Microenvironment Engineering for the Electrocatalytic CO 2 Reduction Reaction

Bioinspired molecule-functionalized Cu with high CO adsorption for efficient CO electroreduction to acetate

Electrochemical reduction of carbon dioxide (CO2) or carbon monoxide (CO) to valuable multi-carbon (C2+) products like acetate is a promising approach for a sustainable energy economy. However, it is still challenging to achieve high activity and selectivity for acetate production, especially in neutral electrolytes. Herein, a bioinspired hemin/Cu hybrid catalyst was developed to enhance the surface *CO coverage for highly efficient electroreduction of CO to acetate fuels. The hemin/Cu electrocatalyst exhibits a remarkable faradaic efficiency of 45.2% for CO-to-acetate electroreduction and a high acetate partial current density of 152.3 mA cm-2. Furthermore, the developed hybrid catalyst can operate stably at 200 mA cm-2 for 14.6 hours, producing concentrated acetate aqueous solutions (0.235 M, 2.1 wt%). The results of in situ Raman spectroscopy and theoretical calculations proved that the Fe-N4 structure of hemin could enhance the CO adsorption and enrich the local concentration of CO, thereby improving C-C coupling for acetate production. In addition, compared to the unmodified Cu catalysts, the Cu catalysts functionalized with cobalt phthalocyanine with a Co-N4 structure also exhibit improved acetate performance, proving the universality of this bioinspired molecule-enhanced strategy. This work paves a new way to designing bioinspired electrolysis systems for producing specific C2+ products from CO2 or CO electroreduction.

Tailoring Cu-Based Electrocatalysts for Enhanced Electrochemical CO2 Reduction to Alcohols: Structure-Selectivity Relationship

The use of CO2 as a feedstock for the production of carbon-based fuels and value-added chemicals offers a promising route toward carbon neutrality. In this study, two Cu-based electrocatalysts, namely, Cu24/N-C and Cu2/N-C, are successfully prepared by thermal treatment of Cu24 metal-organic polyhedron-loaded zeolitic imidazolate framework-8 (ZIF-8) nanocrystals (Cu24/ZIF-8) and Cu2 dinuclear compound-loaded ZIF-8 nanocrystals (Cu2/ZIF-8), respectively. Extensive structural and compositional analyses were conducted to confirm the formation of Cu nanocluster-loaded N-doped porous carbon supports in both Cu24/N-C and Cu2/N-C and Cu nanoparticles encapsulated by graphitic carbons in Cu2/N-C as well. These two Cu-based electrocatalysts exhibited different behaviors in the electrochemical CO2 reduction reaction (CO2RR). The Cu24/N-C electrocatalyst showed high selectivity for CO production, while Cu2/N-C showed a preference for alcohol generation. The excellent stability of Cu2/N-C over a 30 h continuous electrochemical reduction further highlights its potential for practical applications. The difference in electrocatalytic performance observed in the two catalysts for CO2RR was attributed to distinct catalytic sites associated with Cu nanoclusters and nanoparticles. This research reveals the significance of their structures and compositions for the development of highly selective electrocatalysts for CO2 reduction.

Solid Electrolytes for Low-Temperature Carbon Dioxide Valorization: A Review

One of the most promising approaches to address the global challenge of climate change is electrochemical carbon capture and utilization. Solid electrolytes can play a crucial role in establishing a chemical-free pathway for the electrochemical capture of CO2. Furthermore, they can be applied in electrocatalytic CO2 reduction reactions (CO2RR) to increase carbon utilization, produce high-purity liquid chemicals, and advance hybrid electro-biosystems. This review article begins by covering the fundamentals and processes of electrochemical CO2 capture, emphasizing the advantages of utilizing solid electrolytes. Additionally, it highlights recent advancements in the use of the solid polymer electrolyte or solid electrolyte layer for the CO2RR with multiple functions. The review also explores avenues for future research to fully harness the potential of solid electrolytes, including the integration of CO2 capture and the CO2RR and performance assessment under realistic conditions. Finally, this review discusses future opportunities and challenges, aiming to contribute to the establishment of a green and sustainable society through electrochemical CO2 valorization.

d-band center engineering of single Cu atom and atomic Ni clusters for enhancing electrochemical CO2 reduction to CO

The rational design of catalysts with atomic dispersion and a deep understanding of the catalytic mechanism is crucial for achieving high performance in CO2 reduction reaction (CO2RR). Herein, we present an atomically dispersed electrocatalyst with single Cu atom and atomic Ni clusters supported on N-doped mesoporous hollow carbon sphere (CuSANiAC/NMHCS) for highly efficient CO2RR. CuSANiAC/NMHCS demonstrates a remarkable CO Faradaic efficiency (FECO) exceeding 90% across a potential range of -0.6 to -1.2 V vs. reversible hydrogen electrode (RHE) and achieves its peak FECO of 98% at -0.9 V vs. RHE. Theoretical studies reveal that the electron redistribution and modulated electronic structure-notably the positive shift in d-band center of Ni 3d orbital-resulting from the combination of single Cu atom and atomic Ni clusters markedly enhance the CO2 adsorption, facilitate the formation of *COOH intermediate, and thus promote the CO production activity. This study offers fresh perspectives on fabricating atomically dispersed catalysts with superior CO2RR performance.

Stabilizing the oxidation state of catalysts for effective electrochemical carbon dioxide conversion

In the electrocatalytic CO2 reduction reaction (CO2RR), metal catalysts with an oxidation state generally demonstrate more favorable catalytic activity and selectivity than their corresponding metallic counterparts. However, the persistence of oxidative metal sites under reductive potentials is challenging since the transition to metallic states inevitably leads to catalytic degradation. Herein, a thorough review of research on oxidation-state stabilization in the CO2RR is presented, starting from fundamental concepts and highlighting the importance of oxidation state stabilization while revealing the relevance of dynamic oxidation states in product distribution. Subsequently, the functional mechanisms of various oxidation-state protection strategies are explained in detail, and in situ detection techniques are discussed. Finally, the prevailing and prospective challenges associated with oxidation-state protection research are discussed, identifying innovative opportunities for mechanistic insights, technology upgrades, and industrial platforms to enable the commercialization of the CO2RR.

[2+1] Cycloadditions Modulate the Hydrophobicity of Ni-N4 Single-Atom Catalysts for Efficient CO2 Electroreduction

Microenvironment regulation of M-N4 single-atom catalysts (SACs) is a promising way to tune their catalytic properties toward the electrochemical CO2 reduction reaction. However, strategies that can effectively introduce functional groups around the M-N4 sites through strong covalent bonding and under mild reaction conditions are highly desired. Taking the hydrophilic Ni-N4 SAC as a representative, we report herein a [2+1] cycloaddition reaction between Ni-N4 and in situ generated difluorocarbene (F2C:), and enable the surface fluorocarbonation of Ni-N4, resulting in the formation of a super-hydrophobic Ni-N4-CF2 catalyst. Meanwhile, the mild reaction conditions allow Ni-N4-CF2 to inherit both the electronic and structural configuration of the Ni-N4 sites from Ni-N4. Enhanced electrochemical CO2-to-CO Faradaic efficiency above 98 % is achieved in a wide operating potential window from -0.7 V to -1.3 V over Ni-N4-CF2. In situ spectroelectrochemical studies reveal that a highly hydrophobic microenvironment formed by the -CF2- group repels asymmetric H-bonded water at the electrified interface, inhibiting the hydrogen evolution reaction and promoting CO production. This work highlights the advantages of [2+1] cycloaddition reactions on the covalent modification of N-doped carbon-supported catalysts.

Overcoming Low C2+ Yield in Acidic CO2 Electroreduction: Modulating Local Hydrophobicity for Enhanced Performance

Operating electrochemical CO2 reduction reaction (CO2RR) in acidic media has garnered considerable attention due to its sustainable electrolyte cycling and stable performance. Nevertheless, the severe parasitic hydrogen evolution reaction (HER) and decayed multi-carbon species (C2+) yield still hampers efficient CO2RR in acid. Here, this work investigates the influence of local hydrophobicity on the acidic CO2RR. By employing direct electrodeposition, the hydrophobicity of the catalyst layer can be finely tuned over a wide range without additive. It is revealed that the hydrophobic microenvironment significantly suppressed HER, improved CO2RR performance and boosted C2+ yield. A Faradaic efficiency (FE) of ≈74% for C2+ is achieved in pH = 2 on electrodeposited copper with a highly hydrophobic environment. Moreover, this phenomenon can be extended to industrial application. An ≈81% total FE for the CO2RR, along with a ≈62% FE for C2+ species, is achieved even with commercial copper. Remarkably, the system exhibited stable operation for a continuous period exceeding 50 h at an industrially applied current density of 300 mA cm-2. This work highlights the crucial role of interface hydrophobicity in acidic CO2RR and proposes a facile and universally applicable method for achieving efficient and stable CO2RR to high-value products in acidic media.

Advances in Atomically Dispersed Metal and Nitrogen Co-Doped Carbon Catalysts for Advanced Oxidation Technologies and Water Remediation: From Microenvironment Modulation to Non-Radical Mechanisms

Atomically dispersed metal and nitrogen co-doped carbon catalysts (M-N-C) have been attracting tremendous attentions thanks to their unique MNx active sites and fantastic catalytic activities in advanced oxidation technologies (AOTs) for water remediation. However, precisely tailoring the microenvironment of active sites at atomic level is still an intricate challenge so far, and understanding of the non-radical mechanisms in persulfate activation exists many uncertainties. In this review, latest developments on the microenvironment modulation strategies of atomically dispersed M-N-C catalysts including regulation of central metal atoms, regulation of coordination numbers, regulation of coordination heteroatoms, and synergy between single-atom catalysts (SACs) with metal species are systematically highlighted and discussed. Afterwards, progress and underlying limitations about the typical non-radical pathways from production of singlet oxygen, electron transfer mechanism to generation of high-valent metal species are well demonstrated to inspire intrinsic insights about the mechanisms of M-N-C/persulfate systems. Lastly, perspectives for the remaining challenges and opportunities about the further development of carbon-based SACs in environment remediation are also pointed out. It is believed that this review will be much valuable for the further design of active sites in M-N-C/persulfate catalytic systems and promote the wide application of SACs in various fields.

Tandem Acidic CO2 Electrolysis Coupled with Syngas Fermentation: A Two-Stage Process for Producing Medium-Chain Fatty Acids

The tandem application of CO2 electrolysis with syngas fermentation holds promise for achieving heightened production rates and improved product quality. However, the significant impact of syngas composition on mixed culture-based microbial chain elongation remains unclear. Additionally, effective methods for generating syngas with an adjustable composition from acidic CO2 electrolysis are currently lacking. This study successfully demonstrated the production of medium-chain fatty acids from CO2 through tandem acidic electrolysis with syngas fermentation. CO could serve as the sole energy source or as the electron donor (when cofed with acetate) for caproate generation. Furthermore, the results of gas diffusion electrode structure engineering highlighted that the use of carbon black, either alone or in combination with graphite, enabled consistent syngas generation with an adjustable composition from acidic CO2 electrolysis (pH 1). The carbon black layer significantly improved the CO selectivity, increasing from 0% to 43.5% (0.05 M K+) and further to 92.4% (0.5 M K+). This enhancement in performance was attributed to the promotion of K+ accumulation, stabilizing catalytically active sites, rather than creating a localized alkaline environment for CO2-to-CO conversion. This research contributes to the advancement of hybrid technology for sustainable CO2 reduction and chemical production.

Seeding Atomic Silver into Internal Lattice Sites of Transition Metal Oxide for Advanced Electrocatalysis

Transition metal oxides (TMOs) are widely studied for loading of various catalysts due to their low cost and high structure flexibility. However, the prevailing close-packed nature of most TMOs crystals has restricted the available loading sites to surface only, while their internal bulk lattice remains unactuated due to the inaccessible narrow space that blocks out most key reactants and/or particulate catalysts. Herein, using tunnel-structured MnO2, this study demonstrates how TMO's internal lattice space can be activated as extra loading sites for atomic Ag in addition to the conventional surface-only loading, via which a dual-form Ag catalyst within MnO2 skeleton is established. In this design, not only faceted Ag nanoparticles are confined onto MnO2 surface by coherent lattice-sharing, Ag atomic strings are also seeded deep into the sub-nanoscale MnO2 tunnel lattice, enriching the catalytically active sites. Tested for electrochemical CO2 reduction reaction (eCO2RR), such dual-form catalyst exhibits a high Faradaic efficiency (94%), yield (67.3 mol g-1 h-1) and durability (≈48 h) for CO production, exceeding commercial Ag nanoparticles and most Ag-based electrocatalysts. Theoretical calculations further reveal the concurrent effect of such dual-form catalyst featuring facet-dependent eCO2RR for Ag nanoparticles and lattice-confined eCO2RR for Ag atomic strings, inspiring the future design of catalyst-substrate configuration.

Nitrogenous Intermediates in NOx-involved Electrocatalytic Reactions

Chemical manufacturing utilizing renewable sources and energy emerges as a promising path towards sustainability and carbon neutrality. The electrocatalytic reactions involving nitrogen oxides (NOx) offered a potential strategy for synthesizing various nitrogenous chemicals. However, it is currently hindered by low selectivity/efficiency and limited reaction pathways, mainly due to the difficulties in controllable generation and utilization of nitrogenous intermediates. In this minireview, focusing on nitrogenous intermediates in NOx-involved electrocatalytic reactions, we discuss newly developed methodologies for studying and controlling the generation, conversion, and utilizing of nitrogenous intermediates, which enable recent developments in NOx-involved electrocatalytic reactions that yield various products, including ammonia (NH3), organonitrogen molecules, and nitrogenous compounds exhibiting unconventional oxidation states. Furthermore, we also make an outlook to highlight future directions in the emerging field of NOx-involved electrocatalytic reactions.

Surface Engineered Single-atom Systems for Energy Conversion

Single-atom catalysts (SACs) are demonstrated to show exceptional reactivity and selectivity in catalytic reactions by effectively utilizing metal species, making them a favorable choice among the different active materials for energy conversion. However, SACs are still in the early stages of energy conversion, and problems like agglomeration and low energy conversion efficiency are hampering their practical applications. Substantial research focus on support modifications, which are vital for SAC reactivity and stability due to the intimate relationship between metal atoms and support. In this review, a category of supports and a variety of surface engineering strategies employed in SA systems are summarized, including surface site engineering (heteroatom doping, vacancy introducing, surface groups grafting, and coordination tunning) and surface structure engineering (size/morphology control, cocatalyst deposition, facet engineering, and crystallinity control). Also, the merits of support surface engineering in single-atom systems are systematically introduced. Highlights are the comprehensive summary and discussions on the utilization of surface-engineered SACs in diversified energy conversion applications including photocatalysis, electrocatalysis, thermocatalysis, and energy conversion devices. At the end of this review, the potential and obstacles of using surface-engineered SACs in the field of energy conversion are discussed. This review aims to guide the rational design and manipulation of SACs for target-specific applications by capitalizing on the characteristic benefits of support surface engineering.

Selective and Scalable CO2 Electrolysis Enabled by Conductive Zinc Ion-Implanted Zeolite-Supported Cadmium Oxide Nanoclusters

Catalyst supports play an essential role in catalytic reactions, hinting at pronounced metal-support effects. Zeolites are a propitious support in heterogeneous catalysts, while their use in the electrocatalytic CO2 reduction reaction has been limited as yet because of their electrically insulating nature and serious competing hydrogen evolution reaction (HER). Enlightened by theoretical prediction, herein, we implant zinc ions into the structural skeleton of a zeolite Y to strategically tailor a favorable electrocatalytic platform with remarkably enhanced electronic conduction and strong HER inhibition capability, which incorporates ultrafine cadmium oxide nanoclusters as guest species into the supercages of the tailored 12-ring window framework. The metal d-bandwidth tuning of cadmium by skeletal zinc steers the extent of substrate-molecule orbital mixing, enhancing the stabilization of the key intermediate *COOH while weakening the CO poisoning effect. Furthermore, the strong cadmium-zinc interplay causes a considerable thermodynamic barrier for water dissociation in the conversion of H+ to *H, potently suppressing the competing HER. Therefore, we achieve an industrial-level partial current density of 335 mA cm-2 and remarkable Faradaic efficiency of 97.1% for CO production and stably maintain Faradaic efficiency above 90% at the industrially relevant current density for over 120 h. This work provides a proof of concept of tailored conductive zeolite as a favorable electrocatalytic support for industrial-level CO2 electrolysis and will significantly enhance the adaptability of conductive zeolite-based electrocatalysts in a variety of electrocatalysis and energy conversion applications.

Reconstructed Bismuth Oxide through in situ Carbonation by Carbonate-containing Electrolyte for Highly Active Electrocatalytic CO2 Reduction to Formate

The catalyst-reconstruction makes it challenging to clarify the practical active sites and unveil the actual reaction mechanism during the CO2 electroreduction reaction (CO2 RR). However, currently the impact of the electrolyte microenvironment in which the electrolyte is in contact with the catalyst is overlooked and might induce a chemical evolution, thus confusing the reconstruction process and mechanism. In this work, the carbonate adsorption properties of metal oxides were investigated, and the mechanism of how the electrolyte carbonate affect the chemical evolution of catalysts were discussed. Notably, Bi2 O3 with weak carbonate adsorption underwent a chemical reconstruction to form the Bi2 O2 CO3 /Bi2 O3 heterostructure. Furthermore, in situ and ex situ characterizations unveiled the formation mechanism of the heterostructure. The in situ formed Bi2 O2 CO3 /Bi2 O3 heterostructure with strong electron interaction served as the highly active structure for CO2 RR, achieving a formate Faradaic efficiency of 98.1 % at -0.8 Vvs RHE . Theoretical calculations demonstrate that the significantly tuned p-orbit electrons of the Bi sites in Bi2 O2 CO3 /Bi2 O3 optimized the adsorption of the intermediate and lowered the energy barrier for the formation of *OCHO. This work elucidates the mechanism of electrolyte microenvironment for affecting catalyst reconstruction, which contributes to the understanding of reconstruction process and clarification of the actual catalytic structure.

Mechanistic Basis of Conductivity in Carbon Dioxide-Expanded Electrolytes: A Joint Experimental-Theoretical Study

Electrolyte conductivity contributes to the efficiency of devices for electrochemical conversion of carbon dioxide (CO2) into useful chemicals, but the effect of the dissolution of CO2 gas on conductivity has received little attention. Here, we report a joint experimental-theoretical study of the properties of acetonitrile-based CO2-expanded electrolytes (CXEs) that contain high concentrations of CO2 (up to 12 M), achieved by CO2 pressurization. Cyclic voltammetry data and paired simulations show that high concentrations of dissolved CO2 do not impede the kinetics of outer-sphere electron transfer but decrease the solution conductivity at higher pressures. In contrast with conventional behaviors, Jones reactor-based measurements of conductivity show a nonmonotonic dependence on CO2 pressure: a plateau region of constant conductivity up to ca. 4 M CO2 and a region showing reduced conductivity at higher [CO2]. Molecular dynamics simulations reveal that while the intrinsic ionic strength decreases as [CO2] increases, there is a concomitant increase in ionic mobility upon CO2 addition that contributes to stable solution conductivities up to 4 M CO2. Taken together, these results shed light on the mechanisms underpinning electrolyte conductivity in the presence of CO2 and reveal that the dissolution of CO2, although nonpolar by nature, can be leveraged to improve mass transport rates, a result of fundamental and practical significance that could impact the design of next-generation systems for CO2 conversion. Additionally, these results show that conditions in which ample CO2 is available at the electrode surface are achievable without sacrificing the conductivity needed to reach high electrocatalytic currents.

Enhanced CO2 reduction with hydrophobic cationic-ionomer layer-modified zero-gap MEA in acidic electrolyte

A hydrophobic cationic-ionomer layer of quaternary ammonium poly(N-methyl-piperidine-co-p-terphenyl) and PTFE is presented to enhance the CO2 electroreduction in a zero-gap membrane electrode assembly (MEA) electrolyzer under acidic and low alkali ion concentration conditions. The modified MEA achieved a maximum CO faradaic efficiency of 95.6% at 100 mA cm-2.

Nanocluster Surface Microenvironment Modulates Electrocatalytic CO2 Reduction

The catalytic activity and product selectivity of the electrochemical CO2 reduction reaction (eCO2 RR) depend strongly on the local microenvironment of mass diffusion at the nanostructured catalyst and electrolyte interface. Achieving a molecular-level understanding of the electrocatalytic reaction requires the development of tunable metal-ligand interfacial structures with atomic precision, which is highly challenging. Here, the synthesis and molecular structure of a 25-atom silver nanocluster interfaced with an organic shell comprising 18 thiolate ligands are presented. The locally induced hydrophobicity by bulky alkyl functionality near the surface of the Ag25 cluster dramatically enhances the eCO2 RR activity (CO Faradaic efficiency, FECO : 90.3%) with higher CO partial current density (jCO ) in an H-cell compared to Ag25 cluster (FECO : 66.6%) with confined hydrophilicity, which modulates surface interactions with water and CO2 . Remarkably, the hydrophobic Ag25 cluster exhibits jCO as high as -240 mA cm-2 with FECO >90% at -3.4 V cell potential in a gas-fed membrane electrode assembly device. Furthermore, this cluster demonstrates stable eCO2 RR over 120 h. Operando surface-enhanced infrared absorption spectroscopy and theoretical simulations reveal how the ligands alter the neighboring water structure and *CO intermediates, impacting the intrinsic eCO2 RR activity, which provides atomistic mechanistic insights into the crucial role of confined hydrophobicity.

Bioinspired Hydrophobicity for Enhancing Electrochemical CO2 Reduction

Electrochemical carbon dioxide reduction (CO2 R) is a promising pathway for converting greenhouse gasses into valuable fuels and chemicals using intermittent renewable energy. Enormous efforts have been invested in developing and designing CO2 R electrocatalysts suitable for industrial applications at accelerated reaction rates. The microenvironment, specifically the local CO2 concentration (local [CO2 ]) as well as the water and ion transport at the CO2 -electrolyte-catalyst interface, also significantly impacts the current density, Faradaic efficiency (FE), and operation stability. In nature, hydrophobic surfaces of aquatic arachnids trap appreciable amounts of gases due to the "plastron effect", which could inspire the reliable design of CO2 R catalysts and devices to enrich gaseous CO2 . In this review, starting from the wettability modulation, we summarize CO2 enrichment strategies to enhance CO2 R. To begin, superwettability systems in nature and their inspiration for concentrating CO2 in CO2 R are described and discussed. Moreover, other CO2 enrichment strategies, compatible with the hydrophobicity modulation, are explored from the perspectives of catalysts, electrolytes, and electrolyzers, respectively. Finally, a perspective on the future development of CO2 enrichment strategies is provided. We envision that this review could provide new guidance for further developments of CO2 R toward practical applications.

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.

Electrocatalytic CO2 Reduction to Ethylene: From Advanced Catalyst Design to Industrial Applications

The value-added chemicals, monoxide, methane, ethylene, ethanol, ethane, and so on, can be efficiently generated through the electrochemical CO2 reduction reaction (eCO2 RR) when equipped with suitable catalysts. Among them, ethylene is particularly important as a chemical feedstock for petrochemical manufacture. However, despite its high Faradaic efficiency achievable at relatively low current densities, the substantial enhancement of ethylene selectivity and stability at industrial current densities poses a formidable challenge. To facilitate the industrial implementation of eCO2 RR for ethylene production, it is imperative to identify key strategies and potential solutions through comprehending the recent advancements, remaining challenges, and future directions. Herein, the latest and innovative catalyst design strategies of eCO2 RR to ethylene are summarized and discussed, starting with the properties of catalysts such as morphology, crystalline, oxidation state, defect, composition, and surface engineering. The review subsequently outlines the related important state-of-the-art technologies that are essential in driving forward eCO2 RR to ethylene into practical applications, such as CO2 capture, product separation, and downstream reactions. Finally, a greenhouse model that integrates CO2 capture, conversion, storage, and utilization is proposed to present an ideal perspective direction of eCO2 RR to ethylene.

Hierarchical Dual Single-Atom Catalysts with Coupled CoN4 and NiN4 Moieties for Industrial-Level CO2 Electroreduction to Syngas

Renewable-driven electrochemical CO2 reduction reaction (CO2RR) to syngas is an encouraging alternative strategy to traditional fossil fuel-based syngas production, and the development of industrial-level electrocatalysts is vital. Herein, based on theoretical optimization of metal species, hierarchical CoxNi1-x-N-C dual single-atom catalyst (DSAC) with individual NiN4 (CO preferential) and CoN4 (H2 preferential) moieties was constructed by a two-step pyrolysis route. The Co0.5Ni0.5-N-C exhibits a stable CO Faradaic efficiency of 50 ± 5% and an industrial-level current density of 101-365 mA cm-2 in an ultrawide potential window of -0.5 to -1.1 V. The CO/H2 ratio of syngas can be conveniently tuned by regulating the Co/Ni ratio. The coupled effect of NiN4 and CoN4 moieties under a local high-pH microenvironment is responsible for the regulation of the CO/H2 selectivity and yield for the CoxNi1-x-N-C catalyst, which is not present in the mixed Co-N-C and Ni-N-C catalyst. This study provides a promising DSAC strategy for achieving industrial-level syngas production via CO2RR.

A Bismuth-Based Zeolitic Organic Framework with Coordination-Linked Metal Cages for Efficient Electrocatalytic CO2 Reduction to HCOOH

Zeolitic metal-organic frameworks (ZMOFs) have emerged as one of the most promsing catalysts for energy conversion, but they suffer from either weak bonding between metal-organic cubes (MOCs) that decrease their stability during catalysis processes or low activity due to inadequate active sites. In this work, through ligand-directing strategy, we successfully obtain an unprecedented bismuth-based ZMOF (Bi-ZMOF) featuring a ACO topological crystal structure with strong coordination bonding between the Bi-based cages. As a result, it enables efficient reduction of CO2 to formic acid (HCOOH) with Faradaic efficiency as high as 91 %. A combination of in situ surface-enhanced infrared absorption spectroscopy and density functional theory calculation reveals that the Bi-N coordination contributes to facilitating charge transfer from N to Bi atoms, which stabilize the intermediate to boost the reduction efficiency of CO2 to HCOOH. This finding highlights the importance of the coordination environment of metal active sites on electrocatalytic CO2 reduction. We believe that this work will offer a new clue to rationally design zeolitic MOFs for catalytic reaction.

Switching between C2+ Products and CH4 in CO2 Electrolysis by Tuning the Composition and Structure of Rare-Earth/Copper Catalysts

Rational regulation of the reaction pathway to produce the desired products is one of the most significant challenges in the electrochemical CO2 reduction reaction (CO2RR). Herein, we designed a series of rare-earth Cu catalysts with mixed phases. It was found that the products could be switched from C2+ to CH4 by tuning the composition and structure of the catalysts. Particularly at the Cu/Sm atomic ratio of 9/1 (Cu9Sm1-Ox), the Faradaic efficiency (FE) for C2+ products (FEC2+) could reach 81% at 700 mA cm-2 with negligible CH4. However, the FE of CH4 (FECH4) was 65% at 500 mA cm-2 over Cu1Sm9-Ox (Cu/Sm = 1/9), and the FEC2+ was extremely low. Experiments and theoretical studies indicated that the stable CuSm2O4 phase existed in all the catalysts within the Cu/Sm range of 9/1 to 1/9. At a high Cu content, the catalyst was composed of CuSm2O4 and Cu phases. The small amount of Sm could enhance the binding strength of *CO and facilitate C-C coupling. Conversely, at a high Sm content, the catalyst was composed of CuSm2O4 and Sm2O3 phases. Sm could effectively stabilize bivalent Cu and enrich proton donors, lowering the reaction energy of *CO for deep hydrogenation to generate CH4. In both pathways, the stable CuSm2O4 phase could cooperate with the Cu or Sm2O3 phases, which induced the formation of different microenvironments to generate different products. This strategy also had commonality with other Cu-rare-earth (La, Pr, and Eu) catalysts to boost the CO2RR for C2+ or CH4 production.

Emerging materials and technologies for electrocatalytic seawater splitting

The limited availability of freshwater in renewable energy-rich areas has led to the exploration of seawater electrolysis for green hydrogen production. However, the complex composition of seawater presents substantial challenges such as electrode corrosion and electrolyzer failure, calling into question the technological and economic feasibility of direct seawater splitting. Despite many efforts, a comprehensive overview and analysis of seawater electrolysis, including electrochemical fundamentals, materials, and technologies of recent breakthroughs, is still lacking. In this review, we systematically examine recent advances in electrocatalytic seawater splitting and critically evaluate the obstacles to optimizing water supply, materials, and devices for stable hydrogen production from seawater. We demonstrate that robust materials and innovative technologies, especially selective catalysts and high-performance devices, are critical for efficient seawater electrolysis. We then outline and discuss future directions that could advance the techno-economic feasibility of this emerging field, providing a roadmap toward the design and commercialization of materials that can enable efficient, cost-effective, and sustainable seawater electrolysis.

Recent Advances in Confining Polyoxometalates and the Applications

Polyoxometalates (POMs) are widely used in catalysis, energy storage, biomedicine, and other research fields due to their unique acidity, photothermal, and redox features. However, the leaching and agglomeration problems of POMs greatly limit their practical applications. Confining POMs in a host material is an efficient tool to address the above-mentioned issues. POM@host materials have received extensive attention in recent years. They not only inherent characteristics of POMs and host, but also play a significant synergistic effect from each component. This review focuses on the recent advances in the development and applications of POM@host materials. Different types of host materials are elaborated in detail, including tubular, layered, and porous materials. Variations in the structures and properties of POMs and hosts before and after confinement are highlighted as well. In addition, an overview of applications for the representative POM@host materials in electrochemical, catalytic, and biological fields is provided. Finally, the challenges and future perspectives of POM@host composites are discussed.

Confinement of an alkaline environment for electrocatalytic CO2 reduction in acidic electrolytes

Acidic electrochemical CO₂ reduction reaction (CO₂RR) can minimize carbonate formation and eliminate CO₂ crossover, thereby improving long-term stability and enhancing single-pass carbon efficiency (SPCE). However, the kinetically favored hydrogen evolution reaction (HER) is generally predominant under acidic conditions. This paper describes the confinement of a local alkaline environment for efficient CO₂RR in a strongly acidic electrolyte through the manipulation of mass transfer processes in well-designed hollow-structured Ag@C electrocatalysts. A high faradaic efficiency of over 95% at a current density of 300 mA cm^-2 and an SPCE of 46.2% at a CO₂ flow rate of 2 standard cubic centimeters per minute are achieved in the acidic electrolyte, with enhanced stability compared to that under alkaline conditions. Computational modeling results reveal that the unique structure of Ag@C could regulate the diffusion process of OH^- and H⁺, confining a high-pH local reaction environment for the promoted activity. This work presents a promising route to engineer the microenvironment through the regulation of mass transport that permits the CO₂RR in acidic electrolytes with high performance.

Accelerating ammonia synthesis in a membraneless flow electrolyzer through coupling ambient dinitrogen oxidation and water splitting

An electrochemical approach for ammonia production is successfully developed by coupling the anodic dinitrogen oxidation reaction (NOR) and cathodic hydrogen evolution reaction (HER) within a well-designed membraneless flow electrolyzer. The obtained reactor shows the preferential yield of ammonia over nitrogen oxides on the vanadium nitride catalyst surface. At an applied oxidation potential of 2.25 V versus the reversible hydrogen electrode (vs RHE), a promoted ammonia production rate and Faradaic efficiency (FE) were obtained with 9.9 mmol g^-1 h^-1 (0.029 mmol cm^-2 h^-1) and 4.8%, respectively. Besides, the negative affection of ammonia contamination is efficiently alleviated. Density functional theory calculations revealed that the thermodynamic energy needed to produce ammonia (-0.63 eV) is far lower than that of producing nitrogen oxide (0.96 eV) from hydrogenated nitrogen oxides [∗N₂OH] splitting, confirming the coupling of NOR and HER.

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.

The Progress of Metal-Organic Framework for Boosting CO2 Conversion

With the rapid development of modern society, environmental problems, including excessive amounts of CO2 released in the atmosphere, are becoming more and more serious. It is necessary to develop new materials and technologies to reduce pollution. Among them, metal–organic frameworks (MOFs) have shown potential for application in the area of catalysis due to their ultra-high specific surface area, structural versatility, and designability as well as ease of modification and post-synthesis. Herein, we summarize recent research advances by use of MOFs for boosting CO2 conversion. Furthermore, challenges and possible research directions related to further exploration are also discussed.

Rational Design of Metal-Organic Frameworks for Electroreduction of CO2 to Hydrocarbons and Carbon Oxygenates

Since CO₂ can be reutilized by using renewable electricity in form of product diversity, electrochemical CO₂ reduction (ECR) is expected to be a burgeoning strategy to tackle environmental problems and the energy crisis. Nevertheless, owing to the limited selectivity and reaction efficiency for a single component product, ECR is still far from a large-scale application. Therefore, designing high performance electrocatalysts is the key objective in CO₂ conversion and utilization. Unlike most other types of electrocatalysts, metal-organic frameworks (MOFs) have clear, designable, and tunable catalytic active sites and chemical microenvironments, which are highly conducive to establish a clear structure-performance relationship and guide the further design of high-performance electrocatalysts. This Outlook concisely and critically discusses the rational design strategies of MOF catalysts for ECR in terms of reaction selectivity, current density, and catalyst stability, and outlines the prospects for the development of MOF electrocatalysts and industrial applications. In the future, more efforts should be devoted to designing MOF structures with high stability and electronic conductivity besides high activity and selectivity, as well as to develop efficient electrolytic devices suitable for MOF catalysts.

Insights of Fe2O3 and MoO3 Electrodes for Electrocatalytic CO2 Reduction in Aprotic Media

Transition metal oxides (TMO) have been successfully used as electrocatalytically active materials for CO2 reduction in some studies. Because of the lack of understanding of the catalytic behavior of TMOs, electrochemical methods are used to investigate the CO2 reduction in thin-film nanostructured electrodes. In this context, nanostructured thin films of Fe2O3 and MoO3 in an aprotic medium of acetonitrile have been used to study the CO2 reduction reaction. In addition, a synergistic effect between CO2 and the TMO surface is observed. Faradic cathodic processes not only start at lower potentials than those reported with metal electrodes, but also an increase in capacitive currents is observed, which is directly related to an increase in oxygen vacancies. Finally, the results obtained show CO as a product of the reduction.