Highly Efficient Electroreduction of CO2 to Methanol on Palladium-Copper Bimetallic Aerogels

Strong effect-correlated electrochemical CO2 reduction

Electrochemical CO2 reduction (ECR) holds great potential to alleviate the greenhouse effect and our dependence on fossil fuels by integrating renewable energy for the electrosynthesis of high-value fuels from CO2. However, the high thermodynamic energy barrier, sluggish reaction kinetics, inadequate CO2 conversion rate, poor selectivity for the target product, and rapid electrocatalyst degradation severely limit its further industrial-scale application. Although numerous strategies have been proposed to enhance ECR performances from various perspectives, scattered studies fail to comprehensively elucidate the underlying effect-performance relationships toward ECR. Thus, this review presents a comparative summary and a deep discussion with respect to the effects strongly-correlated with ECR, including intrinsic effects of materials caused by various sizes, shapes, compositions, defects, interfaces, and ligands; structure-induced effects derived from diverse confinements, strains, and fields; electrolyte effects introduced by different solutes, solvents, cations, and anions; and environment effects induced by distinct ionomers, pressures, temperatures, gas impurities, and flow rates, with an emphasis on elaborating how these effects shape ECR electrocatalytic activities and selectivity and the underlying mechanisms. In addition, the challenges and prospects behind different effects resulting from various factors are suggested to inspire more attention towards high-throughput theoretical calculations and in situ/operando techniques to unlock the essence of enhanced ECR performance and realize its ultimate application.

Electrochemical CO2 Reduction Reaction: Comprehensive Strategic Approaches to Catalyst Design for Selective Liquid Products Formation

The escalating concern regarding the release of CO2 into the atmosphere poses a significant threat to the contemporary efforts in mitigating climate change. Amidst a multitude of strategies for curtailing CO2 emissions, the electrochemical CO2 reduction presents a promising avenue for transforming CO2 molecules into a diverse array of valuable gaseous and liquid products, such as CO, CH3OH, CH4, HCO2H, C2H4, C2H5OH, CH3CO2H, 1-C3H7OH and others. The mechanistic investigations of gaseous products (e. g. CO, CH4, C2H4, C2H6 and others) broadly covered in the literature. There is a noticeable gap in the literature when it comes to a comprehensive summary exclusively dedicated to coherent roadmap for the designing principles for a selective catalyst all possible liquid products (such as CH3OH, C2H5OH, 1-C3H7OH, 2-C3H7OH, 1-C4H9OH, as well as other C3-C4 products like methylglyoxal and 2,3-furandiol, in addition to HCO2H, AcOH, oxalic acid and others), selectively converted by CO2 reduction. This entails a meticulous analysis to justify these approaches and a thorough exploration of the correlation between materials and their electrocatalytic properties. Furthermore, these insightful discussions illuminate the future prospects for practical applications, a facet not exhaustively examined in prior reviews.

Anionic Coordination Control in Building Cu-Based Electrocatalytic Materials for CO2 Reduction Reaction

Renewable energy-driven conversion of CO2 to value-added fuels and chemicals via electrochemical CO2 reduction reaction (CO2RR) technology is regarded as a promising strategy with substantial environmental and economic benefits to achieve carbon neutrality. Because of its sluggish kinetics and complex reaction paths, developing robust catalytic materials with exceptional selectivity to the targeted products is one of the core issues, especially for extensively concerned Cu-based materials. Manipulating Cu species by anionic coordination is identified as an effective way to improve electrocatalytic performance, in terms of modulating active sites and regulating structural reconstruction. This review elaborates on recent discoveries and progress of Cu-based CO2RR catalytic materials enhanced by anionic coordination control, regarding reaction paths, functional mechanisms, and roles of different non-metallic anions in catalysis. Finally, the review concludes with some personal insights and provides challenges and perspectives on the utilization of this strategy to build desirable electrocatalysts.

Modulating the Active Sites of VS2 by Mn Doping for Highly Selective CO2 Electroreduction to Methanol in a Flow Cell

Methanol is a valuable liquid C1 product in CO2 electroreduction (CO2ER); however, it is hard to achieve high selectivity and a large current density simultaneously. In this work, we construct Mn2+-doped VS2 multilayer nanowafers applied in a flow cell to yield methanol as a single liquid product to tackle this challenge. Mn doping adjusts the electronic structure of VS2 and concurrently introduces sulfur vacancies, forming a critical *COB intermediate and facilitating its sequential hydrogenation to methanol. The optimal Mn4.8%-VS2 exhibits methanol Faradic efficiencies of more than 60% over a wide potential range of -0.4 to -0.8 V in a flow cell, of which the maximal value is 72.5 ± 1.1% at -0.6 V along with a partial current density of 74.3 ± 1.1 mA cm-2. This work opens an avenue to rationally design catalysts for engineering C1 intermediates toward CO2ER to a single liquid methanol in a flow cell.

Catalysts for C-N coupling in urea electrosynthesis under ambient conditions from carbon dioxide and nitrogenous species

Urea is an indispensable nitrogen-containing organic compound in modern human life. However, the current industrial synthesis of urea involves ammonia, which is produced through the Haber-Bosch process under harsh reaction conditions, causing huge energy consumption and heavy environmental pollution. Electrochemical reduction of carbon dioxide (CO2) and nitrogenous species (N2, NOx- and NO) have achieved significant progress, offering a promising approach for the electrochemical C-N coupling to produce urea under ambient conditions. Urea synthesis driven by renewable electricity represents a suitable alternative to the traditional process, contributing to the goal of carbon neutrality and nitrogen cycles. However, challenges such as low yield rate, poor selectivity and unveiled reaction mechanisms still need to be addressed. This review provides a summary of the latest catalysts utilized in urea electrosynthesis, aiming to provide guidance and prospects for the development of high-performance catalysts.

Review on strategies for improving the added value and expanding the scope of CO2 electroreduction products

The electrochemical reduction of CO2 into value-added chemicals has been explored as a promising solution to realize carbon neutrality and inhibit global warming. This involves utilizing the electrochemical CO2 reduction reaction (CO2RR) to produce a variety of single-carbon (C1) and multi-carbon (C2+) products. Additionally, the electrolyte solution in the CO2RR system can be enriched with nitrogen sources (such as NO3-, NO2-, N2, or NO) to enable the synthesis of organonitrogen compounds via C-N coupling reactions. However, the electrochemical conversion of CO2 into valuable chemicals still faces challenges in terms of low product yield, poor faradaic efficiency (FE), and unclear understanding of the reaction mechanism. This review summarizes the promising strategies aimed at achieving selective production of diverse carbon-containing products, including CO, formate, hydrocarbons, alcohols, and organonitrogen compounds. These approaches involve the rational design of electrocatalysts and the construction of coupled electrocatalytic reaction systems. Moreover, this review presents the underlying reaction mechanisms, identifies the existing challenges, and highlights the prospects of the electrosynthesis processes. The aim is to offer valuable insights and guidance for future research on the electrocatalytic conversion of CO2 into carbon-containing products of enhanced value-added potential.

Customizing catalyst surface/interface structures for electrochemical CO2 reduction

Electrochemical CO2 reduction reaction (CO2RR) provides a promising route to converting CO2 into value-added chemicals and to neutralizing the greenhouse gas emission. For the industrial application of CO2RR, high-performance electrocatalysts featuring high activities and selectivities are essential. It has been demonstrated that customizing the catalyst surface/interface structures allows for high-precision control over the microenvironment for catalysis as well as the adsorption/desorption behaviors of key reaction intermediates in CO2RR, thereby elevating the activity, selectivity and stability of the electrocatalysts. In this paper, we review the progress in customizing the surface/interface structures for CO2RR electrocatalysts (including atomic-site catalysts, metal catalysts, and metal/oxide catalysts). From the perspectives of coordination engineering, atomic interface design, surface modification, and hetero-interface construction, we delineate the resulting specific alterations in surface/interface structures, and their effect on the CO2RR process. At the end of this review, we present a brief discussion and outlook on the current challenges and future directions for achieving high-efficiency CO2RR via surface/interface engineering.

Enhancing Cu-ligand interaction for efficient CO2 reduction towards multi-carbon products

Electrochemical CO2 reduction (CO2R) to valuable products provides a promising strategy to enable CO2 utilization sustainably. Here, we report the strategy of using Cu-DAT (3,5-diamino-1,2,4-triazole) as a catalyst precursor for efficient CO2 reduction, demonstrating over 80% selectivity towards multicarbon products at 400 mA cm-2, with intrinsic activity over 19 times higher than that of Cu nanoparticles. The catalyst's active phase is determined to be metallic copper wrapped with the DAT ligand. We attribute this enhanced CO2R performance to the accelerated steps of *CO adsorption and C-C coupling induced by the closely cooperated DAT ligand.

Green solvent systems for material syntheses and chemical reactions

It is of great significance to develop environmentally benign, non-volatile and recyclable green solvents for different applications. This feature article overviews the properties of green solvent systems (e.g., ionic liquids, supercritical carbon dioxide, deep eutectic solvents and mixed green solvent systems) and their applications in (1) framework material syntheses, including metal-organic frameworks, covalent organic frameworks and hydrogen-bonded organic frameworks, and (2) CO2 conversion reactions, including photocatalytic and electrocatalytic reduction reactions. Finally, the future perspective for research on green solvent systems is proposed from different aspects.

Regulation Strategy of Nanostructured Engineering on Indium-Based Materials for Electrocatalytic Conversion of CO2

Electrochemical carbon dioxide reduction (CO2 RR), as an emerging technology, can combine with sustainable energies to convert CO2 into high value-added products, providing an effective pathway to realize carbon neutrality. However, the high activation energy of CO2 , low mass transfer, and competitive hydrogen evolution reaction (HER) leads to the unsatisfied catalytic activity. Recently, Indium (In)-based materials have attracted significant attention in CO2 RR and a series of regulation strategies of nanostructured engineering are exploited to rationally design various advanced In-based electrocatalysts, which forces the necessary of a comprehensive and fundamental summary, but there is still a scarcity. Herein, this review provides a systematic discussion of the nanostructure engineering of In-based materials for the efficient electrocatalytic conversion of CO2 to fuels. These efficient regulation strategies including morphology, size, composition, defects, surface modification, interfacial structure, alloying, and single-atom structure, are summarized for exploring the internal relationship between the CO2 RR performance and the physicochemical properties of In-based catalysts. The correlation of electronic structure and adsorption behavior of reaction intermediates are highlighted to gain in-depth understanding of catalytic reaction kinetics for CO2 RR. Moreover, the challenges and opportunities of In-based materials are proposed, which is expected to inspire the development of other effective catalysts for CO2 RR.

Carbon dioxide conversion to methanol on a PdCo bimetallic catalyst

The CO2 conversion to methanol (CO2-to-CH3OH conversion) is a promising way to resolve greenhouse gas emissions and global energy shortage. Many catalysts are of interest in improving the efficiency of the conversion reaction. The PdCo alloy is a potential catalyst, but no research is available to clarify the CO2-to-CH3OH reaction mechanism of this alloy. Here, using density functional theory combined with the thermodynamic model, we elucidated the reaction mechanism of the CO2-to-CH3OH conversion on the Pd-skin/PdCo alloy catalyst via thermo- and electro-catalytic processes. The adsorption of CO2-to-CH3OH intermediates with key stable intermediates such as HCOO, COOH, and CO was explored. Free-energy diagrams for the CO2-to-CH3OH conversion were constructed. We found that the formate pathway is the most favorable one. The charge transfer plays a crucial role in the substrate-adsorbate interaction via electronic structure analysis. This work provides valuable guidance for designing Pd-based catalysts for the CO2-to-CH3OH conversion.

Designing Surface and Interface Structures of Copper-Based Catalysts for Enhanced Electrochemical Reduction of CO2 to Alcohols

Electrochemical CO2 reduction (ECR) has emerged as a promising solution to address both the greenhouse effect caused by CO2 emissions and the energy shortage resulting from the depletion of nonrenewable fossil fuels. The production of multicarbon (C2+) products via ECR, especially high-energy-density alcohols, is highly desirable for industrial applications. Copper (Cu) is the only metal that produces alcohols with appreciable efficiency and kinetic viability in aqueous solutions. However, poor product selectivity is the main technical problem for applying the ECR technology in alcohol production. Extensive research has resulted in the rational design of electrocatalyst architectures using various strategies. This design significantly affects the adsorption energetics of intermediates and the reaction pathways for alcohol production. In this review, we focus on the design of effective catalysts for ECR to alcohols, discussing fundamental principles, innovative strategies, and mechanism understanding. Furthermore, the challenges and prospects in utilizing Cu-based materials for alcohol production via ECR are discussed.

Integration of MnO2 Nanosheets with Pd Nanoparticles for Efficient CO2 Electroreduction to Methanol in Membrane Electrode Assembly Electrolyzers

It remains a challenge to design a catalyst with high selectivity at a large current density toward CO2 electrocatalytic reduction (CO2ER) to a single C1 liquid product of methanol. Here, we report the design of a catalyst by integrating MnO2 nanosheets with Pd nanoparticles to address this challenge, which can be implemented in membrane electrode assembly (MEA) electrolyzers for the conversion of CO2ER to methanol. Such a strategy modifies the electronic structure of the catalyst and provides additional active sites, favoring the formation of key reaction intermediates and their successive evolution into methanol. The optimal catalyst delivers a Faradaic efficiency of 77.6 ± 1.3% and a partial current density of 250.8 ± 4.3 mA cm-2 for methanol during CO2ER in an MEA electrolyzer by coupling anodic oxygen evolution reaction with a full-cell energy efficiency achieving 29.1 ± 1.2% at 3.2 V. This work opens a new avenue to the control of C1 intermediates for CO2ER to methanol with high selectivity and activity in an MEA electrolyzer.

Electrochemical Manufacturing Routes for Organic Chemical Commodities

Electrochemical synthesis of organic chemical commodities provides an alternative to conventional thermochemical manufacturing and enables the direct use of renewable electricity to reduce greenhouse gas emissions from the chemical industry. We discuss electrochemical synthesis approaches that use abundant carbon feedstocks for the production of the largest petrochemical precursors and basic organic chemical products: light olefins, olefin oxidation derivatives, aromatics, and methanol. First, we identify feasible routes for the electrochemical production of each commodity while considering the reaction thermodynamics, available feedstocks, and competing thermochemical processes. Next, we summarize successful catalysis and reaction engineering approaches to overcome technological challenges that prevent electrochemical routes from operating at high production rates, selectivity, stability, and energy conversion efficiency. Finally, we provide an outlook on the strategies that must be implemented to achieve large-scale electrochemical manufacturing of major organic chemical commodities.

Dual Structural Design of Platinum-Nickel Hydrogels for Wearable Glucose Biosensing with Ultrahigh Stability

Wearable glucose sensors are of great significance and highly required in mobile health monitoring and management but suffering from limited long-term stability and wearable adaptability. Here a simultaneous component and structure engineering strategy is presented, which involves Pt with abundant Ni to achieve three-dimensional, dual-structural Pt-Ni hydrogels with interconnected networks of PtNi nanowires and Ni(OH)₂ nanosheets, showing prominent electrocatalytic activity and stability in glucose oxidation under neutral condition. Specifically, the PtNi_(1:3) dual hydrogels shows 2.0 and 270.6 times' activity in the glucose electro-oxidation as much as the pure Pt and Ni hydrogels. Thanks to the high activity, structural stability, good flexibility, and self-healing property, the PtNi_(1:3) dual gel-based non-enzymatic glucose sensing chip is endowed with high performance. It features a high sensitivity, an excellent selectivity and flexibility, and particularly an outstanding long-term stability over 2 months. Together with a pH sensor and a wireless circuit, an accurate, real-time, and remote monitoring of sweat glucose is achieved. This facile design of novel dual-structural metallic hydrogels sheds light to rationally develop new functional materials for high-performance wearable biosensors.

Electrochemical C-N coupling of CO2 and nitrogenous small molecules for the electrosynthesis of organonitrogen compounds

Electrochemical C-N coupling reactions based on abundant small molecules (such as CO₂ and N₂) have attracted increasing attention as a new "green synthetic strategy" for the synthesis of organonitrogen compounds, which have been widely used in organic synthesis, materials chemistry, and biochemistry. The traditional technology employed for the synthesis of organonitrogen compounds containing C-N bonds often requires the addition of metal reagents or oxidants under harsh conditions with high energy consumption and environmental concerns. By contrast, electrosynthesis avoids the use of other reducing agents or oxidants by utilizing "electrons", which are the cleanest "reagent" and can reduce the generation of by-products, consistent with the atomic economy and green chemistry. In this study, we present a comprehensive review on the electrosynthesis of high value-added organonitrogens from the abundant CO₂ and nitrogenous small molecules (N₂, NO, NO₂^-, NO₃^-, NH₃, etc.) via the C-N coupling reaction. The associated fundamental concepts, theoretical models, emerging electrocatalysts, and value-added target products, together with the current challenges and future opportunities are discussed. This critical review will greatly increase the understanding of electrochemical C-N coupling reactions, and thus attract research interest in the fixation of carbon and nitrogen.

Investigation of Molecular Mechanism of Cobalt Porphyrin Catalyzed CO2 Electrochemical Reduction in Ionic Liquid by In-Situ SERS

This study explores the electrochemical reduction in CO₂ using room temperature ionic liquids as solvents or electrolytes, which can minimize the environmental impact of CO₂ emissions. To design effective CO₂ electrochemical systems, it is crucial to identify intermediate surface species and reaction products in situ. The study investigates the electrochemical reduction in CO₂ using a cobalt porphyrin molecular immobilized electrode in 1-n-butyl-3-methyl imidazolium tetrafluoroborate (BMI.BF4) room temperature ionic liquids, through in-situ surface-enhanced Raman spectroscopy (SERS) and electrochemical technique. The results show that the highest faradaic efficiency of CO produced from the electrochemical reduction in CO₂ can reach 98%. With the potential getting more negative, the faradaic efficiency of CO decreases while H₂ is produced as a competitive product. Besides, water protonates porphyrin macrocycle, producing pholorin as the key intermediate for the hydrogen evolution reaction, leading to the out-of-plane mode of the porphyrin molecule. Absorption of CO₂ by the ionic liquids leads to the formation of BMI·CO₂ adduct in BMI·BF₄ solution, causing vibration modes at 1100, 1457, and 1509 cm^-1. However, the key intermediate of CO2-· radical is not observed. The υ(CO) stretching mode of absorbed CO is affected by the electrochemical Stark effect, typical of CO chemisorbed on a top site.

Challenges and Opportunities in Electrocatalytic CO2 Reduction to Chemicals and Fuels

The global temperature increase must be limited to below 1.5 °C to alleviate the worst effects of climate change. Electrocatalytic CO2 reduction (ECO2 R) to generate chemicals and feedstocks is considered one of the most promising technologies to cut CO2 emission at an industrial level. However, despite decades of studies, advances at the laboratory scale have not yet led to high industrial deployment rates. This Review discusses practical challenges in the industrial chain that hamper the scaling-up deployment of the ECO2 R technology. Faradaic efficiencies (FEs) of about 100 % and current densities above 200 mA cm-2 have been achieved for the ECO2 R to CO/HCOOH, and the stability of the electrolysis system has been prolonged to 2000 h. For ECO2 R to C2 H4 , the maximum FE is over 80 %, and the highest current density has reached the A cm-2 level. Thus, it is believed that ECO2 R may have reached the stage for scale-up. We aim to provide insights that can accelerate the development of the ECO2 R technology.

In situ electrochemical synthesis of Pd aerogels as highly efficient anodic electrocatalysts for alkaline fuel cells

Improving the utilization of noble metals is extremely urgent for fuel cell electrocatalysis, while three-dimensional hierarchical noble metal aerogels with abundant sites and channels are proposed to reinforce their electrocatalytic performances and decrease their amounts. Herein, novel Pd aerogels with tunable surface chemical states were prepared through a facile in situ electrochemical activation, starting with PdO x aerogels by the hydrolysis method. The hierarchical porous Pd aerogels showed unprecedented high activity towards the electrocatalytic oxidation of fuels including methanol (2.99 A mgPd -1), ethanol (8.81 A mgPd -1), and others in alkali, outperforming commercial catalysts (7.12- and 13.66-fold, corresponding to methanol and ethanol). Theoretical investigation unveiled the hybrid surface states with metallic and oxidized Pd species in Pd aerogels to regulate the adsorption of intermediates and facilitate the synergistic oxidation of adsorbed *CO, resulting in enhanced activity with the MOR as the model. Therefore, efficient Pd aerogels through the in situ electrochemical activation of PdO x aerogels were proposed and showed great potential for fuel cell anodic electrocatalysis.

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.

Concentration Optimization of Localized Cu0 and Cu+ on Cu-Based Electrodes for Improving Electrochemical Generation of Ethanol from Carbon Dioxide

Copper-based electrodes can catalyze electroreduction of CO₂ to two-carbon products. However, obtaining a specific product with high efficiency depends on the oxidation state of Cu for the Cu-based materials. In this study, Cu-based electrodes were prepared on fluorinated tin oxide (FTO) using the one-step electrodeposition method. These electrodes were used as efficient electrocatalysts for CO₂ reduction to ethanol. The concentration ratio of Cu⁰ and Cu⁺ on the electrodes was precisely modulated by adding monoethanolamine (MEA). The results of spectroscopic characterization showed that the concentration ratio of localized Cu⁺ and Cu⁰ (Cu⁺/Cu⁰) on the Cu-based electrodes was controlled from 1.24/1 to 1.54/1 by regulating the amount of MEA. It was found that the electrode exhibited the best electrochemical efficiency and ethanol production in the CO₂ reduction reaction at the optimal concentration ratio Cu⁺/Cu⁰ of 1.42/1. The maximum faradaic efficiencies of ethanol and C₂ were 48% and 77%, respectively, at the potential of -0.6 V vs. a reversible hydrogen electrode (RHE). Furthermore, the optimal concentration ratio of Cu⁺/Cu⁰ achieved the balance between Cu⁺ and Cu⁰ with the most favorable free energy for the formation of *CO intermediate. The stable existence of the *CO intermediate significantly contributed to the formation of the C-C bond for ethanol production.

Structural evolution and strain generation of derived-Cu catalysts during CO2 electroreduction

Copper (Cu)-based catalysts generally exhibit high C₂₊ selectivity during the electrochemical CO₂ reduction reaction (CO₂RR). However, the origin of this selectivity and the influence of catalyst precursors on it are not fully understood. We combine operando X-ray diffraction and operando Raman spectroscopy to monitor the structural and compositional evolution of three Cu precursors during the CO₂RR. The results indicate that despite different kinetics, all three precursors are completely reduced to Cu(0) with similar grain sizes (~11 nm), and that oxidized Cu species are not involved in the CO₂RR. Furthermore, Cu(OH)₂- and Cu₂(OH)₂CO₃-derived Cu exhibit considerable tensile strain (0.43%~0.55%), whereas CuO-derived Cu does not. Theoretical calculations suggest that the tensile strain in Cu lattice is conducive to promoting CO₂RR, which is consistent with experimental observations. The high CO₂RR performance of some derived Cu catalysts is attributed to the combined effect of the small grain size and lattice strain, both originating from the in situ electroreduction of precursors. These findings establish correlations between Cu precursors, lattice strains, and catalytic behaviors, demonstrating the unique ability of operando characterization in studying electrochemical processes.

Copper catalysts derived from oxidized precursors typically exhibit high selectivity for CO₂ electroreduction to multicarbon products, yet the influencing factors that control the selectivity need further investigation. Here, the authors reveal that the high selectivity stems from small grain size and lattice strain due to in situ reduction of precursors.

Conversion of Carbon Dioxide into Chemical Vapor Deposited Graphene with Controllable Number of Layers via Hydrogen Plasma Pre-Treatment

In this work, we report the conversion of carbon dioxide (CO₂) gas into graphene on copper foil by using a thermal chemical vapor deposition (CVD) method assisted by hydrogen (H₂) plasma pre-treatment. The synthesized graphene has been characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results show the controllable number of layers (two to six layers) of high-quality graphene by adjusting H₂ plasma pre-treatment powers (100-400 W). The number of layers is reduced with increasing H₂ plasma pre-treatment powers due to the direct modification of metal catalyst surfaces. Bilayer graphene can be well grown with H₂ plasma pre-treatment powers of 400 W while few-layer graphene has been successfully formed under H₂ plasma pre-treatment powers ranging from 100 to 300 W. The formation mechanism is highlighted.

Carbon Aerogels as Electrocatalysts for Sustainable Energy Applications: Recent Developments and Prospects

Carbon aerogel (CA) based materials have multiple advantages, including high porosity, tunable molecular structures, and environmental compatibility. Increasing interest, which has focused on CAs as electrocatalysts for sustainable applications including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and CO₂ reduction reaction (CO₂RR) has recently been raised. However, a systematic review covering the most recent progress to boost CA-based electrocatalysts for ORR/OER/HER/CO₂RR is now absent. To eliminate the gap, this critical review provides a timely and comprehensive summarization of the applications, synthesis methods, and principles. Furthermore, prospects for emerging synthesis, screening, and construction methods are outlined.

Short-Range Diffusion Enables General Synthesis of Medium-Entropy Alloy Aerogels

Medium-entropy alloy aerogels (MEAAs) with the advantages of both multimetallic alloys and aerogels are promising new materials in catalytic applications. However, limited by the immiscible behavior of different metals, achieving single-phase MEAAs is still a grand challenge. Herein, a general strategy for preparing ultralight 3D porous MEAAs with the lowest density of 39.3 mg cm^-3 among the metal materials is reported, through combining auto-combustion and subsequent low-temperature reduction procedures. The homogenous mixing of precursors at the ionic level makes the short-range diffusion of metal atoms possible to drive the formation of single-phase MEAAs. As a proof of concept in catalysis, as-synthesized Ni₅₀ Co₁₅ Fe₃₀ Cu₅ MEAAs exhibit a high mass activity of 1.62 A mg^-1 and specific activity of 132.24 mA cm^-2 toward methanol oxidation reactions, much higher than those of the low-entropy counterparts. In situ Fourier transform infrared and NMR spectroscopies reveal that MEAAs can enable highly selective conversion of methanol to formate. Most importantly, a methanol-oxidation-assisted MEAAs-based water electrolyzer can achieve a low cell voltage of 1.476 V at 10 mA cm^-2 for making value-added formate at the anode and H₂ at the cathode, 173 mV lower than that of traditional alkaline water electrolyzers.

Expanding the Range: AuCu Metal Aerogels from H2O and EtOH

Due to their self-supporting and nanoparticulate structure, metal aerogels have emerged as excellent electrocatalysts, especially in the light of the shift to renewable energy cycles. While a large number of synthesis parameters have already been studied in depth, only superficial attention has been paid to the solvent. In order to investigate the influence of this parameter with respect to the gelation time, crystallinity, morphology, or porosity of metal gels, AuxCuy aerogels were prepared in water and ethanol. It was shown that although gelation in water leads to highly porous gels (60 m2g−1), a CuO phase forms during this process. The undesired oxide could be selectively removed using a post-washing step with formic acid. In contrast, the solvent change to EtOH led to a halving of the gelation time and the suppression of Cu oxidation. Thus, pure Cu aerogels were synthesized in addition to various bimetallic Au3X (X = Ni, Fe, Co) gels. The faster gelation, caused by the lower permittivity of EtOH, led to the formation of thicker gel strands, which resulted in a lower porosity of the AuxCuy aerogels. The advantage given by the solvent choice simplifies the preparation of metal aerogels and provides deeper knowledge about their gelation.

In situ dual doping for constructing efficient CO2-to-methanol electrocatalysts

Methanol is a highly desirable product of CO₂ electroreduction due to its wide array of industrial applications. However, the development of CO₂-to-methanol electrocatalysts with high performance is still challenging. Here we report an operationally simple in situ dual doping strategy to construct efficient CO₂-to-methanol electrocatalysts. In particular, when using Ag,S-Cu₂O/Cu as electrocatalyst, the methanol Faradaic efficiency (FE) could reach 67.4% with a current density as high as 122.7 mA cm^-2 in an H-type cell using 1-butyl-3-methylimidazolium tetrafluoroborate/H₂O as the electrolyte, while the current density was below 50 mA cm^-2 when the FE was greater than 50% over the reported catalysts. Experimental and theoretical studies suggest that the anion S can effectively adjust the electronic structure and morphology of the catalysts in favor of the methanol pathway, whereas the cation Ag suppresses the hydrogen evolution reaction. Their synergistic interactions with host material enhance the selectivity and current density for methanol formation. This work opens a way for designing efficient catalysts for CO₂ electroreduction to methanol.

High Performance 3D Self-Supporting Cu-Bi Aerogels for Electrocatalytic Reduction of CO2 to Formate

The electrocatalytic reduction of CO₂ (CO₂ RR) to CO, formate, methane, and other high-value compounds is a promising technique. However, current electrocatalysts suffer from drawbacks such as few active catalytic sites, poor selectivity and low stability, etc, which restrict the practical application. Although monatomic metal catalysts have been widely reported in recent years, high performance non-noble metal aerogels were rarely investigated for electrocatalytic CO₂ RR. Herein, Cu-Bi aerogels with boosted CO₂ RR activity were well constructed by a simple one-step self-assembly method. The resultant Cu₁ Bi₂ exhibits excellent CO₂ RR activity with high faradaic efficiency (FE) of 96.57 % towards HCOOH at a potential of -0.9 V vs. RHE, and the FE_HCOOH remains over 80.18 % in a wide potential window (-0.8 V to -1.2 V vs. RHE). It demonstrated that the enhanced CO₂ RR activity of Cu-Bi aerogels could be attributed to the 3D self-supporting structure of the catalysis, synergistic effect, and low interfacial charge transfer resistance.

Surface Modification of Nano-Cu2 O for Controlling CO2 Electrochemical Reduction to Ethylene and Syngas

In the surroundings of carbon neutrality, nano-Cu₂ O is considered a promising catalyst for the electrochemical CO₂ reduction reaction (ECO₂ RR), whose improvements in product selectivity still require considerable efforts. Here, we present an efficient strategy for controlling the ECO₂ RR product by modifying the surface of nano-Cu₂ O, i.e., by controlling the exposed facets via a reductant-controlled method to achieve the highest C₂ H₄ selectivity (Faradic efficiency=74.1 %) for Cu₂ O-based catalysts in neutral electrolytes, and introducing a well-suited metal-organic framework (MOF) coating on the surface of nano-Cu₂ O to obtain syngas completely with an appropriate H₂ :CO ratio. Detailed mechanism and key intermediate have been illustrated by DFT calculations. Our systematic strategy is expected to control the ECO₂ RR product, improve the selectivity, and provide a reliable method for CO₂ management and the green production of important carbon resources.

Photo- and Electrocatalytic Reduction of CO2 over Metal-Organic Frameworks and Their Derived Oxides: A Correlation of the Reaction Mechanism with the Electronic Structure

A Ce/Ti-based bimetallic 2-aminoterephthalate metal-organic framework (MOF) was synthesized and evaluated for photocatalytic reduction of CO₂ in comparison with an isoreticular pristine monometallic Ce-terephthalate MOF. Owing to highly selective CO₂ adsorption capability, optimized band gaps, higher flux of photogenerated electron-hole pairs, and a lower rate of recombination, this material exhibited better photocatalytic reduction of CO₂ and lower hydrogen evolution compared to Ce-terephthalate. Thorough probing of the surface and electronic structure inferred that the reducibility of Ce⁴⁺ to Ce³⁺ was due to the introduction of an amine functional group into the linker, and low-lying Ti(3d) orbitals in Ce/Ti-2-aminoterephthalate facilitated the photoreduction reaction. Both the MOFs were calcined to their respective oxides of Ce_1-xTi_xO₂ and CeO₂, and the electrocatalytic reduction of CO₂ was performed over the oxidic materials. In contrast to the photocatalytic reaction mechanism, the lattice substitution of Ti in the CeO₂ fluorite cubic structure showed a better hydrogen evolution reaction and consequently, poorer electroreduction of CO₂ compared to pristine CeO₂. Density functional theory calculations of the competitive hydrogen evolution reaction on the MOF and the oxide surfaces corroborated the experimental findings.

Electrochemical CO2 Reduction on Cu: Synthesis-Controlled Structure Preference and Selectivity

The electrochemical CO2 reduction reaction (ECO2 RR) on Cu catalysts affords high-value-added products and is therefore of great practical significance. The outcome and kinetics of ECO2 RR remain insufficient, requiring essentially the optimized structure design for the employed Cu catalyst, and also the fine synthesis controls. Herein, synthesis-controlled structure preferences and the modulation of intermediate's interactions are considered to provide synthesis-related insights on the design of Cu catalysts for selective ECO2 RR. First, the origin of ECO2 RR intermediate-dominated selectivity is described. Advanced structural engineering approaches, involving alloy/compound formation, doping/defect introduction, and the use of specific crystal facets/amorphization, heterostructures, single-atom catalysts, surface modification, and nano-/microstructures, are then reviewed. In particular, these structural engineering approaches are discussed in association with diversified synthesis controls, and the modulation of intermediate generation, adsorption, reaction, and additional effects. The results pertaining to synthetic methodology-controlled structural preferences and the correspondingly motivated selectivity are further summarized. Finally, the current opportunities and challenges of Cu catalyst fabrication for highly selective ECO2 RR are discussed.

Recent Development of Electrocatalytic CO2 Reduction Application to Energy Conversion

Carbon dioxide (CO₂ ) emission has caused greenhouse gas pollution worldwide. Hence, strengthening CO₂ recycling is necessary. CO₂ electroreduction reaction (CRR) is recognized as a promising approach to utilize waste CO₂ . Electrocatalysts in the CRR process play a critical role in determining the selectivity and activity of CRR. Different types of electrocatalysts are introduced in this review: noble metals and their derived compounds, transition metals and their derived compounds, organic polymer, and carbon-based materials, as well as their major products, Faradaic efficiency, current density, and onset potential. Furthermore, this paper overviews the recent progress of the following two major applications of CRR according to the different energy conversion methods: electricity generation and formation of valuable carbonaceous products. Considering electricity generation devices, the electrochemical properties of metal-CO₂ batteries, including Li-CO₂ , Na-CO₂ , Al-CO₂ , and Zn-CO₂ batteries, are mainly summarized. Finally, different pathways of CO₂ electroreduction to carbon-based fuels is presented, and their reaction mechanisms are illustrated. This review provides a clear and innovative insight into the entire reaction process of CRR, guiding the new electrocatalysts design, state-of-the-art analysis technique application, and reaction system innovation.

Lewis-Basic EDTA as a Highly Active Molecular Electrocatalyst for CO2 Reduction to CH4

The most active catalysts so far successful in hydrogenation reduction of CO₂ are mainly heterogeneous Cu-based catalysts. The complex coordination environments and multiple active sites in heterogeneous catalysts result in low selectivity of target product, while molecular catalysts with well-defined active sites and tailorable structures allow mechanism-based performance optimization. Herein, we firstly report a single ethylenediaminetetraacetic acid (EDTA) molecular-level immobilized on the surface of carbon nanotube as a catalyst for transferring CO₂ to CH₄ with an excellent performance. This catalyst exhibits a high Faradaic efficiency of 61.6 % toward CH₄ , a partial current density of -16.5 mA cm^-2 at a potential of -1.3 V versus reversible hydrogen electrode. Density functional theory calculations reveal that the Lewis basic COO^- groups in EDTA molecule are the active sites for CO₂ reduction reaction (CO₂ RR). The energy barrier for the generation of CO from *CO intermediate is as high as 0.52 eV, while the further protonation of *CO to *CHO follows an energetic downhill path (-1.57 eV), resulting in the high selectivity of CH₄ . This work makes it possible to control the product selectivity for CO₂ RR according to the relationship between the energy barrier of *CO intermediate and molecular structures in the future.

Quasi-square-shaped cadmium hydroxide nanocatalysts for electrochemical CO2 reduction with high efficiency

Powered by a renewable electricity source, electrochemical CO2 reduction reaction is a promising solution to facilitate the carbon balance. However, it is still a challenge to achieve a desired product with commercial current density and high efficiency. Herein we designed quasi-square-shaped cadmium hydroxide nanocatalysts for CO2 electroreduction to CO. It was discovered that the catalyst is very active and selective for the reaction. The current density could be as high as 200 mA cm-2 with a nearly 100% selectivity in a commonly used H-type cell using the ionic liquid-based electrolyte. In addition, the faradaic efficiency of CO could reach 90% at a very low overpotential of 100 mV. Density functional theory studies and control experiments reveal that the outstanding performance of the catalyst was attributed to its unique structure. It not only provides low Cd-O coordination, but also exposes high activity (002) facet, which requires lower energy for the formation of CO. Besides, the high concentration of CO can be achieved from the low concentration CO2 via an adsorption-electrolysis device.