Tunable Selectivity for Electrochemical CO2 Reduction by Bimetallic Cu–Sn Catalysts: Elucidating the Roles of Cu and Sn

Electrocatalytic hydrogenation of acetonitrile to ethylamine in acid

Electrochemical hydrogenation of acetonitrile based on well-developed proton exchange membrane electrolyzers holds great promise for practical production of ethylamine. However, the local acidic condition of proton exchange membrane results in severe competitive proton reduction reaction and poor selection toward acetonitrile hydrogenation. Herein, we conduct a systematic study to screen various metallic catalysts and discover Pd/C exhibits a 43.8% ethylamine Faradaic efficiency at the current density of 200 mA cm-2 with a specific production rate of 2912.5 mmol g-1 h-1, which is about an order of magnitude higher than the other screened metal catalysts. Operando characterizations indicate the in-situ formed PdHx is the active centers for catalytic reaction and the adsorption strength of the *MeCH2NH2 intermediate dictates the catalytic selectivity. More importantly, the theoretical analysis reveals a classic d-band mediated volcano curve to describe the relation between the electronic structures of catalysts and activity, which could provide valuable insights for designing more effective catalysts for electrochemical hydrogenation reactions and beyond.

Modulating the Structure and Composition of Single-Atom Electrocatalysts for CO2 reduction

Electrochemical CO2 reduction reaction (eCO2 RR) is a promising strategy to achieve carbon cycling by converting CO2 into value-added products under mild reaction conditions. Recently, single-atom catalysts (SACs) have shown enormous potential in eCO2 RR due to their high utilization of metal atoms and flexible coordination structures. In this work, the recent progress in SACs for eCO2 RR is outlined, with detailed discussions on the interaction between active sites and CO2 , especially the adsorption/activation behavior of CO2 and the effects of the electronic structure of SACs on eCO2 RR. Three perspectives form the starting point: 1) Important factors of SACs for eCO2 RR; 2) Typical SACs for eCO2 RR; 3) eCO2 RR toward valuable products. First, how different modification strategies can change the electronic structure of SACs to improve catalytic performance is discussed; Second, SACs with diverse supports and how supports assist active sites to undergo catalytic reaction are introduced; Finally, according to various valuable products from eCO2 RR, the reaction mechanism and measures which can be taken to improve the selectivity of eCO2 RR are discussed. Hopefully, this work can provide a comprehensive understanding of SACs for eCO2 RR and spark innovative design and modification ideas to develop highly efficient SACs for CO2 conversion to various valuable fuels/chemicals.

Tandem effect at snowflake-like cuprous sulphide interfaces for highly selective conversion of carbon dioxide to formate by electrochemical reduction

Electrochemical carbon dioxide reduction (ECR) is a commercially promising technology to resolve the energy dilemma and accomplish carbon recycling. Herein, a novel electrocatalyst has been investigated to produce formate (HCOOH) highly selectively during ECR by loading SnO2@C onto cuprous sulphide (Cu2S) to form a triplet effect at the interface. Snowflake-like Cu2S significantly enhances the local concentration of carbon dioxide (CO2) and promotes the binding of CO2 with SnO2, and the addition of carbon spheres enhances the electron transport, which is beneficial to the conversion of CO2 to HCOOH products. The snowflake-like Cu2S loaded with 1 wt% SnO2@C had an HCOOH Faraday Efficiency of 88% at -1.0 V (vs. Reversible Hydrogen Electrode, RHE), and the current density for CO2 reduction was stabilized at 15.6 mA cm-2, which was much higher than the HCOOH Faraday efficiency (FE) of 31.0% for pure Cu2S accompanied by a CO2 reduction current density of 3.9 mA cm-2. Combined investigations using in-situ Fourier transform infrared spectroscopy (FT-IR) with in-situ Raman spectra reveal that the active species is Cu+. Cu2S/1%SnO2@C can effectively promote the adsorption and activation of carbonate and inhibit the production of CO intermediates. The corresponding density functional theory (DFT) demonstrates that Cu2S/1%SnO2@C can well stabilize the HCOO* intermediate during the ECR process. The interaction between Cu2S and SnO2@C adjusts the surface electronic distribution and accelerates electron transfer, which efficiently improves CO2-to-HCOOH conversion. The result obtained from this work provides a simple and efficient electrocatalyst to enhance the HCOOH selectivity of ECR.

Super-fast Charging Biohybrid Batteries through a Power-to-formate-to-bioelectricity Process by Combining Microbial Electrochemistry and CO2 Electrolysis

Extensive study on renewable energy storage has been sparked by the growing worries regarding global warming. In this study, incorporating the latest advancements in microbial electrochemistry and electrochemical CO2 reduction, a super-fast charging biohybrid battery was introduced by using pure formic acid as an energy carrier. CO2 electrolyser with a slim-catholyte layer and a solid electrolyte layer was built, which made it possible to use affordable anion exchange membranes and electrocatalysts that are readily accessible. The biohybrid battery only required a 3-minute charging to accomplish an astounding 25-hour discharging phase. In the power-to-formate-to-bioelectricity process, bioconversion played a vital role in restricting both the overall Faradaic efficiency and Energy efficiency. The CO2 electrolyser was able to operate continuously for an impressive total duration of 164 hours under Gas Stand-By model, by storing N2 gas in the extraction chamber during stand-by periods. Additionally, the electric signal generated during the discharging phase was utilized for monitoring water biotoxicity. Functional genes related to formate metabolism were identified in the bioanode and electrochemically active bacteria were discovered. On the other hand, Paracoccus was predominantly found in the used air cathode. These results advance our current knowledge of exploiting biohybrid technology.

Tuning C1 /C2 Selectivity of CO2 Electrochemical Reduction over in-Situ Evolved CuO/SnO2 Heterostructure

Heterostructured oxides with versatile active sites, as a class of efficient catalysts for CO2 electrochemical reduction (CO2 ER), are prone to undergo structure reconstruction under working conditions, thus bringing challenges to understanding the reaction mechanism and rationally designing catalysts. Herein, we for the first time elucidate the structural reconstruction of CuO/SnO2 under electrochemical potentials and reveal the intrinsic relationship between CO2 ER product selectivity and the in situ evolved heterostructures. At -0.85 VRHE , the CuO/SnO2 evolves to Cu2 O/SnO2 with high selectivity to HCOOH (Faradaic efficiency of 54.81 %). Mostly interestingly, it is reconstructed to Cu/SnO2-x at -1.05 VRHE with significantly improved Faradaic efficiency to ethanol of 39.8 %. In situ Raman spectra and density functional theory (DFT) calculations reveal that the synergetic absorption of *COOH and *CHOCO intermediates at the interface of Cu/SnO2-x favors the formation of *CO and decreases the energy barrier of C-C coupling, leading to high selectivity to ethanol.

Dual-Site Metal Catalysts for Electrocatalytic CO2 Reduction Reaction

Electrocatalytic CO2 reduction reaction (CO2 RR) is a promising and green approach for reducing atmospheric CO2 concentration and achieving high-valued conversion of CO2 under the carbon-neutral policy. In CO2 RR, the dual-site metal catalysts (DSMCs) have received wide attention for their ingenious design strategies, abundant active sites, and excellent catalytic performance attributed to the synergistic effect between dual-site in terms of activity, selectivity and stability, which plays a key role in catalytic reactions. This review provides a systematic summary and detailed classification of DSMCs for CO2 RR, describes the mechanism of synergistic effects in catalytic reactions, and also introduces in situ characterization techniques commonly used in CO2 RR. Finally, the main challenges and prospects of dual-site metal catalysts and even multi-site catalysts for CO2 recycling are analyzed. It is believed that based on the understanding of bimetallic site catalysts and synergistic effects in CO2 RR, well-designed high-performance, low-cost electrocatalysts are promising for achieving CO2 conversion, electrochemical energy conversion and storage in the future.

Dual-site catalysts featuring platinum-group-metal atoms on copper shapes boost hydrocarbon formations in electrocatalytic CO2 reduction

Copper-based catalyst is uniquely positioned to catalyze the hydrocarbon formations through electrochemical CO₂ reduction. The catalyst design freedom is limited for alloying copper with H-affinitive elements represented by platinum group metals because the latter would easily drive the hydrogen evolution reaction to override CO₂ reduction. We report an adept design of anchoring atomically dispersed platinum group metal species on both polycrystalline and shape-controlled Cu catalysts, which now promote targeted CO₂ reduction reaction while frustrating the undesired hydrogen evolution reaction. Notably, alloys with similar metal formulations but comprising small platinum or palladium clusters would fail this objective. With an appreciable amount of CO-Pd₁ moieties on copper surfaces, facile CO^* hydrogenation to CHO^* or CO-CHO^* coupling is now viable as one of the main pathways on Cu(111) or Cu(100) to selectively produce CH₄ or C₂H₄ through Pd-Cu dual-site pathways. The work broadens copper alloying choices for CO₂ reduction in aqueous phases.

Adsorption, activation, and conversion of carbon dioxide on small copper-tin nanoclusters

Carbon dioxide (CO₂) conversion to value-added chemicals is an attractive solution to reduce globally accelerating CO₂ emissions. Among the non-precious and abundant metals tested so far, copper (Cu) is one of the best electrocatalysts to convert CO₂ into more than thirty different hydrocarbons and alcohols. However, the selectivity for desired products is often too low. We present a computational investigation of the effects of nanostructuring, doping, and support on the activity and selectivity of Cu-Sn catalysts. Density functional theory calculations were conducted to explore the possibility of using small Cu-Sn clusters, Cu_4-nSn_n (n = 0-4), isolated or supported on graphene and γ-Al₂O₃, to activate CO₂ and convert it to carbon monoxide (CO) and formic acid (HCOOH). First, a detailed analysis of the structure, stability, and electronic properties of Cu_4-nSn_n clusters and their ability to absorb and activate CO₂ was considered. Then, the kinetics of the gas phase CO₂ direct dissociation on Cu_4-nSn_n to generate CO was determined. Finally, the mechanism of electrocatalytic CO₂ reduction to CO and HCOOH on Cu_4-nSn_n, Cu_4-nSn_n/graphene and Cu_4-nSn_n/γ-Al₂O₃ was computed. The selectivity towards the competitive electrochemical hydrogen evolution reaction on these catalysts was also considered. The Cu₂Sn₂ cluster suppresses the hydrogen evolution reaction and is highly selective towards CO, if unsupported, or HCOOH if supported on graphene. This study demonstrates that the Cu₂Sn₂ cluster is a potential candidate for the electrocatalytic conversion of the CO₂ molecule. Moreover, it identifies insightful structure-property relationships in Cu-based nanocatalysts, highlighting the influence of composition and catalyst support on CO₂ activation.

Electrocatalyst Microenvironment Engineering for Enhanced Product Selectivity in Carbon Dioxide and Nitrogen Reduction Reactions

Carbon and nitrogen fixation strategies are regarded as alternative routes to produce valuable chemicals used as energy carriers and fertilizers that are traditionally obtained from unsustainable and energy-intensive coal gasification (CO and CH₄), Fischer-Tropsch (C₂H₄), and Haber-Bosch (NH₃) processes. Recently, the electrocatalytic CO₂ reduction reaction (CO₂RR) and N₂ reduction reaction (NRR) have received tremendous attention, with the merits of being both efficient strategies to store renewable electricity while providing alternative preparation routes to fossil-fuel-driven reactions. To date, the development of the CO₂RR and NRR processes is primarily hindered by the competitive hydrogen evolution reaction (HER); however, the corresponding strategies for inhibiting this undesired side reaction are still quite limited. Considering such complex reactions involve three gas-liquid-solid phases and successive proton-coupled electron transfers, it appears meaningful to review the current strategies for improving product selectivity in light of their respective reaction mechanisms, kinetics, and thermodynamics. By examining the developments and understanding in catalyst design, electrolyte engineering, and three-phase interface modulation, we discuss three key strategies for improving product selectivity for the CO₂RR and NRR: (i) targeting molecularly defined active sites, (ii) increasing the local reactant concentration at the active sites, and (iii) stabilizing and confining product intermediates.

UV assisted synthesis of folic acid functionalized ZnO-Ag hexagonal nanoprisms for efficient catalytic reduction of Cr+6 and 4-nitrophenol

Chemical-based syntheses of metallic nanoparticles (MNPs) has become a major topic of research exploration in the field of nanotechnology. The utilization of folic acid (FA) as stabilizing and capping agent has been reported as a novel route for the synthesis of bimetallic nanomaterials. The present study includes novel research and brief discussion about preparation of UV light assisted ZnO-Ag nanobars (NBs) using FA as stabilizing agent and its catalytic applications on the reduction of organic pollutants (4-NP and Cr⁺⁶) using NBs as a catalyst alongwith ascorbic acid (AA). Analytical techniques including UV-visible spectroscopy, XRD, SEM, EDX and FT-IR were used for the characterizing synthesized ZnO-Ag NBs. Hexagonal structure of ZnO-Ag NBs were found having crystallite size 5.6 nm and SEM studies revealed the nanobar width 33.2 nm and length 133.5 nm. The prepared ZnO-Ag NBs were tested for their catalytic activity for the reduction of 4-nitrophenol (4-NP) and Cr⁺⁶. In the presence of ZnO-Ag NBs and AA, an effective reduction of 4-nitrophenol (4-NP) and Cr⁺⁶ was achieved up to 93% and 90% in 17 and 26 min with respectively. The successful and efficient catalytic activity of NBs may be attributed to the size of NBs or the concentration of FA employed for synthesis.

Doping and pretreatment optimized the adsorption of *OCHO on bismuth for the electrocatalytic reduction of CO2 to formate

Electrocatalytic reduction of CO₂ to formate is considered as a promising method to achieve carbon neutrality, and the introduction of heteroatoms is an effective strategy to improve the catalytic activity and selectivity of catalysts. However, the structural reconstruction behavior of catalysts driven by voltage is usually ignored. Therefore, we used Cu/Bi₂S₃ as a model to reveal the dynamic reduction process in different atmospheric environments. The catalyst showed an outstanding faradaic efficiency of 94% for formate and a long-term stability of 100 h, and exhibited a high current density of 280 mA cm^-2 in a flow cell. The experimental results and theoretical calculations show that the introduction of copper enhances the adsorption of CO₂, accelerates the charge transfer and reduces the formation barrier of *OCHO, thus promoting the formation of formate. This work draws attention to the effects of saturated gases in the electrolyte during structural evolution and provides a possibility for designing catalysts with high catalytic activity.

Halogen-Incorporated Sn Catalysts for Selective Electrochemical CO2 Reduction to Formate

Electrochemically reducing CO₂ to valuable fuels or feedstocks is recognized as a promising strategy to simultaneously tackle the crises of fossil fuel shortage and carbon emission. Sn-based catalysts have been widely studied for electrochemical CO₂ reduction reaction (CO₂ RR) to make formic acid/formate, which unfortunately still suffer from low activity, selectivity and stability. In this work, halogen (F, Cl, Br or I) was introduced into the Sn catalyst by a facile hydrolysis method. The presence of halogen was confirmed by a collection of ex situ and in situ characterizations, which rendered a more positive valence state of Sn in halogen-incorporated Sn catalyst as compared to unmodified Sn under cathodic potentials in CO₂ RR and therefore tuned the adsorption strength of the key intermediate (*OCHO) toward formate formation. As a result, the halogen-incorporated Sn catalyst exhibited greatly enhanced catalytic performance in electrochemical CO₂ RR to produce formate.

Scalable synthesis of CuSn bimetallic catalyst for selective CO2 electroreduction to CO over a wide potential range

A scalable, and cost-effective method was employed to prepare self-supported CuSn bimetallic catalyst on carbon paper. The obtained CuSn catalyst demonstrates high faradaic efficiency of CO around or above 90% at a broad potential range from -0.7 to -1.8 V vs. reversible hydrogen electrode, greatly surpassing Cu or Sn counterparts.

Liquid Fluxional Ga Single Atom Catalysts for Efficient Electrochemical CO2 Reduction

Precise design and tuning of the micro-atomic structure of single atom catalysts (SACs) can help efficiently adapt complex catalytic systems. Herein, we inventively found that when the active center of the main group element gallium (Ga) is downsized to the atomic level, whose characteristic has significant differences from conventional bulk and rigid Ga catalysts. The Ga SACs with a P, S atomic coordination environment display specific flow properties, showing CO products with FE of ≈92 % at -0.3 V vs. RHE in electrochemical CO₂ reduction (CO₂ RR). Theoretical simulations demonstrate that the adaptive dynamic transition of Ga optimizes the adsorption energy of the *COOH intermediate and renews the active sites in time, leading to excellent CO₂ RR selectivity and stability. This liquid single atom catalysts system with dynamic interfaces lays the foundation for future exploration of synthesis and catalysis.

Nanostructure Engineering of Sn-Based Catalysts for Efficient Electrochemical CO2 Reduction

Excessive anthropogenic CO₂ emission has caused a series of ecological and environmental issues, which threatens mankind's sustainable development. Mimicking the natural photosynthesis process (i.e., artificial photosynthesis) by electrochemically converting CO₂ into value-added products is a promising way to alleviate CO₂ emission and relieve the dependence on fossil fuels. Recently, Sn-based catalysts have attracted increasing research attentions due to the merits of low price, abundance, non-toxicity, and environmental benignancy. In this review, the paradigm of nanostructure engineering for efficient electrochemical CO₂ reduction (ECO₂ R) on Sn-based catalysts is systematically summarized. First, the nanostructure engineering of size, composition, atomic structure, morphology, defect, surficial modification, catalyst/substrate interface, and single-atom structure, are systematically discussed. The influence of nanostructure engineering on the electronic structure and adsorption property of intermediates, as well as the performance of Sn-based catalysts for ECO₂ R are highlighted. Second, the potential chemical state changes and the role of surface hydroxides on Sn-based catalysts during ECO₂ R are introduced. Third, the challenges and opportunities of Sn-based catalysts for ECO₂ R are proposed. It is expected that this review inspires the further development of highly efficient Sn-based catalysts, meanwhile offer protocols for the investigation of Sn-based catalysts.

Electrochemical Reduction of CO2 to C1 and C2 Liquid Products on Copper-Decorated Nitrogen-Doped Carbon Nanosheets

Due to the significant rise in atmospheric carbon dioxide (CO₂) concentration and its detrimental environmental effects, the electrochemical CO₂ conversion to valuable liquid products has received great interest. In this work, the copper-melamine complex was used to synthesize copper-based electrocatalysts comprising copper nanoparticles decorating thin layers of nitrogen-doped carbon nanosheets (Cu/NC). The as-prepared electrocatalysts were characterized by XRD, SEM, EDX, and TEM and investigated in the electrochemical CO₂ reduction reaction (ECO₂RR) to useful liquid products. The electrochemical CO₂ reduction reaction was carried out in two compartments of an electrochemical H-Cell, using 0.5 M potassium bicarbonate (KHCO₃) as an electrolyte; nuclear magnetic resonance (¹H NMR) was used to analyze and quantify the liquid products. The electrode prepared at 700 °C (Cu/NC-700) exhibited the best dispersion for the copper nanoparticles on the carbon nanosheets (compared to Cu/NC-600 & Cu/NC-800), highest current density, highest electrochemical surface area, highest electrical conductivity, and excellent stability and faradic efficiency (FE) towards overall liquid products of 56.9% for formate and acetate at the potential of -0.8V vs. Reversible Hydrogen Electrode (RHE).

Near-Unity Electrochemical CO2 to CO Conversion over Sn-Doped Copper Oxide Nanoparticles

Bimetallic electrocatalysts have emerged as a viable strategy to tune the electrocatalytic CO₂ reduction reaction (eCO₂RR) for the selective production of valuable base chemicals and fuels. However, obtaining high product selectivity and catalyst stability remain challenging, which hinders the practical application of eCO₂RR. In this work, it was found that a small doping concentration of tin (Sn) in copper oxide (CuO) has profound influence on the catalytic performance, boosting the Faradaic efficiency (FE) up to 98% for carbon monoxide (CO) at -0.75 V versus RHE, with prolonged stable performance (FE > 90%) for up to 15 h. Through a combination of ex situ and in situ characterization techniques, the in situ activation and reaction mechanism of the electrocatalyst at work was elucidated. In situ Raman spectroscopy measurements revealed that the binding energy of the crucial adsorbed *CO intermediate was lowered through Sn doping, thereby favoring gaseous CO desorption. This observation was confirmed by density functional theory, which further indicated that hydrogen adsorption and subsequent hydrogen evolution were hampered on the Sn-doped electrocatalysts, resulting in boosted CO formation. It was found that the pristine electrocatalysts consisted of CuO nanoparticles decorated with SnO₂ domains, as characterized by ex situ high-resolution scanning transmission electron microscopy and X-ray photoelectron spectroscopy measurements. These pristine nanoparticles were subsequently in situ converted into a catalytically active bimetallic Sn-doped Cu phase. Our work sheds light on the intimate relationship between the bimetallic structure and catalytic behavior, resulting in stable and selective oxide-derived Sn-doped Cu electrocatalysts.

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.

Electro-Synthesis of Organic Compounds with Heterogeneous Catalysis

Electro-organic synthesis has attracted a lot of attention in pharmaceutical science, medicinal chemistry, and future industrial applications in energy storage and conversion. To date, there has not been a detailed review on electro-organic synthesis with the strategy of heterogeneous catalysis. In this review, the most recent advances in synthesizing value-added chemicals by heterogeneous catalysis are summarized. An overview of electrocatalytic oxidation and reduction processes as well as paired electrocatalysis is provided, and the anodic oxidation of alcohols (monohydric and polyhydric), aldehydes, and amines are discussed. This review also provides in-depth insight into the cathodic reduction of carboxylates, carbon dioxide, CC, C≡C, and reductive coupling reactions. Moreover, the electrocatalytic paired electro-synthesis methods, including parallel paired, sequential divergent paired, and convergent paired electrolysis, are summarized. Additionally, the strategies developed to achieve high electrosynthesis efficiency and the associated challenges are also addressed. It is believed that electro-organic synthesis is a promising direction of organic electrochemistry, offering numerous opportunities to develop new organic reaction methods.

Alloying strategies for tuning product selectivity during electrochemical CO2 reduction over Cu

Excessive reliance on fossil fuels has led to the release and accumulation of large quantities of CO₂ into the atmosphere which has raised serious concerns related to environmental pollution and global warming. One way to mitigate this problem is to electrochemically recycle CO₂ to value-added chemicals or fuels using electricity from renewable energy sources. Cu is the only metallic electrocatalyst that has been shown to produce a wide range of industrially important chemicals at appreciable rates. However, low product selectivity is a fundamental issue limiting commercial applications of electrochemical CO₂ reduction over Cu catalysts. Combining copper with other metals that actively contribute to the electrochemical CO₂ reduction reaction process can selectively facilitate generation of desirable products. Alloying Cu can alter surface binding strength through electronic and geometric effects, enhancing the availability of surface confined carbon species, and stabilising key reduction intermediates. As a result, significant research has been undertaken to design and fabricate copper-based alloy catalysts with structures that can enhance the selectivity of targeted products. In this article, progress with use of alloying strategies for development of Cu-alloy catalysts are reviewed. Challenges in achieving high selectivity and possible future directions for development of new copper-based alloy catalysts are considered.

Isolating Single Sn Atoms in CuO Mesocrystal to Form Ordered Atomic Interfaces: An Effective Strategy for Designing Highly Efficient Mesocrystal Catalysts

Tuning the electronic structures of mesocrystals at the atomic level is an effective approach to obtaining unprecedented properties. Here, a lattice-confined strategy to obtain isolated single-site Sn atoms in CuO mesocrystals to improve catalytic performance is reported. The Sn/CuO mesocrystal composite (Sn/CuO MC) has ordered Sn-O-Cu atomic interfaces originated from the long-range ordering of the CuO mesocrystal itself. X-ray absorption fine structure measurements confirm that the positively charged Sn atoms can tune the electronic structure of the Cu atoms to some extent in Sn/CuO MC, quite different from that in the conventional single-atom Sn-modified CuO nanoparticles and nanoparticulate SnO₂ -modified CuO mesocrystal catalysts. When tested for the Si hydrochlorination reaction to produce trichlorosilane, Sn/CuO MC exhibits significantly better performances than the above two catalysts. Theoretical calculations further reveal the electronic modification to the active Cu component and the induced improvement in HCl adsorption, and thus enhance the catalytic performance. This work demonstrates how to design efficient metal oxide mesocrystal catalysts through an electronic structure modification approach.

Oxidation State Modulation of Bimetallic Tin-Copper Oxide Nanotubes for Selective CO2 Electroreduction to Formate

In this work, the oxidation state of Sn and Cu active sites for CO₂ electroreduction via constructing a Sn-Cun bimetallic oxide composite with a nanotube structure (SnCu-CNS) is successfully modulated. Compared to a single SnO₂ or CuO_x component, the SnCu-CNS composite holds reinforced electronegativity to generate unique extra Sn^δ+ centers and higher CuO centers with enhanced oxidation effect. Based on density functional theory calculations, the enlarged energy difference between Sn^δ+ /CuO centers and the reactants accelerates the electron transfer and decreases the energy barrier for the key intermediates to gain higher formate selectivity. Furthermore, the hollow structure and abundant micropores of SnCu-CNS are also conducive to the reactant transport and availability of active sites during CO₂ electroreduction. In a conventional H-type cell, SnCu-CNS catalyst exhibits a maximum 95.1% faradaic efficiency for formate production. Switching to a flow cell configuration, SnCu-CNS can further deliver partial current densities exceeding 200 mA cm^-2 and over 90% faradaic efficiencies for the formate, superior to most of the reported Sn-based electrocatalysts. This strategy of electronic modulation and morphology engineering in bimetallic oxides can have wide applications to raise electrocatalytic performance.

Current state of copper-based bimetallic materials for electrochemical CO2 reduction: a review

The increasing CO₂ concentration in the atmosphere has caused profound environmental issues such as global warming. The use of CO₂ as a feedstock to replace traditional fossil sources holds great promise to reduce CO₂ emissions. The electrochemical conversion of CO₂ has attracted much attention because it can be powered by renewable sources such as solar energy. In this review article, we provide insight into the important parameters when studying CO₂RR and give a comprehensive review on the description of synthesis methods with electrocatalytic CO₂ reduction over bimetallic copper-based materials. Due to the important bibliographic data on Cu bimetallic materials, we have limited this review to Sn, In, Pd, Zn and Ag. At the end of this review, challenges and perspectives for further upgrading have been included to briefly highlight the important future considerations of this rapidly growing technology.

The increasing CO₂ concentration in the atmosphere has caused profound environmental issues such as global warming.

Isolating Single and Few Atoms for Enhanced Catalysis

Atomically dispersed metal catalysts have triggered great interest in the field of catalysis owing to their unique features. Isolated single or few metal atoms can be anchored on substrates via chemical bonding or space confinement to maximize atom utilization efficiency. The key challenge lies in precisely regulating the geometric and electronic structure of the active metal centers, thus significantly influencing the catalytic properties. Although several reviews have been published on the preparation, characterization, and application of single-atom catalysts (SACs), the comprehensive understanding of SACs, dual-atom catalysts (DACs), and atomic clusters has never been systematically summarized. Here, recent advances in the engineering of local environments of state-of-the-art SACs, DACs, and atomic clusters for enhanced catalytic performance are highlighted. Firstly, various synthesis approaches for SACs, DACs, and atomic clusters are presented. Then, special attention is focused on the elucidation of local environments in terms of electronic state and coordination structure. Furthermore, a comprehensive summary of isolated single and few atoms for the applications of thermocatalysis, electrocatalysis, and photocatalysis is provided. Finally, the potential challenges and future opportunities in this emerging field are presented. This review will pave the way to regulate the microenvironment of the active site for boosting catalytic processes.

Interface Molecular Functionalization of Cu2O for Synchronous Electrocatalytic Generation of Formate

The electrocatalytic generation of valuable fuels and chemicals from carbon dioxide (CO₂) and others with the assistance of clean solar energy is a highly promising way to realize the carbon-neutral cycle, which invokes the systematic development of advanced electrocatalysts for efficient and selective redox reactions of feedstocks. Herein, we demonstrate the interface modification of cuprous oxide with polyvinylpyrrolidone (PVP) to improve the electrocatalytic efficiency for the synchronous formate generation. Density functional theory calculations reveal that the interfacial properties can be effectively regulated by the PVP functionalization for the favorable formation of intermediates to improve the selectivity of formate generation. Importantly, the advanced electrocatalyts enable an efficient coupling of CO₂ reduction with methanol oxidation in an electrochemical cell powered with a solar cell. The work provides a predictive link between the electrocatalytic redox reactions by applying the interfacial regulation strategies of electrocatalysts.

Revealing the Real Role of Etching during Controlled Assembly of Nanocrystals Applied to Electrochemical Reduction of CO2

In recent years, the use of inexpensive and efficient catalysts for the electrocatalytic CO₂ reduction reaction (CO₂RR) to regulate syngas ratios has become a hot research topic. Here, a series of nitrogen-doped iron carbide catalysts loaded onto reduced graphene oxide (N-Fe₃C/rGO-H) were prepared by pyrolysis of iron oleate, etching, and nitrogen-doped carbonization. The main products of the N-Fe₃C/rGO-H electrocatalytic reduction of CO₂ are CO and H₂, when tested in a 0.5 M KHCO₃ electrolyte at room temperature and pressure. In the prepared catalysts, the high selectivity (the Faraday efficiency of CO was 40.8%, at −0.3 V), and the total current density reaches ~29.1 mA/cm² at −1.0 V as demonstrated when the mass ratio of Fe₃O₄ NPs to rGO was equal to 100, the nitrogen doping temperature was 800 °C and the ratio of syngas during the reduction process was controlled by the applied potential (−0.2~−1.0 V) in the range of 1 to 20. This study provides an opportunity to develop nonprecious metals for the electrocatalytic CO₂ reduction reaction preparation of synthesis and gas provides a good reference

Preparation of Amorphous SnO2 -Encapsulated Multiphased Crystalline Cu Heterostructures for Highly Efficient CO2 Reduction

Controlling the architectures and crystal phases of metal@semiconductor heterostructures is very important for modulating their physicochemical properties and enhancing their application performances. Here, a facile one-pot wet-chemical method to synthesize three types of amorphous SnO₂ -encapsulated crystalline Cu heterostructures, i.e., hemicapsule, yolk-shell, and core-shell nanostructures, in which unconventional crystal phases (e.g., 2H, 4H, and 6H) and defects (e.g., stacking faults and twin boundaries) are observed in the crystalline Cu cores, is reported. The hemicapsule Cu@SnO₂ heterostructures, with voids that not only expose the Cu core with unconventional phases but also retain the interface between Cu and SnO₂ , show an excellent electrocatalytic CO₂ reduction reaction (CO₂ RR) selectivity toward the production of CO and formate with high Faradaic efficiency (FE) above 90% in a wide potential window from -1.05 to -1.55 V (vs reversible hydrogen electrode (RHE)), and the highest FE of CO₂ RR (95.3%) is obtained at -1.45 V (vs RHE). This work opens up a new way for the synthesis of new heterostructured nanomaterials with promising catalytic application.