupled with the performance decrease. The observations were rationalized by the adsorption/desorption properties of the samples.In the second part of my presentation I will shed light on the importance of catalyst morphology, using N–C catalysts as a model system. We found that CO2R activity, selectivity, and stability of N–C electrodes are highly dependent on their porosity. The presence of mesopores was demonstrated to be beneficial in achieving high CO selectivity and current density, with an optimal pore size around 27 nm. Even after convoluting factors other than morphology (e.g., surface chemistry, level of graphitization, surface area), the reasons behind the observed trends are complex. CO2 adsorption properties, wetting characteristics, and geometric effects are jointly responsible for the massive difference in the CO2R performance. All these properties must be taken into consideration when we aim to understand the reduction mechanism on different catalysts and while improving the performance further to a technologically relevant level (as alternatives to precious metal catalysts).