Electrochemical Carbon Dioxide Reduction to Ethylene: From Mechanistic Understanding to Catalyst Surface Engineering

Nanoconfinement and tandem catalysis over yolk-shell catalysts towards electrochemical reduction of CO2 to multi-carbon products

Electrocatalytic materials in the electrochemical reduction of carbon dioxide (CO2ER) provide an effective strategy to mitigate CO2 emissions, enable carbon recycling, and synthesize high-value multi-carbon (C2+) chemicals, thereby supporting long-term renewable energy storage. Recent advances highlight that yolk-shell nanostructures, which regulate adsorbed CO intermediates (*CO), offer a promising tandem catalysis pathway to convert CO2 to C2+ products. In this study, we designed Pd@Cu2O/Cu2S yolk-shell catalysts, which demonstrated a Faradaic efficiency (FE) of 81.7 % for C2 products at -0.8 V vs. RHE, with an FE of 44.7 % for ethanol (C2H5OH). This performance is attributed to the synergistic interplay between Pd, which efficiently generates *CO intermediates, and Cu surfaces, which facilitate rapid CC coupling to form C2 products. In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations further reveal that Pd and S modulate the reaction energy barrier of the *OCCOH intermediate, steering selectivity toward C2 products and enabling partial C1-to-C2 conversion. This research offers a strategy for synthesizing Cu-based tandem catalysts and improving C2 product selectivity of CO2ER.

Electronic Modulation of Bismuth by g-C3N4 Constructs Electron-Enriched Active Sites for Accelerated CO2 Electroreduction to Formate

Electrochemical reduction of CO2 (ECO2RR) to formate represents a promising approach to achieving carbon neutrality, yet it faces significant challenges due to the low adsorption efficiency of the CO2 intermediates. In this study, we developed a highly dispersed electron-rich Bi metal catalyst, utilizing low-cost g-C3N4 as a nonmetallic support and electron donor. This design created a conductive network and a multielectron environment around the Bi atoms that facilitated dynamic interfacial charge transfer from g-C3N4 to Bi, thus enhancing the catalytic efficiency of active sites. The assembly catalyst exhibited a formate selectivity of over 90% within a wide potential window and maintained stable catalytic activity in simulated seawater solutions. In situ Raman spectroscopy and DFT calculations indicated that the incorporation of the nonmetallic support shifted the Bi-p band center to more negative values while increasing Bader charge transfer between Bi and *OCHO intermediates. This indicated enhanced adsorption of the *OCHO intermediate by electron-rich Bi, thus improving the selectivity and activity for formate production.

Electrocatalytic CO2 Reduction to C2 Products via Enhanced C─C Coupling Over Cu-based Catalysts: Dynamic Reaction and Regulation Mechanism

Benefiting from the optimal interaction strength between Cu and reactants, Cu-based catalysts exhibit a unique capability of facilitating the formation of various multi-carbon products in electricity-driven CO2 reduction reactions (CO2ERR). Nonetheless, the CO2ERR process on these catalysts is characterized by intricate polyproton-electron transfer mechanisms that are frequently hindered by high energy barriers, sluggish reaction kinetics, and low C─C coupling efficiency. This review employs advanced characterization techniques, such as sum frequency generation technology, to provide a comprehensive analysis of the CO2ERR mechanism on the Cu surface, examining it from both spatial and temporal dimensions and proposing a spatial-temporal coupling reaction mechanism. To improve C─C coupling efficiency, a series of regulatory strategies are focused on surface microenvironment, catalyst surface structure, and internal electronic structure, thereby offering novel insights for the upcoming design and enhancement of Cu-based electrocatalysts.

Doping and defect engineering in carbon-based electrocatalysts for enhanced electrochemical CO2 reduction: From 0D to 3D materials

The increasing atmospheric CO2 levels and the urgent need for sustainable energy solutions have driven research into electrochemical CO2 reduction. Carbon-based materials have received significant attention for their potential as electrocatalysts, yet their inert nature often limits their performance. Defect engineering and heteroatom doping have emerged as transformative approaches to overcome these limitations, enhancing both catalytic activity and Faradaic efficiency. This review systematically examines the role of these strategies across diverse carbon materials, including graphene, carbon nanotubes, carbon dots, and boron-doped diamond. Special attention is given to the incorporation of heteroatoms, such as nitrogen and boron, and the modulation of defect structures to optimize CO2 reduction pathways. By exploring the interplay between dopant type, defect density, and material dimensionality, we provide a comprehensive understanding of how tailored carbon-based electrocatalysts can drive advancements in sustainable electrochemical CO2 conversion. This work underscores the potential of defect-engineered and doped carbon materials to revolutionize the field of electrocatalysis, paving the way for innovative solutions to environmental and energy challenges.

Anti-Sintering Ni-W Catalytic Layer on Reductive Tungsten Carbides for Superior High-Temperature CO2 Reduction

The reverse water-gas shift (RWGS) reaction stands out as a promising approach for selectively converting CO2 into CO, which can then be upgraded into high-value-added products. While designing high selectivity and stability catalysts for RWGS reaction remains a significant challenge. In this study, an efficient and ultra-stable Ni-W catalytic layer on reductive WC (NiAWC) is designed as an anti-sintering catalyst for superior high-temperature RWGS reaction. Benefiting from the unique structures, the NiAWC catalyst exhibits exceptionally high performances with a CO production rate of 1.84 molCO gNi -1 h-1 and over 95% CO selectivity, maintaining stability for 120 h at 500 °C. Even after 300 h of continuous testing at 600 °C and five aging cycles at 800 °C, the activity loss is only 0.34% and 0.83%, respectively. Unlike the conventional mechanism in RWGS reaction, it is demonstrated that the Ni-W limited coordination can stabilize the Ni sites and allow a pre-oxidation of Niδ+ by CO, which produces an O* electronic reservoir and hinders the charge transfer from Ni to W-O, thereby avoiding the dissolution of Ni atoms. The design of new, efficient, and selective catalysts through metal-substrate synergistic effects is suggested to offer a promising path to engineering superior thermal catalysts.

Bimetallic Tandem Strategy for Effective Modulation of CO2 Electrocatalytic Selectivity on Relatively Inert Cu Interfaces

The development of effective strategies to enhance the activity and selectivity of Cu-based catalysts for the CO2 reduction reaction (CO2RR) remains a critical challenge, particularly on relatively inert Cu facets that are highly active in the competitive hydrogen evolution reaction (HER). In this study, a series of Cu-M (M = Au, Ag, Pd) bimetallic tandem interfaces are fabricated on Cu nanocolumn arrays (Cu NCAs) with predominantly exposed Cu (200) facets. These interfaces excited a significant number of Cu+ species and modulated the adsorption behavior of critical intermediates for CO2RR, resulting in improved CO2RR activity and a substantial reduction in the competitive HER. Notably, the Cu-Au, Cu-Ag, and Cu-Pd NCAs displayed excellent selectivity for C2H4, CO, and HCOOH products, with optimized faradaic efficiency (FE) of ≈43.2, ≈48.0, and ≈50.7%, respectively. According to in situ spectroscopic analysis, each Cu-M interface exhibited distinct catalytic pathways: Cu-Au favored *COOH and *CO adsorption followed by C-C coupling for C2H4 production, Cu-Ag promoted *CO desorption for CO generation, and Cu-Pd facilitated *OCHO formation for HCOOH production. This study provides a strategy to design high-performance and more practical bimetallic Cu-based catalytic electrodes by directly modifying various commercial Cu substrates.

Design of Ultra-Stable Solid Amine Adsorbents and Mechanisms of Hydroxyl Group-Dependent Deactivation for Reversible CO2 Capture from Flue Gas

Although supported solid amine adsorbents have attracted great attention for CO2 capture, critical chemical deactivation problems including oxidative degradation and urea formation have severely restricted their practical applications for flue gas CO2 capture. In this work, we reveal that the nature of surface hydroxyl groups (metal hydroxyl Al-OH and nonmetal hydroxyl Si-OH) plays a key role in the deactivation mechanisms. The polyethyleneimine (PEI) supported on Al-OH-containing substrates suffers from severe oxidative degradation during the CO2 capture step due to the breakage of amine-support hydrogen bonding networks, but exhibits an excellent anti-urea formation feature by preventing dehydration of carbamate products under a pure CO2 regeneration atmosphere. In contrast, PEI supported on Si-OH-containing substrates exhibits excellent anti-oxidative stability under simulated flue gas conditions by forming a robust hydrogen bonding protective network with Si-OH, but suffers from obvious urea formation during the pure CO2 regeneration step. We also reveal that the urea formation problem for PEI-SBA-15 can be avoided by the incorporation of an OH-containing PEG additive. Based on the intrinsic understanding of degradation mechanisms, we successfully synthesized an adsorbent 40PEI-20PEG-SBA-15 that demonstrates outstanding stability and retention of a high CO2 capacity of 2.45 mmol g-1 over 1000 adsorption-desorption cycles, together with negligible capacity loss during aging in simulated flue gas (10% CO2 + 5% O2 + 3% H2O) for one month at 60-70 °C. We believe this work makes great contribution to the advancement in the field of ultra-stable solid amine-based CO2 capture materials.

Electrocatalytic reduction of CO2 to produce the C2+ products: from selectivity to rational catalyst design

Electrocatalytic reduction of CO2 (eCO2RR) into valuable multi-carbon (C2+) products is an effective strategy for combating climate change and mitigating energy crises. The high-energy density and diverse applications of C2+ products have attracted considerable interest. However, the complexity of the reaction pathways and the high energy barriers to C-C coupling lead to lower selectivity and faradaic efficiency for C2+ products than for C1 products. Therefore, a thorough understanding of the underlying mechanisms and identification of reaction conditions that influence selectivity, followed by the rational design of catalysts, are considered promising methods for the efficient and selective synthesis of multi-carbon products. This review first introduces the critical steps involved in forming multi-carbon products. Then, we discuss the reaction conditions that influence the selectivity of C2+ products and explore different catalyst design strategies to enhance the selective production of C2+ products. Finally, we summarize the significant challenges currently facing the eCO2RR field and suggest future research directions to address these challenges.

Ce3+/Ce4+ Ion Redox Shuttle Stabilized Cuδ+ for Efficient CO2 Electroreduction to C2H4

The CO2 electroreduction reaction has advantages in clean and pollution-free carbon conversion, but it still faces challenges in carbon utilization efficiency and improving the selectivity of C2 products. Although the dynamic Cuδ+ state is known to favor the C-C coupling process, the suitable Cuδ+ species for electrocatalytic reduction of CO2 are difficult to maintain under the conditions of strong reduction and large current. Herein, we propose a Ce doping strategy to stabilize the Cuδ+ state (Ce/CuOx) during the CO2RR process, which enables a high Faradaic efficiency of 60 % for multi-carbon products (40 % for C2H4, 14 % for CH3CH2OH, and 6 % for CH3COOH), and 25 h stability at -1.2 V versus the reversible hydrogen electrode. In situ infrared spectroscopy, in situ X-ray photoelectron spectroscopy combined with density functional theory calculations reveal that the Cuδ+ is stabilized by the redox ion pairs of Ce, which reduces the energy barrier of *CO coupling, and improves the Faraday efficiency of electrocatalytic CO2 reduction of C2H4. This work provides a new idea to make full use of lanthanide variable value metals for advanced catalysis and clean energy conversion.

Reversibly Modulating the Selectivity of Carbon Dioxide Reduction via Ligand-Driven Spin Crossover

Selectivity is an essential aspect in catalysis. At present, the improvement of the selectivity for complex reactions with multiple pathways/products, for example the carbon dioxide reduction reaction (CO2RR), can usually be achieved for only one pathway/product. It is still a challenge to reversibly modulate the selectivity between two reaction pathways or products of the CO2RR by one catalyst. Here, we propose the reversible modulation of selectivity between two products via spin crossover. By employing first-principles calculations, six spin crossover molecular catalysts are found among 17 kinds of transition metal embedded porphyrin derivatives (ppy_TM), where the changes in axial ligand configurations can reversibly switch the spin state of catalysts between high spin and low spin. For ppy_Os and ppy_Ru, the alteration in spin state can effectively influence the reduction of CO2 into either formic acid or carbon monoxide by changing the relative stability of the key intermediates *COOH and *HCOO.

Electrochemical CO2 Reduction to Multicarbon Products on Non-Copper Based Catalysts

Electrochemical CO2 reduction reaction (eCO2RR) to value-added multicarbon (C2+) products offers a promising approach for achieving carbon neutrality and storing intermittent renewable energy. Copper (Cu)-based electrocatalysts generally play the predominant role in this process. Yet recently, more and more non-Cu materials have demonstrated the capability to convert CO2 into C2+, which provides impressive production efficiency even exceeding those on Cu, and a wider variety of C2+ compounds not achievable with Cu counterparts. This motivates us to organize the present review to make a timely and tutorial summary of recent progresses on developing non-Cu based catalysts for CO2-to-C2+. We begin by elucidating the reaction pathways for C2+ formation, with an emphasis on the unique C-C coupling mechanisms in non-Cu electrocatalysts. Subsequently, we summarize the typical C2+-involved non-Cu catalysts, including ds-, d- and p-block metals, as well as metal-free materials, presenting the state-of-the-art design strategies to enhance C2+ efficiency. The system upgrading to promote C2+ productivity on non-Cu electrodes covering microbial electrosynthesis, electrolyte engineering, regulation of operational conditions, and synergistic co-electrolysis, is highlighted as well. Our review concludes with an exploration of the challenges and future opportunities in this rapidly evolving field.

Ugi's amine based coordination polymers as synergistic catalysts for the electrocatalytic reduction of carbon dioxide

The escalating concentration of carbon dioxide in the atmosphere is a pressing environmental concern, necessitating the development of efficient technologies for CO2 reduction and utilization. In this context, metal-organic frameworks (MOFs) emerge as promising catalysts due to their tunable structures and unique chemical properties. This study focuses on the synthesis, characterization, and evaluation of amino-functionalized MOFs with cobalt and nickel nodes for the electrochemical reduction of CO2. Electrochemical investigations reveal that a cobalt-based MOF primarily facilitates the production of methane, demonstrating high selectivity and efficiency under controlled conditions. In contrast, a nickel-based MOF exhibits a broader array of reduction products, including methane, CO, and ethanol, with a significant conversion efficiency. These differences underscore the impact of the central metal node on the catalytic activity and product distribution. This comprehensive study not only advances our understanding of MOF-based catalysts for CO2 reduction but also underscores the significance of molecular engineering in enhancing the selectivity and efficiency of these processes. By demonstrating the potential of amino-functionalized MOFs with specific metal nodes, we contribute to the development of sustainable solutions for carbon capture and utilization, aligning with global efforts to mitigate climate changes and foster a green chemical industry.

Design and synthesis of magnesium-modified copper oxide nanosheets as efficient electrocatalysts for CO2 reduction

Electroreduction of carbon dioxide (CO2) to multiple carbon products plays a significant role in carbon neutrality and the production of valuable chemicals. Herein, we developed a magnesium-modified copper oxide nanosheet catalyst (Mg-CuO) using a post-impregnation method. Comprehensive elemental analysis demonstrated the effective incorporation of magnesium into CuO nanosheets, resulting in a noticeable alteration of the electron density of Cu atoms. Consequently, the Mg-CuO nanosheets exhibited an increased efficiency for CO2 electroreduction in comparison with the unmodified CuO nanosheets. The optimized Mg-CuO catalyst exhibited faradaic efficiencies of 46.33% for ethylene production and 62.64% for C2+ production at -1.3 V vs. reversible hydrogen electrode (RHE). DFT proved that the introduction of Mg species could increase the charge density of Cu and decrease the adsorption energy of *CO, which promoted C-C coupling and enhanced the selectivity of C2+ products. This study presents an effective way to adjust the electronic structure of common copper-based electrocatalysts and the corresponding interaction with *CO, resulting in an improved faradaic efficiency of C2+ products.

Mechanistic insights into C-C coupling in electrocatalytic CO2 reduction reaction

The utilization of CO2 has become an emerging area of research in response to climate change and global warming. The electrochemical CO2 reduction reaction (CO2RR) holds significant promise as a technology to address this issue by converting CO2 molecules into various commercially valuable chemicals. While CO2RR to C1 hydrocarbons has achieved high activity and selectivity, the C-C coupling to produce higher hydrocarbons remains challenging due to low energy efficiency and the prevalent hydrogen evolution reaction (HER) on the same catalyst, leading to high hydrogenation rates. In this review, we aim to elucidate the fundamental challenges of C-C coupling and explore potential strategies to enhance the selectivity for higher hydrocarbon products. We discuss the mechanisms underlying the formation of C2 and C3 products, focusing on molecular catalysts that facilitate C-C coupling by positioning CO2 molecules in close proximity. Additionally, we provide a comprehensive overview of different approaches to improve higher hydrocarbon selectivity, along with future suggestions and recommendations for new researchers in the field. This review serves as a valuable resource for both academic researchers and industrial stakeholders aiming for the commercialization of CO2RR technologies.

In Situ Electropolymerizing Toward EP-CoP/Cu Tandem Catalyst for Enhanced Electrochemical CO2-to-Ethylene Conversion

Electrochemical CO2 reduction has garnered significant interest in the conversion of sustainable energy to valuable fuels and chemicals. Cu-based bimetallic catalysts play a crucial role in enhancing *CO concentration on Cu sites for efficient C─C coupling reactions, particularly for C2 product generation. To enhance Cu's electronic structure and direct its selectivity toward C2 products, a novel strategy is proposed involving the in situ electropolymerization of a nano-thickness cobalt porphyrin polymeric network (EP-CoP) onto a copper electrode, resulting in the creation of a highly effective EP-CoP/Cu tandem catalyst. The even distribution of EP-CoP facilitates the initial reduction of CO2 to *CO intermediates, which then transition to Cu sites for efficient C─C coupling. DFT calculations confirm that the *CO enrichment from Co sites boosts *CO coverage on Cu sites, promoting C─C coupling for C2+ product formation. The EP-CoP/Cu gas diffusion electrode achieves an impressive current density of 726 mA cm-2 at -0.9 V versus reversible hydrogen electrode (RHE), with a 76.8% Faraday efficiency for total C2+ conversion and 43% for ethylene, demonstrating exceptional long-term stability in flow cells. These findings mark a significant step forward in developing a tandem catalyst system for the effective electrochemical production of ethylene.

Selective CO2 Electroreduction to Multi-Carbon Products on Organic-Functionalized CuO Nanoparticles by Local Micro-Environment Modulation

Surface functionalization of Cu-based catalysts has demonstrated promising potential for enhancing the electrochemical CO2 reduction reaction (CO2RR) toward multi-carbon (C2+) products, primarily by suppressing the parasitic hydrogen evolution reaction and facilitating a localized CO2/CO concentration at the electrode. Building upon this approach, we developed surface-functionalized catalysts with exceptional activity and selectivity for electrocatalytic CO2RR to C2+ in a neutral electrolyte. Employing CuO nanoparticles coated with hexaethynylbenzene organic molecules (HEB-CuO NPs), a remarkable C2+ Faradaic efficiency of nearly 90% was achieved at an unprecedented current density of 300 mA cm-2, and a high FE (> 80%) was maintained at a wide range of current densities (100-600 mA cm-2) in neutral environments using a flow cell. Furthermore, in a membrane electrode assembly (MEA) electrolyzer, 86.14% FEC2+ was achieved at a partial current density of 387.6 mA cm-2 while maintaining continuous operation for over 50 h at a current density of 200 mA cm-2. In-situ spectroscopy studies and molecular dynamics simulations reveal that reducing the coverage of coordinated K⋅H2O water increased the probability of intermediate reactants (CO) interacting with the surface, thereby promoting efficient C-C coupling and enhancing the yield of C2+ products. This advancement offers significant potential for optimizing local micro-environments for sustainable and highly efficient C2+ production.

Advancing electrocatalytic reactions through mapping key intermediates to active sites via descriptors

Descriptors play a crucial role in electrocatalysis as they can provide valuable insights into the electrochemical performance of energy conversion and storage processes. They allow for the understanding of different catalytic activities and enable the prediction of better catalysts without relying on the time-consuming trial-and-error approaches. Hence, this comprehensive review focuses on highlighting the significant advancements in commonly used descriptors for critical electrocatalytic reactions. First, the fundamental reaction processes and key intermediates involved in several electrocatalytic reactions are summarized. Subsequently, three types of descriptors are classified and introduced based on different reactions and catalysts. These include d-band center descriptors, readily accessible intrinsic property descriptors, and spin-related descriptors, all of which contribute to a profound understanding of catalytic behavior. Furthermore, multi-type descriptors that collectively determine the catalytic performance are also summarized. Finally, we discuss the future of descriptors, envisioning their potential to integrate multiple factors, broaden application scopes, and synergize with artificial intelligence for more efficient catalyst design and discovery.

Automatic Monitoring Methods for Greenhouse and Hazardous Gases Emitted from Ruminant Production Systems: A Review

The research on automatic monitoring methods for greenhouse gases and hazardous gas emissions is currently a focal point in the fields of environmental science and climatology. Until 2023, the amount of greenhouse gases emitted by the livestock sector accounts for about 11-17% of total global emissions, with enteric fermentation in ruminants being the main source of the gases. With the escalating problem of global climate change, accurate and effective monitoring of gas emissions has become a top priority. Presently, the determination of gas emission indices relies on specialized instrumentation such as breathing chambers, greenfeed systems, methane laser detectors, etc., each characterized by distinct principles, applicability, and accuracy levels. This paper first explains the mechanisms and effects of gas production by ruminant production systems, focusing on the monitoring methods, principles, advantages, and disadvantages of monitoring gas concentrations, and a summary of existing methods reveals their shortcomings, such as limited applicability, low accuracy, and high cost. In response to the current challenges in the field of equipment for monitoring greenhouse and hazardous gas emissions from ruminant production systems, this paper outlines future perspectives with the aim of developing more efficient, user-friendly, and cost-effective monitoring instruments.

Linkage Engineering in Covalent Organic Frameworks for Metal-Free Electrocatalytic C2H4 Production from CO2

Electrocatalytic carbon dioxide reduction reaction (CO2RR) to produce ethylene (C2H4) is conducive to sustainable development of energy and environment. At present, most electrocatalysts for C2H4 production are limited to the heavy metal copper, meanwhile, achieving metal-free catalysis remains a challenge. Noted piperazine with sp3 N hybridization is beneficial to CO2 capture, but CO2RR performance and mechanism have been lacking. Herein, based on linkage engineering, we construct a novel high-density sp3 N catalytic array via introducing piperazine into the crystalline and microporous aminal-linked covalent organic frameworks (COFs). Thanks to its high sp3 N density, strong CO2 capture capacity and great hydrophilicity, aminal-linked COF successfully achieves the conversion of CO2 to C2H4 with a Faraday efficiency up to 19.1 %, which is stand out in all reported metal-free COF electrocatalysts. In addition, a series of imine-linked COFs are synthesized and combined with DFT calculations to demonstrate the critical role of sp3 N in enhancing the kinetics of CO2RR. Therefore, this work reveals the extraordinary potential of linkage engineering in COFs to break through some catalytic bottlenecks.

A two-dimensional iron-doped carbon-based nanoenzyme with catalase-like activity for the detection of alkaline phosphatase and ascorbate oxidase

Herein, we successfully synthesized two-dimensional iron-doped carbon-based nanosheets (Fe-N800 CS) with catalase-like activity through doping Fe into Zn MOF and introducing graphitic C3N4 (g-C3N4). The interaction of the Fe-N800 CS with hydrogen peroxide could generated abundant reactive oxygen species (ROS) and further oxidize o-Phenylenediamine (OPD) to 2,3-diaminophenazine (DAP) which has constant fluorescence at 560 nm. Ascorbic acid (AA) could be generated via the hydrolysis reaction between alkaline phosphatase (ALP) and ascorbic acid 2-phosphate (AAP). AA can be oxidized to dehy-droascorbic acid (DHA) by ROS, and then combined with OPD to generate 3-(1,2-dihydroxyethyl)furo[3,4b]-quinoxaline (QXD) with fluorescence at 440 nm, which could increase as the concentration of AA enhanced. DHA could also be generated through oxidation of AA by ascorbate oxidase (AAO). Thus, by monitoring the fluorescence ratio (I560/I440), a ratiometric fluorescence biosensing platform for ALP and AAO was established with the linear ranges in 0.2-10 U/L and 1-60 U/L, respectively. The limit of detection for ALP and AAO were 0.12 U/L and 0.59 U/L. Furthermore, the biosensing platform was successfully applied for the detection of ALP and AAO activity in human serum samples. This work provides a potential tool for future biomedical diagnostics.

Current Status and Perspectives of Dual-Atom Catalysts Towards Sustainable Energy Utilization

The exploration of sustainable energy utilization requires the implementation of advanced electrochemical devices for efficient energy conversion and storage, which are enabled by the usage of cost-effective, high-performance electrocatalysts. Currently, heterogeneous atomically dispersed catalysts are considered as potential candidates for a wide range of applications. Compared to conventional catalysts, atomically dispersed metal atoms in carbon-based catalysts have more unsaturated coordination sites, quantum size effect, and strong metal-support interactions, resulting in exceptional catalytic activity. Of these, dual-atomic catalysts (DACs) have attracted extensive attention due to the additional synergistic effect between two adjacent metal atoms. DACs have the advantages of full active site exposure, high selectivity, theoretical 100% atom utilization, and the ability to break the scaling relationship of adsorption free energy on active sites. In this review, we summarize recent research advancement of DACs, which includes (1) the comprehensive understanding of the synergy between atomic pairs; (2) the synthesis of DACs; (3) characterization methods, especially aberration-corrected scanning transmission electron microscopy and synchrotron spectroscopy; and (4) electrochemical energy-related applications. The last part focuses on great potential for the electrochemical catalysis of energy-related small molecules, such as oxygen reduction reaction, CO2 reduction reaction, hydrogen evolution reaction, and N2 reduction reaction. The future research challenges and opportunities are also raised in prospective section.

Rare earth oxide based electrocatalysts: synthesis, properties and applications

As an important strategic resource, rare earths (REs) constitute 17 elements in the periodic table, namely 15 lanthanides (Ln) (La-Lu, atomic numbers from 57 to 71), scandium (Sc, atomic number 21) and yttrium (Y, atomic number 39). In the field of catalysis, the localization and incomplete filling of 4f electrons endow REs with unique physical and chemical properties, including rich electronic energy level structures, variable coordination numbers, etc., making them have great potential in electrocatalysis. Among various RE catalytic materials, rare earth oxide (REO)-based electrocatalysts exhibit excellent performances in electrocatalytic reactions due to their simple preparation process and strong structural variability. At the same time, the electronic orbital structure of REs exhibits excellent electron transfer ability, which can reduce the band gap and energy barrier values of rate-determining steps, further accelerating the electron transfer in the electrocatalytic reaction process; however, there is a lack of systematic review of recent advances in REO-based electrocatalysis. This review systematically summarizes the synthesis, properties and applications of REO-based nanocatalysts and discusses their applications in electrocatalysis in detail. It includes the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), methanol oxidation reaction (MOR), nitrogen reduction reaction (NRR) and other electrocatalytic reactions and further discusses the catalytic mechanism of REs in the above reactions. This review provides a timely and comprehensive summary of the current progress in the application of RE-based nanomaterials in electrocatalytic reactions and provides reasonable prospects for future electrocatalytic applications of REO-based materials.

Contemporary advances in photocatalytic CO2 reduction using single-atom catalysts supported on carbon-based materials

The persistent issue of CO2 emissions and their subsequent impact on the Earth's atmosphere can be effectively addressed through the utilization of efficient photocatalysts. Employing a sustainable carbon cycle via photocatalysis presents a promising technology for simultaneously managing the greenhouse effect and the energy dilemma. However, the efficiency of energy conversion encounters limitations due to inadequate carrier utilization and a deficiency of reactive sites. Single-atom catalysts (SACs) have demonstrated exceptional performance in efficiently addressing the aforementioned challenges. This review article commences with an overview of SAC types, structures, fundamentals, synthesis strategies, and characterizations, providing a logical foundation for the design and properties of SACs based on the correlation between their structure and efficiency. Additionally, we delve into the general mechanism and the role of SACs in photocatalytic CO2 reduction. Furthermore, we furnish a comprehensive survey of the latest advancements in SACs concerning their capacity to enhance efficiency, long-term stability, and selectivity in CO2 reduction. Carbon-structured support materials such as covalent organic frameworks (COFs), graphitic carbon nitride (g-C3N4), metal-organic frameworks (MOFs), covalent triazine frameworks (CTFs), and graphene-based photocatalysts have garnered significant attention due to their substantial surface area, superior conductivity, and chemical stability. These carbon-based materials are frequently chosen as support matrices for anchoring single metal atoms, thereby enhancing catalytic activity and selectivity. The motivation behind this review article lies in evaluating recent developments in photocatalytic CO2 reduction employing SACs supported on carbon substrates. In conclusion, we highlight critical issues associated with SACs, potential prospects in photocatalytic CO2 reduction, and existing challenges. This review article is dedicated to providing a comprehensive and organized compilation of recent research findings on carbon support materials for SACs in photocatalytic CO2 reduction, with a specific focus on materials that are environmentally friendly, readily accessible, cost-effective, and exceptionally efficient. This work offers a critical assessment and serves as a systematic reference for the development of SACs supported on MOFs, COFs, g-C3N4, graphene, and CTFs support materials to enhance photocatalytic CO2 conversion.