Crystal facet-dependent electrocatalytic performance of metallic Cu in CO2 reduction reactions

Tailoring ultra-small ZnO nanoparticles through cobalt doping to enhance photocatalytic CO2 reduction

Photocatalytic CO2 reduction offers a promising pathway for achieving sustainable development. However, the effectiveness of this method faces challenges related to imbalanced charge transfer/utilization. To address these issues, this paper reports on cobalt-doped zinc oxide nanoparticles (Co-ZnO NPs). The cobalt doping not only increases light absorption but also improves charge transfer/separation kinetics and modulates the reduction reaction dynamics. Notably, photocatalytic tests show that cobalt-doped zinc oxide (Co-ZnO) achieves a CO yield of 143.90 μmol g-1 h-1, which is 15.73 times higher than that of undoped ZnO, and exhibits excellent stability. This study emphasizes the importance of polarization states induced by doping for achieving efficient charge separation, providing a new approach to enhance the efficiency of photoredox catalysis.

Carbon-Supported Nano-Dispersed Metallic Copper Derived From Carbonization of MOF-199 for Electrocatalytic CO2 Reduction

CO2 emissions and accumulation in the ecosystem have exacerbated climate change and increased the global temperature. This study focused on the activation of hydrothermally synthesized Cu metal-organic framework (MOF-199) with potassium citrate (C6H5K3O7) to produce MOF-derived carbon incorporated with nano-dispersed metallic Cu and oxidative Cu species to facilitate electrochemical CO2 reduction. Among all MOF samples, the resulting MOF-derived carbon, activated by C6H5K3O7, demonstrated the highest electrocatalytic current and lowest charge transfer resistance, achieving a Faradaic efficiency exceeding 50% for the production of acetic acid (CH3COOH) at an applied potential of - 1.1 V (vs RHE). The addition of C6H5K3O7 during preparation endowed the MOF-derived C with a mesoporous structure, thereby enhancing CO2 adsorption and activation. A proposed reaction pathway suggested that the generation of nano-dispersed metallic Cu is critical for forming Cu─C bonds for producing CH3COOH. This study indicates that Cu-containing MOF-derived carbon with beneficial properties for electrocatalytic applications owing to its nanoispersed Cu features could be readily synthesized.

Size-, shape-, facet- and support-dependent selectivity of Cu nanoparticles in CO2 reduction through multiparameter optimization

This study investigates the limited selectivity of the Cu111 surface for C-C bond formation during CO2 reduction and explores the factors influencing selectivity using Cu nanoparticles smaller than 2 nm. The optimal nanoparticle size for C-C bond formation on the 111 facet with minimal overpotential is determined using density functional theory. A suitable supporting surface to enhance the stability and catalytic performance of the Cu-based nanoparticles is identified. Various Cu catalyst geometries, including planar surfaces and cuboctahedral, icosahedral, and truncated octahedral Cu nanoparticles, are considered. Size-dependent effects on the binding energies of reaction intermediates and hydrogen atoms are examined. Carbon-based surfaces, particularly 2SO2-doped graphene nanoribbons, are stable hosts for the Cu nanoparticles and help in retaining the activity for CO2 reduction. Scaling relations between the binding energies of the intermediates suggest COOH binding energy as an energy descriptor. Through multiparameter optimization and with the help of parity line and graphical construction, Cu38 and Cu79 are found to be the most promising surface for C2 product generation. This study provides insights into the factors influencing the selectivity and catalytic performance of Cu nanoparticles, aiding the development of efficient catalysts for CO2 reduction.

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.

State of Play of Critical Mineral-Based Catalysts for Electrochemical E-Refinery to Synthetic Fuels

The pursuit of decarbonization involves leveraging waste CO2 for the production of valuable fuels and chemicals (e.g., ethanol, ethylene, and urea) through the electrochemical CO2 reduction reactions (CO2RR). The efficacy of this process heavily depends on electrocatalyst performance, which is generally reliant on high loading of critical minerals. However, the supply of these minerals is susceptible to shortage and disruption, prompting concerns regarding their usage, particularly in electrocatalysis, requiring swift innovations to mitigate the supply risks. The reliance on critical minerals in catalyst fabrication can be reduced by implementing design strategies that improve the available active sites, thereby increasing the mass activity. This review seeks to discuss and analyze potential strategies, challenges, and opportunities for improving catalyst activity in CO2RR with a special attention to addressing the risks associated with critical mineral scarcity. By shedding light onto these aspects of critical mineral-based catalyst systems, this review aims to inspire the development of high-performance catalysts and facilitates the practical application of CO2RR technology, whilst mitigating adverse economic, environmental, and community impacts.

MOFs-Based Materials with Confined Space: Opportunities and Challenges for Energy and Catalytic Conversion

Metal-Organic Frameworks (MOFs) are a very promising material in the fields of energy and catalysis due to their rich active sites, tunable pore size, structural adaptability, and high specific surface area. The concepts of "carbon peak" and "carbon neutrality" have opened up huge development opportunities in the fields of energy storage, energy conversion, and catalysis, and have made significant progress and breakthroughs. In recent years, people have shown great interest in the development of MOFs materials and their applications in the above research fields. This review introduces the design strategies and latest progress of MOFs are included based on their structures such as core-shell, yolk-shell, multi-shelled, sandwich structures, unique crystal surface exposures, and MOF-derived nanomaterials in detail. This work comprehensively and systematically reviews the applications of MOF-based materials in energy and catalysis and reviews the research progress of MOF materials for atmospheric water harvesting, seawater uranium extraction, and triboelectric nanogenerators. Finally, this review looks forward to the challenges and opportunities of controlling the synthesis of MOFs through low-cost, improved conductivity, high-temperature heat resistance, and integration with machine learning. This review provides useful references for promoting the application of MOFs-based materials in the aforementioned fields.

Enhancing local K+ adsorption by high-density cube corners for efficient electroreduction of CO2 to C2+ products

Reducing carbon dioxide (CO2) to high value-added chemicals using renewable electricity is a promising approach to reducing CO2 levels in the air and mitigating the greenhouse effect, which depends on high-efficiency electrocatalysts. Copper-based catalysts can be used for electroreduction of CO2 to produce C2+ products with high added value, but suffer from poor stability and low selectivity. Herein, we propose a strategy to enhance the field effect by varying the cubic corner density on the surface of Cu2O microspheres for improving the electrocatalytic performance of CO2 reduction to C2+ products. Finite element method (FEM) simulation results show that the high density of cubic corners helps to enhance the local electric field, which increases the K+ concentration on the catalyst surface. The results of CO2 electroreduction tests show that the FEC2+ of the Cu2O catalyst with high-density cubic corners is 71% at a partial current density of 497 mA cm-2. Density functional theory (DFT) calculations reveal that Cu2O (111) and Cu2O (110) can effectively reduce the energy barrier of C-C coupling and improve the FEC2+ at high K+ concentrations relative to Cu2O (100). This study provides a new perspective for the design and development of efficient CO2RR catalysts.

Steering the Selectivity of Carbon Dioxide Electroreduction from Single-Carbon to Multicarbon Products on Metal-Organic Frameworks via Facet Engineering

Although metal-organic frameworks (MOFs) have attracted more attention for the electrocatalytic CO2 reduction reaction (CO2RR), obtaining multicarbon products with a high Faradaic efficiency (FE) remains challenging, especially under neutral conditions. Here, we report the controlled synthesis of stable Cu(I) 5-mercapto-1-methyltetrazole framework (Cu-MMT) nanostructures with different facets by rationally modulating the reaction solvents. Significantly, Cu-MMT nanostructures with (001) facets are acquired using isopropanol as a solvent, which favor multicarbon production with an FE of 73.75% and a multicarbon:single-carbon ratio of 3.93 for CO2RR in a neutral electrolyte. In sharp contrast, Cu-MMT nanostructures with (100) facets are obtained utilizing water, promoting single-carbon generation with an FE of 63.98% and a multicarbon: single-carbon ratio of only 0.18. Furthermore, this method can be extended to other Cu-MMT nanostructures with different facets in tuning the CO2 reduction selectivity. This work opens up new opportunities for the highly selective and efficient CO2 electroreduction to multicarbon products on MOFs via facet engineering.

Catalysts and electrolyzers for the electrochemical CO2 reduction reaction: from laboratory to industrial applications

To cope with the urgent environmental pressure and tight energy demand, using electrocatalytic methods to drive the reduction of carbon dioxide molecules and produce a variety of fuels and chemicals, is one of the effective pathways to achieve carbon neutrality. In recent years, many significant advances in the study of the electrochemical carbon dioxide reduction reaction (CO2RR) have been made, but most of the works exhibit low current density, small electrode area and poor long-term stability, which are not suitable for large-scale industrial applications. Herein, combining the research achievements obtained in laboratories and the practical demand of industrial production, we summarize recent frontier progress in the field of the electrochemical CO2RR, including the fundamentals of catalytic reactions, catalyst design and preparation, and the construction of electrolyzers. In addition, we discuss the bottleneck problem of industrial CO2 electrolysis, and further present the prospect of the essential issues to be solved by the available technology for industrial electrolysis. This review can provide some basic understanding and knowledge accumulation for the development and practical application of electrochemical CO2RR technology.

Hollow carbon-based materials for electrocatalytic and thermocatalytic CO2 conversion

Electrocatalytic and thermocatalytic CO2 conversions provide promising routes to realize global carbon neutrality, and the development of corresponding advanced catalysts is important but challenging. Hollow-structured carbon (HSC) materials with striking features, including unique cavity structure, good permeability, large surface area, and readily functionalizable surface, are flexible platforms for designing high-performance catalysts. In this review, the topics range from the accurate design of HSC materials to specific electrocatalytic and thermocatalytic CO2 conversion applications, aiming to address the drawbacks of conventional catalysts, such as sluggish reaction kinetics, inadequate selectivity, and poor stability. Firstly, the synthetic methods of HSC, including the hard template route, soft template approach, and self-template strategy are summarized, with an evaluation of their characteristics and applicability. Subsequently, the functionalization strategies (nonmetal doping, metal single-atom anchoring, and metal nanoparticle modification) for HSC are comprehensively discussed. Lastly, the recent achievements of intriguing HSC-based materials in electrocatalytic and thermocatalytic CO2 conversion applications are presented, with a particular focus on revealing the relationship between catalyst structure and activity. We anticipate that the review can provide some ideas for designing highly active and durable catalytic systems for CO2 valorization and beyond.

High dispersion dendritic fibrous morphology nanospheres for electrochemical CO2 reduction to C2H4

The electrochemical CO2 reduction to specific multi-carbon product on copper-based catalysts is subjected to low activity and poor selectivity. Herein, catalyst structure, morphology, and chemical component are systematically studied for bolstering the activity and selectivity of as-prepared catalyzers in this study. Dendritic fibrous nano-silica spheres favor the loading of active species and the transport of reactant from the central radial channel. Cu/DFNS with high dispersion active sites are fabricated through urea-assisted precipitation way. The coexistence of Cu(I)/Cu(II) induces a close combination of Cu active sites and CO2 on the Cu/DFNS interface, promoting the CO2 activation and CC coupling. The Cu-O-Si interface (Cu phyllosilicate) can improve CO2 and CO attachment. Cu/DFNS show the utmost Faradaic efficiency of C2H4 with a value of 53.04% at -1.2 V vs. RHE. And more importantly, in-situ ATR-SEIRAS reveals that the CC coupling is boosted for effectively producing C2H4 as a consequence of the existence of *COL, *COOH, and *COH intermediates. The mechanism reaction path of Cu/DFNS is inferred to be *CO2 → *COOH → *CO → *CO*COH → C2H4. Our findings will be helpful to gain insight into the links between morphology, texture, chemical component of catalyzers, and electrochemical reduction of CO2, providing valuable guidance in the design of more efficient catalysts.

Electroreduction of CO2 on Au(310)@Cu High-index Facets

The chemical selectivity and faradaic efficiency of high-index Cu facets for the CO₂ reduction reaction (CO₂ RR) is investigated. More specifically, shape-controlled nanoparticles enclosed by Cu {hk0} facets are fabricated using Cu multilayer deposition at three distinct layer thicknesses on the surface facets of Au truncated ditetragonal nanoprisms (Au DTPs). Au DTPs are shapes enclosed by 12 high-index {310} facets. Facet angle analysis confirms DTP geometry. Elemental mapping analysis shows Cu surface layers are uniformly distributed on the Au {310} facets of the DTPs. The 7 nm Au@Cu DTPs high-index {hk0} facets exhibit a CH₄  : CO product ratio of almost 10 : 1 compared to a 1 : 1 ratio for the reference 7 nm Au@Cu nanoparticles (NPs). Operando Fourier transform infrared spectroscopy spectra disclose reactive adsorbed *CO as the main intermediate, whereas CO stripping experiments reveal the high-index facets enhance the *CO formation followed by rapid desorption or hydrogenation.

Honeycomb-like CuO@C for electroreduction of carbon dioxide to ethylene

The electrochemical CO₂ reduction (ECR) of high-value multicarbon products is an urgent challenge for catalysis and energy resources. Herein, we reported a simple polymer thermal treatment strategy for preparing honeycomb-like CuO@C catalysts for ECR with remarkable C₂H₄ activity and selectivity. The honeycomb-like structure favored the enrichment of more CO₂ molecules to improve the CO₂-to-C₂H₄ conversion. Further experimental results indicate that the CuO loaded on amorphous carbon with a calcination temperature of 600 °C (CuO@C-600) has a Faradaic efficiency (FE) as high as 60.2% towards C₂H₄ formation, significantly outperforming pure CuO-600 (18.3%), CuO@C-500 (45.1%) and CuO@C-700 (41.4%), respectively. The interaction between the CuO nanoparticles and amorphous carbon improves the electron transfer and accelerates the ECR process. Furthermore, in situ Raman spectra demonstrated that CuO@C-600 can adsorb more adsorbed *CO intermediates, which enriches the CC coupling kinetics and promotes C₂H₄ production. This finding may offer a paradigm to design high-efficiency electrocatalysts, which can be beneficial to achieve the "double carbon goal."

Single-Site Metal-Organic Framework and Copper Foil Tandem Catalyst for Highly Selective CO2 Electroreduction to C2 H4

Tandem catalysis is a promising way to break the limitation of linear scaling relationship for enhancing efficiency, and the desired tandem catalysts for electrochemical CO₂ reduction reaction (CO₂ RR) are urgent to be developed. Here, a tandem electrocatalyst created by combining Cu foil (CF) with a single-site Cu(II) metal-organic framework (MOF), named as Cu-MOF-CF, to realize improved electrochemical CO₂ RR performance, is reported. The Cu-MOF-CF shows suppression of CH₄ , great increase in C₂ H₄ selectivity (48.6%), and partial current density of C₂ H₄ at -1.11 V versus reversible hydrogen electrode. The outstanding performance of Cu-MOF-CF for CO₂ RR results from the improved microenvironment of the Cu active sites that inhibits CH₄ production, more CO intermediate produced by single-site Cu-MOF in situ for CF, and the enlarged active surface area by porous Cu-MOF. This work provides a strategy to combine MOFs with copper-based electrocatalysts to establish high-efficiency electrocatalytic CO₂ RR.

Graphdiyne supported Ag-Cu tandem catalytic scheme for electrocatalytic reduction of CO2 to C2+ products

The electrochemical CO₂ reduction reaction (CO₂RR) to added-value C₂₊ products is a worthy way to effectively reduce CO₂ levels in the atmosphere. Cu nanomaterials have been proposed as efficient CO₂RR catalysts for producing C₂₊ products; however, the difficulties in controlling their efficiency and selectivity hinder their applications. Herein, we propose a simple routine to construct a graphdiyne (GDY) supported Ag-Cu nanocluster as a C₂₊ product-selective electrocatalyst and optimize the composition by electrochemical performance screening. The synthesized Ag-Cu nanoclusters are uniformly distributed on the surface of GDY with particle sizes constricted to 3.7 nm due to the strong diyne-Cu interaction. Compared to Cu/GDY, Ag-Cu/GDY tandem schemes exhibited superior CO₂RR to C₂₊ performance with a Faraday efficiency (FE) of up to 55.1% and a current density of 48.6 mA cm^-2 which remain stable for more than 33 hours. Theoretical calculations show that the adsorption energy of CO is much higher on Cu (-1.066 eV) than on Ag (-0.615 eV), thus promoting the drift of *CO from Ag to Cu. Moreover, the calculations indicate that the key C-C coupling reaction of *CO with *COH is more favored on Ag-Cu/GDY than on the original Cu/GDY which contributes to the formation of C₂₊ products. Our findings shed light on a new strategy of combining a GDY support with a tandem catalytic scheme for developing new CO₂RR catalysts with superior selectivity and activity for C₂₊ products.

Copper-Based Catalysts for Electrochemical Reduction of Carbon Dioxide to Ethylene

Electrochemical reduction of CO₂ into high energy density multi-carbon chemicals or fuels (e. g., ethylene) via new renewable energy storage has extraordinary implications for carbon neutrality. Copper (Cu)-based catalysts have been recognized as the most promising catalysts for the electrochemical reduction of CO₂ to ethylene (C₂ H₄ ) due to their moderate CO adsorption energy and moderate hydrogen precipitation potential. However, the poor selectivity, low current density and high overpotential of the CO₂ RR into C₂ H₄ greatly limit its industrial applications. Meanwhile, the complex reaction mechanism is still unclear, which leads to blindness in the design of catalysts. Herein, we systematically summarized the latest research, proposed possible conversion mechanisms and categorized the general strategies to adjust of the structure and composition for CO₂ RR, such as tip effect, defect engineering, crystal plane catalysis, synergistic effect, nanoconfinement effect and so on. Eventually, we provided a prospect of the future challenges for further development and progress in CO₂ RR. Previous reviews have summarized catalyst designs for the reduction of CO₂ to multi-carbon products, while lacking in targeting C₂ H₄ alone, an important industrial feedstock. This Review mainly aims to provide a comprehensive understanding for the design strategies and challenges of electrocatalytic CO₂ reduction to C₂ H₄ through recent researches and further propose some guidelines for the future design of copper-based catalysts for electroreduction of CO₂ to C₂ H₄ .

Bimetallic Cu-Bi catalysts for efficient electroreduction of CO2 to formate

Electrochemical CO₂ reduction offers an effective means to store renewable electricity in value-added chemical feedstocks. Much effort has been made to develop catalysts that achieve high Faradaic efficiency toward Formate production, but the catalysts still need high operating potentials to drive the CO₂–to–formate reduction. Here we report physical vapor deposition to fabricate homogeneously alloyed, compositionally controlled Cu_1-xBi_x bimetallic catalysts over a large area with excellent electrical conductivity. Operating electrochemical studies in Ar-saturated and CO₂-saturated electrolytes identified that Cu–Bi catalysts notably suppress the competing H₂ evolution reaction and enhance CO₂–to–formate selectivity. We reported a formate Faradaic efficiency of >95% at an improved cathodic potential of ∼−0.72 V vs. RHE and a high formate cathodic energy efficiency of ∼70%. The electrochemical reaction is stable over 24 h at a current density of 200 mA cm⁻². The work shows the advantages of bimetallic catalysts over single metal catalysts for increased reaction activity and selectivity.