Catalytic conversion of CO2 to value added fuels: Current status, challenges, and future directions

Molecular Engineering of Copper Phthalocyanine for CO2 Electroreduction to Methane

Efficient electrochemical CO2 reduction reaction (ECO2RR) to multi-electron reductive products remains a great challenge. Herein, molecular engineering of copper phthalocyanines (CuPc) was explored by modifying electron-withdrawing groups (EWGs) (cyano, sulfonate anion) and electron-donating groups (EDGs) (methoxy, amino) to CuPc, then supporting onto carbon paper or carbon cloth by means of droplet coating, loading with carbon nanotubes and coating in polypyrrole (PPy). The results showed that the PPy-coated CuPc effectively catalysed ECO2RR to CH4. Interestingly, experimental results and DFT calculations indicated EWGs markedly improved the selectivity of methane for the reason that the introduction of EWGs reduces electron density of catalytic active center, resulting in a positive move to initial reduction potential. Otherwise, the modification of EDGs significantly reduces the selectivity towards methane. This electronic effect and heterogenization of CuPc are facile and effective molecular engineering, benefitting the preparation of electrocatalysts for further reduction of CO2.

Cutting-Edge Electrocatalysts for CO2RR

A world-wide growing concern relates to the rising levels of CO₂ in the atmosphere that leads to devastating consequences for our environment. In addition to reducing emissions, one alternative strategy is the conversion of CO₂ (via the CO₂ Reduction Reaction, or CO₂RR) into added-value chemicals, such as CO, HCOOH, C₂H₅OH, CH₄, and more. Although this strategy is currently not economically feasible due to the high stability of the CO₂ molecule, significant progress has been made to optimize this electrochemical conversion, especially in terms of finding a performing catalyst. In fact, many noble and non-noble metal-based systems have been investigated but achieving CO₂ conversion with high faradaic efficiency (FE), high selectivity towards specific products (e.g., hydrocarbons), and maintaining long-term stability is still challenging. The situation is also aggravated by a concomitant hydrogen production reaction (HER), together with the cost and/or scarcity of some catalysts. This review aims to present, among the most recent studies, some of the best-performing catalysts for CO₂RR. By discussing the reasons behind their performances, and relating them to their composition and structural features, some key qualities for an "optimal catalyst" can be defined, which, in turn, will help render the conversion of CO₂ a practical, as well as economically feasible process.

Mesostructured γ-Al2O3-Based Bifunctional Catalysts for Direct Synthesis of Dimethyl Ether from CO2

In this work, we propose two bifunctional nanocomposite catalysts based on acidic mesostructured γ-Al2O3 and a Cu/ZnO/ZrO2 redox phase. γ-Al2O3 was synthesized by an Evaporation-Induced Self-Assembly (EISA) method using two different templating agents (block copolymers Pluronic P123 and F127) and subsequently functionalized with the redox phase using an impregnation method modified with a self-combustion reaction. These nanocomposite catalysts and their corresponding mesostructured supports were characterized in terms of structural, textural, and morphological features as well as their acidic properties. The bifunctional catalysts were tested for the CO2-to-DME process, and their performances were compared with a physical mixture consisting of the most promising support as a dehydration catalyst together with the most common Cu-based commercial redox catalyst (CZA). The results highlight that the most appropriate Pluronic for the synthesis of γ-Al2O3 is P123; the use of this templating agent allows us to obtain a mesostructure with a smaller pore size and a higher number of acid sites. Furthermore, the corresponding composite catalyst shows a better dispersion of the redox phase and, consequently, a higher CO2 conversion. However, the incorporation of the redox phase into the porous structure of the acidic support (chemical mixing), favoring an intimate contact between the two phases, has detrimental effects on the dehydration performances due to the coverage of the acid sites with the redox nanophase. On the other hand, the strategy involving the physical mixing of the two phases, distinctly preserving the two catalytic functions, assures better performances.

DFT-based Machine Learning for Ensemble Effect of Pd@Au Electrocatalysts on CO2 Reduction Reaction

The ensemble effect due to variation of Pd content in Pd-Au alloys have been widely investigated for several important reactions, including CO₂ reduction reaction (CO₂ RR), however, identifying the stable Pd arrangements on the alloyed surface and picking out the active sites are still challenging. Here we use a density functional theory (DFT) based machine-learning (ML) approach to efficiently find the low-energy configurations of Pd-Au(111) surface alloys and the potentially active sites for CO₂ RR, fully covering the Pd content from 0 to 100 %. The ML model is actively learning process to improve the predicting accuracy for the configuration formation energy and to find the stable Pd-Au(111) alloyed surfaces, respectively. The local surface properties of adsorption sites are classified into two classes by the K-means clustering approach, which are closely related to the Pd content on Au surface. The classification is reflected in the variation of adsorption energy of CO and H: In the low Pd content range (0-60 %) the adsorption energies over the surface alloys can be tuned significantly, and in the medium Pd content (37-68 %), the catalytic activity of surface alloys for CO₂ RR can be increased by increase the Pd content and attributed to the meta-stable active site over the surface. Thus, the active site-dependent reaction mechanism is elucidated based on the ensemble effect, which provides new physical insights to understand the surface-related properties of catalysts.

Mechanism and Selectivity of Electrochemical Reduction of CO2 on Metalloporphyrin Catalysts from DFT Studies

Electrochemical reduction of CO₂ to value-added chemicals has been hindered by poor product selectivity and competition from hydrogen evolution reactions. This study aims to unravel the origin of the product selectivity and competitive hydrogen evolution reaction on [MP]⁰ catalysts (M = Fe, Co, Rh and Ir; P is porphyrin ligand) by analyzing the mechanism of CO₂ reduction and H₂ formation based on the results of density functional theory calculations. Reduction of CO₂ to CO and HCOO^- proceeds via the formation of carboxylate adduct ([MP-COOH]⁰ and ([MP-COOH]^-) and metal-hydride [MP-H]^-, respectively. Competing proton reduction to gaseous hydrogen shares the [MP-H]^- intermediate. Our results show that the pK_a of [MP-H]⁰ can be used as an indicator of the CO or HCOO^-/H₂ preference. Furthermore, an ergoneutral pH has been determined and used to determine the minimum pH at which selective CO₂ reduction to HCOO^- becomes favorable over the H₂ production. These analyses allow us to understand the product selectivity of CO₂ reduction on [FeP]⁰, [CoP]⁰, [RhP]⁰ and [IrP]⁰; [FeP]⁰ and [CoP]⁰ are selective for CO whereas [RhP]⁰ and [IrP]⁰ are selective for HCOO^- while suppressing H₂ formation. These descriptors should be applicable to other catalysts in an aqueous medium.

Cobalt Phthalocyanine Cross-Linked Polypyrrole for Efficient Electroreduction of Low Concentration CO2 To CO

Immobilizing cobalt phthalocyanine (CoPc) onto the electrode surface is a significant approach to performing efficient electrochemical CO₂ reduction reaction (ECO₂ RR). Herein, sulfylphenoxy decorated CoPc cross-linked polypyrrole is prepared by in situ polymerization on the surface of carbon cloth. The synthesized N-rich catalyst exhibits above 95 % Faradaic efficiency toward CO (FE_CO ) at -0.9 V versus reversible hydrogen electrode (RHE) at least for 10 h in aqueous solution and even enables direct electrolysis at low CO₂ concentrations, being potential for coupling ECO₂ RR with CO₂ capture. This facile in situ polymerization strategy would pave the way for developing efficient and practical electrocatalysis for ECO₂ RR.

Design of Full-Temperature-Range RWGS Catalysts: Impact of Alkali Promoters on Ni/CeO2

Reverse water gas shift (RWGS) competes with methanation as a direct pathway in the CO₂ recycling route, with methanation being a dominant process in the low-temperature window and RWGS at higher temperatures. This work showcases the design of multi-component catalysts for a full-temperature-range RWGS behavior by suppressing the methanation reaction at low temperatures. The addition of alkali promoters (Na, K, and Cs) to the reference Ni/CeO₂ catalyst allows identifying a clear trend in RWGS activation promotion in both low- and high-temperature ranges. Our characterization data evidence changes in the electronic, structural, and textural properties of the reference catalyst when promoted with selected dopants. Such modifications are crucial to displaying an advanced RWGS performance. Among the studied promoters, Cs leads to a more substantial impact on the catalytic activity. Beyond the improved CO selectivity, our best performing catalyst maintains high conversion levels for long-term runs in cyclable temperature ranges, showcasing the versatility of this catalyst for different operating conditions. All in all, this work provides an illustrative example of the impact of promoters on fine-tuning the selectivity of a CO₂ conversion process, opening new opportunities for CO₂ utilization strategies enabled by multi-component catalysts.

Electrocatalytic reduction of CO2 in water by a C-functionalized Ni-cyclam complex grafted onto carbon

We present here a novel strategy based on the covalent grafting of a C-functionalized Ni-cyclam complex onto glassy carbon to achieve heterogeneous electrocatalytic CO₂ reduction in neutral water at low overpotential (-500 mV vs. NHE), with moderate turnover number (TON = 454), high selectivity (85% CO produced) and good faradaic efficiency (56% CO). Direct comparison with the N-functionalized Ni-cyclam analogue highlights the benefits of this approach in terms of CO₂ electroreduction.

Preanodized Cu Surface for Selective CO2 Electroreduction to C1 or C2+ Products

The electrochemical CO₂ reduction over Cu catalysts has shown great potential in producing a wide range of valuable chemicals, but it is still plagued by a poor controllability on product distribution. Herein, we demonstrate an effective regulation of CO₂ reduction paths through a preanodization treatment of Cu foil electrodes in different electrolytes. The Cu electrode exhibits a superior C₁ and C₂₊ product selectivity after being preanodized in NaClO₄ (Cu-NaClO₄) and Na₂HPO₄ electrolyte (Cu-Na₂HPO₄), respectively. Combined with in situ electrochemical Raman, ATR-SEIRAS, and SEM characterizations, the preferential C₁ path is due to the deposition of many Cu nanocrystals with dominant Cu(111) facets on the Cu-NaClO₄ electrode. In contrast, the preferential C₂₊ path over the Cu-Na₂HPO₄ is attributed to formation of a unique Cu nanodendritic morphology, which strengthens the *CO intermediate adsorption and induces an environment of low local H₂O/CO₂ stoichiometric ratio, thus facilitating C-C coupling for C₂₊ production. Our findings may shed light on the rational control of the CO₂ reduction path through engineering of the Cu surface structure.

Zeolitic imidazolate framework-derived composites with SnO2 and ZnO phase components for electrocatalytic carbon dioxide reduction

Zeolitic imidazolate framework (ZIF) and its derivatives have attracted a great deal of attention in the field of electrocatalysis. In this paper, a series of tin (Sn)-modified ZIF-based composites (ZSO-X/Y) are synthesized and used as catalysts for the electrochemical reduction of CO2 to produce low-carbon fuels. Among the catalysts obtained, ZSO-2/8 shows the best formate (HCOO-) selectivity compared with others. A faradaic efficiency of 76.70% and a catalytic current density of -9.81 mA cm-2 can be respectively achieved at a potential of -1.16 V vs. reversible hydrogen electrode (VRHE). The high catalytic performance can be attributed to the stable coexistence of two-phase components of SnO2/ZnO inside the catalyst. This work provides an insight into the development of high performance ZIF-based catalysts for the electrochemical reduction of CO2.

Single-component, metal-free, solvent-free HO-functionalized 1,2,3-triazole-based ionic liquid catalysts for efficient CO2 conversion

A series of HO-functionalized 1,2,3-triazolic ionic liquids (1–9b) bearing different alkyl chains and counter-anions was evaluated as green, single-component, bifunctional catalysts for cycloaddition reactions involving CO2 and epoxides.

CuZnAl-Oxide Nanopyramidal Mesoporous Materials for the Electrocatalytic CO2 Reduction to Syngas: Tuning of H2/CO Ratio

Inspired by the knowledge of the thermocatalytic CO₂ reduction process, novel nanocrystalline CuZnAl-oxide based catalysts with pyramidal mesoporous structures are here proposed for the CO₂ electrochemical reduction under ambient conditions. The XPS analyses revealed that the co-presence of ZnO and Al₂O₃ into the Cu-based catalyst stabilize the CuO crystalline structure and introduce basic sites on the ternary as-synthesized catalyst. In contrast, the as-prepared CuZn- and Cu-based materials contain a higher amount of superficial Cu⁰ and Cu¹⁺ species. The CuZnAl-catalyst exhibited enhanced catalytic performance for the CO and H₂ production, reaching a Faradaic efficiency (FE) towards syngas of almost 95% at −0.89 V vs. RHE and a remarkable current density of up to 90 mA cm⁻² for the CO₂ reduction at −2.4 V vs. RHE. The physico-chemical characterizations confirmed that the pyramidal mesoporous structure of this material, which is constituted by a high pore volume and small CuO crystals, plays a fundamental role in its low diffusional mass-transfer resistance. The CO-productivity on the CuZnAl-catalyst increased at more negative applied potentials, leading to the production of syngas with a tunable H₂/CO ratio (from 2 to 7), depending on the applied potential. These results pave the way to substitute state-of-the-art noble metals (e.g., Ag, Au) with this abundant and cost-effective catalyst to produce syngas. Moreover, the post-reaction analyses demonstrated the stabilization of Cu₂O species, avoiding its complete reduction to Cu⁰ under the CO₂ electroreduction conditions.

CeO2/CuO/TiO2heterojunction photocatalysts for conversion of CO2to ethanol

An attempt to reduce CO₂emissions has led to the development of CeO₂/CuO/TiO₂heterojunction photocatalysts for photoconversion of CO₂to useful products, e.g. ethanol. Composite photocatalysts were simply prepared by mixing TiO₂(P25) with different mass ratios of CeO₂(1 wt%) and CuO (2 or 3 wt%) by ball milling. The prepared photocatalysts had uniformly distributed CeO₂and CuO phases, throughout the TiO₂phase. The integration of CeO₂and CuO into TiO₂at 1 wt% CeO₂and 3 wt% CuO produced a composite, with a reduced band gap of 2.88 eV, allowing absorption of lower energy light and a lower electron-hole recombination rate. The 1%CeO₂/3%CuO/TiO₂photocatalysts yielded ethanol at 30.5μmol g_cat^-1h^-1, almost three times higher than the yield from pure TiO₂. This improved CO₂conversion efficiency was due to contributions from properties of both additives: CeO₂increased light absorption, while CuO acted as an electron trap and enhanced CO₂adsorption. In addition, the heterojunction at the interfaces facilitated the photogenerated charge separation, which, in turn, increased the charge participation in the catalyzed conversion reactions.

Performance Analysis of TiO2-Modified Co/MgAl2O4 Catalyst for Dry Reforming of Methane in a Fixed Bed Reactor for Syngas (H2, CO) Production

Co/TiO2–MgAl2O4 was investigated in a fixed bed reactor for the dry reforming of methane (DRM) process. Co/TiO2–MgAl2O4 was prepared by modified co-precipitation, followed by the hydrothermal method. The active metal Co was loaded via the wetness impregnation method. The prepared catalyst was characterized by XRD, SEM, TGA, and FTIR. The performance of Co/TiO2–MgAl2O4 for the DRM process was investigated in a reactor with a temperature of 750 °C, a feed ratio (CO2/CH4) of 1, a catalyst loading of 0.5 g, and a feed flow rate of 20 mL min−1. The effect of support interaction with metal and the composite were studied for catalytic activity, the composite showing significantly improved results. Moreover, among the tested Co loadings, 5 wt% Co over the TiO2–MgAl2O4 composite shows the best catalytic performance. The 5%Co/TiO2–MgAl2O4 improved the CH4 and CO2 conversion by up to 70% and 80%, respectively, while the selectivity of H2 and CO improved to 43% and 46.5%, respectively. The achieved H2/CO ratio of 0.9 was due to the excess amount of CO produced because of the higher conversion rate of CO2 and the surface carbon reaction with oxygen species. Furthermore, in a time on stream (TOS) test, the catalyst exhibited 75 h of stability with significant catalytic activity. Catalyst potential lies in catalyst stability and performance results, thus encouraging the further investigation and use of the catalyst for the long-run DRM process.

Electrocatalytic Reduction of CO2 to Ethylene by Molecular Cu-Complex Immobilized on Graphitized Mesoporous Carbon

The electrochemical reduction of carbon dioxide (CO₂ ) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO₂ to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO₂ to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO₂ in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions.

Fabrication of ZnO-Fe-MXene Based Nanocomposites for Efficient CO2 Reduction

A ZnO-Fe-MXene nanocomposite was fabricated and examined with diverse spectroscopic techniques. The hexagonal structure of ZnO, MXene, and ZnO-Fe-MXene nanocomposites were validated through XRD. FTIR showed the characteristic vibrational frequencies of ZnO and MXene. The micrographs of the SEM showed nanoparticles with a flower-like structure. The electrocatalytic reduction efficiency of ZnO-Fe-MXene nanocomposite was analyzed through cyclic voltammetry and electrochemical impedance spectroscopy methods. The ZnO-Fe-MXene electrode was confirmed to have a high current density of 18.75 mA/cm2 under a CO2 atmosphere. Nyquist plots also illustrated a decrease in the impedance of the ZnO-Fe-MXene layer, indicating fast charge transfer between the Zn and MXene layers. Additionally, this electrochemical study highlights new features of ZnO-Fe-MXene for CO2 reduction.

Recent Development of CO2 Electrochemistry from Li-CO2 Batteries to Zn-CO2 Batteries

Metal-CO₂ batteries with CO₂ as cathode active species give rise to opportunities to deal with energy and environmental issues simultaneously. This technology is more appealing when CO₂ is flexibly reduced to chemicals and fuels driven by surplus electricity because it represents a low-cost and controllable approach to maximized electricity utilization and value-added CO₂ utilization. Nonaqueous metal-CO₂ batteries exhibited high discharge voltage and capacity with carbon and oxalate as reduction products from CO₂ electrochemistry that lacks proton. In contrast, aqueous Zn-CO₂ batteries implemented flexible CO₂ electrochemistry for more value-added products accompanied by energy storage based on a proton-coupled electron transfer mechanism. In this Account, we have exemplified our recent results in the development of CO₂ electrochemistry from nonaqueous Li-CO₂ batteries to aqueous Zn-CO₂ batteries toward practical value-added CO₂ conversion. Aimed at the challengingly limited CO₂ electrochemistry and high cost of nonaqueous Li-CO₂ batteries, we proposed aqueous Zn-CO₂ batteries. Our previous works on nonaqueous Li-CO₂ batteries, aqueous Zn-air batteries, and aqueous CO₂ reduction electrocatalysts further shed light on battery mechanism, device construction, and electrocatalyst design. For example, bipolar membranes maintain the stability of the basic anolyte and neutral catholyte, as well as the kinetics of ion transport at the same time, forming the device base for aqueous Zn-CO₂ batteries. Moreover, in terms of the electrocatalyst catalyzing both discharge and charge reactions on the cathode, the design of multifunctional electrocatalysts is of great importance for not only CO₂ electrochemistry but also spontaneous discharge and energy efficiency of aqueous Zn-CO₂ batteries. We have explored a series of multifunctional electrocatalyst cathodes, including noble metal, transition metal, and metal-free materials, all of which facilitated CO₂ electrochemistry in aqueous Zn-CO₂ batteries with value-added carbon-based products. Meanwhile, several operating models for practical complicated situations are presented, such as rechargeable, reversible, dual-model, and solid-state batteries. Zn-CO₂ batteries with different models require different design mechanisms for electrocatalyst cathodes. Reversible aqueous Zn-CO₂ batteries with HCOOH generation were enabled by electrocatalysts capable of catalyzing the interconversion of CO₂ and HCOOH at low overpotentials, rechargeable aqueous Zn-CO₂ batteries were allowed by electrocatalysts capable of catalyzing efficient CO₂ reduction and O₂ evolution, and dual-model aqueous Zn-CO₂ batteries were realized by electrocatalysts capable of catalyzing CO₂ reduction, water oxidation, and oxygen reduction. Concluding remarks include a summary of recent CO₂ electrochemistry in metal-CO₂ batteries and a brief discussion of future challenges and opportunities for practical aqueous Zn-CO₂ batteries, such as highly reduced products and high production rate.

Electrochemical Reduction of CO2 to Formate on Easily Prepared Carbon-Supported Bi Nanoparticles

Herein, the electrochemical reduction of CO2 to formate on carbon-supported bismuth nanoparticles is reported. Carbon-supported Bi nanoparticles (about 10 nm in size) were synthesized using a simple, fast and scalable approach performed under room conditions. The so-prepared Bi electrocatalyst was characterized by different physicochemical techniques, including transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction and subsequently air-brushed on a carbon paper to prepare electrodes. These electrodes were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and also by cyclic voltammetry. Finally, CO2 electroreduction electrolyses were performed at different electrode potentials for 3 h. At the optimal electrode potential (-1.6 V vs AgCl/Ag), the concentration of formate was about 77 mM with a faradaic efficiency of 93 ± 2.5%. A 100% faradaic efficiency was found at a lower potential (-1.5 V vs AgCl/Ag) with a formate concentration of about 55 mM. In terms of stability, we observed that after about 70 h (in 3 h electrolysis experiments at different potentials), the electrode deactivates due to the gradual loss of metal as shown by SEM/EDX analyses of the deactivated electrodes.

Post-modified porphyrin imine gels with improved chemical stability and efficient heterogeneous activity in CO2 transformation

Gel catalysts have been developed based on dynamic covalent chemistry and post-modification methods for improved chemical stability and catalytic activity.

Active sites of copper-complex catalytic materials for electrochemical carbon dioxide reduction

Restructuring-induced catalytic activity is an intriguing phenomenon of fundamental importance to rational design of high-performance catalyst materials. We study three copper-complex materials for electrocatalytic carbon dioxide reduction. Among them, the copper(II) phthalocyanine exhibits by far the highest activity for yielding methane with a Faradaic efficiency of 66% and a partial current density of 13 mA cm⁻² at the potential of – 1.06 V versus the reversible hydrogen electrode. Utilizing in-situ and operando X-ray absorption spectroscopy, we find that under the working conditions copper(II) phthalocyanine undergoes reversible structural and oxidation state changes to form ~ 2 nm metallic copper clusters, which catalyzes the carbon dioxide-to-methane conversion. Density functional calculations rationalize the restructuring behavior and attribute the reversibility to the strong divalent metal ion–ligand coordination in the copper(II) phthalocyanine molecular structure and the small size of the generated copper clusters under the reaction conditions.

The catalytic conversion of carbon dioxide into value-added products requires an understanding of the active species present under working conditions. Here, the authors discover copper-containing complexes to reversibly transform during electrocatalysis into methane-producing copper nanoclusters.

Cationic Zn-Porphyrin Polymer Coated onto CNTs as a Cooperative Catalyst for the Synthesis of Cyclic Carbonates

The development of solid catalysts containing multiple active sites that work cooperatively is very attractive for biomimetic catalysis. Herein, we report the synthesis of bifunctional catalysts by supporting cationic porphyrin-based polymers on carbon nanotubes (CNTs) using the direct reaction of 5,10,15,20-tetrakis(4-pyridyl)porphyrin zinc(II), di(1H-imidazol-1-yl)methane, and 1,4-bis(bromomethyl)benzene in the presence of CNTs. The bifunctional catalysts could efficiently catalyze the cycloaddition reaction of epoxides and CO₂ under solvent-free conditions with porphyrin zinc(II) as the Lewis acid site and a bromine anion as a nucleophilic agent working in a cooperative way. Furthermore, a relative amount of porphyrin zinc(II) and quaternary ammonium bromide could be facilely adjusted for facilitating cooperative behavior. The bifunctional catalyst with a TOF up to 2602 h^-1 is much more active than the corresponding homogeneous counterpart and is one of the most active heterogeneous catalysts ever reported under cocatalyst-free conditions. The high activity is mainly attributed to the enhanced cooperation effect of the bifunctional catalyst. With a wide substrate scope, the bifunctional catalyst could be stably recycled. This work demonstrates a new approach for the generation of a cooperative activation effect for solid catalysts.

Tailoring gas-phase CO2 electroreduction selectivity to hydrocarbons at Cu nanoparticles

Copper-based surfaces appear as the most active catalysts for CO₂ electroreduction to hydrocarbons, even though formation rates and efficiencies still need to be improved. The aim of the present work is to evaluate the continuous gas-phase CO₂ electroreduction to hydrocarbons (i.e. ethylene and methane) at copper nanoparticulated-based surfaces, paying attention to particle size influence (ranging from 25-80 nm) on reaction productivity, selectivity, and Faraday efficiency (FE) for CO₂ conversion. The effect of the current density and the presence of a microporous layer within the working electrode are then evaluated. Copper-based gas diffusion electrodes are prepared by airbrushing the catalytic ink onto carbon supports, which are then coupled to a cation exchange membrane (Nafion) in a membrane electrode assembly. The results show that the use of smaller copper nanoparticles (25 nm) leads to a higher ethylene production (1148 μmol m^-2 s^-1) with a remarkable high FE (92.8%), at the same time, diminishing the competitive hydrogen evolution reaction in terms of FE. This work demonstrates the importance of nanoparticle size on reaction selectivity, which may be of help to design enhanced electrocatalytic materials for CO₂ valorization to hydrocarbons.

Self-Cleaning Catalyst Electrodes for Stabilized CO2 Reduction to Hydrocarbons

A surface-restructuring strategy is presented that involves self-cleaning Cu catalyst electrodes with unprecedented catalytic stability toward CO₂ reduction. Under the working conditions, the Pd atoms pre-deposited on Cu surface induce continuous morphological and compositional restructuring of the Cu surface, which constantly refreshes the catalyst surface and thus maintains the catalytic properties for CO₂ reduction to hydrocarbons. The Pd-decorated Cu electrode can catalyze CO₂ reduction with relatively stable selectivity and current density for up to 16 h, which is one of the best catalytic durability performances among all Cu electrocatalysts for effective CO₂ conversion to hydrocarbons. The generality of this approach of utilizing foreign metal atoms to induce surface restructuring toward stabilizing Cu catalyst electrodes against deactivation by carbonaceous species accumulation in CO₂ reduction is further demonstrated by replacing Pd with Rh.