Recent Advances in Interface Engineering for Electrocatalytic CO2 Reduction Reaction

Harnessing Coordination Microenvironment of Metal-bis(dithiolene) Sites for Modulating Electrocatalytic CO2 Reduction by Metal-Organic Framework

Nature's metalloenzymes inspire biomimetic catalysts for the CO2 reduction reaction (CO2RR), particularly using metal-bis(dithiolene) ([MS4]) cores in frameworks. While prior research focused on tuning the chelating atoms of Ni-centered sites or [NiS4] in metal-organic frameworks (MOFs), how different metal centers affect the electronic structure and catalytic activity is often overlooked. Notably, reported [NiS4] molecular analogues exhibits a Faradaic efficiency (FE) of less than 70% for the major carbon product and shows operational stability for only about 4 hours (say falling FE and current density beyond). In this study, MOFs are used to host [MS4] units with varying central metals (M = Ni, Cu, Co, Fe) to assess how the metal center affects electrocatalytic CO2RR. Among the studied MS4-In MOFs, NiS4-In demonstrates the best performance, achieving a FECO of 88.54% and operational stability greater than 6 hours-significantly outlasting the ≈200 seconds of the [NiS4] molecule. This work underscores the importance of frameworks in stabilizing [MS4] units and highlights [MS4] as essential for CO2 binding and reduction, with [NiS4] exhibiting optimal catalytic performance due to its favorable electronic properties. This findings clarify how substituting the metal center within the framework enhances electronic structure and coordination, leading to improved electrocatalytic performance.

Interfacial Engineering to Fabricate Nanoporous FeMo Bimetallic Nitride for Enhanced Electrochemical Ammonia Synthesis

The electrochemical N2 reduction reaction (NRR) currently represents a green and sustainable approach to ammonia production. However, the further progress of NRR is significantly hampered by poor catalytic activity and selectivity, necessitating the development of efficient and stable electrocatalysts. Herein, a nanoporous Fe-Mo bimetallic nitride (Fe3N-MoN) is synthesized using a molten-salt preparation method. This catalyst demonstrates notable NRR performance, achieving a high NH3 yield rate of 45.1 µg h-1 mg-1 and a Faradaic efficiency (FE) of 26.5% at -0.2 V (vs RHE) under ambient conditions. Detailed experimental studies and density functional theory (DFT) calculations reveal that the fabricated interface between Fe3N and MoN effectively modulates the surface electronic structure of the catalyst. The interface induces an increase in the degree of electron deficiency at the nitrogen-vacancy sites on the catalyst surface, allowing N2 molecules to occupy the nitrogen vacancies more easily, thereby promoting N2 adsorption/activation during the NRR process. Consequently, the Fe3N-MoN catalyst exhibits outstanding NRR activity. The insights gained from fabricating the Fe3N-MoN interface in this work pave the way for further development of interfacial engineering to prepare high-efficient electrocatalyst.

MnCe-based catalysts for removal of organic pollutants in urban wastewater by advanced oxidation processes - A critical review

With Advanced oxidation processes (AOPs) widely promoted, MnCe-based catalysts have received extensive attention under the advantages of high efficiency, stability and economy for refractory organic pollutants present in urban wastewater. Driven by multiple factors such as environmental pollution, technological development, and policy promotion, a systematic review of MnCe-based catalysts is urgently needed in the current research situation. This research provides a critical review of MnCe-based catalysts for removal of organic pollutants in urban wastewater by AOPs. It is found that co-precipitation and sol-gel methods are more appropriate methods for catalyst preparation. Among a host of influence factors, catalyst composition and pH are crucial in the catalytic oxidation processes. The synergistic effect of the free radical pathway and surface catalysis results in better pollutants degradation. It is more valuable to utilize multiple systems for oxidation (e.g., photo-Fenton technology) to improve the catalytic efficiency. This review provides theoretical guidance for MnCe-based catalysts and offers a reference direction for future research in the AOPs of organic pollutants removal from urban wastewater.

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.

Photocatalytic reduction of carbon dioxide by BiTeX (X = Cl, Br, I) under visible-light irradiation

In this study, a series of BiTeX (X = Cl, Br, I) photocatalysts were successfully synthesized via a simple hydrothermal method. The synthesis process involved dissolving BiX3 and Te powder in toluene to identify the most efficient material for photocatalytic activity. The main objective of this approach is to facilitate the conversion of carbon dioxide into sustainable solar fuels, such as alcohols and hydrocarbons, offering an appealing solution to address environmental concerns and energy crises. The BiTeX photocatalysts demonstrated significant proficiency in converting CO2 into CH4, particularly BiTeCl exhibited a notable photocatalytic conversion rate of up to 0.51 μmolg-1h-1. The optimized BiTeX photocatalysts displayed a gradual and selective transition from CO2 to CH4, ultimately producing valuable hydrocarbons (C2+). Furthermore, owing to their ability to reduce CO2, these photocatalysts show promise as materials for mitigating environmental pollution.

Advances of Synergistic Electrocatalysis Between Single Atoms and Nanoparticles/Clusters

Combining single atoms with clusters or nanoparticles is an emerging tactic to design efficient electrocatalysts. Both synergy effect and high atomic utilization of active sites in the composite catalysts result in enhanced electrocatalytic performance, simultaneously provide a radical analysis of the interrelationship between structure and activity. In this review, the recent advances of single-atomic site catalysts coupled with clusters or nanoparticles are emphasized. Firstly, the synthetic strategies, characterization, dynamics and types of single atoms coupled with clusters/nanoparticles are introduced, and then the key factors controlling the structure of the composite catalysts are discussed. Next, several clean energy catalytic reactions performed over the synergistic composite catalysts are illustrated. Eventually, the encountering challenges and recommendations for the future advancement of synergistic structure in energy-transformation electrocatalysis are outlined.

Crystal-Phase-Engineered High-Entropy Alloy Aerogels for Enhanced Ethylamine Electrosynthesis from Acetonitrile

Crystal-phase engineering that promotes the rearrangement of active atoms to form new structural frameworks achieves excellent result in the field of electrocatalysis and optimizes the performance of various electrochemical reactions. Herein, for the first time, it is found that the different components in metallic aerogels will affect the crystal-phase transformation, especially in high-entropy alloy aerogels (HEAAs), whose crystal-phase transformation during annealing is more difficult than medium-entropy alloy aerogels (MEAAs), but they still show better electrochemical performance. Specifically, PdPtCuCoNi HEAAs with the parent phase of face-centered cubic (FCC) PdCu possess excellent 89.24% of selectivity, 746.82 mmol h-1 g-1 cat. of yield rate, and 90.75% of Faraday efficiency for ethylamine during acetonitrile reduction reaction (ARR); while, maintaining stability under 50 h of long-term testing and ten consecutive electrolysis cycles. The structure-activity relationship indicates that crystal-phase regulation from amorphous state to FCC phase promotes the atomic rearrangement in HEAAs, thereby optimizing the electronic structure and enhancing the adsorption strength of reaction intermediates, improving the catalytic performance. This study provides a new paradigm for developing novel ARR electrocatalysts and also expands the potential of crystal-phase engineering in other application areas.

Promoting hydrophilic cupric oxide electrochemical carbon dioxide reduction to methanol via interfacial engineering modulation

Copper-based catalysts have been extensively investigated in electrochemical carbon dioxide (CO2) reduction to promote carbon products generated by requiring multiple electron transfer. However, hydrophilic electrodes are unfavourable for CO2 mass transfer and preferentially hydrogen (H2) evolution in electrochemical CO2 reduction. In this paper, a hydrophilic cupric oxide (CuO) electrode with a grassy morphology was prepared. CuO-derived Cu was confirmed as the active site for electrochemical CO2 reduction through wettability modulation. To enhance the intrinsic catalytic activity, a metal-oxide heterogeneous interface was created by engineering modulation at the interface, involving the loading of palladium (Pd) on CuO (CuO/Pd). Both the electrochemically active area and the electron transfer rate were enhanced by Pd loading, and significantly the reduced work function further facilitated the electron transfer between the electrode surface and the electrolyte. Consequently, the CuO/Pd electrode exhibited excellent excellent performance in electrochemical CO2 reduction, achieving a 54 % Faraday efficiency at -0.65 V for methanol (CH3OH). The metal-oxide interfacial effect potentially improves the intrinsic catalytic activity of hydrophilic CuO electrodes in electrochemical CO2 reduction, providing a conducive pathway for optimizing hydrophilic oxide electrodes in this process.

Revealing the Intrinsic Restructuring of Bi2O3 Nanoparticles into Bi Nanosheets during Electrochemical CO2 Reduction

Bismuth is a catalyst material that selectively produces formate during the electrochemical reduction of CO2. While different synthesis strategies have been employed to create electrocatalysts with better performance, the restructuring of bismuth precatalysts during the reaction has also been previously reported. The mechanism behind the change has, however, remained unclear. Here, we show that Bi2O3 nanoparticles supported on Vulcan carbon intrinsically transform into stellated nanosheet aggregates upon exposure to an electrolyte. Liquid cell transmission electron microscopy observations first revealed the gradual restructuring of the nanoparticles into nanosheets in the presence of 0.1 M KHCO3 without an applied potential. Our experiments also associated the restructuring with solubility of bismuth in the electrolyte. While the consequent agglomerates were stable under moderate negative potentials (-0.3 VRHE), they dissolved over time at larger negative potentials (-0.4 and -0.5 VRHE). Operando Raman spectra collected during the reaction showed that under an applied potential, the oxide particles reduced to metallic bismuth, thereby confirming the metal as the working phase for producing formate. These results inform us about the working morphology of these electrocatalysts and their formation and degradation mechanisms.

Local reaction environment in electrocatalysis

Beyond conventional electrocatalyst engineering, recent studies have unveiled the effectiveness of manipulating the local reaction environment in enhancing the performance of electrocatalytic reactions. The general principles and strategies of local environmental engineering for different electrocatalytic processes have been extensively investigated. This review provides a critical appraisal of the recent advancements in local reaction environment engineering, aiming to comprehensively assess this emerging field. It presents the interactions among surface structure, ions distribution and local electric field in relation to the local reaction environment. Useful protocols such as the interfacial reactant concentration, mass transport rate, adsorption/desorption behaviors, and binding energy are in-depth discussed toward modifying the local reaction environment. Meanwhile, electrode physical structures and reaction cell configurations are viable optimization methods in engineering local reaction environments. In combination with operando investigation techniques, we conclude that rational modifications of the local reaction environment can significantly enhance various electrocatalytic processes by optimizing the thermodynamic and kinetic properties of the reaction interface. We also outline future research directions to attain a comprehensive understanding and effective modulation of the local reaction environment.

Engineering organic polymers as emerging sustainable materials for powerful electrocatalysts

Cost-effective and high-efficiency catalysts play a central role in various sustainable electrochemical energy conversion technologies that are being developed to generate clean energy while reducing carbon emissions, such as fuel cells, metal-air batteries, water electrolyzers, and carbon dioxide conversion. In this context, a recent climax in the exploitation of advanced earth-abundant catalysts has been witnessed for diverse electrochemical reactions involved in the above mentioned sustainable pathways. In particular, polymer catalysts have garnered considerable interest and achieved substantial progress very recently, mainly owing to their pyrolysis-free synthesis, highly tunable molecular composition and microarchitecture, readily adjustable electrical conductivity, and high stability. In this review, we present a timely and comprehensive overview of the latest advances in organic polymers as emerging materials for powerful electrocatalysts. First, we present the general principles for the design of polymer catalysts in terms of catalytic activity, electrical conductivity, mass transfer, and stability. Then, the state-of-the-art engineering strategies to tailor the polymer catalysts at both molecular (i.e., heteroatom and metal atom engineering) and macromolecular (i.e., chain, topology, and composition engineering) levels are introduced. Particular attention is paid to the insightful understanding of structure-performance correlations and electrocatalytic mechanisms. The fundamentals behind these critical electrochemical reactions, including the oxygen reduction reaction, hydrogen evolution reaction, CO2 reduction reaction, oxygen evolution reaction, and hydrogen oxidation reaction, as well as breakthroughs in polymer catalysts, are outlined as well. Finally, we further discuss the current challenges and suggest new opportunities for the rational design of advanced polymer catalysts. By presenting the progress, engineering strategies, insightful understandings, challenges, and perspectives, we hope this review can provide valuable guidelines for the future development of polymer catalysts.

Cu-Based Materials for Enhanced C2+ Product Selectivity in Photo-/Electro-Catalytic CO2 Reduction: Challenges and Prospects

Carbon dioxide conversion into valuable products using photocatalysis and electrocatalysis is an effective approach to mitigate global environmental issues and the energy shortages. Among the materials utilized for catalytic reduction of CO2, Cu-based materials are highly advantageous owing to their widespread availability, cost-effectiveness, and environmental sustainability. Furthermore, Cu-based materials demonstrate interesting abilities in the adsorption and activation of carbon dioxide, allowing the formation of C2+ compounds through C-C coupling process. Herein, the basic principles of photocatalytic CO2 reduction reactions (PCO2RR) and electrocatalytic CO2 reduction reaction (ECO2RR) and the pathways for the generation C2+ products are introduced. This review categorizes Cu-based materials into different groups including Cu metal, Cu oxides, Cu alloys, and Cu SACs, Cu heterojunctions based on their catalytic applications. The relationship between the Cu surfaces and their efficiency in both PCO2RR and ECO2RR is emphasized. Through a review of recent studies on PCO2RR and ECO2RR using Cu-based catalysts, the focus is on understanding the underlying reasons for the enhanced selectivity toward C2+ products. Finally, the opportunities and challenges associated with Cu-based materials in the CO2 catalytic reduction applications are presented, along with research directions that can guide for the design of highly active and selective Cu-based materials for CO2 reduction processes in the future.

Emerging Xene-Based Single-Atom Catalysts: Theory, Synthesis, and Catalytic Applications

In recent years, the emergence of novel 2D monoelemental materials (Xenes), e.g., graphdiyne, borophene, phosphorene, antimonene, bismuthene, and stanene, has exhibited unprecedented potentials for their versatile applications as well as addressing new discoveries in fundamental science. Owing to their unique physicochemical, optical, and electronic properties, emerging Xenes have been regarded as promising candidates in the community of single-atom catalysts (SACs) as single-atom active sites or support matrixes for significant improvement in intrinsic activity and selectivity. In order to comprehensively understand the relationships between the structure and property of Xene-based SACs, this review represents a comprehensive summary from theoretical predictions to experimental investigations. Firstly, theoretical calculations regarding both the anchoring of Xene-based single-atom active sites on versatile support matrixes and doping/substituting heteroatoms at Xene-based support matrixes are briefly summarized. Secondly, controlled synthesis and precise characterization are presented for Xene-based SACs. Finally, current challenges and future opportunities for the development of Xene-based SACs are highlighted.

Enrichment Strategies for Efficient CO2 Electroreduction in Acidic Electrolytes

Electrochemical CO2 reduction reaction (CO2 RR) has been recognized as an appealing route to remarkably accelerate the carbon-neutral cycle and reduce carbon emissions. Notwithstanding great catalytic activity that has been acquired in neutral and alkaline conditions, the carbonates generated from the inevitable reaction of the input CO2 with the hydroxide severely lower carbon utilization and energy efficiency. By contrast, CO2 RR in an acidic condition can effectively circumvent the carbonate issues; however, the activity and selectivity of CO2 RR in acidic electrolytes will be decreased significantly due to the competing hydrogen evolution reaction (HER). Enriching the CO2 and the key intermediates around the catalyst surface can promote the reaction rate and enhance the product selectivity, providing a promising way to boost the performance of CO2 RR. In this review, the catalytic mechanism and key technique challenges of CO2 RR are first introduced. Then, the critical progress of enrichment strategies for promoting the CO2 RR in the acidic electrolyte is summarized with three aspects: catalyst design, electrolyte regulation, and electrolyzer optimization. Finally, some insights and perspectives for further development of enrichment strategies in acidic CO2 RR are expounded.

Understanding Bridging Sites and Accelerating Quantum Efficiency for Photocatalytic CO2 Reduction

We report a novel double-shelled nanoboxes photocatalyst architecture with tailored interfaces that accelerate quantum efficiency for photocatalytic CO2 reduction reaction (CO2RR) via Mo-S bridging bonds sites in Sv-In2S3@2H-MoTe2. The X-ray absorption near-edge structure shows that the formation of Sv-In2S3@2H-MoTe2 adjusts the coordination environment via interface engineering and forms Mo-S polarized sites at the interface. The interfacial dynamics and catalytic behavior are clearly revealed by ultrafast femtosecond transient absorption, time-resolved, and in situ diffuse reflectance-Infrared Fourier transform spectroscopy. A tunable electronic structure through steric interaction of Mo-S bridging bonds induces a 1.7-fold enhancement in Sv-In2S3@2H-MoTe2(5) photogenerated carrier concentration relative to pristine Sv-In2S3. Benefiting from lower carrier transport activation energy, an internal quantum efficiency of 94.01% at 380 nm was used for photocatalytic CO2RR. This study proposes a new strategy to design photocatalyst through bridging sites to adjust the selectivity of photocatalytic CO2RR.

Microwave-Assisted Synthesis as a Promising Tool for the Preparation of Materials Containing Defective Carbon Nanostructures: Implications on Properties and Applications

In this review, we focus on a small section of the literature that deals with the materials containing pristine defective carbon nanostructures (CNs) and those incorporated into the larger systems containing carbon atoms, heteroatoms, and inorganic components.. Briefly, we discuss only those topics that focus on structural defects related to introducing perturbation into the surface topology of the ideal lattice structure. The disorder in the crystal structure may vary in character, size, and location, which significantly modifies the physical and chemical properties of CNs or their hybrid combination. We focus mainly on the method using microwave (MW) irradiation, which is a powerful tool for synthesizing and modifying carbon-based solid materials due to its simplicity, the possibility of conducting the reaction in solvents and solid phases, and the presence of components of different chemical natures. Herein, we will emphasize the advantages of synthesis using MW-assisted heating and indicate the influence of the structure of the obtained materials on their physical and chemical properties. It is the first review paper that comprehensively summarizes research in the context of using MW-assisted heating to modify the structure of CNs, paying attention to its remarkable universality and simplicity. In the final part, we emphasize the role of MW-assisted heating in creating defects in CNs and the implications in designing their properties and applications. The presented review is a valuable source summarizing the achievements of scientists in this area of research.

Toward high-efficiency photovoltaics-assisted electrochemical and photoelectrochemical CO2 reduction: Strategy and challenge

The realization of a complete techno-economy through a significant carbon dioxide (CO2) reduction in the atmosphere has been explored to promote a low-carbon economy in various ways. CO2 reduction reactions (CO2RRs) can be induced using sustainable energy, including electric and solar energy, using systems such as electrochemical (EC) CO2RR and photoelectrochemical (PEC) systems. This study summarizes various fabrication strategies for non-noble metal, copper-based, and metal-organic framework-based catalysts with excellent Faradaic efficiency (FE) for target carbon compounds, and for noble metals with low overvoltage. Although EC and PEC systems achieve high energy conversion efficiency with excellent catalysts, they still require external power and lack complete bias-free operation. Therefore, photovoltaics, which can overcome the limitations of these systems, have been introduced. The utilization of silicon and perovskite-based solar cells for photovoltaics-assisted EC (PV-EC) and photovoltaics-assisted PEC (PV-PEC) CO2RR systems are cost-efficient, and the III-V semiconductor photoabsorbers achieved high solar-to-carbon efficiency. This work focuses on PV-EC and PV-PEC CO2RR systems and their components and then summarizes the special cell configurations, including the tandem and stacked structures. Additionally, the study discusses current issues, such as low energy conversion, expensive PV, theoretical limits, and industrial scale-up, along with proposed solutions.

Dual-Doped Nickel Sulfide for Electro-Upgrading Polyethylene Terephthalate into Valuable Chemicals and Hydrogen Fuel

Electro-upcycling of plastic waste into value-added chemicals/fuels is an attractive and sustainable way for plastic waste management. Recently, electrocatalytically converting polyethylene terephthalate (PET) into formate and hydrogen has aroused great interest, while developing low-cost catalysts with high efficiency and selectivity for the central ethylene glycol (PET monomer) oxidation reaction (EGOR) remains a challenge. Herein, a high-performance nickel sulfide catalyst for plastic waste electro-upcycling is designed by a cobalt and chloride co-doping strategy. Benefiting from the interconnected ultrathin nanosheet architecture, dual dopants induced up-shifting d band centre and facilitated in situ structural reconstruction, the Co and Cl co-doped Ni3S2 (Co, Cl-NiS) outperforms the single-doped and undoped analogues for EGOR. The self-evolved sulfide@oxyhydroxide heterostructure catalyzes EG-to-formate conversion with high Faradic efficiency (> 92%) and selectivity (> 91%) at high current densities (> 400 mA cm-2). Besides producing formate, the bifunctional Co, Cl-NiS-assisted PET hydrolysate electrolyzer can achieve a high hydrogen production rate of 50.26 mmol h-1 in 2 M KOH, at 1.7 V. This study not only demonstrates a dual-doping strategy to engineer cost-effective bifunctional catalysts for electrochemical conversion processes, but also provides a green and sustainable way for plastic waste upcycling and simultaneous energy-saving hydrogen production.

Creating interfaces of Cu0/Cu+ in oxide-derived copper catalysts for electrochemical CO2 reduction to multi-carbon products

Electrochemical carbon dioxide reduction reaction (CO₂RR) is an effective approach to capture CO₂ and convert it into value-added chemicals and fuels, thereby reducing excess CO₂ emissions. Recent reports have shown that copper-based catalysts exhibit excellent performance in converting CO₂ into multi-carbon compounds and hydrocarbons. However, theselectivityto the couplingproductsispoor. Therefore, tuningCO₂-reductionselectivitytoward C₂₊productsover Cu-based catalyst is one of the most important issues in CO₂RR. Herein, we prepare a nanosheet catalyst with interfaces of Cu⁰/Cu⁺. The catalyst achieves Faraday efficiency (FE) of C₂₊ over 50% in a wide potential window between - 1.2 V to - 1.5 V versus reversible hydrogen electrode (vs. RHE). Moreover, the catalyst exhibits maximum FE of 44.5% and 58.9% towards C₂H₄ and C₂₊, with a partial current density of 10.5 mA cm^-2 at - 1.4 V. Density functional theory (DFT) calculations show that the interface of Cu⁰/Cu⁺ facilitates CC coupling to form C₂₊ products, while inhibits CO₂conversion toC₁products.

Applications of Metal-Organic Frameworks and Their Derivatives in Electrochemical CO2 Reduction

Electrochemically reducing CO2 to more reduced chemical species is a promising way that not only enables the conversion of intermittent energy resources to stable fuels, but also helps to build a closed-loop anthropogenic carbon cycle. Among various electrocatalysts for electrochemical CO2 reduction, multifunctional metal-organic frameworks (MOFs) have been employed as highly efficient and selective heterogeneous electrocatalysts due to their ultrahigh porosity and topologically diverse structures. Up to now, great progress has been achieved in the design and synthesis of highly active and selective MOF-related catalysts for electrochemical CO2 reduction reaction (CO2RR), and their corresponding reaction mechanisms have been thoroughly studied. In this review, we summarize the recent progress of applying MOFs and their derivatives in CO2RR, with a focus on the design strategies for electrocatalysts and electrolyzers. We first discussed the reaction mechanisms for different CO2RR products and introduced the commonly applied electrolyzer configurations in the current CO2RR system. Then, an overview of several categories of products (CO, HCOOH, CH4, CH3OH, and multi-carbon chemicals) generated from MOFs or their derivatives via CO2RR was discussed. Finally, we offer some insights and perspectives for the future development of MOFs and their derivatives in electrochemical CO2 reduction. We aim to provide new insights into this field and further guide future research for large-scale applications.

Editorial

Surface and interface engineering has been considered as a promising strategy to enhance the performance of catalysts towards CO₂ reduction. In their editorial to this special collection, guest editors Zhicheng Zhang, Zhen Zhang, Zhenyu Sun, Shaoqi Zhan and Guoxiong Wang provide a brief overview of this field and highlight the state-of-the-art contributions featured in this special collection.

Effective perspiration is essential to uphold the stability of zero-gap MEA-based cathodes used in CO2 electrolysers

The application of gas diffusion electrodes (GDEs) for the electrochemical reduction of CO2 to value-added products creates the possibility of achieving current densities of a few hundred mA cm-2. To achieve stable operation at such high reaction rates remains, however, a challenging task, due to the flooding of the GDE. In order to mitigate flooding in a zero-gap membrane-electrode assembly (MEA) configuration, paths for effective electrolyte perspiration inside the GDE structure have to be kept open during the electrolysis process. Here we demonstrate that apart from the operational parameters of the electrolysis and the structural properties of the supporting gas diffusion layers, also the chemical composition of the applied catalyst inks can play a decisive role in the electrolyte management of GDEs used for CO2 electroreduction. In particular, the presence of excess amounts of polymeric capping agents (used to stabilize the catalyst nanoparticles) can lead to a blockage of micropores, which hinders perspiration and initiates the flooding of the microporous layer. Here we use a novel ICP-MS analysis-based approach to quantitatively monitor the amount of perspired electrolyte that exits a GDE-based CO2 electrolyser, and we show a direct correlation between the break-down of effective perspiration and the appearance of flooding-the latter ultimately leading to a loss of electrolyser stability. We recommend the use of an ultracentrifugation-based approach by which catalyst inks containing no excess amount of polymeric capping agents can be formulated. Using these inks, the stability of electrolyses can be ensured for much longer times.

Recent Advances of Core-Shell Cu-Based Catalysts for the Reduction of CO2 to C2+ Products

Copper is a key metal for carbon dioxide (CO₂ ) reduction reaction, which can reduce CO₂ to value-added products. The core-shell structure can effectively promote the C-C coupling process due to its strong synergistic effect originated from its unique electronic structure and interface environment. Therefore, the combination of copper and core-shell structure to design an efficient Cu-based core-shell structure catalyst is of great significance for electrocatalytic CO₂ reduction (CO₂ RR). In this review, we first briefly summarize the basic principle of CO₂ RR. In addition, we outline the advantages of core-shell structure for catalysis. Then, we review the recent research progresses of Cu-based core-shell structures for the selective reduction of multi-carbon (C₂₊ ) products. In the end, the challenges of using core-shell catalyst for CO₂ RR are described, and the future development of this field is prospected.

Proton Transfer Dynamics-Mediated CO2 Electroreduction

Electrochemical CO₂ reduction reaction (CO₂ RR) is crucial to addressing environmental crises and producing chemicals. Proton activation and transfer are essential in CO₂ RR. To date, few research reviews have focused on this process and its effect on catalytic performance. Recent studies have demonstrated ways to improve CO₂ RR by regulating proton transfer dynamics. This Concept highlights the use of regulating proton transfer dynamics to enhance CO₂ RR for the target product and discusses modulation strategies for proton transfer dynamics and operative mechanisms in typical systems, including single-atom catalysts, molecular catalysts, metal heterointerfaces, and organic-ligand modified metal catalysts. Characterization methods for proton transfer dynamics during CO₂ RR are also discussed, providing powerful tools for the hydrogen-involving electrochemical study. This Concept offers new insights into the CO₂ RR mechanism and guides the design of efficient CO₂ RR systems.

Surface and Interface Engineering for the Catalysts of Electrocatalytic CO2 Reduction

The massive use of fossil fuels releases a great amount of CO₂ , which substantially contributes to the global warming. For the global goal of putting CO₂ emission under control, effective utilization of CO₂ is particularly meaningful. Electrocatalytic CO₂ reduction reaction (eCO₂ RR) has great potential in CO₂ utilization, because it can convert CO₂ into valuable carbon-containing chemicals and feedstock using renewable electricity. The catalyst design for eCO₂ RR is a key challenge to achieving efficient conversion of CO₂ to fuels and useful chemicals. For a typical heterogeneous catalyst, surface and interface engineering is an effective approach to enhance reaction activity. Herein, the development and research progress in CO₂ catalysts with focus on surface and interface engineering are reviewed. First, the fundaments of eCO₂ RR is briefly discussed from the reaction mechanism to performance evaluation methods, introducing the role of the surface and interface engineering of electrocatalyst in eCO₂ RR. Then, several routes to optimize the surface and interface of CO₂ electrocatalysts, including morphology, dopants, atomic vacancies, grain boundaries, surface modification, etc., are reviewed and representative examples are given. At the end of this review, we share our personal views in future research of eCO₂ RR.

A Pair-Electrosynthesis for Formate at Ultra-Low Voltage Via Coupling of CO2 Reduction and Formaldehyde Oxidation

Formate can be synthesized electrochemically by CO₂ reduction reaction (CO₂RR) or formaldehyde oxidation reaction (FOR). The CO₂RR approach suffers from kinetic-sluggish oxygen evolution reaction at the anode. To this end, an electrochemical system combining cathodic CO₂RR with anodic FOR was developed, which enables the formate electrosynthesis at ultra-low voltage. Cathodic CO₂RR employing the BiOCl electrode in H-cell exhibited formate Faradaic efficiency (FE) higher than 90% within a wide potential range from - 0.48 to - 1.32 V_RHE. In flow cell, the current density of 100 mA cm^-2 was achieved at - 0.67 V_RHE. The anodic FOR using the Cu₂O electrode displayed a low onset potential of - 0.13 V_RHE and nearly 100% formate and H₂ selectivity from 0.05 to 0.35 V_RHE. The CO₂RR and FOR were constructed in a flow cell through membrane electrode assembly for the electrosynthesis of formate, where the CO₂RR//FOR delivered an enhanced current density of 100 mA cm^-2 at 0.86 V. This work provides a promising pair-electrosynthesis of value-added chemicals with high FE and low energy consumption.

A review on ZnS-based photocatalysts for CO2 reduction in all-inorganic aqueous medium

Photocatalytic CO₂ reduction mimics natural photosynthesis, which is a potential technology for "carbon neutrality". This article will review the recent research progress of a class of distinguished photocatalytic CO₂ reduction systems based on ZnS nanocrystal photocatalysts. We will focus on the pathway of maximizing the photoreduction rate of CO₂ by continuously optimizing the catalyst design and the composition of the reaction medium. Such discussions will be meaningful and beneficial for developing universal strategies of solar fuel production. Finally, an outlook will be provided to brighten the prospects of ZnS-based photocatalytic CO₂ reduction systems.

MOF-Transformed In2O3-x@C Nanocorn Electrocatalyst for Efficient CO2 Reduction to HCOOH

For electrochemical CO2 reduction to HCOOH, an ongoing challenge is to design energy efficient electrocatalysts that can deliver a high HCOOH current density (JHCOOH) at a low overpotential. Indium oxide is good HCOOH production catalyst but with low conductivity. In this work, we report a unique corn design of In2O3-x@C nanocatalyst, wherein In2O3-x nanocube as the fine grains dispersed uniformly on the carbon nanorod cob, resulting in the enhanced conductivity. Excellent performance is achieved with 84% Faradaic efficiency (FE) and 11 mA cm-2 JHCOOH at a low potential of - 0.4 V versus RHE. At the current density of 100 mA cm-2, the applied potential remained stable for more than 120 h with the FE above 90%. Density functional theory calculations reveal that the abundant oxygen vacancy in In2O3-x has exposed more In3+ sites with activated electroactivity, which facilitates the formation of HCOO* intermediate. Operando X-ray absorption spectroscopy also confirms In3+ as the active site and the key intermediate of HCOO* during the process of CO2 reduction to HCOOH.

Cu-based Organic-Inorganic Composite Materials for Electrochemical CO2 Reduction

Electrochemical CO2 reduction reaction (CO2RR) is an attractive pathway to convert CO2 into value-added chemicals and fuels. Copper (Cu) is the most effective monometallic catalyst for converting CO2 into multi-carbon products, but suffers from high overpotentials and poor selectivity. Therefore, it is essential to design efficient Cu-based catalyst to improve the selectivity of specific products. Due to the combination of advantages of organic and inorganic composite materials, organic-inorganic composites exhibit high catalytic performance towards CO2RR, and have been extensively studied. In this review, the research advances of various Cu-based organic-inorganic composite materials in CO2RR, i.e., organic molecular modified-metal Cu composites, Cu-based molecular catalyst/carbon carrier composites, Cu-based metal organic framework (MOF) composites, and Cu-based covalent organic framework (COF) composites are systematically summarized. Particularly, the synthesis strategies of Cu-based composites, structure-performance relationship, and catalytic mechanisms are discussed. Finally, the opportunities and challenges of Cu-based organic-inorganic composite materials in CO2RR are proposed.

Hetero-Interfaces on Cu Electrode for Enhanced Electrochemical Conversion of CO2 to Multi-Carbon Products

Electrochemical CO₂ reduction reaction (CO₂RR) to multi-carbon products would simultaneously reduce CO₂ emission and produce high-value chemicals. Herein, we report Cu electrodes modified by metal-organic framework (MOF) exhibiting enhanced electrocatalytic performance to convert CO₂ into ethylene and ethanol. The Zr-based MOF, UiO-66 would in situ transform into amorphous ZrO_x nanoparticles (a-ZrO_x), constructing a-ZrO_x/Cu hetero-interface as a dual-site catalyst. The Faradaic efficiency of multi-carbon (C2+) products for optimal UiO-66-coated Cu (0.5-UiO/Cu) electrode reaches a high value of 74% at - 1.05 V versus RHE. The intrinsic activity for C2+ products on 0.5-UiO/Cu electrode is about two times higher than that of Cu foil. In situ surface-enhanced Raman spectra demonstrate that UiO-66-derived a-ZrO_x coating can promote the stabilization of atop-bound CO* intermediates on Cu surface during CO₂ electrolysis, leading to increased CO* coverage and facilitating the C-C coupling process. The present study gives new insights into tailoring the adsorption configurations of CO₂RR intermediate by designing dual-site electrocatalysts with hetero-interfaces.

Insight into the effects of the crystal phase of Ru over ultrathin Ru@Pt core-shell nanosheets for methanol electrooxidation

Coating a second metal on the surface of ultrathin 2D nanosheets (NSs) could induce lattice strain and modify the electronic structure, thereby changing the surface reactivity. Herein, we report the effects of different crystal phases of Ru on the electrocatalytic performance of ultrathin Ru@Pt core-shell NSs for the methanol oxidation reaction (MOR). Importantly, Ru with a novel face-centered-cubic phase was found to have more effect on the electronic structure of Pt than Ru with a conventional hexagonal close-packed phase, thereby leading to improved electrocatalytic activity toward the MOR under acidic and basic conditions. It is believed that the strategy presented here would offer a new approach to the construction of bimetallic core-shell nanostructures with various promising applications.

Operando Converting BiOCl into Bi2O2(CO3)xCly for Efficient Electrocatalytic Reduction of Carbon Dioxide to Formate

Bismuth-based materials (e.g., metallic, oxides and subcarbonate) are emerged as promising electrocatalysts for converting CO2 to formate. However, Bio-based electrocatalysts possess high overpotentials, while bismuth oxides and subcarbonate encounter stability issues. This work is designated to exemplify that the operando synthesis can be an effective means to enhance the stability of electrocatalysts under operando CO2RR conditions. A synthetic approach is developed to electrochemically convert BiOCl into Cl-containing subcarbonate (Bi2O2(CO3)xCly) under operando CO2RR conditions. The systematic operando spectroscopic studies depict that BiOCl is converted to Bi2O2(CO3)xCly via a cathodic potential-promoted anion-exchange process. The operando synthesized Bi2O2(CO3)xCly can tolerate - 1.0 V versus RHE, while for the wet-chemistry synthesized pure Bi2O2CO3, the formation of metallic Bio occurs at - 0.6 V versus RHE. At - 0.8 V versus RHE, Bi2O2(CO3)xCly can readily attain a FEHCOO- of 97.9%, much higher than that of the pure Bi2O2CO3 (81.3%). DFT calculations indicate that differing from the pure Bi2O2CO3-catalyzed CO2RR, where formate is formed via a *OCHO intermediate step that requires a high energy input energy of 2.69 eV to proceed, the formation of HCOO- over Bi2O2(CO3)xCly has proceeded via a *COOH intermediate step that only requires low energy input of 2.56 eV.

Isotype Heterojunction-Boosted CO2 Photoreduction to CO

Photocatalytic conversion of CO₂ to high-value products plays a crucial role in the global pursuit of carbon-neutral economy. Junction photocatalysts, such as the isotype heterojunctions, offer an ideal paradigm to navigate the photocatalytic CO₂ reduction reaction (CRR). Herein, we elucidate the behaviors of isotype heterojunctions toward photocatalytic CRR over a representative photocatalyst, g-C₃N₄. Impressively, the isotype heterojunctions possess a significantly higher efficiency for the spatial separation and transfer of photogenerated carriers than the single components. Along with the intrinsically outstanding stability, the isotype heterojunctions exhibit an exceptional and stable activity toward the CO₂ photoreduction to CO. More importantly, by combining quantitative in situ technique with the first-principles modeling, we elucidate that the enhanced photoinduced charge dynamics promotes the production of key intermediates and thus the whole reaction kinetics.

Highly efficient and stable indium single-atom catalysts for electrocatalytic reduction of CO2 to formate

Indium single-atom catalysts display a large total current density (38.94 to 81.08 mA cm^-2) over an extensive potential window (-0.91 to -1.41 V vs. RHE) for electrocatalytic CO₂ reduction to formate with high selectivity (85.2% faradaic efficiency at -1.31 V).