Carbon Dioxide Electroreduction Research Articles

Machine learning assisted prediction of copper-based catalysts towards carbon dioxide electroreduction into carbon monoxide

Copper-based catalyst is very active for electroreduction of carbon dioxide (CO2) to carbon monoxide (CO). However, the Faraday efficiency of copper-based catalysts for CO production can be affected by many complex factors, such as catalyst elemental composition, morphology, supporting substrate, synthesis method, catalyst size, electrolyte concentration, and test potential with unknown correlations, hindering the efficient exploration of active copper-based CO2 reduction catalysts with high CO Faraday efficiency. In this study, a machine learning (ML) model is proposed towards rapid screening of copper-based catalysts with high CO selectivity using experimental database. The significance of different catalyst-related features on the CO Faraday efficiency was evaluated using feature importance and Spearman correlation coefficients. The ML model predicted that the dendrite Pd-doped copper oxides catalyst electroless deposited on copper mesh has the highest CO Faraday efficiency (92.8%). This ML study provides a useful guidance for the screening of copper-based catalysts towards the reduction of CO2 to CO.

A dendritic porous copper foam-carbonic anhydrase biohybrid for carbon dioxide electroreduction.

Carbonic anhydrase (CA) is bound to a dendritic porous copper foam (3D-Cu) via electrostatic interaction to form a biohybrid (CA/3D-Cu), which exhibits high selectivity and Faraday efficiency in the electroreduction of carbon dioxide (CO2) to formic acid (selectivity of 98.7%, Faraday efficiency of 82.1%) due to the large specific surface area of the 3D-Cu and the ultra-high CO2 hydration capacity of CA.

Guanine-derived carbon nanosheet encapsulated Ni nanoparticles for efficient CO2 electroreduction.

Developing novel electrocatalysts for achieving high selectivity and faradaic efficiency in the carbon dioxide reduction reaction (CO2RR) poses a major challenge. In this study, a catalyst featuring a nitrogen-doped carbon shell-coated Ni nanoparticle structure is designed for efficient carbon dioxide (CO2) electroreduction to carbon monoxide (CO). The optimal Ni@NC-1000 catalyst exhibits remarkable CO faradaic efficiency (FECO) values exceeding 90% across a broad potential range of -0.55 to -0.9 V (vs. RHE), and attains the maximum FECO of 95.6% at -0.75 V (vs. RHE) in 0.5 M NaHCO3. This catalyst exhibits sustained carbon dioxide electroreduction activity with negligible decay after continuous electrolysis for 20 h. More encouragingly, a substantial current density of 200.3 mA cm-2 is achieved in a flow cell at -0.9 V (vs. RHE), reaching an industrial-level current density. In situ Fourier transform infrared spectroscopy and theoretical calculations demonstrate that its excellent catalytic performance is attributed to highly active pyrrolic nitrogen sites, promoting CO2 activation and significantly reducing the energy barrier for generating *COOH. To a considerable extent, this work presents an effective strategy for developing high-efficiency catalysts for electrochemical CO2 reduction across a wide potential window.

Status and challenges for CO2 electroreduction to CH4: advanced catalysts and enhanced strategies

Sustainable energy-powered carbon dioxide (CO2) electroreduction into methane (CH4) under ambient conditions holds great promise for achieving carbon neutrality and mitigating environmental pollution.

CeO2-promoted Cu2O-based catalyst sprayed on the gas diffusion layer for the electroreduction of carbon dioxide to ethylene

In the catalytic system based on Cu2O–CeO2-C, the interaction between Cu2O and CeO2-C creates intrinsic sites (Cux–CeO2−x; Cux = Cu2+, Cu+, Cu0), which are beneficial for achieving competitive ethylene production from CO2RR.

Alkyl sulfonate surfactant mediates electroreduction of carbon dioxide to ethylene or ethanol over hydroxide-derived copper catalysts.

For CO2 electroreduction (CO2ER) to C2 compounds, it is generally accepted that the formation of ethylene and ethanol shares the same intermediate, *HCCOH. The majority of studies have achieved high faradaic efficiency (FE) towards ethylene, but faced challenges to get high ethanol FE. Herein, we present an alkyl sulfonate surfactant (e.g., sodium dodecyl sulfonate, SDS) mediated CO2ER to a C2 product over an in situ generated Cu catalyst (Cu@SDS) from SDS-modified Cu(OH)2. It achieves the CO2ER to ethylene as the sole C2 product at low applied voltages with a FE of 55% at -0.6 V vs. RHE and to ethanol as the main product at potentials ≥0.7 V with a maximum FE of 64% and a total C2 FE of 86% at -0.8 V, with a current density of 231 mA cm-2 in a flow cell. Mechanism investigation indicates that SDS modifies the oxidation state of the in situ formed Cu species in Cu@SDS, thus tuning the catalyst activity for CO2ER and lowering the C-C coupling energy barrier; meanwhile, it tunes the adsorption mode of the *HCCOH intermediates on the catalyst, thus mediating the selectivity of CO2ER towards C2 products.

Easily constructed porous silver films for efficient catalytic CO2 reduction and Zn-CO2 batteries.

For the electroreduction of carbon dioxide into high value-added chemicals, highly active and selective catalysts are crucial, and metallic silver is one of the most intriguing candidate materials available at a reasonable cost. Herein, through a novel two-step operation of Ag paste/SBA-15 coating and HF etching, porous silver films on a commercial carbon paper with a waterproofer (p-Ag/CP) could be easily fabricated on a large scale as highly efficient carbon dioxide reduction reaction (CO2RR) electrocatalysts with a CO Faraday efficiency (FECO) as high as 96.7% at -1.0 V vs. the reversible hydrogen electrode (RHE), and it still reaches up to 90% FECO over applied potentials ranging from -0.8 to -1.1 V vs. the RHE. Meanwhile, the membrane electrode assembly (MEA) utilizing the p-Ag/CP catalyst has achieved a current density, FECO, and stability of ∼60 mA cm-2, >91%, and 11 h, respectively. Furthermore, the assembled aqueous Zn-CO2 battery using p-Ag/CP cathode yielded a peak power density of 0.34 mW cm-2, 75 charge-discharge cycles for 25 h, and 64% FECO at 2.5 mA cm-2. Compared with flat Ag/CP, the significant enhancement in the CO2RR activity of p-Ag/CP was mainly attributed to the distinctive porous structure and an improved three-phase boundary, which is capable of inducing the stabilization of *COOH intermediates, increased active specific surface areas, fast electron transfer kinetic and mass transportation. Further, theoretical calculations revealed that p-Ag/CP possessed an optimized energy barrier for *COOH intermediates.

Theoretical study of transition metal-doped β12 borophene as a new single-atom catalyst for carbon dioxide electroreduction.

The electrocatalytic carbon dioxide reduction reaction (CO2RR) presents a viable and cost-effective approach for the elimination of CO2 by transforming it into valuable products. Nevertheless, this process is impeded by the absence of exceptionally active and stable catalysts. Herein, a new type of electrocatalyst of transition metal (TM)-doped β12-borophene (TM@β12-BM) is investigated via density functional theory (DFT) calculations. Through comprehensive screening, two promising single-atom catalysts (SACs), Sc@β12-BM and Y@β12-BM, are successfully identified, exhibiting high stability, catalytic activity and selectivity for the CO2RR. The C1 products methane (CH4) and methanol (CH3OH) are synthesized with limiting potentials (UL) of -0.78 V and -0.56 V on Sc@β12-BM and Y@β12-BM, respectively. Meanwhile, CO2 is more favourable for reduction into the C2 product ethanol (CH3CH2OH) compared to ethylene (C2H4) via C-C coupling on these two SACs. More importantly, the dynamic barriers of the key C-C coupling step are 0.53 eV and 0.73 eV for the "slow-growth" sampling approach in the explicit water molecule model. Furthermore, Sc@β12-BM and Y@β12-BM exhibit higher selectivity for producing C1 compounds (CH4 and CH3OH) than C2 (CH3CH2OH) in the CO2RR. Compared with Sc@β12-BM, Y@β12-BM demonstrates superior inhibition of the competitive hydrogen evolution reaction (HER) in the liquid phase. These results not only demonstrate the great potential of SACs for direct reduction of CO2 to C1 and C2, but also help in rationally designing high-performance SACs.

Inert is not inactive: origin of carbon dioxide electroreduction activity over a carbon current collector-based electrode

Commercial carbon paper (CP), a classical current collector, does not remain inert when subjected to CO2 electroreduction in a non-aqueous electrolyte.

A defective bismuth–indium catalyst promotes water dissociation for selective carbon dioxide electroreduction to HCOOH

A defective BiIn bimetallic catalyst derived from a P-doped BiIn pre-catalyst is developed, which enables CO2 conversion to HCOOH with high activity and selectivity.

Electroreduction of carbon dioxide (CO2) with flow cell system using tin-modified copper foam electrode

In this study, modification of the copper foam (Cuf) electrode with tin (Sn) was carried out with the electrodeposition method for application in CO2 electroreduction. Characterization using SEM EDX, FTIR, and XRD confirmed the presence of Cu2O, CuO, and SnO2 thin layer mixture on the Cuf/Sn electrode. The electrochemical characteristics of the electrode were examined by using the cyclic voltammetry (CV) technique. Under optimized conditions, electrochemical reduction of CO2 in a flow cell system. At the optimum condition of CO2 reduction in a flow cell system (flow rate of 75 mL/min and –0.6 V vs Ag/AgCl applied potential), the Cuf/Sn electrode exhibited a remarkable 75.79% with an 8.84 µmol/h formic acid production rate. In a comparable experiment, the Cuf/Sn flow system revealed a twofold improvement in the faradaic efficiency compared to the batch system and a threefold increase compared to the unmodified Cuf electrode in the flow system. Stability tests demonstrated consistent performance up to the 4th cycle, followed by a decline in the 5th cycle, potentially indicative of surface deterioration. The elevated performance is attributed to the synergistic effect of the Cu-Sn oxide layer, reinforcing the catalyst’s potential for efficient electrochemical CO2 reduction to formic acid.

(Invited) Stabilization and Activation of Copper(I)-Oxide-Semiconducting Interfaces for Photoelectrochemical Reduction of Carbon Dioxide

Electroreduction of carbon dioxide to simple organic fuels and chemicals is a topic of growing scientific and technological interest. The reaction provides means for both reducing emissions of CO2 into atmosphere and storing renewable energy. The presentation will address low-temperature CO2-conversion processes based on electrocatalytic and photoelectrochemical approaches. Among important issues are choice of the catalytic or semiconducting materials, their morphology and operating conditions including temperature, solvent, electrolyte, pH etc. There is a need to improve the reaction dynamics and selectivity toward specific products. In practical electrolysis cells, the CO2-reduction (at cathode) is accompanied by water oxidation (at anode or photoanode).Recently, we have concentrated on the development of hybrid materials by utilizing combination of metal oxide semiconductors thus capable of effective photoelectrochemical reduction of carbon dioxide. For example, the combination of conducting polymers, or titanium (IV) oxide, and copper (I) oxide has been considered before and after sunlight illumination. Application of the hybrid system composed of both above-mentioned oxides resulted in high current densities originating from photoelectrochemical reduction of carbon dioxide mostly to methanol (CH3OH) as demonstrated upon identification of final products. Among important issue is intentional stabilization, activation, and functionalization of the mixed-metal-oxide-based photoelectrochemcal interface toward better long-term performance and selectivity production of small organic molecules (C1-C4) and other chemicals. In this respect, ultra-thin films of conducting polymers (simple or polyoxometallate-derivatized) and supramolecular complexes (with nitrogen containing ligands and certain transition metal sites), sub-monolayers of metals (Cu, Au), networks of noble metal (Au, Ag) nanoparticles or layers of robust bacterial biofilms have been considered. The photobiocathode utilizing robust biofilms have also been demonstrated to stabilize copper(I) oxide surfaces and to induce the system’s activity toward reduction of carbon dioxide under illuminations with visible light.In the presentation, special attention will be paid to the mechanistic aspects of electroreduction of carbon dioxide, fabrication and characterization of highly selective and durable semiconductor photoelectrode materials and to the importance of the reaction conditions.

Carbon Supported Pd Nanostructures for Electrochemical Reduction of Carbon Dioxide – Effects of Ozonation

Out of the transition metals capable of electrochemical carbon dioxide reduction, Pd is interesting as it can convert carbon dioxide electrochemically into formate or carbon monoxide depending on the applied potential. In fact, it is capable of producing formate at the most positive known potentials that are close to zero overpotentials although at an unfortunately low activity and at the cost of deactivation by carbon monoxide poisoning. One aim is to improve the activity and stability of Pd-based electrocatalysts towards formate production in low overpotentials. As Pd is a critical raw material, we also wish to decrease the amount of Pd required while maintaining high carbon dioxide electroreduction capability. These goals can be achieved by nanostructuring and supporting the Pd catalyst. Here, we have employed a simple wet impregnation synthesis approach to prepare small nanoparticles and nanowires of Pd supported on single walled carbon nanotubes and tested the optimum loading of Pd to obtain high formate yield with improved activity and stability. Reactive sites can be created on the carbon support by subjecting it to ozonation prior to supporting the metal, which may help certain interesting nanostructures, such as nanowires, to grow. Additionally, the oxygen functional groups on the carbon surface are expected to affect the wettability of the electrode which is important for achieving an efficient carbon dioxide electroreduction and a longer-term stability of the reaction. Therefore, we also studied the effects of ozonation of the carbon supports on the electrochemical reduction of carbon dioxide into both formate and syngas (mixture of hydrogen and carbon monoxide) on Pd. Carbon atoms inevitably participate in hydrogen evolution reaction and, thus, in syngas production on Pd-supported catalysts at higher overpotentials. Our results show that ozonation greatly enhances the activity of the catalyst material and improves its stability when applying low overpotentials for formate formation in comparison to the pristine carbon support. The current density on Pd supported ozone treated carbon nanotube material remains stable over 4h of carbon dioxide electrolysis at an applied potential of -0.45 V (vs. RHE) while Pd on pristine carbon support deactivates during the initial 30 min of the experiment. Longer electrolysis times do reveal slow changes in product distribution although activity on ozone-treated single walled carbon nanotube-supported catalyst is excellent. Additionally, the different support materials cause interesting changes in product selectivity upon applying higher overpotentials for the production of syngas. Pd supported on pristine nanotubes produces syngas with carbon monoxide-to-hydrogen ratios of 0.72 and 1.38 at applied potentials of -0.85 V (vs. RHE) and -0.95 V (vs. RHE), respectively, while ozone treated material produces less than 10% of carbon monoxide. Through physico-chemical characterizations of the materials we aim at understanding the observed changes in electrochemical reduction of carbon dioxide on carbon supported Pd nanostructures.

Surface Dual-Modification of Nano-Cu2o for Controlling CO2 Electrochemical Reduction to Ethylene and Syngas

Carbon dioxide (CO2) is an important substance in the natural carbon cycle, and the gradual increase of CO2 emissions has exceeded the amount that can be absorbed by the nature, which has brought a huge impact on climate conditions and ecological environment. In addition, CO2 is an important C1 resource, and it is of great significance to convert it by electrochemical methods to important chemical raw materials (such as ethylene and syngas) needed for human life. Cu2O is an ideal electrocatalyst due to its relatively low cost and unique product selectivity, as well as the abundant Cu reserves on the earth. However, there is still a lack of systematic studies on the improvement of the C2H4 selectivity of Cu2O-based catalyst and the regulation of product selectivity.In this work, different exposed facet nano-Cu2O were obtained by induction of reducing agent. Combined with in-situ characterization and theoretical calculation, it was found that the terrace × step structure (332) crystal surface can significantly reduce the free energy of C-C coupling process, and greatly improve the selectivity of electrochemical CO2 reduction to C2H4, which is the highest value (74.1%) obtained by Cu2O based catalyst with neutral electrolyte.Subsequently, the ZIF-8 shell is introduced in-situ on the surface of Cu2O nanoparticles. The coated ZIF-8 shell effectively regulates the hydrophilic and hydrophobic environment of the material, and provides a material exchange channel for reactants and product molecules simultaneously, which promote the desorption of CO molecules and improve the adsorption of CO2, realizing the switch of product from C2H4 to syngas.In carbon dioxide reduction, it is an important strategy to modify the surface of metal/metal oxide by interface engineering to regulate the microenvironment at the reaction interface. In this paper, from the aspects of material design, synthesis and regulation of reaction products, the great advantages of facet structure and MOFs for improving the stability and activity of catalyst are demonstrated. Combined with in situ characterization and theoretical calculation, a new idea is provided for the design of efficient carbon dioxide electroreduction catalyst in the future. Figure 1

What Is Needed for Industrial Carbon-Dioxide Electroreduction: From Electrode Development to Process Optimization

Electrochemical reduction of CO2 is a promising method for converting a greenhouse gas into value-added products, utilizing renewable energy. Novel catalysts, electrode assemblies, and cell configurations are all necessary to achieve economically appealing performance. In this talk, I am going to present a zero gap electrolyzer cell, which converts gas phase CO2 to products without the need for any liquid catholyte. This is the first report of a CO2 electrolyzer cell, where multiple cells are connected into a stack, thus scaling up the electrolysis process. I will show how proper cell components and operational conditions result in unprecedentedly high partial current densities in zero-gap cells. I will demonstrate the role of each component of the membrane electrode assembly, such as the catalysts, the porous transport layers, the membrane, and the ionomers.In the second part of my talk, I will show that while precipitate formation in the cathode gas diffusion electrode is detrimental for the long-term stability, the presence of alkali metal cations at the cathode improves performance. To overcome this contradiction, I will present different approaches which help to extend the lifetime of the electrolyzer cell. As an outlook, I will present a complex machine learning based approach, through which we aim to find the optimal operating conditions of such CO2 electrolyzer cells.

Improving Stability of CO2 Electroreduction by Incorporating Ag NPs in N-Doped Ordered Mesoporous Carbon Structures.

The electroreduction of carbon dioxide (eCO2RR) to CO using Ag nanoparticles as an electrocatalyst is promising as an industrial carbon capture and utilization (CCU) technique to mitigate CO2 emissions. Nevertheless, the long-term stability of these Ag nanoparticles has been insufficient despite initial high Faradaic efficiencies and/or partial current densities. To improve the stability, we evaluated an up-scalable and easily tunable synthesis route to deposit low-weight percentages of Ag nanoparticles (NPs) on and into the framework of a nitrogen-doped ordered mesoporous carbon (NOMC) structure. By exploiting this so-called nanoparticle confinement strategy, the nanoparticle mobility under operation is strongly reduced. As a result, particle detachment and agglomeration, two of the most pronounced electrocatalytic degradation mechanisms, are (partially) blocked and catalyst durability is improved. Several synthesis parameters, such as the anchoring agent, the weight percentage of Ag NPs, and the type of carbonaceous support material, were modified in a controlled manner to evaluate their respective impact on the overall electrochemical performance, with a strong emphasis on operational stability. The resulting powders were evaluated through electrochemical and physicochemical characterization methods, including X-ray diffraction (XRD), N2-physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy (SEM-EDS), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-EDS, electron tomography, and X-ray photoelectron spectroscopy (XPS). The optimized Ag/soft-NOMC catalysts showed both a promising selectivity (∼80%) and stability compared with commercial Ag NPs while decreasing the loading of the transition metal by more than 50%. The stability of both the 5 and 10 wt % Ag/soft-NOMC catalysts showed considerable improvements by anchoring the Ag NPs on and into a NOMC framework, resulting in a 267% improvement in CO selectivity after 72 h (despite initial losses) compared to commercial Ag NPs. These results demonstrate the promising strategy of anchoring Ag NPs to improve the CO selectivity during prolonged experiments due to the reduced mobility of the Ag NPs and thus enhanced stability.

Low cost 3D printable flow reactors for electrochemistry

Transition to carbon neutrality requires the development of more sustainable pathways to synthesize the next generation of chemical building blocks. Electrochemistry is a promising pathway to achieve this goal, as it allows for the use of renewable energy to drive chemical transformations. While the electroreduction of carbon dioxide (CO2) and hydrogen evolution are attracting significant research interest, fundamental challenges exist in moving the research focus toward performing these reactions on scales relevant to industrial applications. To bridge this gap, we aim to facilitate researchers' access to flow reactors, which allow the characterization of electrochemical transformations under conditions closer to those deployed in the industry. Here, we provide a 3D-printable flow cell design (manufacturing cost < $5), which consists of several plates, offering a customizable alternative to commercially available flow reactors (cost > $6,000). The proposed design and detailed build instructions allow the performance of a wide variety of chemical reactions in flow, including gas and liquid phase electroreduction, electro(less)plating, and photoelectrochemical reactions, providing researchers with more flexibility and control over their experiments. By offering an accessible, low-cost reactor alternative, we reduce the barriers to performing research on sustainable electrochemistry, supporting the global efforts necessary to realize the paradigm shift in chemical manufacturing.

FeOOH with Low Spin State Iron as Electron Acceptors for High Yield Rate Electrosynthesis of Urea from Nitrate and Carbon Dioxide.

Co electroreduction of carbon dioxide and nitrate to synthesize urea provides an alternative strategy to high energy-consumption traditional methods. However, the complexity of the reaction mechanism and the high energy barrier of nitrate reduction result in a diminished production of urea. Herein, a convenient electrodeposition technique to prepare the FeOOH with low spin state iron that increases the yield rate of urea efficiently is employed. According to soft X-ray Absorption Spectroscopy and theoretical calculations, the unique configuration of low spin state iron as electron acceptors can effectively induce electron pair transfer from the occupied σ orbitals of intermediate * NO to empty d orbitals of iron. This σ→d donation mechanism leads to a reduction in the energy barrier associated with the rate-determining step (* NOOH→* NO+* OH), hence augmenting the urea generation. The low spin state iron presents a high urea yield rate of 512µgh-1 cm-2 , representing approximately two times compared to the medium spin state iron. The key intermediates (* NH2 and * CO) in the formation of C─N bond are detected with in situ Fourier transform infrared spectroscopy. The coupling of * NH2 and * CO contributes to the formation of * CONH2 , which subsequently endures multi-step proton-coupled electron transfer to generate urea.

Coupled electroreduction of CO&lt;sub&gt;2&lt;/sub&gt; and H&lt;sup&gt;+&lt;/sup&gt; in the presence of substituted salts of 2,2'-bipyridine

The possibility of conjugate electroreduction of carbon dioxide and hydrogen in the presence of 2,2'-bipyridine and its N -substituted salts in the presence of acids with different pKa values was studied. It was revealed how the strength of the acid affects the efficiency of the process; in particular, it was determined that the presence of methylsulfonic acid in the system promotes the conjugate formation of hydrogen and the reduction of carbon dioxide to formic acid. Probable mechanisms for the reactions occurring have been proposed.

In-Induced Electronic Structure Modulations of Bi─O Active Sites for Selective Carbon Dioxide Electroreduction to Liquid Fuel in Strong Acid.

The formation of carbonate in neutral/alkaline solutions leads to carbonate crossover, severely reducing carbon dioxide (CO2 ) single pass conversion efficiency (SPCE). Thus, CO2 electrolysis is a prospective route to achieve high CO2 utilization under acidic environment. Bimetallic Bi-based catalysts obtained utilizing metal doping strategies exhibit enhanced CO2 -to-formic acid (HCOOH) selectivity in alkaline/neutral media. However, achieving high HCOOH selectivity remains challenging in acidic media. To this end, Indium (In) doped Bi2O2CO3 via hydrothermal method is prepared for in-situ electroreduction to In-Bi/BiOx nanosheets for acidic CO2 reduction reaction (CO2RR). In doping strategy regulates the electronic structure of Bi, promoting the fast derivatization of Bi2O2CO3 into Bi-O active sites to enhance CO2RR catalytic activity. The optimized Bi2 O2 CO3 -derived catalyst achieves the maximum HCOOH faradaic efficiency (FE) of 96% at 200 mA cm-2 . The SPCE for HCOOH production in acid is up to 36.6%, 2.2-fold higher than the best reported catalysts in alkaline environment. Furthermore, in situ Raman and X-ray photoelectron spectroscopy demonstrate that In-induced electronic structure modulation promotes a rapid structural evolution from nanobulks to Bi/BiOx nanosheets with more active species under acidic CO2 RR, which is a major factor in performance improvement.