Catalyst For CO2 Reduction Reaction Research Articles

Recent advances and future perspectives of metal-organic frameworks as efficient electrocatalysts for CO2 reduction

AbstractThe conversion of carbon dioxide (CO2) to the reduced chemical compounds offers substantial environmental benefits through minimizing the emission of greenhouse gas and fostering sustainable practices. Recently, the unique properties of metal-organic frameworks (MOFs) make them attractive candidates for electrocatalytic CO2 reduction reaction (CO2RR), providing many opportunities to develop efficient, selective, and environmentally sustainable processes for mitigating CO2 emissions and utilizing CO2 as a valuable raw material for the synthesis of fuels and chemicals. Here, the recent advances in MOFs as efficient catalysts for electrocatalytic CO2RR are summarized. The detailed characteristics, electrocatalytic mechanisms, and practical approaches for improving the electrocatalytic efficiency, selectivity, and durability of MOFs under realistic reaction conditions are also clarified. Furthermore, the outlooks on the prospects of MOF-based electrocatalysts in CO2RR are provided.

Harnessing in-situ oxidation of nanostructured mxene to modulate the electronic structure for improved selectivity for electrochemical carbon dioxide reduction

The electrochemical CO2 reduction reaction (CO2RR) is a promising approach to valorizing CO2. Ti3C2TX as a support material has received significant interest in enhancing CO2RR performance for tuning the electronic structure. However, there has been relatively less focus on changes to the Ti3C2TX electronic structure induced by loading catalysts onto the Ti3C2TX. Because Ti3C2TX has an intrinsic activity for both CO2RR and the competitive hydrogen evolution reaction (HER), electronic structure changes can affect the balance between CO2RR and HER selectivity. Therefore, tuning the electronic structure of Ti3C2TX can control the competition between CO2RR and HER and tune the selectivity and activity. Herein, we report that Ti3C2TX’s electronic structure can be tuned by the Ag+ loading method via redox interactions, tuning the reaction selectivity and activity for CO2RR. To illustrate this effect, we compare the CO2RR performance of in-situ formed Ag nanoparticles (NPs) on Ti3C2TX (0.9Ag-IS-Ti3C2TX) with physically mixed Ag NPs and Ti3C2TX (0.9Ag/P/Ti3C2TX). Here, ‘0.9’ refers to the molar ratio between Ag precursor and Ti3C2Tx, and ‘IS’ vs. ‘P’ refers to in-situ formed vs. physically mixed Ag NPs. 0.9Ag-IS-Ti3C2TX demonstrates a higher oxidation state for Ti and a higher proportion of Ti-O bonds than 0.9Ag/P/Ti3C2TX. Compared to 0.9Ag/P/Ti3C2TX, 0.9Ag-IS-Ti3C2TX exhibits higher CO Faradaic efficiency (FE), rising from 8.1 % with a partial current density of −2.0 mA cm−2 to 49.6 % with a partial current density of −20.1 mA cm−2 at −1.4 V vs. RHE (reversible hydrogen electrode). To harness this effect, we demonstrate control over the CO: H2 ratio of syngas formed from CO2RR over our Ti3C2TX-supported catalysts. Further electrochemical anodic oxidation experiments reveal the critical oxidation potential of Ti3C2TX (0.8 V vs. RHE) and show that HER can be partially suppressed by partial oxidation of Ti3C2TX. This work highlights the importance of considering the changes in Ti3C2TX (and other) supports when supporting catalysts for CO2RR and other electrochemical reactions.

Tuning the interfacial reaction environment via pH-dependent and induced ions to understand C–N bonds coupling performance in NO3− integrated CO2 reduction to carbon and nitrogen compounds over dual Cu-based N-doped carbon catalyst

Dual atomic catalysts (DAC), particularly copper (Cu2)-based nitrogen (N) doped graphene, show great potential to effectively convert CO2 and nitrate (NO3−) into important industrial chemicals such as ethylene, glycol, acetamide, and urea through an efficient catalytical process that involves C–C and C–N coupling. However, the origin of the coupling activity remained unclear, which substantially hinders the rational design of Cu-based catalysts for the N-integrated CO2 reduction reaction (CO2RR). To address this challenge, this work performed advanced density functional theory calculations incorporating explicit solvation based on a Cu2-based N-doped carbon (Cu2N6C10) catalyst for CO2RR. These calculations are aimed to gain insight into the reaction mechanisms for the synthesis of ethylene, acetamide, and urea via coupling in the interfacial reaction micro-environment. Due to the sluggishness of CO2, the formation of a solvation electric layer by anions (F−, Cl−, Br−, and I−) and cations (Na+, Mg2+, K+, and Ca2+) leads to electron transfer towards the Cu surface. This process significantly accelerates the reduction of CO2. These results reveal that *CO intermediates play a pivotal role in N-integrated CO2RR. Remarkably, the Cu2-based N-doped carbon catalyst examined in this study has demonstrated the most potential for C–N coupling to date. Our findings reveal that through the process of a condensation reaction between *CO and NH2OH for urea synthesis, *NO3− is reduced to *NH3, and *CO2 to *CCO at dual Cu atom sites. This dual-site reduction facilitates the synthesis of acetamide through a nucleophilic reaction between NH3 and the ketene intermediate. Furthermore, we found that the I− and Mg2+ ions, influenced by pH, were highly effective for acetamide and ammonia synthesis, except when F− and Ca2+ were present. Furthermore, the mechanisms of C–N bond formation were investigated via ab-initio molecular dynamics simulations, and we found that adjusting the micro-environment can change the dominant side reaction, shifting from hydrogen production in acidic conditions to water reduction in alkaline ones. This study introduces a novel approach using ion-H2O cages to significantly enhance the efficiency of C–N coupling reactions.

Sulfur Modified Copper Nitride for Electrochemical CO2 Reduction Reaction

Metallic copper has been attracted attention as efficient catalyst for electrochemical CO2 reduction reaction (CO2RR). However, the activity of the catalyst with a single adsorption site is limited by the imbalance of the intermediate binding energy, so-called “scaling relationship”. [1] Therefore, it is crucial to break the scaling relationship between reaction intermediates in order to increase product selectivity and lower overpotential. One of the candidates to overcome this scaling relationship is metal sulfide. According to the computational study, since sulfur atoms work as an adsorption site, metal sulfide is expected to be a suitable catalyst for CO2RR with multiple adsorption sites.[2] In addition, surface modification by sulfur is also effective approach to enhance product selectivity in CO2RR. Increase of formate (HCOO-) selectivity by sulfur introduction on Cu has been reported in some previous reports.[3]-[5] On the other hand, the repulsion between the oxygen lone pair electrons of the CO2 molecule and the electronic clouds of the surface sulfur atoms become an obstacle on CO2RR.[6] A potential solution to this problem is the construction of sulfide-nitride composite. Because of the difference in electronegativity between nitrogen and metal or sulfur, it is considered that the electronic structure of the metal sulfide is altered to reduce the repulsion between oxygen and sulfur.[7] Based on these backgrounds, it is expected that the CO2RR activity of copper nitride (Cu3N) will be enhanced by sulfur introduction.Here, sulfur modified Cu3N with different amount of sulfur were synthesized by reflux method with some modification of previously reported method.[8] X-ray diffraction pattern and SEM-EDX elemental analysis result indicate that the sulfur ratio increases and copper sulfide (Cu2S) crystal phase appears with the amount of sulfur source precursor. CO2RR activity was evaluated in 0.1M KHCO3 electrolyte, and volcano trend was identified between the amount of sulfur and methane selectivity. Among all the catalysts including pure Cu3N and Cu2S which were synthesized by the same method, 4.2 mol% sulfur containing Cu3N showed the highest methane faradaic efficiency (41.4 %). This faradaic efficiency is more than 10 times higher than that of Cu3N (0.48 %) and Cu2S (1.3 %). This finding offers valuable insights into the sulfur role on the modified catalyst.

Rational Design and Synthesis of CO2 Reduction Reaction Catalysts of High Faradaic Efficiency Toward C2 + Chemical Conversions

Carbon dioxide emission from fossil fuel combustion poses a major threat to global environment and ecological systems.Carbon capture, sequestration and conversion technologies are widely pursued as possible solutions to mitigate negative impact by CO2. The electrochemical CO2 reduction reaction (CO2RR) to fuels and chemicals using renewable electricity offers attractive “carbon-neutral” and “carbon-negative” mitigation strategies. Various catalysts have been investigated as the electrocatalysts for CO2RR. Key challenges facing the current catalyst and electrolyzer designs include insufficient energy efficiency and low single product selectivity.CO2RR to C2+ chemicals represent a highly important area for CO2 reduction and utilization. For example, ethanol, ethylene, propanol, etc. are among the most produced chemicals by the industry and are widely used for various applications. Using CO2 as raw material for chemical production through electrocatalysis not only improves the carbon cycling, but also reduces the overall emissions from chemical production. While CO2RR via two proton-electron pairs (PEPs), such as the conversion of CO2 to CO or formate, have been proven high selective with fast kinetics, conversions to C2+ chemicals are significantly more difficult due to the rapid escalation of required PEPs to much higher numbers (for example, 12 for ethanol and 18 for propanol), in addition to C-C bond coupling. The increased PEPs substantially complicate the conversion by required multiple steps along the electrochemical coordinate, leading to a high probability of branching reactions and low single product Faradaic efficiency (FE).To address these challenges, the design criteria for CO2RR to C2+ chemicals should be based on high uniformity of active center for directing identical catalytic path and suppressing competing reactions, strong catalyst-reactant binding in capturing the transient species through multiple PEP transfers, and microenvironment with nanoconfinement for retaining reaction intermediates during extended catalytic processes.Recently, we developed a new amalgamated lithium metal (ALM) synthesis method of preparing highly selective and active CO2RR catalyst and achieved > 90% FE for conversion of CO2 to ethanol [1]. Our have since expanded the approach to other C2 + chemicals including acetate, acetone, glycerol, isopropanol, etc., all with FE at or higher than 80%. To better formulate our catalyst design strategy, we not only measured the CO2RR performance over a variety of electrocatalysts, but also investigated their activity-structure relationship through advanced material characterizations, combined with the first-principle computation. We found many interesting properties uniquely associated to CO2RR mechanism and kinetics, such as catalyst-size and electro-potential modulated single selectivity. In this presentation, we will share our recent discoveries and future perspective on the development of highly selective CO2RR catalysts for C2+ chemical conversions. Acknowledgement: This work is supported by U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy - Industrial Efficiency & Decarbonization Office and by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.[1] “Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically dispersed copper” Haiping Xu, Dominic Rebollar, Haiying He, Lina Chong, Yuzi Liu, Cong Liu, Cheng-Jun Sun, Tao Li, John V. Muntean, Randall E. Winans, Di-Jia Liu and Tao Xu, (2020) Nature Energy, 5, 623–632

Selective electroreduction of CO2 to C2+ products on cobalt decorated copper catalysts

Cu-catalyzed electrochemical CO2 reduction reaction (CO2RR) to multi-carbon (C2+) products is often plagued by low selectivity because the adsorption energies of different reaction intermediates are in a linear scaling relationship. Development of Cu-based bimetallic catalysts has been considered as an attractive strategy to address this issue; however, conventional bimetallic catalysts often avoid metals with strong CO adsorption energies to prevent surface poisoning. Herein, we demonstrated that limiting the amount of Co in CuCo bimetallic catalysts can enhance C2+ product selectivity. Specifically, we synthesized a series of CuCox catalysts with trace amounts of Co (0.07-1.8 at%) decorated on the surface of Cu nanowires using a simple dip coating method. Our results revealed a volcano-shaped correlation between Co loading and C2+ selectivity, with the CuCo0.4% catalyst exhibiting a 2-fold increase in C2+ selectivity compared to the Cu nanowire sample. In situ Raman and Infrared spectroscopies suggested that an optimal amount of Co could stabilize the Cu oxide/hydroxide species under the CO2RR condition and promote the adsorption of CO, thus enhancing the C2+ selectivity. This work expands the potential for developing Cu-based bimetallic catalysts for CO2RR.

Enhancing *CO coverage on Sm-Cu2O via 4f-3d orbital hybridization for highly efficient electrochemical CO2 reduction to C2H4

The electrocatalytic conversion of CO2 into valuable chemical feedstocks using renewable electricity offers a compelling strategy for closing the carbon loop. While copper-based materials are effective in catalyzing CO2 to C2+ products, the instability of Cu+ species, which tend to reduce to Cu0 at cathodic potentials during CO2 reduction, poses a significant challenge. Here, we report the development of Sm-Cu2O and investigate the influence of f-d orbital hybridization on the CO2 reduction reaction (CO2RR). Supported by density functional theory (DFT) calculations, our experimental results demonstrate that hybridization between Sm3+ 4f and Cu+ 3d orbitals not only improves the adsorption of *CO intermediates and increases CO coverage to stabilize Cu+ but also facilitates CO2 activation and lowers the energy barriers for CC coupling. Notably, Sm-Cu2O achieves a Faradaic efficiency for C2H4 that is 38% higher than that of undoped Cu2O. Additionally, it sustains its catalytic activity over an extended operational period exceeding 7 h, compared to merely 2 h for the undoped sample. This research highlights the potential of f-d orbital hybridization in enhancing the efficacy of copper-based catalysts for CO2RR, pointing towards a promising direction for the development of durable, high-performance electrocatalysts for sustainable chemical synthesis.

Promises of MOF‐Based and MOF‐Derived Materials for Electrocatalytic CO2 Reduction

AbstractElectrocatalytic CO2 reduction (ECR) powered by renewable electricity is a promising technology to mitigate carbon emissions and lessen the dependence on fossil fuels toward a carbon‐neutral energy cycle. Metal–organic frameworks (MOFs) and their derivatives, due to their excellent intrinsic activity, have emerged as promising materials for the ECR to high‐demand products. However, challenges such as unsatisfactory energy efficiency, selectivity, and relatively low production rates hinder their industrial scalability. Here, a comprehensive and critical review is presented that summarizes the state‐of‐the‐art progress in MOF‐based and MOF‐derived CO2 electroreduction catalysts from design and functionality perspectives. The fundamentals of CO2 reduction reaction (CO2RR) over heterogeneous catalysts, reaction mechanisms, and key challenges faced by ECR are described first to establish a solid foundation for forthcoming in‐depth analyses. MOF's building blocks, properties, and shortcomings pertinent to ECR including low conductivity and stability, are systematically discussed. Moreover, comprehensive discussions are provided on MOF‐based and MOF‐derived catalysts design, fabrication, characterization, and CO2RR activity to pinpoint the intricate structure‐property‐performance relationship. Finally, promising recommendations are put forward for enhancing MOF electrocatalysts activity, selectivity, and durability. This work may serve as a guideline for developing high‐performance MOF‐related catalysts for CO2RR, benefiting researchers working in this growing and potentially game‐changing area.

FeN4-Embedded Graphene as a Highly Sensitive and Selective Single-Atom Sensor for Reaction Intermediates of Electrochemical CO2 Reduction.

Exploring effective ways to detect intermediates during the electrochemical CO2 reduction reaction (CO2RR) process is pivotal for understanding reaction pathways and underlying mechanisms. Recently, two-dimensional FeN4-embedded graphene has received increasing attention as a promising catalyst for CO2RR. Here, by means of density functional theory computations combined with the non-equilibrium Green's function (NEGF) method, we proposed a detection device to evaluate the performance of FeN4-embedded graphene in intermediates detection during the CO2RR process. Our results reveal that the four key intermediates, including *COOH, *OCHO, *CHO, and *COH, can be chemisorbed on FeN4-embedded graphene with high adsorption energies and appropriate charge transfer. The computed current-voltage (I-V) characteristics and transmission spectra suggest that the adsorption of these intermediates induces significant type-dependent changes in currents and transmission coefficients of FeN4-embedded graphene. Remarkably, the FeN4-embedded graphene is more sensitive to *COOH and *COH than to *OCHO and *CHO within the entire bias window. Consequently, our theoretical study indicates that the FeN4-embedded graphene can effectively detect the key intermediates during the CO2RR process, providing a practical scheme for identifying catalytic reaction pathways and elucidating underlying reaction mechanisms.

Recent Advances on CO2 Electrochemical Reduction over Cu‐Based Nanocrystals

The electrochemical CO2 reduction reaction (CO2RR) has recently attracted increasing attention of chemists for converting CO2 to value‐added chemicals with the assistance of electrical energy. Over the past decades, substantial efforts have been devoted to CO2RR, however, this process still suffers the challenges of low conversion and poor selectivity to target product due to the thermodynamic stability and kinetic inertness of CO2. Among those catalysts, Cu has been widely used for CO2RR to produce hydrocarbons with relatively high efficiency in spite of the poor selectivity to products. Therefore, it is highly desired to developed highly active and selective Cu based catalysts for CO2RR. This mini‐review will summary the recent advances on CO2RR over Cu‐based nanocrystals (NCs) with a special focus on the control of selectivity of product via surface modification. We hope this mini‐review will motivate chemists to develop efficient catalysts for CO2RR, and also promote the fundamental research on catalyst design in heterogeneous catalysis.

Revealing the structure of the active sites for the electrocatalytic CO2 reduction to CO over Co single atom catalysts using operando XANES and machine learning.

Transition-metal nitrogen-doped carbons (TM-N-C) are emerging as a highly promising catalyst class for several important electrocatalytic processes, including the electrocatalytic CO2 reduction reaction (CO2RR). The unique local environment around the singly dispersed metal site in TM-N-C catalysts is likely to be responsible for their catalytic properties, which differ significantly from those of bulk or nanostructured catalysts. However, the identification of the actual working structure of the main active units in TM-N-C remains a challenging task due to the fluctional, dynamic nature of these catalysts, and scarcity of experimental techniques that could probe the structure of these materials under realistic working conditions. This issue is addressed in this work and the local atomistic and electronic structure of the metal site in a Co-N-C catalyst for CO2RR is investigated by employing time-resolved operando X-ray absorption spectroscopy (XAS) combined with advanced data analysis techniques. This multi-step approach, based on principal component analysis, spectral decomposition and supervised machine learning methods, allows the contributions of several co-existing species in the working Co-N-C catalysts to be decoupled, and their XAS spectra deciphered, paving the way for understanding the CO2RR mechanisms in the Co-N-C catalysts, and further optimization of this class of electrocatalytic systems.

Tailoring Cu-Based Electrocatalysts for Enhanced Electrochemical CO2 Reduction to Alcohols: Structure-Selectivity Relationship.

The use of CO2 as a feedstock for the production of carbon-based fuels and value-added chemicals offers a promising route toward carbon neutrality. In this study, two Cu-based electrocatalysts, namely, Cu24/N-C and Cu2/N-C, are successfully prepared by thermal treatment of Cu24 metal-organic polyhedron-loaded zeolitic imidazolate framework-8 (ZIF-8) nanocrystals (Cu24/ZIF-8) and Cu2 dinuclear compound-loaded ZIF-8 nanocrystals (Cu2/ZIF-8), respectively. Extensive structural and compositional analyses were conducted to confirm the formation of Cu nanocluster-loaded N-doped porous carbon supports in both Cu24/N-C and Cu2/N-C and Cu nanoparticles encapsulated by graphitic carbons in Cu2/N-C as well. These two Cu-based electrocatalysts exhibited different behaviors in the electrochemical CO2 reduction reaction (CO2RR). The Cu24/N-C electrocatalyst showed high selectivity for CO production, while Cu2/N-C showed a preference for alcohol generation. The excellent stability of Cu2/N-C over a 30 h continuous electrochemical reduction further highlights its potential for practical applications. The difference in electrocatalytic performance observed in the two catalysts for CO2RR was attributed to distinct catalytic sites associated with Cu nanoclusters and nanoparticles. This research reveals the significance of their structures and compositions for the development of highly selective electrocatalysts for CO2 reduction.

Coordination-tuned Ru single-atom catalyst for efficient catalysis of CO2 to CH4 on RuBxN4-x@TiN (x=0–4)

Creating useful chemicals or fuels from CO2 is one of the most promising ways to reach carbon neutral. In this work, through the formation of Lewis acid sites, a string of boron-atom-coordinated Ru single-atom catalysts (SACs), namely RuBxN4-x@TiN (x=0–4), were constructed, and their CO2 reduction reaction (CO2RR) was systematically studied. The results show that o-RuB2N2@TiN, p-RuB2N2@TiN, and RuB3N1@TiN are able to efficiently inhibit the competitive hydrogen evolution reaction (HER) and activate CO2, with a potential-determining step lower than 0.7 eV and high selectivity for CH4 generation. This work shows that the synergistic effect of B and Ru atoms are able to effectively improve the catalytic activity, which is expected to offer a possible tactic for the sensible creation of effective CO2RR catalysts.

Effect of hydrogen sources toward the CO2 photoreduction on boron decorated crystalline carbon nitride

Photocatalytic CO2 conversion to industrial fuels is considered an effective measure to solve energy and environmental problems. Presently, Catalysts for CO2 reduction reaction (CO2RR) are mostly confined to metal-based materials, but non-metal materials are less explored. We decorate the highly crystalline carbon nitride, i.e., poly(triazine) imides (PTI), with non-metallic boron (B) to obtain two B/PTI catalysts: Bi/PTI with B being deposited into the six-fold cavity of the PTI, and Bs/PTI with B substituting for C in PTI. For CO2RR, Bi/PTI follows a quasi Mars-van Krevelen process, but the high exposure of Bi results in an overly strong interaction with intermediates, inhibiting the reactivity. In contrast, Bs/PTI enhances the binding with intermediates by introducing Lewis acid-base pairs (B-N), which reduce the ring conjugation effect and induce the enrichment of electrons at the pyridine N. Hence, CO2 reduction with the adsorbed H* (Ha) hydrogenation mechanism in Bs/PTI has a significant reactivity.

Addressing the Carbonate Issue: Electrocatalysts for Acidic CO2 Reduction Reaction.

Electrochemical CO2 reduction reaction (CO2RR) powered by renewable energy provides a promising route to CO2 conversion and utilization. However, the widely used neutral/alkaline electrolyte consumes a large amount of CO2 to produce (bi)carbonate byproducts, leading to significant challenges at the device level, thereby impeding the further deployment of this reaction. Conducting CO2RR in acidic electrolytes offers a promising solution to address the "carbonate issue"; however, it presents inherent difficulties due to the competitive hydrogen evolution reaction, necessitating concerted efforts toward advanced catalyst and electrode designs to achieve high selectivity and activity. This review encompasses recent developments of acidic CO2RR, from mechanism elucidation to catalyst design and device engineering. This review begins by discussing the mechanistic understanding of the reaction pathway, laying the foundation for catalyst design in acidic CO2RR. Subsequently, an in-depth analysis of recent advancements in acidic CO2RR catalysts is provided, highlighting heterogeneous catalysts, surface immobilized molecular catalysts, and catalyst surface enhancement. Furthermore, the progress made in device-level applications is summarized, aiming to develop high-performance acidic CO2RR systems. Finally, the existing challenges and future directions in the design of acidic CO2RR catalysts are outlined, emphasizing the need for improved selectivity, activity, stability, and scalability.

Lattice-dislocated bismuth nanowires formed by in-situ chemical etching on copper foam for enhanced electrocatalytic CO2 reduction

Electrochemical CO2 reduction reaction (CO2RR) to HCOOH is one of the most feasible and economical methods to achieve carbon neutrality. Bismuth (Bi), as a metal catalyst for CO2RR, is considered to have great potential for application and has been widely studied due to its high formate selectivity, low toxicity, cheapness, and abundance. Unfortunately, low current density and short electrode lifetime have hindered its progress towards practical applications. In this work, we present a method that enables the chemical etching of Bi on Cu, which is capable of spontaneously accomplishing the loading of Bi on Cu foam in the liquid phase at room temperature. Additionally, to provide more abundant catalytically active sites, twisted Bi nanowires (BiNWs) with lattice dislocations were successfully prepared on the surface of Cu foam using a three-step chemical method involving oxidation, reduction, and in-situ etching. The Cu Foam@BiNWs was found to be a highly active electrocatalyst for CO2 reduction to formate at a low applied potential, achieving a faradaic efficiency for formate (FEFormate) of 95 % and a formate partial current density of ∼ 12 mA cm−2 at −0.78 V vs. RHE (reversible hydrogen electrode). Even within such a wide potential window of −0.68 ∼ -1.08 V vs. RHE, the FEFormate is consistently above 90 %. Such exceptional CO2 reduction activity can be attributed to the distortions and lattice dislocations present in the surface BiNWs. Furthermore, the Cu Foam@BiNWs electrode demonstrated a total current density close to 100 mA cm−2 at −0.98 V in an alkaline flow cell, while maintaining excellent catalytic stability over a prolonged 30-hour period of high current density electrochemical activity, thus showing potential for advancing the industrialisation of formate production. This work emphasizes the crucial role of size-dependent catalysis and crystal defect engineering strategies in the field of electrocatalysis, elucidates the mechanism of the rate-determining step (RDS) in the electrocatalytic CO2 reduction process on the developed catalysts, which can provide valuable insights into the design and development of high performance electrocatalysts not only in CO2RR but also in other fields.

Novel flexible aromatic Cu3 metal-organic π-cluster for electrocatalytic CO2 reduction reaction

Producing Cn products through electrocatalytic CO2 reduction reaction (CO2RR) is of great significance in addressing the global warming crisis. Organic-inorganic hybrid catalysts, characterized by precise and controllable active sites and metal-ligand synergistic interactions, can enhance the reaction activity and stability of Cu-based catalysts. Herein, based on density functional theory (DFT), a novel flexible aromatic Cu3 metal-organic π-cluster (Cu3-π cluster) was constructed, consisting of triple-atom active centers and pentalyne ligands. During the catalytic CO2RR process, the adsorption of H can promote the activation of CO2, this converts the competing hydrogen evolution reaction (HER) into promoting CO2RR. Enhanced aromaticity of its cluster core is credited with stabilizing the coadsorption of H and CO2 (H* + CO2*), consequently lowering the reaction free energy of the CO2 activation process. Research has shown that Cu3-π cluster have high catalytic activity for electrocatalytic CO2 generation of C2H4. Considering the solvation effect, the limit potential of this reaction is −0.60 V. Furthermore, the reaction free energies suggest that the Cu3-π cluster is more inclined to yield C2H4(g) products via COCO* coupling. Moreover, the high CO coverage at the triple-atom active centers not only makes it more challenging for this cluster to adsorb H, but also reduces the energy barrier of the COCO* coupling reaction.In the entire reaction pathway of C2H4(g), there exhibits dynamic self-adaptive behavior in the bond lengths and bond angles of the three Cu atoms in the cluster core, leading to fluctuations in aromaticity. The flexibility and aromaticity changes in this structure enable the Cu3-π cluster to better stabilize intermediates. This work provides theoretical guidance for the application of metal-organic π-clusters, accelerates the screening of catalysts for CO2RR, and provides powerful theoretical guidance for the structure-activity relationships between aromaticity and catalytic activity.

Spherical and porous Cu2O nanocages with Cu2O/Cu(OH)2 Surface: Synthesis and their promising selectivity for catalysing CO2 electroreduction to C2H4

In the production of C2H4, a vital raw material in the synthesis of polyethylene and polyvinyl chloride, Cu2O is a highly promising catalyst with excellent Faradaic efficiency and selectivity. We propose a method involving the partial reduction of Cu(OH)2 to Cu2O by sodium L-ascorbate for the synthesis of spherical and porous Cu2O nanocages (SPNCs) with a surface containing both Cu2O and Cu(OH)2. High-resolution transmission electron microscopy and electron diffraction measurements revealed ∼ 3-nm pores and a (13¯2) high-index facet on the SPNC, respectively. As SPNCs have a porous structure, their specific surface area is greater (31.10 m2 g−1) than that (6.35 m2 g−1) of spherical Cu2O nanocrystals (SNCs) with solid interiors. Furthermore, SPNCs, when applied as electrocatalysts for catalysing the CO2 reduction reaction (CO2RR), demonstrated remarkable mass activities (16.92 mA mg−1 at −1.15 V vs. reversible hydrogen electrode) for C2H4 production, with a Faraday efficiency reaching an impressive 55.3 %. Stability test data showed a consistent CO2RR current density over 6 h, owing to the porous structure and the presence of both Cu(OH)2 and Cu2O on the catalyst surface. Our proposed SPNC catalysts can be employed as effective CO2RR catalysts for producing C2H4, which may help in reducing the present reliance on petrochemical processes.

Bioinspired Binickel Catalyst for Carbon Dioxide Reduction: The Importance of Metal-ligand Cooperation.

Catalyst design for the efficient CO2 reduction reaction (CO2RR) remains a crucial challenge for the conversion of CO2 to fuels. Natural Ni-Fe carbon monoxide dehydrogenase (NiFe-CODH) achieves reversible conversion of CO2 and CO at nearly thermodynamic equilibrium potential, which provides a template for developing CO2RR catalysts. However, compared with the natural enzyme, most biomimetic synthetic Ni-Fe complexes exhibit negligible CO2RR catalytic activities, which emphasizes the significance of effective bimetallic cooperation for CO2 activation. Enlightened by bimetallic synergy, we herein report a dinickel complex, NiIINiII(bphpp)(AcO)2 (where NiNi(bphpp) is derived from H2bphpp = 2,9-bis(5-tert-butyl-2-hydroxy-3-pyridylphenyl)-1,10-phenanthroline) for electrocatalytic reduction of CO2 to CO, which exhibits a remarkable reactivity approximately 5 times higher than that of the mononuclear Ni catalyst. Electrochemical and computational studies have revealed that the redox-active phenanthroline moiety effectively modulates the electron injection and transfer akin to the [Fe3S4] cluster in NiFe-CODH, and the secondary Ni site facilitates the C-O bond activation and cleavage through electron mediation and Lewis acid characteristics. Our work underscores the significant role of bimetallic cooperation in CO2 reduction catalysis and provides valuable guidance for the rational design of CO2RR catalysts.

Backbone Engineering of Polymeric Catalysts for High-Performance CO2 Reduction in Bipolar Membrane Zero-Gap Electrolyzer.

Bipolar membranes (BPMs) have emerged as a promising solution for mitigating CO2 losses, salt precipitation and high maintenance costs associated with the commonly used anion-exchange membrane electrode assembly for CO2 reduction reaction (CO2RR). However, the industrial implementation of BPM-based zero-gap electrolyzer is hampered by the poor CO2RR performance, largely attributed to the local acidic environment. Here, we report a backbone engineering strategy to improve the CO2RR performance of molecular catalysts in BPM-based zero-gap electrolyzers by covalently grafting cobalt tetraaminophthalocyanine onto a positively charged polyfluorene backbone (PF-CoTAPc). PF-CoTAPc shows a high acid tolerance in BPM electrode assembly (BPMEA), achieving a high FE of 82.6 % for CO at 100 mA/cm2 and a high CO2 utilization efficiency of 87.8 %. Notably, the CO2RR selectivity, carbon utilization efficiency and long-term stability of PF-CoTAPc in BPMEA outperform reported BPM systems. We attribute the enhancement to the stable cationic shield in the double layer and suppression of proton migration, ultimately inhibiting the undesired hydrogen evolution and improving the CO2RR selectivity. Techno-economic analysis shows the least energy consumption (957 kJ/mol) for the PF-CoTAPc catalyst in BPMEA. Our findings provide a viable strategy for designing efficient CO2RR catalysts in acidic environments.