CO2 Electrolysis Research Articles

In Situ Self-Assembled Active and Stable Ir@MnOx/La0.7Sr0.3Cr0.9Ir0.1O3-δ Interfaces for CO2 Electrolysis.

Solid oxide electrolysis cells are prospective approaches for CO2 utilization but face significant challenges due to the sluggish reaction kinetics and poor stability of the fuel electrodes. Herein, we strategically addressed the long-standing trade-off phenomenon between enhanced exsolution and improved structural stability via topotactic ion exchange. The surface dynamic reconstruction of the MnOx/La0.7Sr0.3Cr0.9Ir0.1O3-δ (LSCIr) catalyst was visualized at the atomic scale. Compared with the Ir@LSCIr interface, the in situ self-assembled Ir@MnOx/LSCIr interface exhibited greater CO2 activation and easily removable carbonate intermediates, thus reached a 42 % improvement in CO2 electrolysis performance at 1.6 V. Furthermore, an improved CO2 electrolysis stability was achieved due to the uniformly wrapped MnOx shell of the Ir@MnOx/LSCIr cathode. Our approach enables a detailed understanding of the dynamic microstructure evolution at active interfaces and provides a roadmap for the rational design and evaluation of efficient metal/oxide catalysts for CO2 electrolysis.

Mesh GDEs: An alternative to carbon-based electrodes for CO2 reduction at higher current densities

Scaling up the electrolysis of CO2 to multi-carbon products remains a challenge due to the instability of conventional carbon-based gas diffusion materials at higher current densities. In this study, we investigate the use of a CuMesh-Polytetrafluoroethylene (PTFE) sandwich electrode, which is both scalable and can conduct large amounts of current on account of its metallic structure. Although we showcase CO2RR activity up to –500 mA cm−2, the trends we observe indicate this value can be pushed beyond –1 A cm−2. We find that we can achieve a higher ethylene (C2H4) partial current density by increasing mesh sizes (i.e., smaller pores). Furthermore, 100 h durability tests revealed that both morphological changes and reaction-driven electrolyte contamination are critical for steady C2H4 performance even if flooding is mitigated. Thus, substantial room for optimization exists for future works. To conclude, the mesh based GDE we propose herein opens up possibilities for achieving robust industrial-scale CO2 and CO reduction.

Reinforced chemical adsorption ability for efficient CO2 electrolysis in solid oxide electrolysis cell via a dual-exsolution strategy

Accelerating sluggish kinetics of CO2 reduction reaction (CO2RR) is of great importance for efficiently converting CO2 into valuable chemical products in solid oxide electrolysis cells (SOECs). Here, a novel dual-exsolution strategy is proposed to enhance CO2 electrolysis properties of La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) cathode. With simultaneously exsolved CoFe alloy and Bi nanoparticles on LSCFN cathodic matrix, the as-prepared SOEC delivers a high current density of 539 mA cm−2 for CO2 electrolysis at 800 °C and 1.5 V, and successfully runs over 170 h without any attenuation. The introduction of Bi exsolution not only promotes CoFe exsolution, provides additional oxygen vacancies, but also greatly boost the kinetics of CO2 adsorption/dissociation/activation. This work offers new insights into tailoring perovskite electrocatalysts for the CO2 electrolysis via dual-exsolution strategy.

Contrasting Views of the Electric Double Layer in Electrochemical CO2 Reduction: Continuum Models vs Molecular Dynamics.

In the field of electrochemical CO2 reduction, both continuum models and molecular dynamics (MD) models have been used to understand the electric double layer (EDL). MD often focuses on the region within a few nm of the electrode, while continuum models can span up to the device level (cm). Still, both methods model the EDL, and for a cohesive picture of the CO2 electrolysis system, the two methods should agree in the regions where they overlap length scales. To this end, we make a direct comparison between state-of-the-art continuum models and classical MD simulations under the conditions of CO2 reduction on a Ag electrode. For continuum modeling, this includes the Poisson-Nernst-Planck formulation with steric (finite ion size) effects, and in MD the electrode is modeled with the constant potential method. The comparison yields numerous differences between the two modeling methods. MD shows cations forming two adsorbed layers, including a fully hydrated outer layer and a partial hydration layer closer to the electrode surface. The strength of the inner adsorbed layer increases with cation size (Li+ < Na+ < K+ < Cs+) and with more negative applied potentials. Continuum models that include steric effects predict CO2 to be mostly excluded within 1 nm of the cathode due to tightly packed cations, yet we find little evidence to support these predictions from the MD results. In fact, MD shows that the concentration of CO2 increases within a few Å of the cathode surface due to interactions with the Ag electrode, a factor not included in continuum models. The EDL capacitance is computed from the MD results, showing values in the range of 7-9 μF cm-2, irrespective of the electrolyte concentration, cation identity, or applied potential. The direct comparison between the two modeling methods is meant to show the areas of agreement and disagreement between the two views of the EDL, so as to improve and better align these models.

Cu-In Dual Sites with Sulfur Defects toward Superior Ethanol Electrosynthesis from CO2 Electrolysis.

The electrosynthesis of multi-carbon chemicals from excess carbon dioxide (CO2) is an area of great interest for research and commercial applications. However, improving both the yield of CO2-to-ethanol conversion and the stability of the catalyst at the same time is proving to be a challenging issue. Here it is proposed to stabilize active Cu(I) and In dual sites with sulfur defects through an electro-driven intercalation strategy, which leads to the delocalization of electron density that enhances orbital hybridizations between the Cu-C and In-H bonds. Hence, the energy barrier for the rate-limiting *CHO formation step is reduced toward the key *OCHCHO* formation during ethanol production, which is also facilitated by the combined Cu site enabling C-C coupling and In site with a higher oxygen affinity based on both thermodynamic and kinetic calculations. Accordingly, such dual-site catalyst achieves a high partial current density toward ethanol of 409 ± 15mAcm⁻2 for over 120 h. Furthermore, a scaled-up flow cell is assembled with an industrial-relevant current of 5.7 A for over 36 h, in which the carbon loss is less than 2.5% and single-pass carbon efficiency is ≈19%.

CO2 electrolysis to multi-carbon products in strong acid at ampere-current levels on La-Cu spheres with channels

Achieving satisfactory multi-carbon (C2+) products selectivity and current density under acidic condition is a key issue for practical application of electrochemical CO2 reduction reaction (CO2RR), but is challenging. Herein, we demonstrate that combining microenvironment modulation by porous channel structure and intrinsic catalytic activity enhancement via doping effect could promote efficient CO2RR toward C2+ products in acidic electrolyte (pH ≤ 1). The La-doped Cu hollow sphere with channels exhibits a C2+ products Faradaic efficiency (FE) of 86.2% with a partial current density of −775.8 mA cm−2. CO2 single-pass conversion efficiency for C2+ products can reach 52.8% at −900 mA cm−2. Moreover, the catalyst still maintains a high C2+ FE of 81.3% at −1 A cm−2. The channel structure plays a crucial role in accumulating K+ and OH- species near the catalyst surface and within the channels, which effectively suppresses the undesired hydrogen evolution and promotes C–C coupling. Additionally, the La doping enhances the generation of *CO intermediate, and also facilitates C2+ products formation.

Self-Powered Electrochemical CO2 Conversion Enabled by a Multifunctional Carbon-Based Electrocatalyst and a Rechargeable Zn-Air Battery.

Multifunctional electrocatalysts are required for diverse clean energy-related technologies (e.g., electrochemical CO2 reduction reaction (CO2RR) and metal-air batteries). Herein, a nitrogen and fluorine co-doped carbon nanotube (NFCNT) is reported to simultaneously achieve multifunctional catalytic activities for CO2RR, oxygen reduction reaction (ORR), and oxygen evolution reaction (OER). Theoretical calculations reveal that the superior multifunctional catalytic activities of NFCNT are attributed to the synergistic effect of nitrogen and fluorine co-doping to induce charge redistribution and decrease the energy barrier of rate-determining step for different electrocatalytic reactions. Furthermore, the rechargeable Zn-air battery (ZAB) with NFCNT electrode delivers a high peak power density of 230mWcm-2 and superior durability over 100 cycles, outperforming the ZAB with Pt/C+RuO2 based electrodes. More importantly, a self-driven CO2 electrolysis unit powered by the as-assembled ZABs is developed, which achieves 80% CO Faraday efficiency and 60% total energy efficiency. This work provides a new insight into the exploration of highly efficient multifunctional carbon-based electrocatalysts for novel energy-related applications.

Kilowatt-scale tandem CO2 electrolysis for enhanced acetate and ethylene production

Kilowatt-scale tandem CO2 electrolysis for enhanced acetate and ethylene production

Pre-pilot-scale tandem CO2 electrolysis

Pre-pilot-scale tandem CO2 electrolysis

A 2D Porous Cu3N Catalyst for Efficient CO Electroreduction to Multicarbon Products at an Ampere Level Current Density

AbstractThe maturation of CO2 electrolysis to CO technology has rendered a cascade catalysis scheme, utilizing CO reduction as a media step, a promising strategy to produce high‐value C2+ fuel. However, the current catalysts employed in CO electroreduction (ECORR) face severe hydrogen evolution reactions at high current densities. Herein, a 2D porous Cu3N (2D‐P‐Cu3N) catalyst is reported with outstanding ECORR performance prepared by a two‐step pyrolysis strategy. This strategy mainly relies on the sequential annealing of the Cu2(OH)2CO3 precursors in an oxidation and reduction atmosphere, which can not only convert it into high‐purity Cu3N, but also endow it with an abundant hierarchical pores structure. The pores can significantly improve the in‐plane conductivity and mass transfer capacity of Cu3N, enabling a C2+ faradaic efficiency exceeding 90% at a current density of 0.6 A cm−2. Even at an ampere grade current density of 1 A cm−2, it maintains an impressive 87% selectivity, surpassing most of the reported Cu‐based catalysts. In‐situ Raman spectroscopy confirms that 2D‐P‐Cu3N exhibits high coverage and adsorption of CO intermediates, thus enhancing C‐C coupling and promoting the generation of C2+ products. This discovery opens further exploration of catalysts for selective CORR to C2+ products.

High-loading Au nanoparticles on carbon by engineering surface charge and specific surface area of substrates

Energy transition towards net-zero society calls for utilization of renewable power to drive CO2 conversion in an efficient electrochemical way. The development of a commercial CO2 electrolyzer with positive tech-eco effect calls for active and durable electrocatalysts. High-loading gold on carbon (Au/C) with reduced particle size is the prerequisite for the highly-selective and highly energy-efficient CO production in such a CO2 electrolyzer, but a scalable synthetic method is missing. With combined control of ligand, substrate and pH value, Au/C catalysts with particle size within 5 ​nm and metal loading of 40 ​wt% and 60 ​wt% are synthesized on low and high surface-area carbon, respectively. We also provide a thorough investigation of the effect of the ligand type, surface charge of gold nanoparticles (Au NPs) and surface area of carbon substrate on the loading limit of Au/C.

Experimental and Computational Study Toward Identifying Active Sites of Supported SnOx Nanoparticles for Electrochemical CO2 Reduction Using Machine-Learned Interatomic Potentials.

SnOx has received great attention as an electrocatalyst for CO2 reduction reaction (CO2RR), however; it still suffers from low activity. Moreover, the atomic-level SnOx structure and the nature of the active sites are still ambiguous due to the dynamism of surface structure and difficulty in structure characterization under electrochemical conditions. Herein, CO2RR performance is enhanced by supporting SnO2 nanoparticles on two common supports, vulcan carbon and TiO2. Then, electrolysis of CO2 at various temperatures in a neutral electrolyte reveals that the application window for this catalyst is between 12 and 30°C. Furthermore, this study introduces a machine learning interatomic potential method for the atomistic simulation to investigate SnO2 reduction and establish a correlation between SnOx structures and their CO2RR performance. In addition, selectivity is analyzed computationally with density functional theory simulations to identify the key differences between the binding energies of *H and *CO2 -, where both are correlated with the presence of oxygen on the nanoparticle surface. This study offers in-depth insights into the rational design and application of SnOx-based electrocatalysts for CO2RR.

Enhancing Electrochemical Efficiency of Solid Oxide Electrolysis Cells for Carbon Dioxide Reduction Through Nickel‐Doped Titanate‐Based Cathode with Doped Ceria Electrolyte

AbstractSolid oxide electrolysis cell (SOEC) is a potential technology for converting the principal greenhouse gas, carbon dioxide (CO2), into carbon monoxide (CO) by employing renewable energy. SOECs have great potential, including high‐energy efficiency, fast electrode kinetics, and competitive cost; however, this technology still has challenges in developing highly active, robust CO2 cathode electrocatalysts. In this work, we report the Ni‐doped lanthanum strontium calcium titanate (La0.20Sr0.25Ca0.45Ni0.05Ti0.95O3−δ) cathode for application as the cathode of CO2 electrolysis with gadolinia‐doped ceria (Gd0.1Ce0.9O1.95) electrolyte in SOEC. The exsolution of Ni nanoparticles is achieved by a simple in situ growth method at 800 °C. The Ni doping in LSCT significantly improved the electrochemical activity of the catalyst by increasing oxygen vacancies, and the Ni metallic nanoparticles can afford much more active sites for CO2 reduction. The CO2 electrolysis mechanism is studied by the distribution of relaxation time analysis of impedance spectroscopy. Ni‐LSCT renders a higher activity for electrolysis of CO2 with an exceptionally high reduction current density of 3.89 A cm−2 at 2.5 V potential applied and 800 °C temperature with GDC (Gd0.1Ce0.9O1.95) electrolyte. Ni doping is a crucial factor in controlling the electrochemical performance and catalytic activity in SOEC and GDC electrolytes, which is further helped by the high ionic conductivity.

Nonconductive Metal Oxide Gas Diffusion Layer for Mitigating Electrowetting during CO2 Electrolysis.

Gas diffusion electrodes (GDEs) are extensively used for high current density electrochemical CO2 electrolysis (ECO2R), enabled by significantly reducing mass transfer resistance of CO2 to the catalyst layer. Conventionally, these GDEs are based upon hydrophobic carbon-based gas-diffusion layers (GDLs) that facilitate the gas transport; however, these supports are prone to flood with electrolyte during electrolysis. This potential-induced flooding, known as electrowetting, is related to the inherent conductivity of carbon and limits the activity of ECO2R. To investigate the effect of electrical conductivity more carefully, a GDE is constructed based on a Cu mesh with a nonconductive microporous GDL applied to this substrate, the latter composed of a mixture of metal oxide and polytetrafluoroethylene. With alumina as the metal oxide, a stable operation is obtained at -200 mA cm-2 with 70% selectivity for ECO2R (with over half toward C2+ products) without flooding as observed by in situ microscopy. On the contrary, with a Vulcan carbon-based GDL, the initial activity is rapidly lost as severe flooding ensues. It is reasoned that electrowetting is averted by virtue of the nonconductive nature of alumina, providing a new perspective on alternative GDL compositions and their influence on ECO2R performance.

Harnessing the electrocatalytic potential of in-situ exsolution of Ni nanoparticles on lanthanum and calcium co-doped strontium titanate for CO2 reduction in solid oxide electrolysis cells

The exsolution phenomenon of metal nanoparticles from a perovskite oxide involves the creation of oxygen vacancies, contributing to improved catalytic activity for CO2 reduction. In this context, a B-site Ni-doped and A-site La, Ca co-doped strontium titanate, denoted as La0.20Sr0.25Ca0.45Ni0.05Ti0.95O3-δ (Ni-LSCT), is synthesized with the aim of serving as a highly efficient cathode in conjunction with LSM as the anode and YSZ as the electrolyte for CO2 reduction via solid oxide electrolysis process. The incorporation of 5 mol% Ni doping at the B-site of the perovskite is successfully achieved, leading to the subsequent release of highly dispersed nanoparticles upon exposure to a reducing environment. YSZ-electrolyte-supported SOECs featuring the Ni-LSCT cathode demonstrate a notable current density of 0.93 A/cm2 at an applied voltage of 2.5 V at 800 °C in pure CO2. Moreover, at the same temperature, the reduction current density measures 1.21 A/cm2 when the Ni-LSCT serves as the cathode in a 70/30 molar ratio (CO2/H2) environment and 1.73 A/cm2 with a 50/50 molar ratio of the feed gas, both at an applied voltage of 2.5 V. This suggests an enhanced CO2 reduction performance in a reducing atmosphere. The introduction of Ni doping into LSCT enhances the electrochemical activity of the cathode by augmenting oxygen vacancies, while the presence of Ni nanoparticles on the cathode surface intensifies the active sites. Collectively, this innovative electrocatalyst configuration presents promising prospects for CO2 electrolysis within the SOEC framework.

Pure-Water-Fed Forward-Bias Bipolar Membrane CO2 Electrolyzer.

Coupling renewable electricity to reduce carbon dioxide (CO2) electrochemically into carbon feedstocks offers a promising pathway to produce chemical fuels sustainably. While there has been success in developing materials and theory for CO2 reduction, the widespread deployment of CO2 electrolyzers has been hindered by challenges in the reactor design and operational stability due to CO2 crossover and (bi)carbonate salt precipitation. Herein, we design asymmetrical bipolar membranes assembled into a zero-gap CO2 electrolyzer fed with pure water, solving both challenges. By investigating and optimizing the anion-exchange-layer thickness, cathode differential pressure, and cell temperature, the forward-bias bipolar membrane CO2 electrolyzer achieves a CO faradic efficiency over 80% with a partial current density over 200 mA cm-2 at less than 3.0 V with negligible CO2 crossover. In addition, this electrolyzer achieves 0.61 and 2.1 mV h-1 decay rates at 150 and 300 mA cm-2 for 200 and 100 h, respectively. Postmortem analysis indicates that the deterioration of catalyst/polymer-electrolyte interfaces resulted from catalyst structural change, and ionomer degradation at reductive potential shows the decay mechanism. All these results point to the future research direction and show a promising pathway to deploy CO2 electrolyzers at scale for industrial applications.

Collective Synergistic Catalysis of Electrochemical CO2 Reduction on Nonstoichiometric Double Perovskites

AbstractPerovskite oxides show great promise as an alternative catalyst to the conventional nickel cermets for CO2 reduction reactions (CO2RR) in solid oxide electrolysis cells (SOECs) owing to their advantages of redox stability and coking resistance. Nevertheless, practical applications of these oxides are prevented largely by their poor CO2RR activities. Herein, a novel donor and acceptor co‐doped nonstoichiometric double perovskite, La0.3Sr1.55Fe1.5Ni0.1Mo0.4O6−δ (LSFNM), is developed with in situ exsolved FeNi3 nanoparticles to efficiently catalyze CO2RR in SOECs. Pure CO2 electrolysis over the impregnated FeNi3@LSFNM catalysts is evaluated on two types of SOECs—one with thin (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 (SSZ) electrolytes supported on 430L alloys and the other with thin La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolytes supported on impregnated SmBa0.5Sr0.5Co2O5+δ (SBSCO)@LSGM anodes, producing unprecedently high current densities of 2.84 A cm−2 for the former and 3.07 A cm−2 for the latter at 1.5 V and 800 °C. Experimental analysis and density‐functional theory (DFT) calculations reveal collective synergistic catalysis of oxygen vacancies (), the doping Ni2+ ions and FeNi3 nanoparticles via the cooperative ‐O(CO2), and Ni(II)–C(sp) and Ni(0)–O(CO2) interactions in LSFNM, not only facilitating CO2 chemisorption on oxygen vacancies but also destabilizing and dissociating surface carbonates in the vicinity of FeNi3 spontaneously into CO.

CO2 electrolysis to formic acid for carbon neutralization

To avoid carbonate precipitation for CO2 electrolysis, developing CO2 conversion in an acid electrolyte is viewed as an ultimately challenging technology. In Nature, Xia et al. recently explored a proton-exchange membrane system for reducing CO2 to formic acid with a Pb–PbSO4 composite catalyst derived from waste lead-acid batteries based on the lattice carbon activation mechanism. Up to 93% Faradaic efficiency was realized when formic acid was produced by this technology.

Artificial synthesis of polyesters at ambient condition via consecutive CO2 electrolysis and fermentation

Artificial synthesis of polyesters at ambient condition via consecutive CO2 electrolysis and fermentation

Correlating Electrolyte Infiltration with Accessible Surface Area in Macroporous Electrodes using Neutron Radiography

Carbon-based porous electrodes are commonly employed in electrochemical technologies as they provide a high surface area for reactions, an open structure for fluid transport, and enable compact reactor architectures. In electrochemical cells that sustain liquid electrolytes (e.g., redox flow batteries, CO2 electrolyzers, capacitive deionization), the nature of the interaction between the three phases - solid, liquid and gas - determines the accessible surface area for reactions, which fundamentally determines device performance. Thus, it is critical to understand the correlation between the electrolyte infiltration in the porous electrode and the resulting accessible surface area in realistic reactor architectures. To tackle this question, here we simultaneously perform neutron radiography with electrochemical measurements to correlate macroscopic electrode saturation/wetting with accessible surface area. We find that for untreated electrodes featuring neutral wettability with water, the electrode area remains underutilized even at elevated flow rates, both for interdigitated and parallel flow fields. Conversely, increasing the electrode hydrophilicity results in an order-of-magnitude increase in accessible surface area at comparable electrode saturation, and is less influenced by the electrolyte flow rate. Ultimately, we reveal useful correlations between reactor architectures and electrode utilization and provide a method that is broadly applicable to flow electrochemical reactors.