CO2 Electroreduction Performance Research Articles

Effect of loading and pyrolysis of carbon-supported cobalt phthalocyanine on the electrocatalytic reduction of CO2

Understanding the structure-activity relationship of materials that are active for the CO2 electrochemical reduction reaction (CO2ERR) is crucial for developing stable, high-performance catalysts. In this research, it is first shown that ball-milling is a highly efficient way to disperse cobalt phthalocyanine (CoPC) onto carbon black without influencing the CO2 electroreduction performance of the resulting materials. Then, the link between the loadings of the CoPC precursor on the carbon support and the CO2ERR activity of the pyrolyzed materials is demonstrated. With CO current efficiencies higher than 45% and CO current densities as high as -20 mA cm−2 at -0.77 V vs. RHE, the materials with CoPC loadings of 7.9 wt% and higher were still surprisingly active after pyrolysis at 800 and 900 °C. On the other hand, the CO2ERR activity of the materials containing less than 6.1 wt% CoPC was drastically reduced after pyrolysis at these temperatures, with CO current efficiencies lower than 10 %. X-ray powder diffraction revealed that only the materials containing crystalline CoPC before pyrolysis showed good CO2ERR activity after pyrolysis at 800 and 900 °C. Furthermore, X-ray absorption spectroscopy showed that the loading of the CoPC precursor influenced the structure of the active sites in the pyrolyzed CoPC/C materials. Overall, this study highlights the importance of the dispersion of CoPC when forming a material that is catalytically active for CO2ERR after pyrolysis.

Carbon dioxide reduction in solid oxide electrolyzer cells utilizing nickel bimetallic alloys infiltrated into Gd0.1Ce0.9O1.95 (GDC10) scaffolds

This study evaluates the electrochemical performance of Gd0.1Ce0.9O1.95 (GDC10) cathodes infiltrated with bimetallic Ni-Co and Ni-Cu alloy electrocatalysts for CO2 electroreduction in solid oxide electrolyzer cells (SOECs). The electrochemical reduction performance of SOECs with cathodes infiltrated with Ni-Co and Ni-Cu alloys was compared to the performance of SOECs having cathodes infiltrated with Ni, Co, and Cu. Electrochemical performance was evaluated at 750, 800, and 850 °C. Cells with Co, Ni0.50Co0.50, Ni0.75Co0.25, and Ni infiltrated cathodes displayed relatively similar CO2 electroreduction performance; however, SOECs having Co infiltrated cathodes had slightly better catalytic performance towards CO2 reduction as demonstrated by their lower polarization resistance (Rp) values of 8.54, 4.03, and 1.25 Ω·cm2 when measured under open circuit voltage (OCV) at 750, 800, and 850 °C, respectively. Cells having Co, Ni0.50Co0.50, Ni0.75Co0.25, and Ni infiltrated cathodes showed a stable long-term CO2 electroreduction performance with Faradaic efficiency values approaching 100 % when tested under 0.20 A·cm−2 for 48 h and at 750 °C. Results indicate that SOECs with Ni infiltrated cathodes possessed better short- and long-term CO2 electroreduction performance compared to SOECs featuring cathodes infiltrated with Cu, Ni0.25Cu0.75, and Ni0.50Cu0.50. Increasing Ni percentage within the Ni-Cu alloy structure had a positive impact on the electrochemical performance as cells with Ni0.50Cu0.50 infiltrated cathodes showed relatively close voltage values to those of cells with Ni infiltrated cathodes during short-term galvanostatic tests. Although the SOEC with Ni0.50Cu0.50 infiltrated cathode experienced performance degradation throughout the long-term test period, it demonstrated better electroreduction performance having Faradaic efficiency values approaching 100 % compared to cells with Cu and Ni0.25Cu0.75 infiltrated cathodes when evaluated under 0.20 A·cm−2 for 48 h and at 750 °C.

Oxygen-tolerant CO2 electroreduction over covalent organic frameworks via photoswitching control oxygen passivation strategy

The direct use of flue gas for the electrochemical CO2 reduction reaction is desirable but severely limited by the thermodynamically favorable oxygen reduction reaction. Herein, a photonicswitching unit 1,2-Bis(5’-formyl-2’-methylthien-3’-yl)cyclopentene (DAE) is integrated into a cobalt porphyrin-based covalent organic framework for highly efficient CO2 electrocatalysis under aerobic environment. The DAE moiety in the material can reversibly modulate the O2 activation capacity and electronic conductivity by the framework ring-closing/opening reactions under UV/Vis irradiation. The DAE-based covalent organic framework with ring-closing type shows a high CO Faradaic efficiency of 90.5% with CO partial current density of −20.1 mA cm−2 at −1.0 V vs. reversible hydrogen electrode by co-feeding CO2 and 5% O2. This work presents an oxygen passivation strategy to realize efficient CO2 electroreduction performance by co-feeding of CO2 and O2, which would inspire to design electrocatalysts for the practical CO2 source such as flue gas from power plants or air.

Dynamically Reconstructed Triple-Copper-Vacancy Associates Confined in Cu Nanowires Enabling High-Rate and Selective CO2 Electroreduction to C2+ Products.

Electrochemically reconstructed Cu-based catalysts always exhibit enhanced CO2 electroreduction performance; however, it still remains ambiguous whether the reconstructed Cu vacancies have a substantial impact on CO2 -to-C2+ reactivity. Herein, Cu vacancies are first constructed through electrochemical reduction of Cu-based nanowires, in which high-angle annular dark-field scanning transmission electron microscopy image manifests the formation of triple-copper-vacancy associates with different concentrations, confirmed by positron annihilation lifetime spectroscopy. In situ attenuated total reflection-surface enhanced infrared absorption spectroscopy discloses the triple-copper-vacancy associates favor *CO adsorption and fast *CO dimerization. Moreover, density-functional-theory calculations unravel the triple-copper-vacancy associates endow the nearby Cu sites with enriched and disparate local charge density, which enhances the *CO adsorption and reduces the CO-CO coupling barrier, affirmed by the decreased *CO dimerization energy barrier by 0.4eV. As a result, the triple-copper-vacancy associates confined in Cu nanowires achieve a high Faradaic efficiency of over 80% for C2+ products in a wide current density range of 400-800mA cm-2 , outperforming most reported Cu-based electrocatalysts.

Organic Thin Films Enable Retaining the Oxidation State of Copper Catalysts during CO2 Electroreduction.

A key challenge in electrocatalysis remains controlling a catalyst's structural, chemical, and electrical properties under reaction conditions. While organic coatings showed promise for enhancing the selectivity and stability of catalysts for CO2 electroreduction (CO2RR), their impact on the chemical state of underlying metal electrodes has remained unclear. In this study, we show that organic thin films on polycrystalline copper (Cu) enable retaining Cu+ species at reducing potentials down to -1.0 V vs RHE, as evidenced by operando Raman and quasi in situ X-ray photoelectron spectroscopy. In situ electrochemical atomic force microscopy revealed the integrity of the porous organic film and nearly unaltered Cu electrode morphology. While the pristine thin film enhances the CO2-to-ethylene conversion, the addition of organic modifiers into electrolytes gives rise to improved CO2RR performance stability. Our findings showcase hybrid metal-organic systems as a versatile approach to control, beyond morphology and local environment, the oxidation states of catalysts and energy conversion materials.

Enhancing CO2 electroreduction performance through transition metal atom doping and strain engineering in γ-GeSe: a first-principles study.

The development of electrocatalysts that exhibit stability, high activity, and selectivity for CO2 reduction reactions (CO2RR) remains a significant challenge. Single-atom catalysts (SACs) hold promise in addressing this challenge due to their high atomic utilization efficiency. In this study, we explore the potential of monolayer γ-GeSe doped with transition metals, referred to as TM@γ-GeSe, for facilitating electrocatalytic CO2RR. Among the 26 TM@γ-GeSe SACs systematically designed, we have identified four stable transition metal catalysts (TM = Rh, Pd, Pt, and Au). Mechanistic investigations into the CO2RR pathways reveal exceptional electrocatalytic activity for Rh@γ-GeSe and Pd@γ-GeSe, with limiting potentials of -0.26 and -0.35 V, respectively. Particularly, Pd@γ-GeSe exhibits outstanding product selectivity toward formic acid. The introduction of strain engineering induces modifications in the catalytic activity and selectivity of Rh@γ-GeSe. Notably, a 1% tensile strain promotes formic acid as the preferred product, thereby improving the specific product selectivity of Rh@γ-GeSe. Conversely, compressive strain reduces CO2RR activity while enhancing the hydrogen evolution reaction, leading to a decrease in CO2RR selectivity. Furthermore, we use the work function as a descriptor to elucidate the underlying mechanism of strain tunability. We hope that our theoretical study will offer valuable insights for the design of catalysts based on γ-GeSe for electrocatalytic CO2RR.

Boosting oxygen-resistant CO2 electroreduction reaction in acidic media over conjugated frameworks

A cobalt polyphthalocyanine framework coated by polyaniline shows excellent oxygen-resistant CO2 electroreduction performance with high CO selectivity of up to 87.4% and an industry-level jCO of −270 mA cm−2 under 5% O2 feed gas in acidic media.

Facile synthesis of single‐nickel‐atomic dispersed mesoporous carbon nanosheets with controllable nitrogen doping for efficient electrochemical CO2 reduction

AbstractThe catalytic conversion of CO2 into high value‐added chemical products driven by electricity was an effective strategy to reduce atmospheric CO2 concentration. The development of high efficiency catalysts had always been the core for electrocatalytic reduction of CO2. The single transition metal sites anchored on nitrogen‐doped carbon showed great potential in CO2 reduction reaction (CO2RR). In this paper, the atomically dispersed Ni−N sites are constructed on the two‐dimensional mesoporous carbon nanosheets by the secondary pyrolysis method. The rich mesoporous structure of the two‐dimensional nanosheets is beneficial to CO2 diffusion and adsorption during CO2RR, and the high nitrogen contents could increase the Ni single atom loadings. The nitrogen content and type could be controlled by regulating the ratio of nitrogen source to carbon source, and the catalyst activity is improved as the proportion of nitrogen sources increases. When the ratio of nitrogen source to carbon source is four, the oxidation state of Ni single atoms Ni@NMCN4 is between 0 and +2, and Ni single atoms exists as Ni−N4 structure with pyridinic N of 32.78 %, which exhibits the best electrochemical CO2RR activity. The active site of Ni@NMCN4 is confirmed as the highly stable Ni single atoms. Moreover, the pyridinic N species are proved to play an important role in enhancing the CO2 electroreduction performance. This work provides a new perspective to adjust the nitrogen content and type in transition metal monatomic‐N‐doped carbon electrocatalysts for CO2RR.

SiFeN6-graphene: A promising dual-atom catalyst for enhanced CO2-to-CH4 conversion

The synergistic effects in heteronuclear dual-atom catalysts create opportunities for designing highly efficient catalysts. In this work, we theoretically designed a stable SiFeN6-graphene with excellent CO2 electroreduction performance. The complementary properties of Si and Fe in the Si-Fe dual-atom center result in enhanced CO2 adsorption and activation, as well as weakened binding strength of the critical intermediate ∗OH, compared to SiN3- and FeN3-graphene. A low onset potential of −0.60 V is predicted for selective conversion of CO2 to CH4, with moderate kinetic barriers (less than 0.66 eV) during the whole reaction, readily surmountable under experimental conditions. This study provides vital insights into the rational design of dual-atom electrocatalysts by exploiting synergistic interactions between strategically paired atoms.

Low‐Coordinated Single‐Atom Catalysts Modulated by Metal Ionic Liquids for Efficient CO2 Electroreduction

AbstractModulating the coordination environment of single‐atom catalysts (SACs) is an attractive approach for maximizing the catalytic activity of single‐atom centers. Currently, the synthesis of low‐coordinated SACs is mainly confined to increasing the pyrolysis temperature (≥900 °C) to control C─N volatile fragments. Herein, a novel and universal strategy for the low‐coordinated SACs modulation is presented using transition metal (e.g., Ni, Co, Zn) ionic liquid precursors under relatively mild temperature of 600 °C, which regulates the L‐shell electronic structure and decreases nearly 50% electrophilic reactivity by ionization of 4‐position N atom, thereby orienting synthesis of the SACs with metal‐N3 centers. The Ni‐N3 SACs exhibit exceptional CO2 electroreduction performance of 99.7% CO Faraday efficiency with an ultra‐high CO partial current density of 467.55 mA·cm−2 as well as a CO production rate up to 10417.51 µmol·h−1·cm−2 in flow cell. The superior catalytic activity achieves over twofold increase compared with the Ni‐N4 SACs prepared by non‐metal ionic liquid precursors due to the lower free energy of the key intermediate *COOH and the stronger adsorption energy.

Efficient utilization of nickel single atoms for CO2 electroreduction by constructing 3D interconnected nitrogen-doped carbon tube network

The CO2 electroreduction (CO2RR) is extensively deemed as a promising route to reach carbon neutralization, while the single-atom catalysts (SACs) are proved to be effective in CO2RR. However, most SACs cannot further amplify performance due to their powdery feature. Herein, we present numerous isolated nickel single atoms anchored on 3D interconnected N-doped carbon tubes (NiSAs@3D-INCT) network as a self-supported electrode. The NiSAs@ 3D-INCT has truly interconnected and highly ordered vertical and lateral carbon tube-channels, which promote the CO2 interaction and electrolyte transmission. The NiSAs@3D-INCT exhibits a superior CO2RR performance with an appreciable CO partial current density of 51.8 mA cm −2 at − 0.96 V versus the reversible hydrogen electrode (RHE). X-ray absorption fine structure spectroscopy and theoretical computations reveal the NiSAs are loaded on the 3D-INCT network with Ni-N4 configuration as highly active sites for CO2RR. This work will shed a new light on opening up high performance SACs for CO2RR.

Electronic Tuning of CO2 Interaction by Oriented Coordination of N-Rich Auxiliary in Porphyrin Metal-Organic Frameworks for Light-Assisted CO2 Electroreduction.

The efficient CO2 electroreduction into high-value products largely relies on the CO2 adsorption/activation or electron-transfer of electrocatalysts, thus site-specific functionalization methods that enable boosted related interactions of electrocatalysts are much desired. Here, an oriented coordination strategy is reported to introduce N-rich auxiliary (i.e., hexamethylenetetramine, HMTA) into metalloporphyrin metal organic frameworks (MOFs) to synthesize a series of site-specific functionalized electrocatalysts (HMTA@MOF-545-M, M=Fe, Co, and Ni) and they are successfully applied in light-assisted CO2 electroreduction. Noteworthy, thus-obtained HMTA@MOF-545-Co presents approximately two times enhanced CO2 adsorption-enthalpy and electrochemical active surface-area with largely decreased impedance-value after modification, resulting in almost twice higher CO2 electroreduction performance than its unmodified counterpart. Besides, its CO2 electroreduction performance can be further improved under light-illumination and displays superior FECO (≈100%), high CO generation rate (≈5.11molm-2 h-1 at -1.1V) and energy efficiency (≈70% at -0.7V). Theoretical calculations verify that the oriented coordination of HMTA can increase the charge density of active sites, almost doubly enhance the CO2 adsorption energy, and largely reduce the energy barrier of rate determining step for the boosted performance improvement. This work might promote the development of modifiable porous crystalline electrocatalysts in high-efficiency CO2 electroreduction.

Carbon dioxide reduction in solid oxide electrolyzer cells using transition metals infiltrated into Gd0.1Ce0.9O1.95 (GDC10) scaffolds

This study reports the catalytic activity of transition metal electrocatalysts (Co, Ni, and Cu) incorporated into Gd0.1Ce0.9O1.95 (GDC10) cathodes for the electroreduction of CO2 in solid oxide electrolyzer cells (SOECs). CO2 electroreduction performance of cells having porous and non-infiltrated GDC10 cathodes was compared with the performance of cells containing transition metal electrocatalysts infiltrated into porous GDC10 cathodes at 750, 800, and 850 °C. Results showed that cells with Co infiltrated cathodes had the best catalytic activity towards CO2 electroreduction. Furthermore, these cells displayed good stability towards CO2 electroreduction, having a faradaic efficiency value close to 100% with insignificant voltage increase when tested for 48 h at 750 and 850 °C under the current densities of 0.2, and 0.4 A cm −2, respectively.

Constructing nano-Au/reduced-CeO2 interface through high cathodic voltage in solid oxide electrolysis cells at high temperature

CeO2 is often used as the buffer layer for CO2 electroreduction in solid oxide electrolysis cells (SOECs) because of their limited electrocatalytic activity and low reactivity with electrolytes and electrodes. In this work, we propose a novel cathodic electrochemically activation method to construct a nano-Au/reduced-CeO2 interface, and achieve significantly improved CO2 electroreduction performance. The Gd-doped CeO2 (GDC) cathode activated at 2.9 V exhibits the highest current density of 0.241 A cm−2 at 1.2 V, which is 3.65 times that of the GDC cathode activated at 2.0 V. After being activated at 2.9 V, lots of oxygen vacancies are generated on the surface of ceria-based-cathodes, which facilitate the Au nanoparticles dispersion and enhance CO2 adsorption. Au nanoparticles, reduced-ceria particles and CO2 gas together form lots of three-phase boundaries (TPBs), which are beneficial for CO2 electroreduction. Our work explores a novel cathodic electrochemically activation method to restructure the metal-oxides interface.

Efficient CO2 reduction to formate in a photoanode-driven photoelectrocatalysis system using a Bi2Se3/Bi2O3 nanocomposite cathode

The conversion of CO2 into valuable chemical fuels is considered as a prospective way to solve the energy crisis and environmental problems. Photoelectrocatalysis can integrate the merits of photocatalysis and electrocatalysis to lower energy consumption and improve the catalytic efficiency. In this work, a photoanode-driven photoelectrocatalysis system was prepared with TiO2 nanotubes photoanode and Bi2Se3-Bi2O3 nanocomposite electrocathode for CO2 reduction. The electrocatalytic test results demonstrated that Bi2Se3-Bi2O3-3 cathode exhibited excellent CO2 electroreduction performance with the formate Faraday efficiency of 81.33 % at −0.9 V vs RHE and an overpotential as low as 500 mV. In the photoanode-driven photoelectrocatalysis system, the formate yield was 1.6 times higher than that in the electrocatalytic system at −1.0 V vs RHE. The increased catalytic performance in the photoelectrocatalysis system may be due to the synergistic effect between photocatalysis and electrocatalysis caused by the photoanode. This work provides a reference for developing efficient CO2 reduction approaches and high-performance electrocatalysts.

Nanoconfinement effects on CuBi3 alloy catalyst for efficient CO2 electroreduction to formic acid

Electrochemical reduction reaction of CO2 (CO2RR) toward chemical and fuel production is a compelling component of the new energy system. The dual-metal site strategy is an effective way to realize efficient CO2 electroreduction into formic acid, however, the limited interfacial area and low activity of traditional dual-metal catalysts result in unsatisfactory CO2 electroreduction performance. Herein, we proposed a co-deposition strategy to prepare designed Cu-Bi alloy (CuBi3) which with unique nanoconfinement effect for the mass transport and enlarge the interfacial active area for CO2RR. As expected, the CuBi3 exhibits excellent electrochemical performance on CO2 reduction to formic acid with Faradaic efficiency (FE) of 98.4% and formic acid partial current density of − 21.2 mA cm−2 in 0.1 M KHCO3. Experiment and density functional theory (DFT) calculations suggest that CuBi3 catalyst with regulation of electron state and outstanding adsorption capacity of CO2 provide lattice and spatial confinement environment for active sites. This confinement environment can significantly lower the energy barrier for the formation of *HCOO, which are responsible for the high activity and selectivity toward CO2-to-formic acid conversion.

Hydrophobicity graded gas diffusion electrode with enhanced CO intermediate coverage for high-performance electroreduction of CO2 to ethylene

Electroreduction using a gas diffusion electrode (GDE) provides an efficient method for high rate conversion of CO2 to value-added chemicals. However, long term production with high yields remains challenging due to rapid electrolyte flooding through the hydrophobic gas diffusion layer (GDL). Here, we report a universal strategy to convert a commercial GDL into a hydrophobicity graded GDL (HGGDL) that resists electrolyte flooding. The CO2 electroreduction performance of a family of tandem catalysts consisting of a nickel-single-atom catalyst and Cu nanoparticles immobilized on GDLs and HGGDLs is compared with respect to ethylene production. In situ Raman studies reveal that the HGGDL increases the CO intermediate coverage as a result of the higher differential pressure across the electrodes. Lower carbonate formation also is observed. Enhanced ethylene production efficiency and an order of magnitude improvement in long term stability is achieved in a membrane electrode assembly electrolyzer.

Ni Nanoclusters Anchored on Ni-N-C Sites for CO2 Electroreduction at High Current Densities.

Transition metal catalyst-based electrocatalytic CO2 reduction is a highly attractive approach to fulfill the renewable energy storage and a negative carbon cycle. However, it remains a great challenge for the earth-abundant VIII transition metal catalysts to achieve highly selective, active, and stable CO2 electroreduction. Herein, bamboo-like carbon nanotubes that anchor both Ni nanoclusters and atomically dispersed Ni-N-C sites (NiNCNT) are developed for exclusive CO2 conversion to CO at stable industry-relevant current densities. Through optimization of gas-liquid-catalyst interphases via hydrophobic modulation, NiNCNT exhibits as high as Faradaic efficiency (FE) of 99.3% for CO formation at a current density of -300 mA·cm-2 (-0.35 V vs reversible hydrogen electrode (RHE)), and even an extremely high CO partial current density (jCO) of -457 mA·cm-2 corresponding to a CO FE of 91.4% at -0.48 V vs RHE. Such superior CO2 electroreduction performance is ascribed to the enhanced electron transfer and local electron density of Ni 3d orbitals upon incorporation of Ni nanoclusters, which facilitates the formation of the COOH* intermediate.

Advances and challenges of electrolyzers for large-scale CO2 electroreduction

CO2 electroreduction (CO2ER) to high value-added chemicals is considered as a promising technology to achieve sustainable carbon neutralization. By virtue of the progressive research in recent years aiming at design and understanding of catalytic materials and electrolyte systems, the CO2ER performance (such as current density, selectivity, stability, CO2 conversion, etc.) has been continually increased. Unfortunately, there has been relatively little attention paid to the large-scale CO2 electrolyzers, which stand just as one obstacle, alongside series-parallel integration, challenging the practical application of this infant technology. In this review, the latest progress on the structures of low-temperature CO2 electrolyzers and scale-up studies was systematically overviewed. The influence of the CO2 electrolyzer configurations, such as the flow channel design, gas diffusion electrode (GDE) and ion exchange membrane (IEM), on the CO2ER performance was further discussed. The review could provide inspiration for the design of large-scale CO2 electrolyzers so as to accelerate the industrial application of CO2ER technology.

The bio-inspired heterogeneous single-cluster catalyst Ni100-Fe4S4 for enhanced electrochemical CO2 reduction to CH4.

Electrochemical conversion of CO2-to-CH4 is a process of converting the inert greenhouse gas into energy molecules. It offers great promise for the transformation of carbon-neutral economy. However, achieving high CH4 activity and selectivity remains a major challenge because the electrochemical reduction of CO2-to-CH4 is accompanied by various C1 intermediates at the catalytic site, involving multiple proton-coupled electron transfer processes. Herein, different from the traditional designing strategy, we propose a bio-inspired theoretical design approach to construct a heterogeneous single-cluster catalyst Ni100-Fe4S4 at the atomic level, which may show high CO2 electroreduction performance. Combined with the crystallographic data and theoretical calculations, Ni100-Fe4S4 and CO dehydrogenase exhibit highly similar catalytic geometric active centers and CO2 binding modes. By exploring the origin of the catalytic activity of this biomimetic structure, we found that the activation of CO2 on Ni100-Fe4S4 theoretically exceeds that on natural CO dehydrogenase. Density functional theory calculations reveal that the dehydrogenase enzyme-liked Fe-Ni active site serves as an electron enrichment 'electro-bridge' (an electron-rich highly active catalytic site), which can activate CO2 molecules efficiently and stabilize various intermediates in multistep elementary reactions to selectively produce CH4 at a low overpotential (0.13 eV). The calculated CO2 electroreduction pathways are well consistent with the nickel-based catalytic materials reported in experimental studies. Our work showcases and highlights the rational design of high-performance catalytic materials via the biomimetic methodology at the atomic level.