Electrochemical Conversion Of CO2 Research Articles

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

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

Electrochemical Characterization of Nickel / Gadolinia Doped Ceria Fuel Electrodes under H2/H2O/CO/CO2-Atmospheres

Abstract Modelling of the co-electrolysis process requires understanding of the underlying reaction pathways under H2/H2O/CO/CO2-atmospheres. These include the electrochemical steam reduction/hydrogen oxidation, the electrochemical CO2 reduction/CO oxidation and their coupling via the catalytic (reverse) water gas shift reaction ((R)WGS). The assumption of a very fast RWGS and therefore neglectable electrochemical CO2 conversion is commonly used to model the co-electrolysis process. In contrast, previous studies on Ni/GDC fuel electrodes suggest that the electrochemical conversion of CO / CO2 can be present in H2/H2O/CO/CO2-atmospheres. To deconvolute surface-related and non-surface-related processes in the impedance response we present results from a complex variation of operating parameters for process identification by the use of electrochemical impedance spectroscopy and the subsequent impedance analysis by the distribution of relaxation times. A physically meaningful equivalent circuit model, based on a single channel transmission line, is then derived. The model enables quantification of the surface reaction resistance under varied C/H-ratios. From a kinetic analysis it is shown that the electrochemical H2/H2O conversion is dominant for y_CO+y_(CO_2 )≤ 50% and electrochemical CO/CO2-conversion onsets from y_CO+y_(CO_2 )≥ 60%.

Visualizing Electrochemical CO2 Conversion via the Emerging Scanning Electrochemical Microscope: Fundamentals, Applications and Perspectives.

With the rapid development and maturity of electrochemical CO2 conversion involving cathodic CO2 reduction reaction (CO2RR) and anodic oxygen evolution reaction (OER), conventional ex situ characterizations gradually fall behind in detecting real-time products distribution, tracking intermediates, and monitoring structural evolution, etc. Nevertheless, advanced in situ techniques, with intriguing merits like good reproducibility, facile operability, high sensitivity, and short response time, can realize in situ detection and recording of dynamic data, and observe materials structural evolution in real time. As an emerging visual technique, scanning electrochemical microscope (SECM) presents local electrochemical signals on various materials surface through capturing micro-current caused by reactants oxidation and reduction. Importantly, SECM holds particular potentials in visualizing reactive intermediates at active sites and obtaining instantaneous morphology evolution images to reveal the intrinsic reactivity of active sites. Therefore, this review focuses on SECM fundamentals and its specific applications toward CO2RR and OER, mainly including electrochemical behavior observation on local regions of various materials, target products and onset potentials identification in real-time, reaction pathways clarification, reaction kinetics exploration under steady-state conditions, electroactive materials screening and multi-techniques coupling for a joint utilization. This review undoubtedly provides a leading guidance to extend various SECM applications to other energy-related fields.

Boosting electrochemical conversion of CO2 to ethanol through the confinement of pyridinic N-B layer on copper nanoparticles

Developing efficient electrocatalysts for CO2 reduction has gained significant attention in the field of sustainable energy, especially the Cu-based catalysts for CO2 conversion to valuable alcohols. In this study, we developed Cu nanoparticles supported on pyridinic N-B doped graphene nanoribbons/amorphous carbon (Cu/BNC-1) as an electrocatalyst for CO2 reduction, exhibiting substantially improved ethanol (EtOH) conversion rate in terms of activity, selectivity, and stability. The Cu/BNC-1 achieved a remarkable 58.64 % Faradaic efficiency (FE) for producing EtOH at −1.0 V vs. RHE with a current density of 20.4 mA cm−2 in 0.5 M KHCO3 electrolyte. In-situ Raman, FT-IR, and density functional theory (DFT) calculations demonstrated that the high C2+ product selectivity of Cu/BNC-1 attributed to the pyridinic N-B modulation, lowering the CO dimerization barrier. Moreover, the synergistic confinement effect of Cu and BNC can stabilize the C-O bond of the *HOCCH intermediate, thereby increasing the yield of EtOH.

Electrochemical and Catalytic Conversion of CO2 into Formic Acid on Cu-InO2 Nano alloy Decorated on Reduced Graphene Oxide (Cu-InO2@rGO)

Electrochemical and Catalytic Conversion of CO2 into Formic Acid on Cu-InO2 Nano alloy Decorated on Reduced Graphene Oxide (Cu-InO2@rGO)

Electrodeposition of Cu with Amino Acids toward Electrocatalytic Enhancement of CO2 Reduction Reaction

This study investigates the effect of five amino acids on the electrodeposition of Cu to enhance its electrocatalytic performance in CO2 reduction reactions (CO2RR). The amino acids significantly influenced the deposition potential, crystallite size, and surface morphology of the electrodeposited Cu. Electrodeposited Cu with amino acids exhibit significantly smaller crystallites and higher particle density on carbon paper relative to amino acid-free samples. The integration of amino acids into the electrodeposited Cu was confirmed via high-angle annular dark-field scanning transmission electron microscopy, energy dispersive X-ray spectroscopy and hard X-ray photoelectron spectroscopy. All electrodeposited Cu exhibits a higher faradaic efficiency (FE) in the electrochemical reduction of CO2 to CH4 relative to Cu foil (24.2%), regardless of the presence or absence (55.0%) of amino acids when the electrolysis was conducted at −1.27 V vs RHE. Electrodeposited Cu with L-histidine, containing an imidazole group, demonstrates a higher FE of CH4 (67.6%) and effectively suppressed the hydrogen evolution reaction, highlighting the crucial role of amino acid functional groups, particularly imidazole, in augmenting the electrochemical conversion of CO2 to CH4. The study demonstrates the critical influence of specific functional groups in amino acids on the catalytic efficiency of electrodeposited Cu in CO2RR electrocatalysis applications.

Evolution of bismuth electrodes activating electrosynthesis of formate from carbon dioxide reduction

Electrochemical conversion of CO2 into valuable chemicals and fuels has emerged as a promising approach to achieving the net-zero emission target. In this work, bismuth (Bi)-based gas diffusion electrodes (GDEs) are prepared via scalable inkjet printing of the precursor on carbon papers, and subsequent thermal treatment. The optimization of the GDEs aims at the efficient CO2 reduction to formate (HCOO−) with good selectivity and high current density. Ex situ FESEM, XRD, and XPS analyses evidence the morphological and structural transformations of Bi-based catalysts during electrolysis. In situ Raman spectroscopy illustrates the dynamic evolution of the electrocatalysts in a range of potentials. The complete procedure is represented as the transformation of Bi2O3 polyhedral microcrystals to a flower-like assembly of Bi2O2CO3 nanoflakes when exposed to KHCO3 electrolyte under electrochemical conditions, and then to metallic Bi at more negative potentials (< −0.6 V vs. RHE). The evolution of Bi-GDEs confirms that metallic Bi nanostructure provides abundant active sites for selective conversion of CO2 to HCOO−, and is highly promising for applications at industrially relavant scales.

Cathode Surface pH Modulates Multicarbon Product Selectivity during the Electrochemical Conversion of CO2 Capture Solutions

Cathode Surface pH Modulates Multicarbon Product Selectivity during the Electrochemical Conversion of CO₂ Capture Solutions

Extrinsic hydrophobicity-controlled silver nanoparticles as efficient and stable catalysts for CO2 electrolysis.

To realize economically feasible electrochemical CO2 conversion, achieving a high partial current density for value-added products is particularly vital. However, acceleration of the hydrogen evolution reaction due to cathode flooding in a high-current-density region makes this challenging. Herein, we find that partially ligand-derived Ag nanoparticles (Ag-NPs) could prevent electrolyte flooding while maintaining catalytic activity for CO2 electroreduction. This results in a high Faradaic efficiency for CO (>90%) and high partial current density (298.39 mA cm‒2), even under harsh stability test conditions (3.4 V). The suppressed splitting/detachment of Ag particles, due to the lipid ligand, enhance the uniform hydrophobicity retention of the Ag-NP electrode at high cathodic overpotentials and prevent flooding and current fluctuations. The mass transfer of gaseous CO2 is maintained in the catalytic region of several hundred nanometers, with the smooth formation of a triple phase boundary, which facilitate the occurrence of CO2RR instead of HER. We analyze catalyst degradation and cathode flooding during CO2 electrolysis through identical-location transmission electron microscopy and operando synchrotron-based X-ray computed tomography. This study develops an efficient strategy for designing active and durable electrocatalysts for CO2 electrolysis.

Local CO Generator Enabled by a CO-Producing Core for Kinetically Enhancing Electrochemical CO2 Reduction to Multicarbon Products.

CO plays a crucial role as an intermediate in electrochemical CO2 conversion to generate multicarbon (C2+) products. However, optimizing the coverage of the CO intermediate (*CO) to improve the selectivity of C2+ products remains a great challenge. Here, we designed a hierarchically structured double hollow spherical nanoreactor featuring atomically dispersed nickel (Ni) atoms as the core and copper (Cu) nanoparticles as the shell, which can greatly improve the catalytic activity and selectivity for C2+ compounds. Within this configuration, CO generated at the active Ni sites on the inner layer accumulates in the cavity before spilling over neighboring Cu sites on the outer layer, thus enhancing CO dimerization within the cavity. Notably, this setup achieves a sustained faradaic efficiency of 74.4% for C2+ production, with partial current densities reaching 337.4 mA cm-2. In situ Raman spectroscopy and finite-element method (FEM) simulations demonstrate that the designed local CO generator can effectively increase the local CO concentration and restrict CO evolution, ultimately boosting C-C coupling. The hierarchically ordered architectural design represents a promising solution for achieving highly selective C2+ compound production in the electroreduction of CO2.

Performance of Transition Metals in Imidazolium‐Assisted CO2 Reduction in Acetonitrile

AbstractThis study explores the electrochemical reduction of CO2 in dry acetonitrile containing 1,3‐dimethyl imidazolium cations, utilizing late‐transition metals (Au, Ag, Zn, Cu, and Ni). All metals exhibit remarkable selectivity, nearing 100 %, for CO formation. Particularly noteworthy is Au, which manifests the lowest (−2.37 V vs. Ag/Ag+) overpotential in chronopotentiometry experiments. We propose that, for metals with lower CO binding energies compared to Au (Ag and Zn electrodes) – calculated by DFT, the rate‐determining step is the adsorption of CO2. This distinction in CO2 adsorption is reinforced by the examination of partial charge transfer from negatively charged slabs to CO2 (−0.241 a.u with the Au electrode and +0.002 a.u with the Zn electrode). Conversely, the greater CO binding energy calculated for Cu and Ni likely diminishes electrocatalytic activity relative to the Au electrode. Our results unveil a volcano trend in catalyst activity, albeit with smaller performance disparities between the late‐transition metals and Au than previously observed in aqueous conditions, possibly due to the co‐catalytic influence of imidazolium cations. This study suggests that metals unsuitable for aqueous environments hold promise for cost‐effective and viable electrochemical conversion of CO2 to CO in non‐aqueous media containing imidazolium compounds.

Process Cascade for the Production of Green Polymers from CO2 and Electric Energy

AbstractProduction processes based on CO2 as raw material offer high scalability and sustainability. Here, a novel process cascade is introduced, combining the advantages of electrochemical CO2 conversion with the synthetic potential of industrial biotechnology: CO2 is electrocatalytically reduced to formic acid as substrate for the metabolically engineered bacterium Methylorubrum extorquens that produces l‐lysine as precursor of the polymer building block 1,5‐diaminopentane (cadaverine). Cadaverine is purified through targeted downstream processing and finally used in a polycondensation process to produce polyamide materials.

Strong electric field at the sharp tips of Cu(OH)2 nanochrysanthemums for selective electrochemical CO2 conversion into ethylene

Electrochemical CO2 reduction reaction (CO2RR) is an attractive approach for the mitigation of CO2 emissions and the production of value-added chemicals. However, it remains a challenge to achieve high selectivity of desirable C2 products like ethylene (C2H4) with high economic value and large market. Herein, we report the fabrication of unprecedented Cu(OH)2 nanochrysanthemums catalyst layer (CL). Interestingly, Cu(OH)2 nanochrysanthemums CL exhibits a C2H4 Faradaic efficiency (FE) of 51.2 ± 0.5% and a FE(C2H4+C2H5OH) of 70.0 ± 0.5% in pH nearly neutral electrolytes. It is worth mentioning that Cu(OH)2 nanochrysanthemums CL achieves the highest FEC2 among documented Cu(OH)2 electrocatalysts. The high FEC2H4 and FEC2 can be attributed to the high electrochemical surface area (ECSA, 21.9 mF/cm2) of Cu(OH)2 nanochrysanthemums. In addition, the wellbalanced hydrophilicity-hydrophobicity of the Cu(OH)2 nanochrysanthemums CL also contributes to the high FEC2H4 and FEC2 by simultaneously satisfying efficient transfer of hydrophobic CO2 and C2H4 as well as hydrophilic H2O and C2H5OH. COMSOL multiphysics simulations and density functional theory (DFT) calculations further suggest that the negatively charged sharp tips of Cu(OH)2 nanochrysanthemums would trigger the accumulation of K+ and offer strong local electric field of 9.8 V/μm, promoting C–C coupling and suppressing hydrogen evolution reaction (HER).

Hollow carbon sphere featuring highly dispersed Co-Nx sites for efficient and controllable syngas electrosynthesis from CO2

Electrochemical reduction of CO2 and H2O powered by green electricity provides a sustainable way to produce syngas. However, this reaction still suffers from insufficient syngas selectivity, slow charge kinetic process, and poor controllability of the CO/H2 ratio. In this work, we report a hollow carbon sphere electrocatalyst featuring highly dispersed Co-Nx sites (Co-NHCS-x) for efficient and controllable syngas electrosynthesis. The Co-NHCS-400 sample exhibits a high syngas production rate with a steady CO/H2 ratio (≈1:2) over a wide range of operating potential from −0.6 V to −1.1 V vs. RHE. The variation in synthesis temperature can finely tune the coordination environment of Co-Nx in the catalyst. Consequently, the adsorption behaviors of the CO and hydrogen atoms can be manipulated, allowing for the precise adjustment of CO and H2 proportions in the product gas. The findings are potentially applicable to the exploitation of promising carbon-based electrocatalysts for electrochemical CO2 conversion into syngas.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction.

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Achieving high selectivity and activity of CO2 electroreduction to formate by in-situ synthesis of single atom Pb doped Cu catalysts

Exploring highly selective and stable electrocatalysts is of great significance for the electrochemical conversion of CO2 into fuel. Herein, a three-dimensional (3D) nanostructure catalyst was developed by doping Pb single-atom (PbSA) in-situ on carbon paper (PbSA100-Cu/CP) through a low-energy and economical method. The designed catalyst exhibited abundant active sites and was beneficial to CO2 adsorption, activation, and subsequent conversion to fuel. Interestingly, PbSA100-Cu/CP showed a prominent Faraday efficiency (FE) of 97 % at –0.9 V versus reversible hydrogen electrode (vs. RHE) and a high partial current density of 27.9 mA·cm−2 for formate. Also, the catalyst remained significantly stable for 60 h during the durability test. The reaction mechanism was investigated by density functional theory (DFT), demonstrating that the doping PbSA induced the electrons redistribution, promoted the formate generation, reduced the rate-determining step (RDS) energy barrier, and inhibited the hydrogen evolution reaction. The study aims to provide a new strategy for developing of single-atom catalysts with high selectivity and stability, which will help reduce environmental pressure and alleviate energy problems.

Mastering the Lattice Strain in Bismuth‐Based Electrocatalysts for Efficient CO2‐to‐Formate Conversion

AbstractTuning the lattice strain of catalysts represents a powerful strategy to alter their electronic structures and ultimately regulate catalytic performance. Electrocatalytic CO2 reduction is a promising avenue to accomplish the carbon‐neutral cycle, however, there still lacks a distinct and systematic understanding of the lattice strain effect in CO2 electrochemical conversion. In this work, the influence of lattice strain on Bi (012) facets to formate production is studied. The pre‐executed density functional theory (DFT) calculations reveal that lattice compression promotes the wrinkling of exposed Bi surface and increases the total density of state (DOS) of active sites at the Fermi level. As the gradual intensification of lattice contraction, the selectivity of CO2 reduction exhibits a volcanic alteration, with an optimal lattice contraction of 3%. Experimentally synthesized Bi2O2CO3/Bi heterogeneous catalyst confirms the effect of lattice compression. When compression reaches −3.04% on Bi (012) facets, the catalyst possesses the highest Faraday efficiency (FE) of 96.17% at −1.2 VRHE and an industrially scalable current density of −600 mA cm−2. Additionally, in seawater‐based electrolysis, the catalyst also exhibits excellent remarkable FE of 95.43% of formate production.

Low‐Voltage Acidic CO2 Reduction Enabled by a Diaphragm‐Based Electrolyzer

AbstractLarge‐scale implementation of electrochemical CO2 conversion to value‐added products is currently hampered by high electrolyzer cell voltages, resulting in low energy efficiency and high operating costs. Cell voltages are typically well above 3 V and need to be significantly lowered whilst maintaining current densities greater than 200 mA cm−2 to enable energy‐efficient CO2 electroreduction. This can be addressed through modification of the resistive components of the device to reduce energy consumption and lower operating costs. Electrodes, electrolyte solutions, and the separator between compartments, provide the largest contributions to the overall cell voltage, therefore decreasing their resistance can lower the electricity input required to drive effective CO2 conversion. Here, by careful analysis and tuning of the various sources of voltage drops within the cell, an optimized diaphragm‐based CO2R device is presented, which is able to operate at an industrially relevant current density of 200 mA cm−2 with an |Ecell| as low as 2.89 V, amongst the lowest reported values to date.

Experimental and first-principles insights into an enhanced performance of Ru-doped copper phosphate electrocatalyst during oxygen evolution reaction

The oxygen evolution reaction (OER) is a vital half-reaction in many applications, such as the electrochemical H2O splitting, CO2, and N2 conversion processes. The OER involves a four-electron transfer and is a kinetically sluggish reaction that requires additional potential to drive. To enhance the electrochemical performance of the above-mentioned applications, highly efficient, corrosion-resistant, earth-abundant, and eco-friendly electrocatalysts are required. Here, we report a highly porous, minimally Ru-doped copper phosphate electrocatalyst obtained through co-precipitation. The optimized electrocatalyst (5% Ru-doped copper phosphate) exhibits a low overpotential of 340 mV to achieve 10 mA cm−2 compared to copper-based materials, and it remains stable over 20 h. The high performance is attributed to a high electrochemically effective surface area (ECSA) of 30.25 cm2, facilitating effective ion transportation at the electrode/electrolyte interface and excellent electrical conductivity. This result is supported by density functional theory calculations, which demonstrate that ruthenium enhances the electrochemical properties by increasing electronic conductivity, reducing the theoretical overpotential, and influencing the rate-determining step of the oxygen evolution reaction. Herein, the electrocatalyst is attractive for commercialization due to its utilization of minimal ruthenium in earth-abundant electrocatalysts, which offer competitive performance.

1 nm Tin Oxide Cluster for the Electrochemical Conversion of Carbon Dioxide to Formate at Low Overpotential

Due to its cost-effectiveness and high product selectivity, tin oxide has been regarded as a promising catalyst for the electrochemical conversion of CO2 to formate. However, formate production is hindered by the high overpotential; there is a need to reduce the overpotential to enhance energy efficiency and lower electricity cost for the implementation of carbon utilization technology. Here, we report a facile synthesis method for 1 nm-sized SnO2 cluster catalysts, which can be used for CO2-to-formate conversion. SnO2 clusters were prepared through impregnation of porous carbon with a tin precursor solution. The SnO2 clusters showed a low overpotential, generating a current density of 10 mA cm-2 at a potential of -0.34 V vs. RHE in 1 M KOH. They also achieved high Faradaic efficiencies of 90.5% and 81.5% at 200 and 300 mA cm−2, respectively. Their electrocatalytic performance was strongly dependent on the annealing conditions, which affected the particle size, electrochemical active surface area, and metal oxidation state. This paper presents a versatile method for synthesizing metal oxide cluster catalysts, apart from providing insights into the catalytic activity for the electrochemical conversion of CO2 to formate.