Ultrastable atomic copper nanosheets for selective electrochemical reduction of carbon dioxide

Bubble-triggered piezocatalytic generation of hydrogen peroxide by copper nanosheets-modified polyvinylidene fluoride films for organic pollutant degradation and water disinfection

Piezocatalysis has emerged as an attractive technology for environmental remediation by the effective transformation of mechanical energy into electrical energy. Herein, copper nanosheets-modified polyvinylidene fluoride films (CuNS/PVDF) are synthesized via a facile wet-chemistry route and exhibit a much-enhanced piezoelectric property, as compared to pristine PVDF. This is ascribed to CuNS that increases the stress response point and Young's modulus of the PVDF host. Among the series, CuNS4%/PVDF, with a 4 wt% loading of CuNS and a d33 coefficient (39 pC N-1) 2.6 times that of PVDF, exhibits the highest rate of H₂O₂ generation (163.3 μM g⁻¹ h⁻¹) by water oxidation in pure water under air bubbling, which is 3.7 times that of PVDF. This can be exploited for organic pollutant degradation and water disinfection, achieving a degradation rate of 99.8%, 98.37%, 89.02% and 81.60% for chlortetracycline hydrochloride, tetracycline, ofloxacin and ciprofloxacin, respectively, after 80 min's air bubbling, and 99.7% bactericidal efficiency against Escherichia coli after 12 h's co-culture, along with excellent stability and recyclability. Notably, such a performance remains prominent in actual wastewater, seawater, tap water and other water environments. The reaction mechanisms are unraveled by the combined studies of spectroscopic measurements and theoretical calculations. Results from this work highlight the significance of structural engineering in enhancing the piezocatalytic activity of PVDF for water treatment and disinfection.

Microwave-Assisted Fabrication of Copper Oxide/N-Doped Carbon Nanocatalyst for Efficient Electrochemical CO2 Conversion to Liquid Fuels

Electrochemical CO2 reduction reaction (CO2RR), which is driven by electricity generated from renewable energy sources, is a promising technology for sustainably producing carbon-based chemicals or fuels. Several CO2RR catalysts have been explored to date, among which copper-based electrocatalysts are the most widely known for electrochemical CO2RR and are extensively studied for their ability to generate an array of products. Their low selectivity, however, hinders their possibility of being used for practical purposes. In this work, a microwave-assisted one-pot synthesized CuxO/N-doped carbon demonstrates the electrochemical conversion of carbon dioxide into multiple C1 products (mainly formate and methanol), with a maximum Faradaic efficiency of 95% in 0.10 m KHCO3 aqueous solution at a moderately low applied potential of -0.55 V versus RHE (reversible hydrogen electrode). The in-depth theoretical study reveals the key contribution of pyridinic N-based N-doped carbon sites and Cu2O clusters in CO2 adsorption and its subsequent conversion to formate and methanol via an energetically favorable formate pathway. The electrocatalyst continued to demonstrate CO2 reduction to valuable C1 products when a simulated flue gas stream containing 15% CO2 along with 500 ppm SOx and 200 ppm NOx is used as an inlet feed.

Highly Active and Stable Cu-Cd Bimetallic Oxides for Enhanced Electrochemical CO2 Reduction

Electrochemical reduction of carbon dioxide (CO2) can produce value-added chemicals such as carbon monoxide (CO) and multicarbon (C2+). However, the complex reaction pathways of CO2 electro-reduction reaction (CO2RR) greatly limit the product selectivity and conversion efficiency. Herein, the Cu-Cd bimetallic oxides catalyst was designed and applied for the CO2RR. The optimized 4.73 %Cd-CuO exhibits remarkable electrocatalytic CO2RR activity for selective CO production in H-cell using 0.5 M 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6)/MeCN as electrolyte. The Faradaic efficiency of CO (FE(CO)) can be maintained above 90 % over a wide potential range of -2.0 to -2.4 V vs. Ag/Ag+. Particularly, the catalyst achieves an impressive FE(CO) of 96.3 % with a current density of 60.7 mA cm-2 at -2.2 V vs. Ag/Ag+. Furthermore, scaling up the 4.73 %Cd-CuO catalyst into a flow cell can reach 56.64 % FE of C2+ products (ethylene, ethanol and n-propanol) with a current density as high as 600 mA cm-2 steadily. The excellent CO2RR performance of the as-synthesized 4.73 %Cd-CuO can be mainly attributed to the introduction of CdO to improve the ability of CuO to activate CO2, the electronic interactions between Cu and Cd can boost the activation and conversion the key intermediates of CO2RR and ensure the continuous stability of the 4.73 %Cd-CuO in electrolysis process.

Strategies for Achieving Carbon Neutrality: Dual-Atom Catalysts in Focus

Carbon neutrality is a fundamental strategy for achieving the sustainable development of human society. Catalyzing CO2 reduction into various high-value-added fuels serves as an effective pathway to achieve this strategic objective. Atom-dispersed catalysts have received extensive attention due to their maximum atomic utilization, high catalytic selectivity, and exceptional catalytic performance. Dual-atom catalysts (DACs), as an extension of single-atom catalysts (SACs), not only retain the advantages of SACs, but also produce many new properties. This review initiates its exploration by elucidating the mechanism of CO2 reduction reaction (CO2RR) from CO2 adsorption and CO2 activation. Then, a comprehensive summary of recently developed preparation methods of DACs is presented. Importantly, the mechanisms underlying the promoted catalytic performance of DACs in comparison to SACs are subjected to a comprehensive analysis from adjustable adsorption capacity, tunable electronic structure, strong synergistic effect, and enhanced spacing effect, elucidating their respective superiorities in CO2RR. Subsequently, the application of DACs in CO2RR is discussed in detail. Conclusively, the prospective trajectories and inherent challenges of CO2RR are expounded upon concerning the continued advancement of DACs. This thorough review not only enhances the comprehension of DACs within CO2RR but also accentuates the prospective developments in the design of sophisticated catalytic materials.

Synthesis of defect-rich La2O2CO3 supports for enhanced CO2-to-methanol conversion efficiency

Converting CO2 to methanol is crucial for addressing fuel scarcity and mitigating the greenhouse effect. Cu-based catalysts, with their diverse surface states, offer the potential to control reaction pathways and generate reactive H* species. However, a major challenge lies in oxidizing active Cu0 species by water generated during the catalytic process. While nonreducible metal oxides are beneficial in stabilizing metallic states, their limited capability to generate surface oxygen vacancies (OV) hinders CO2 activation. Herein, we present a strategy by doping Nd into a La2O2CO3 (LOC) support, enhancing OV formation by disrupting its lattice dyadicity. This leads to higher Cu0 concentration and improved CO2 activation. The resulting Cu/LOC:Nd catalyst notably outperforms Cu/LOC and CuZnAl catalysts, achieving a methanol yield of 9.9 moles of methanol per hour per mole of Cu. Our approach opens up possibilities for enhancing Cu-based catalysts in CO2 conversion.

Lithium extraction from brine through a decoupled and membrane-free electrochemical cell design

The sustainability of lithium-based energy storage or conversion systems, e.g., lithium-ion batteries, can be enhanced by establishing methods of efficient lithium extraction from harsh brines. In this work, we describe a decoupled membrane-free electrochemical cell that cycles lithium ions between iron-phosphate electrodes and features cathode (brine) and anode (fresh water) compartments that are isolated from each other yet electrochemically connected through a pair of silver/silver-halide redox electrodes. This design is compatible with harsh brines having magnesium/lithium molar ratios of up to 3258 and lithium concentrations down to 0.15 millimolar, enabling the production of battery-grade (>99.95% pure) lithium carbonate. Energy savings of up to ~21.5% were realized by efficiently harvesting the osmotic energy of the brines. A pilot-scale cell with an electrode surface area of 33.75 square meters was used to realize lithium extraction from Dead Sea brine with a recovery rate of 84.0%.

Full Selectivity Control over the Catalytic Hydrogenation of Nitroaromatics Into Six Products

A full selectivity control over the catalytic hydrogenation of nitroaromatics leads to the production of six possible products, i.e., nitroso, hydroxylamine, azoxy, azo, hydrazo or aniline compounds, which has however not been achieved in the field of heterogeneous catalysis. Currently, there is no sufficient evidence to support that the catalytic hydrogenation of nitroaromatics with the use of heterogeneous metal catalysts would follow the Haber's mechanistic scheme based on electrochemical reduction. We now demonstrate in this work that it is possible to fully control the catalytic hydrogenation of nitroaromatics into their all six products using a single catalytic system under various conditions. Employing SnO2-supported Pt nanoparticles facilitated by the surface coordination of ethylenediamine and vanadium species enabled this unprecedented selectivity control. Through systematic investigation into the controlled production of all products and their chemical reactivities, we have constructed a detailed reaction network for the catalytic hydrogenation of nitroaromatics. Crucially, using oxygen-isolated characterization techniques is essential for identifying unstable compounds such as nitroso, hydroxylamine, hydrazo compounds. The insights gained from this research offer invaluable guidance for selectively transforming nitroaromatics into a wide array of functional N-containing compounds, both advancing fundamental understanding and fostering practical applications in various fields.

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

Elevated levels of carbon dioxide (CO2) in the atmosphere and the diminishing reserves of fossil fuels have raised profound concerns regarding the resulting consequences of global climate change and the future supply of energy. Hence, the reduction and transformation of CO2 not only mitigates environmental pollution but also generates value-added chemicals, providing a dual remedy to address both energy and environmental challenges. Despite notable advancements, the low conversion efficiency of CO2 remains a major obstacle, largely attributed to its inert chemical nature. It is imperative to engineer catalysts/materials that exhibit high conversion efficiency, selectivity, and stability for CO2 transformation. With unparalleled precision at the atomic level, atomic layer deposition (ALD) and molecular layer deposition (MLD) methods utilize various strategies, including ultrathin modification, overcoating, interlayer coating, area-selective deposition, template-assisted deposition, and sacrificial-layer-assisted deposition, to synthesize numerous novel metal-based materials with diverse structures. These materials, functioning as active materials, passive materials or modifiers, have contributed to the enhancement of catalytic activity, selectivity, and stability, effectively addressing the challenges linked to CO2 transformation. Herein, this review focuses on ALD and MLD's role in fabricating materials for electro-, photo-, photoelectro-, and thermal catalytic CO2 reduction, CO2 capture and separation, and electrochemical CO2 sensing. Significant emphasis is dedicated to the ALD and MLD designed materials, their crucial role in enhancing performance, and exploring the relationship between their structures and catalytic activities for CO2 transformation. Finally, this comprehensive review presents the summary, challenges and prospects for ALD and MLD-designed materials for CO2 transformation.

Constructing Asymmetric Charge Polarized NiCo Prussian Blue Analogue for Promoted Electrocatalytic Methanol to Formate Conversion

The highly selective electrochemical conversion of methanol to formate is of great significance for various clean energy devices, but understanding the structure-to-property relationship remains unclear. Here, the asymmetric charge polarized NiCo prussian blue analogue (NiCo PBA-100) is reported to exhibit remarkable catalytic performance with high current density (210 mA cm-2 @1.65 V vs RHE) and Faraday efficiency (over 90%). Meanwhile, the hybrid water splitting and Zinc-methanol-battery assembled by NiCo PBA-100 display the promoted performance with decent stability. X-ray absorption spectroscopy (XAS) and operando Raman spectroscopy indicate that the asymmetric charge polarization in NiCo PBA leads to more unoccupied states of Ni and occupied states of Co, thereby facilitating the rapid transformation of the high-active catalytic centers. Density functional theory calculations combining operando Fourier transform infrared spectroscopy demonstrate that the final reconstructed catalyst derived by NiCo PBA-100 exhibits rearranged d band properties along with a lowered energy barrier of the rate-determining step and favors the desired formate production.

In Situ Probing the Structure Change and Interaction of Interfacial Water and Hydroxyl Intermediates on Ni(OH)2 Surface over Water Splitting

There is growing acknowledgment that the properties of the electrochemical interfaces play an increasingly pivotal role in improving the performance of the hydrogen evolution reaction (HER). Here, we present, for the first time, direct dynamic spectral evidence illustrating the impact of the interaction between interfacial water molecules and adsorbed hydroxyl species (OHad) on the HER properties of Ni(OH)2 using Au/core-Ni(OH)2/shell nanoparticle-enhanced Raman spectroscopy. Notably, our findings highlight that the interaction between OHad and interfacial water molecules promotes the formation of weakly hydrogen-bonded water, fostering an environment conducive to improving the HER performance. Furthermore, the participation of OHad in the reaction is substantiated by the observed deprotonation step of Au@2 nm Ni(OH)2 during the HER process. This phenomenon is corroborated by the phase transition of Ni(OH)2 to NiO, as verified through Raman and X-ray photoelectron spectroscopy. The significant redshift in the OH-stretching frequency of water molecules during the phase transition confirms that surface OHad disrupts the hydrogen-bond network of interfacial water molecules. Through manipulation of the shell thickness of Au@Ni(OH)2, we additionally validate the interaction between OHad and interfacial water molecules. In summary, our insights emphasize the potential of electrochemical interfacial engineering as a potent approach to enhance electrocatalytic performance.

Ultrathin LayCoOx Nanosheets with High Porosity Featuring Boosted Catalytic Oxidation of Benzene: Mechanism Elucidation via an Experiment-Theory Combined Paradigm

Designing transition-metal oxides for catalytically removing the highly toxic benzene holds significance in addressing indoor/outdoor environmental pollution issues. Herein, we successfully synthesized ultrathin LayCoOx nanosheets (thickness of ∼1.8 nm) with high porosity, using a straightforward coprecipitation method. Comprehensive characterization techniques were employed to analyze the synthesized LayCoOx catalysts, revealing their low crystallinity, high surface area, and abundant porosity. Catalytic benzene oxidation tests demonstrated that the La0.029CoOx-300 nanosheet exhibited the most optimal performance. This catalyst enabled complete benzene degradation at a relatively low temperature of 220 °C, even under a high space velocity (SV) of 20,000 h-1, and displayed remarkable durability throughout various catalytic assessments, including SV variations, exposure to water vapor, recycling, and long time-on-stream tests. Characterization analyses confirmed the enhanced interactions between Co and doped La, the presence of abundant adsorbed oxygen, and the extensive exposure of Co3+ species in La0.029CoOx-300 nanosheets. Theoretical calculations further revealed that La doping was beneficial for the formation of oxygen vacancies and the adsorption of more hydroxyl groups. These features strongly promoted the adsorption and activation of oxygen, thereby accelerating the benzene oxidation processes. This work underscores the advantages of doping rare-earth elements into transition-metal oxides as a cost-effective yet efficient strategy for purifying industrial exhausts.

Graphene quantum dot-mediated anchoring of highly dispersed bismuth nanoparticles on porous graphene for enhanced electrocatalytic CO2 reduction to formate

The electrocatalytic reduction of CO2 to produce formic acid is gaining prominence as a critical technology in the pursuit of carbon neutrality. Nonetheless, it remains challenging to attain both substantial formic acid production and high stability across a wide voltage range, particularly when utilizing bismuth-based catalysts. Herein, we present a novel graphene quantum dot-mediated synthetic strategy to achieve the uniform deposition of highly dispersed bismuth nanoparticles on porous graphene. This innovative design achieves an elevated faradaic efficiency for formate of 87.0% at -1.11 V vs. RHE with high current density and long-term stability. When employing a flow cell, a maximum FEformate of 80.0% was attained with a total current density of 156.5 mA cm-2. The exceptional catalytic properties can be primarily attributed to the use of porous graphene as the support and the auxiliary contribution of graphene quantum dots, which enhance the dispersion of bismuth nanoparticles. This improved dispersion, in turn, has a significantly positive impact on CO2 activation and the generation of *HCOO intermediates to facilitate the formation of formate. This work presents a straightforward technique to create uniform metal nanoparticles on carbon materials for advancing various electrolytic applications.

A dendritic porous copper foam-carbonic anhydrase biohybrid for carbon dioxide electroreduction

Carbonic anhydrase (CA) is bound to a dendritic porous copper foam (3D-Cu) via electrostatic interaction to form a biohybrid (CA/3D-Cu), which exhibits high selectivity and Faraday efficiency in the electroreduction of carbon dioxide (CO2) to formic acid (selectivity of 98.7%, Faraday efficiency of 82.1%) due to the large specific surface area of the 3D-Cu and the ultra-high CO2 hydration capacity of CA.

Non-Noble Metal Incorporated Transition Metal Dichalcogenide Monolayers for Electrochemical CO2 Reduction: A First-Principles Study

Using non-noble metal atoms as catalysts is attractive for decreasing the cost of the CO2 reduction reaction (CO2RR). By screening first-row transition metals and noble metals through extensive first-principles calculations, non-noble Sc and Ti single atoms binding on vacancy-defected transition metal dichalcogenide (TMD) monolayers exhibit better catalytic performance and selectivity for electrochemical CO2RR than noble metal single atoms. The overpotentials of Sc and Ti atoms for the CO2RR can be reduced lower than 0.09 V after applying suitable biaxial tensile strains on vacancy-defected TMDs, which are approximately 1 order of magnitude lower than that of most reported metal atom catalysts. The vacancy defects of TMDs and charge transfer to metal atoms induced by tensile strain play a key role in improving the catalytic activity of non-noble metal single atoms. These results highlight a possible way to design new single atom catalysts for electrochemical CO2RR by utilizing the combination of non-noble metal atoms, defected TMDs, and strain engineering.

Stability Issues in Electrochemical CO2 Reduction: Recent Advances in Fundamental Understanding and Design Strategies

Electrochemical CO2 reduction reaction (CO2 RR) offers a promising approach to close the anthropogenic carbon cycle and store intermittent renewable energy in fuels or chemicals. On the path to commercializing this technology, achieving the long-term operation stability is a central requirement but still confronts challenges. This motivates to organize the present review to systematically discuss the stability issue of CO2 RR. This review starts from the fundamental understanding on the destabilization mechanisms of CO2 RR, with focus on the degradation of electrocatalyst and change of reaction microenvironment during continuous electrolysis. Subsequently, recent efforts on catalyst design to stabilize the active sites are summarized, where increasing atomic binding strength to resist surface reconstruction is highlighted. Next, the optimization of electrolysis system to enhance the operation stability by maintaining reaction microenvironment especially mitigating flooding and carbonate problems is demonstrated. The manipulation on operation conditions also enables to prolong CO2 RR lifespan through recovering catalytically active sites and mass transport process. This review finally ends up by indicating the challenges and future opportunities.

Efficient Catalytic Production of Hydrogen Peroxide Using Tin-containing Zeolite Fixed Palladium Nanoparticles with Oxidation Resistance

The metal surfaces tend to be oxidized in air through dissociation of the O-O bond of oxygen to reduce the performances in various fields. Although several ligand modification routes have alleviated the oxidation of bulky metal surfaces, it is still a challenge for the oxidation resistance of small-size metal nanoparticles. Herein, we fixed the small-size Pd nanoparticles in tin-contained MFI zeolite crystals, where the tin acts as an electron donor to efficiently hinder the oxidation of Pd by weakening the adsorption of molecular oxygen and suppressing the O-O cleavage. This oxidation-resistant Pd catalyst exhibited superior performance in directly synthesizing hydrogen peroxide from hydrogen and oxygen, with the productivity of hydrogen peroxide at ≈10,170 mmol gPd -1 h-1 , steadily outperforming the catalysts tested previously. This work leads to the hypothesis that tin is an electron donor to realize oxidation-resistant Pd within zeolite crystals for efficient catalysis to overcome the limitation of generally supported Pd catalysts and further motivates the use of oxidation-resistant metal nanoparticles in various fields.

Electrochemical Reversible Reforming between Ethylamine and Acetonitrile on Heterostructured Pd-Ni(OH)2 Nanosheets

Rational design of electrocatalysts is essential to achieve desirable performance of electrochemical synthesis process. Heterostructured catalysts have thus attracted widespread attention due to their multifunctional intrinsic properties, and diverse catalytic applications with corresponding outstanding activities. Here, we report an in situ restoration strategy for the synthesis of ultrathin Pd-Ni(OH)2 nanosheets. Such Pd-Ni(OH)2 nanosheets exhibit excellent activity and selectivity towards reversible electrochemical reforming of ethylamine and acetonitrile. In the acetonitrile reduction process, Pd acts as reaction center, while Ni(OH)2 provide proton hydrogen through promoting the dissociation of water. Also ethylamine oxidation process can be achieved on the surface of the heterostructured nanosheets with abundant Ni(II) defects. More importantly, an electrolytic cell driven by solar cells was successfully constructed to realize ethylamine-acetonitrile reversible reforming. This work demonstrates the importance of heterostructure engineering in the rational synthesis of multifunctional catalysts towards electrochemical synthesis of fine chemicals.

Sequential *CO management via controlling in situ reconstruction for efficient industrial-current-density CO2-to-C2+ electroreduction

Sequentially managing the coverage and dimerization of *CO on the Cu catalysts is desirable for industrial-current-density CO2 reduction (CO2R) to C2+, which required the multiscale design of the surface atom/architecture. However, the oriented design is colossally difficult and even no longer valid due to unpredictable reconstruction. Here, we leverage the synchronous leaching of ligand molecules to manipulate the seeding-growth process during CO2R reconstruction and construct Cu arrays with favorable (100) facets. The gradient diffusion in the reconstructed array guarantees a higher *CO coverage, which can continuously supply the reactant to match its high-rate consumption for high partial current density for C2+. Sequentially, the lower energy barriers of *CO dimerization on the (100) facets contribute to the high selectivity of C2+. Profiting from this sequential *CO management, the reconstructed Cu array delivers an industrial-relevant FEC2+ of 86.1% and an FEC2H4 of 60.8% at 700 mA cm-2. Profoundly, the atomic-molecular scale delineation for the evolution of catalysts and reaction intermediates during CO2R can undoubtedly facilitate various electrocatalytic reactions.

Nanoarchitectonics of Metallene Materials for Electrocatalysis

Controlling the synthesis of metal nanostructures is one approach for catalyst engineering and performance optimization in electrocatalysis. As an emerging class of unconventional electrocatalysts, two-dimensional (2D) metallene electrocatalysts with ultrathin sheet-like morphology have gained ever-growing attention and exhibited superior performance in electrocatalysis owing to their distinctive properties originating from structural anisotropy, rich surface chemistry, and efficient mass diffusion capability. Many significant advances in synthetic methods and electrocatalytic applications for 2D metallenes have been obtained in recent years. Therefore, an in-depth review summarizing the progress in developing 2D metallenes for electrochemical applications is highly needed. Unlike most reported reviews on the 2D metallenes, this review starts by introducing the preparation of 2D metallenes based on the classification of the metals (e.g., noble metals, and non-noble metals) instead of synthetic methods. Some typical strategies for preparing each kind of metal are enumerated in detail. Then, the utilization of 2D metallenes in electrocatalytic applications, especially in the electrocatalytic conversion reactions, including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, fuel oxidation reaction, CO₂ reduction reaction, and N₂ reduction reaction, are comprehensively discussed. Finally, current challenges and opportunities for future research on metallenes in electrochemical energy conversion are proposed.

Insight into the Electrochemical CO2-to-Ethanol Conversion Catalyzed by Cu2S Nanocrystal-Decorated Cu Nanosheets

Ethanol (C₂H₅OH) is an economically ideal C₂ product in electrochemical CO₂ reduction. However, the CO₂-to-C₂H₅OH conversion yield has been rather low and the underlying catalytic mechanism remains vague or unexplored in most cases. Herein, by decorating small Cu₂S nanocrystals uniform ly on Cu nanosheets, three desirable features are integrated into the electrocatalyst, including a relatively high positive local charge on Cu (Cu^δ+), abundant interfaces between Cu^δ+ and zero-valence Cu⁰, and a non-flat, stepped catalyst surface, leading to the promoted affinity of *CO, decreased *COCO formation barrier, and thermodynamically preferred *CH₂CHO-to-*CH₃CHO conversion. As a result, a high partial current density of ∼20.7 mA cm^-2 and a Faraday efficiency of 46% for C₂H₅OH are delivered at -1.2 V vs reversible hydrogen electrode in an H-cell containing a 0.1 M KHCO₃ solution. This work proposes an efficient strategy for the high-yield CO₂-to-C₂H₅OH conversion, emphasizing the promise for the industrial production of alcohol and related products from 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.

Highly Selective CO2 Electroreduction to C2+ Products over Cu2O-Decorated 2D Metal-Organic Frameworks with Rich Heterogeneous Interfaces

The electroreduction of carbon dioxide into high-value-added products is an effective approach to alleviating the energy crisis and pollution issues. However, there are still significant challenges for multicarbon (C₂₊) product production due to the lack of efficient catalysts with high selectivity. Herein, a Cu-rich electrocatalyst, where Cu₂O nanoparticles are decorated on two-dimensional (2D) Cu-BDC metal-organic frameworks (MOFs) with abundant heterogeneous interfaces, is synthesized for highly selective CO₂ electroreduction into C₂₊ products. A high C₂₊ Faradaic efficiency of 72.1% in an H-type cell and 58.2% in a flow cell are obtained, respectively. The heterogeneous interfaces of Cu₂O/Cu-BDC can optimize the adsorption energy of reaction intermediates during CO₂ electroreduction. An in situ infrared spectroscopy study indicates that the constructed interfaces can maintain the particular distribution of Cu valence states, where the C-C coupling is promoted to efficiently produce C₂₊ products owing to the stabilization of *CHO and *COH intermediates.

Two-Dimensional Metal Nanostructures: From Theoretical Understanding to Experiment

This paper reviews recent studies on the preparation of two-dimensional (2D) metal nanostructures, particularly nanosheets. As metal often exists in the high-symmetry crystal phase, such as face centered cubic structures, reducing the symmetry is often needed for the formation of low-dimensional nanostructures. Recent advances in characterization and theory allow for a deeper understanding of the formation of 2D nanostructures. This Review firstly describes the relevant theoretical framework to help the experimentalists understand chemical driving forces for the synthesis of 2D metal nanostructures, followed by examples on the shape control of different metals. Recent applications of 2D metal nanostructures, including catalysis, bioimaging, plasmonics, and sensing, are discussed. We end the Review with a summary and outlook of the challenges and opportunities in the design, synthesis, and application of 2D metal nanostructures.

A hydrophobic Cu/Cu2O sheet catalyst for selective electroreduction of CO to ethanol

Electrocatalytic reduction of carbon monoxide into fuels or chemicals with two or more carbons is very attractive due to their high energy density and economic value. Herein we demonstrate the synthesis of a hydrophobic Cu/Cu₂O sheet catalyst with hydrophobic n-butylamine layer and its application in CO electroreduction. The CO reduction on this catalyst produces two or more carbon products with a Faradaic efficiency of 93.5% and partial current density of 151 mA cm^-2 at the potential of -0.70 V versus a reversible hydrogen electrode. A Faradaic efficiency of 68.8% and partial current density of 111 mA cm^-2 for ethanol were reached, which is very high in comparison to all previous reports of CO₂/CO electroreduction with a total current density higher than 10 mA cm^-2. The as-prepared catalyst also showed impressive stability that the activity and selectivity for two or more carbon products could remain even after 100 operating hours. This work opens a way for efficient electrocatalytic conversion of CO₂/CO to liquid fuels.

Bionic Construction of Helical Bi2 O3 Microfibers for Highly Efficient CO2 Electroreduction

Helical Bi₂ O₃ microfibers (HBM) were prepared with the assistance of cotton template through a simple heating treatment in air. This twisted structure induced the lattice strains, enriched the oxygen vacancies of Bi₂ O₃ , and promoted the sufficient exposure of active sites simultaneously, thus performing outstanding activity and selectivity as catalyst for CO₂ electroreduction to formate. The faradaic efficiency (FE) of formate reached 100.4±1.9 % at -0.90 V vs. reversible hydrogen electrode (RHE) in an H-cell, and the partial current density was boosted to 226 mA cm^-2 with FE_formate of 96 % at -1.08 V vs. RHE in a flow cell. This work may open a new era for construction of metal oxide fibers by bionic strategy as high-performance electrocatalysts.

The Mechanism of Li Deposition on the Cu Substrates in the Anode-Free Li Metal Batteries

Due to the rapid growth in the demand for high-energy-density Lithium (Li) batteries and insufficient global Li reserves, the anode-free Li metal batteries are receiving increasing attention. Various strategies, such as surface modification and structural design of copper (Cu) current collectors, have been proposed to stabilize the anode-free Li metal batteries. Unfortunately, the mechanism of Li deposition on the Cu surfaces with the different Miller indices is poorly understood, especially on the atomic scale. Here, the large-scale molecular dynamics simulations of Li deposition on the Cu substrates are performed in the anode-free Li metal batteries. The results show that the surface properties of the Li panel can be altered through the different Cu substrate surfaces. Through surface similarity analysis, potential energy distributions,and inhomogeneous deposition simulations, it is found that the Li atoms exhibit different potential energy variances and kinetic characteristics on the different Cu surfaces. Furthermore, a proposal to reduce the fraction of the (110) facet in commercial Cu foils is made to improve the reversibility and stability of Li plating/stripping in the anode-free Li metal batteries.

FTIR-Assisted Electroreduction of CO2 and H2O to CO and H2 by Electrochemically Deposited Copper on Oxidized Graphite Felt

Obtaining CO and H₂ from electrochemical CO₂ reduction (CO₂RR) offers a viable alternative to reduce CO₂ emissions and produce chemicals and fuels. Herein, we report a simple strategy for obtaining polycrystalline copper deposited on oxidized graphite felt (Cu-OGF) and its performance on the selective conversion of CO₂ and H₂O to CO and H₂. For the electrode obtaining, graphite felt (GF) was first oxidized (OGF) in order to make the substrate hydrophilic and then copper particles were electrochemically deposited onto OGF. The pH of deposition was investigated, and the CO₂RR activity was assessed for the prepared electrodes at each pH (2.0, 4.0, 6.0, 8.0, and 10.0). It was found that pH 2.0 was the most promising for CO₂RR due to the presence of hexagonal copper microparticles. Fourier transform infrared analysis of the produced gases showed that this is a low-cost catalyst capable of reducing CO₂ and H₂O to CO and H₂, with Faradaic efficiencies between 0.50 and 5.21% for CO and 50.87 to 98.30% for H₂, depending on the experimental conditions. Hence, it is possible for this gas mixture to be used as a fuel gas or to be enriched with CO for use in Fischer-Tropsch processes.

Cu/CuOx@C Composite as a High-Efficiency Electrocatalyst for Oxygen Reduction Reactions

Among clean energy transformation devices, fuel cells have gained special attention over the past years; however, advancing appropriate non-valuable metal impetuses to halfway supplant the customary Pt/C impetus is still in progress. In this paper, we propose a specific electrocatalyst in the formula of highly-active Cu species, associated with coated carbon (Cu@C-800), for oxygen reduction reaction (ORR) through post-treatment of a self-assembled precursor. The optimized catalyst Cu@C-800 showed excellent ORR performance (i.e., the onset potential was 1.00 V vs. RHE, and half-wave potential of 0.81 V vs. RHE), high stability, resistance to methanol, and high four-electron selectivity. The enhancement is attributed to the synergy between the carbon matrix and a high explicit surface region and rich Cu nano-species.

Sn Dopants with Synergistic Oxygen Vacancies Boost CO2 Electroreduction on CuO Nanosheets to CO at Low Overpotential

Using the electrochemical CO₂ reduction reaction (CO₂RR) with Cu-based electrocatalysts to achieve carbon-neutral cycles remains a significant challenge because of its low selectivity and poor stability. Modulating the surface electron distribution by defects engineering or doping can effectively improve CO₂RR performance. Herein, we synthesize the electrocatalyst of V_o-CuO(Sn) nanosheets containing oxygen vacancies and Sn dopants for application in CO₂RR-to-CO. Density functional theory calculations confirm that the incorporation of oxygen vacancies and Sn atoms substantially reduces the energy barrier for *COOH and *CO intermediate formation, which results in the high efficiency, low overpotential, and superior stability of the CO₂RR to CO conversion. This electrocatalyst possesses a high Faraday efficiency (FE) of 99.9% for CO at a low overpotential of 420 mV and a partial current density of up to 35.22 mA cm^-2 at -1.03 V versus reversible hydrogen electrode (RHE). The FE_CO of V_o-CuO(Sn) could retain over 95% within a wide potential area from -0.48 to -0.93 V versus RHE. Moreover, we obtain long-term stability for more than 180 h with only a slight decay in its activity. Therefore, this work provides an effective route for designing environmentally friendly electrocatalysts to improve the selectivity and stability of the CO₂RR to CO conversion.

Heterostructured Ru/Ni(OH)2 Nanomaterials as Multifunctional Electrocatalysts for Selective Reforming of Ethanol

The electrochemical reforming of ethanol into hydrogen and hydrocarbons can reduce the electric potential energy barrier of hydrogen production from electrochemical water splitting, obtaining high value-added anode products. In this work, Ru/Ni(OH)₂ heterostructured nanomaterials were synthesized successfully by an in situ reduction strategy with remarkable multifunctional catalytic properties. In the hydrogen evolution reaction, Ru/Ni(OH)₂ exhibits a smaller overpotential of 31 mV to obtain a current density of 10 mA/cm², which is better than that of commercial Pt/C. Notably, such heterostructured Ru/Ni(OH)₂ nanomaterials also perform an outstanding catalytic selectivity toward an acetaldehyde product in the oxidation of ethanol. DFT calculations reveal that abundant Ru(0)-Ni(II) heterostructured sites are the key factor for the excellent performances. As a result, an ethanol-selective reforming electrolyzer driven by a 2 V solar cell is constructed to produce hydrogen and acetaldehyde in the cathodic and anodic part, respectively, via using Ru/Ni(OH)₂ heterostructured catalysts. This work provides a forward-looking technical guidance for the design of novel energy conversion systems.

Triple-Phase Interface Engineered Hierarchical Porous Electrode for CO2 Electroreduction to Formate

The aqueous electrochemical CO2 reduction to valuable products is seen as one of the most promising candidates to achieve carbon neutrality yet still suffers from poor selectivity and lower current density. Highly efficient CO2 reduction significantly relies on well-constructed electrode to realize efficient and stable triple-phase contact of CO2 , electrolyte, and active sites. Herein, a triple-phase interface engineering approach featuring the combination of hierarchical porous morphology design and surface modification is presented. A hierarchical porous electrode is constructed by depositing bismuth nanosheet array on copper foam followed by trimethoxy (1H,1H,2H,2H-heptadecafluorodecyl) silane modification on the nanosheet surface. This electrode not only achieves highly selective and efficient CO2 reduction performance with formate selectivity above 90% over wide potentials and a partial current density over -90 mA cm-2 in H-cell but also maintains a superior stability during the long-term operation. It is demonstrated that this remarkable performance is attributed to the construction of efficient and stable triple-phase interface. Theoretical calculations also show that the modified surface optimizes the activation path by lowering thermodynamic barriers of the key intermediates *OCHO for the formation of formate during electrochemical CO2 reduction.

In Situ Surface Restraint-Induced Synthesis of Transition-Metal Nitride Ultrathin Nanocrystals as Ultrasensitive SERS Substrate with Ultrahigh Durability

It is a major challenge to synthesize crystalline transition-metal nitride (TMN) ultrathin nanocrystals due to their harsh reaction conditions. Herein, we report that highly crystalline tungsten nitride (W₂N, WN, W₃N₄, W₂N₃) nanocrystals with small size and excellent dispersibility are prepared by a mild and general in situ surface restraint-induced growth method. These ultrafine tungsten nitride nanocrystals are immobilized in ultrathin carbon layers, forming an interesting hybrid nanobelt structure. The hybrid WN/C nanobelts exhibit a strong localized surface plasmon resonance (LSPR) effect and surface-enhanced Raman scattering (SERS) effect, including a lowest detection limit of 1 × 10^-12 M and a Raman enhancement factor of 6.5 × 10⁸ comparable to noble metals, which may be one of the best records for non-noble metal SERS substrates. Moreover, they even can maintain the SERS performance in a variety of harsh environments, showing outstanding corrosion resistance, radiation resistance, and oxidation resistance, which is not available on traditional noble metal and semiconductor SERS substrates. A synergistic Raman enhancement mechanism of LSPR and interface charge transfer is found in the carbon-coated tungsten nitride substrate. A microfluidic SERS channel integrating the enrichment and detection of trace substances is constructed with the WN/C nanobelt, which realizes high-throughput dynamic SERS analysis.

Wet-chemical synthesis of two-dimensional metal nanomaterials for electrocatalysis

Two-dimensional (2D) metal nanomaterials have gained ever-growing research interest owing to their fascinating physicochemical properties and promising application, especially in the field of electrocatalysis. In this review, we briefly introduce the recent advances in wet-chemical synthesis of 2D metal nanomaterials. Subsequently, the catalytic performances of 2D metal nanomaterials in a variety of electrochemical reactions are illustrated. Finally, we summarize current challenges and highlight our perspectives on preparing high-performance 2D metal electrocatalysts.

Surface Reconstruction with a Sandwich-like C/Cu/C Catalyst for Selective and Stable CO2 Electroreduction

For the steady electroreduction of carbon dioxide (CO₂RR) to value-added chemicals with high efficiency, the uncontrollable surface reconstruction under highly reducing conditions is a critical issue in electrocatalyst design. Herein, we construct a catalyst model with a sandwich-like structure composed of highly reactive metallic Cu nanosheet that is confined in thin carbon layers (denoted as C/Cu/C nanosheet). The sandwich-like C/Cu/C nanosheet avoids the oxidation of the active site of metallic Cu at an ambient atmosphere owing to the protective coating of the carbon layer, which inhibits the surface reconstruction that occurs via the dissolution of copper oxides and redeposition of dissolved Cu ions. The as-prepared C/Cu/C nanosheet exhibits a prominent Faradaic efficiency (FE) of 47.8% for CH₄ products at -1.0 V with a current density of 20.3 mA·cm^-2 and stable production of CH₄ during 12 h operation with negligible selectivity loss. Our findings provide an effective strategy of restraining surface reconstruction for the design of selective and stable electrocatalysts toward CO₂RR.

Opportunities and challenges in CO2 utilization

CO₂ utilizations are essential to curbing the greenhouse gas effect and managing the environmental pollutant in an energy-efficient and economically-sound manner. This paper seeks to critically analyze these technologies in the context of each other and highlight the most important utilization avenues available thus far. This review will introduce and analyze each major pathway, and discuss the overall applicability, potential extent, and major limitations of each of these pathways to utilizing CO₂. This will include the analysis of some previously underreported utilization avenues, including CO₂ utilization in industrial filtration and the processing of raw industrial materials such as iron and alumina. The core theme of this paper is to seek to treat CO₂ as a commodity instead of a liability.

A Robust Approach to In Situ Exsolve Highly Dispersed and Stable Electrocatalysts

Catalysts made of in situ exsolved metal nanoparticles often demonstrate promising activity and high stability in many applications. However, the traditional approach is limited by perovskites as prevailing precursor and requires high temperature typically above 900 K. Here, with the guidance of theoretical calculation, an unprecedented and substantially facile technique is demonstrated for Cu nanoparticles exsolved from interstitially Cu cations doped nickel-based hydroxide, which is accomplished swiftly at room temperature and results in metal nanoparticles with a quasi-uniform size of 4 nm, delivering an exceptional CO faradaic efficiency of 95.6% for the electrochemical reduction of CO₂ with a notable durability. This design principle is further proven to be generally applicable to other metals and foregrounded for guiding the development of advanced catalytic materials.

Highly efficient electrochemical carbon dioxide reduction to syngas with tunable ratios over pyridinic- nitrogen rich ultrathin carbon nanosheets

Developing nonmetallic carbon-based electrocatalysts that are affordable and have high activity and stability for carbon dioxide (CO₂) reduction to syngas is a new and challenging strategy for solving the energy crisis. Here, we prepared a highly active ultrathin nitrogen (N)-doped carbon nanosheet (UNCN) electrocatalyst. By tuning the applied potential of the UNCN-900 (900 represents the carbonization temperature) electrode, we could tune the H₂/CO ratio in clean syngas within a wide range with extra-high Faradic efficiency (FE). The maximum FE_CO reached 91%, which represented the highest value among the reported nonmetallic carbon-based electrocatalysts for CO₂ reduction to syngas. According to the results of experiments and density functional theory calculations, we proved that pyridinic-N in UNCNs-900 is the active site of the CO₂ reduction reaction (CO₂RR) and that graphitic-N may be the active site for the hydrogen evolution reaction. These results provide a useful case for electrochemical CO₂ reduction to syngas with a tunable H₂/CO ratio using nonmetallic carbon-based electrocatalysts.

Printed copper-nanoplate conductor for electro-magnetic interference

As one of the conductive ink materials with high electric conductivity, elemental copper (Cu) based nanocrystals promise for printable electronics. Here, single crystalline Cu nanoplates were synthesized using a facile hydrothermal method. Size engineering of Cu nanoplates can be rationalized by using the LaMer model and the versatile Cu conductive ink materials are suitable for different printing technologies. The printed Cu traces show high electric conductivity of 6 MS m^-1, exhibiting electro-magnetic interference shielding efficiency value of 75 dB at an average thicknesses of 11μm. Together with flexible alumina ceramic aerogel substrates, it kept 87% conductivity at the environmental temperature of 400 °C, demonstrating the potential of Cu conductive ink for high-temperature printable electronics applications.

Two-dimensional materials for electrochemical CO2 reduction: materials, in situ/operando characterizations, and perspective

Electrochemical CO₂ reduction (CO₂ ECR) is an efficient approach to achieving eco-friendly energy generation and environmental sustainability. This approach is capable of lowering the CO₂ greenhouse gas concentration in the atmosphere while producing various valuable fuels and products. For catalytic CO₂ ECR, two-dimensional (2D) materials stand as promising catalyst candidates due to their superior electrical conductivity, abundant dangling bonds, and tremendous amounts of surface active sites. On the other hand, the investigations on fundamental reaction mechanisms in CO₂ ECR are highly demanded but usually require advanced in situ and operando multimodal characterizations. This review summarizes recent advances in the development, engineering, and structure-activity relationships of 2D materials for CO₂ ECR. Furthermore, we overview state-of-the-art in situ and operando characterization techniques, which are used to investigate the catalytic reaction mechanisms with the spatial resolution from the micron-scale to the atomic scale, and with the temporal resolution from femtoseconds to seconds. Finally, we conclude this review by outlining challenges and opportunities for future development in this field.

Emerging beyond-graphene elemental 2D materials for energy and catalysis applications

Elemental two-dimensional (2D) materials have emerged as promising candidates for energy and catalysis applications due to their unique physical, chemical, and electronic properties. These materials are advantageous in offering massive surface-to-volume ratios, favorable transport properties, intriguing physicochemical properties, and confinement effects resulting from the 2D ultrathin structure. In this review, we focus on the recent advances in emerging energy and catalysis applications based on beyond-graphene elemental 2D materials. First, we briefly introduce the general classification, structure, and properties of elemental 2D materials and the new advances in material preparation. We then discuss various applications in energy harvesting and storage, including solar cells, piezoelectric and triboelectric nanogenerators, thermoelectric devices, batteries, and supercapacitors. We further discuss the explorations of beyond-graphene elemental 2D materials for electrocatalysis, photocatalysis, and heterogeneous catalysis. Finally, the challenges and perspectives for the future development of elemental 2D materials in energy and catalysis are discussed.

Heterostructuring Mesoporous 2D Iridium Nanosheets with Amorphous Nickel Boron Oxide Layers to Improve Electrolytic Water Splitting

2D heterostructures exhibit a considerable potential in electrolytic water splitting due to their high specific surface areas, tunable electronic properties, and diverse hybrid compositions. However, the fabrication of well-defined 2D mesoporous amorphous-crystalline heterostructures with highly active heterointerfaces remains challenging. Herein, an efficient 2D heterostructure consisting of amorphous nickel boron oxide (Ni-B_i ) and crystalline mesoporous iridium (meso-Ir) is designed for water splitting, referred to as Ni-B_i /meso-Ir. Benefiting from well-defined 2D heterostructures and strong interfacial coupling, the resulting mesoporous dual-phase Ni-B_i /meso-Ir possesses abundant catalytically active heterointerfaces and boosts the exposure of active sites, compared to their crystalline and amorphous mono-counterparts. The electronic state of the iridium sites is tuned favorably by hybridizing with Ni-B_i layers. Consequently, the Ni-B_i /meso-Ir heterostructures show superior and stable electrochemical performance toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte.

Hierarchically Porous CuAg via 3D Printing/Dealloying for Tunable CO2 Reduction to Syngas

Electrochemical CO₂ reduction reaction (CO₂RR) coupled with hydrogen evolution reaction (HER) is a renewable route to produce syngas (CO + H₂), an essential feedstock for liquid fuel production. However, the development of high-performance electrocatalyst with tunable H₂/CO ratio, high-rate syngas production, and long-term electrochemical stability remains challenging. Here, a metal three-dimensional (3D) printing technique followed by dealloying was utilized to develop three-dimensional hierarchical porous (termed as 3D hp) CuAg catalysts for the concurrent generation of CO and H₂. By purposely designing the precursor compositions, the resultant 3D hp CuAg catalysts with a high density of phase-segregated Ag and Cu nanodomains exhibit a tunable H₂/CO ratio from 3:1 to 1:2. Through further porosity engineering, the 3D hp CuAg catalysts show significantly enhanced syngas production rate of 140 μmol/h/cm² and electrochemical stability up to 140 h (which is the highest value reported so far). The remarkable electrochemical stability of the 3D hp CuAg arises from three-level hierarchical porous configurations, wherein the macroporous structure benefits gas bubble growth and detachment, the microporous structure stabilizes the active nanoporous layer, while the nanoporous structure provides a large active surface area and enables efficient mass transfer. The results of this study offer a new vision for the development of hierarchically porous catalysts for CO₂ reduction.

Advances and Challenges for the Electrochemical Reduction of CO2 to CO: From Fundamentals to Industrialization

The electrochemical carbon dioxide reduction reaction (CO₂ RR) provides an attractive approach to convert renewable electricity into fuels and feedstocks in the form of chemical bonds. Among the different CO₂ RR pathways, the conversion of CO₂ into CO is considered one of the most promising candidate reactions because of its high technological and economic feasibility. Integrating catalyst and electrolyte design with an understanding of the catalytic mechanism will yield scientific insights and promote this technology towards industrial implementation. Herein, we give an overview of recent advances and challenges for the selective conversion of CO₂ into CO. Multidimensional catalyst and electrolyte engineering for the CO₂ RR are also summarized. Furthermore, recent studies on the large-scale production of CO are highlighted to facilitate industrialization of the electrochemical reduction of CO₂ . To conclude, the remaining technological challenges and future directions for the industrial application of the CO₂ RR to generate CO are highlighted.