Synthesis of Cu/CeO2-x Nanocrystalline Heterodimers with Interfacial Active Sites To Promote CO2 Electroreduction

Promotion of CO2 Electroreduction on Bismuth Nanosheets with Cerium Oxide nanoparticles

Formic acid (HCOOH) is a highly energy efficient product of the electrochemical CO2 reduction reaction (CO2RR). Bismuth-based catalysts have shown promise in the conversion of CO2 to formic acid, but there is still a great need for further improvement in selectivity and activity. Herein, we report the preparation of Bi nanosheets decorated by cerium oxide nanoparticles (CeOx) with high Ce3+/Ce4+ ratio and rich oxygen vacancies. The CeOx nanoparticles affect the electronic structures of bismuth, enhance CO2 adsorption, and thus promote the CO2RR properties of Bi nanosheets. Compared with elemental Bi nanosheets, the hetero-structured CeOx/Bi nanosheets exhibit much higher activity over a wide potential window, showing a current density of 16.1 mA cm-2 with a Faradaic efficiency of 91.1% at -0.9 V vs. reversible hydrogen electrode.

Advances and challenges in the electrochemical reduction of carbon dioxide

The electrocatalytic carbon dioxide reduction reaction (ECO2RR) is a promising way to realize the transformation of waste into valuable material, which can not only meet the environmental goal of reducing carbon emissions, but also obtain clean energy and valuable industrial products simultaneously. Herein, we first introduce the complex CO2RR mechanisms based on the number of carbons in the product. Since the coupling of C-C bonds is unanimously recognized as the key mechanism step in the ECO2RR for the generation of high-value products, the structural-activity relationship of electrocatalysts is systematically reviewed. Next, we comprehensively classify the latest developments, both experimental and theoretical, in different categories of cutting-edge electrocatalysts and provide theoretical insights on various aspects. Finally, challenges are discussed from the perspectives of both materials and devices to inspire researchers to promote the industrial application of the ECO2RR at the earliest.

Promoting CO Electroreduction to C2+ Oxygenates by Distribution of Water Dissociation Sites

The electrocatalytic CO2 or CO reduction reaction is a complex proton-coupled electron transfer reaction, in which protons in the electrolyte have a critical effect on the surface adsorbed *H species and the multi-carbon oxygenate products such as ethanol. However, the coupling of *H and carbon-containing intermediates into C2+ oxygenates can be severely hampered by the inappropriate distributions of those species in the catalytic interfaces. In this work, the controlled distribution of highly dispersed CeOx nanoclusters is demonstrated on Cu nanosheets as an efficient CO electroreduction catalyst, with Faradaic efficiencies of ethanol and total oxygenates of 35% and 58%, respectively. The CeOx nanoclusters (2-5 nm) enabled efficient water dissociation and appropriate distribution of adsorbed *H species on the Cu surface with carbon-containing species, thus facilitating the generation of C2+ oxygenate products. In contrast, pristine Cu without CeOx tended to form ethylene, while the aggregated CeOx nanoparticles promoted the surface density of *H and subsequent H2 evolution.

Hybrid oxide coatings generate stable Cu catalysts for CO2 electroreduction

Hybrid organic/inorganic materials have contributed to solve important challenges in different areas of science. One of the biggest challenges for a more sustainable society is to have active and stable catalysts that enable the transition from fossil fuel to renewable feedstocks, reduce energy consumption and minimize the environmental footprint. Here we synthesize novel hybrid materials where an amorphous oxide coating with embedded organic ligands surrounds metallic nanocrystals. We demonstrate that the hybrid coating is a powerful means to create electrocatalysts stable against structural reconstruction during the CO2 electroreduction. These electrocatalysts consist of copper nanocrystals encapsulated in a hybrid organic/inorganic alumina shell. This shell locks a fraction of the copper surface into a reduction-resistant Cu2+ state, which inhibits those redox processes responsible for the structural reconstruction of copper. The electrocatalyst activity is preserved, which would not be possible with a conventional dense alumina coating. Varying the shell thickness and the coating morphology yields fundamental insights into the stabilization mechanism and emphasizes the importance of the Lewis acidity of the shell in relation to the retention of catalyst structure. The synthetic tunability of the chemistry developed herein opens new avenues for the design of stable electrocatalysts and beyond.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Rare-earth Element-based Electrocatalysts Designed for CO2 Electro-reduction

Electrochemical CO2 reduction presents a promising approach for synthesizing fuels and chemical feedstocks using renewable energy sources. Although significant advancements have been made in the design of catalysts for CO2 reduction reaction (CO2RR) in recent years, the linear scaling relationship of key intermediates, selectivity, stability, and economical efficiency are still required to be improved. Rare earth (RE) elements, recognized as pivotal components in various industrial applications, have been widely used in catalysis due to their unique properties such as redox characteristics, orbital structure, oxygen affinity, large ion radius, and electronic configuration. Furthermore, RE elements could effectively modulate the adsorption strength of intermediates and provide abundant metal active sites for CO2RR. Despite their potential, there is still a shortage of comprehensive and systematic analysis of RE elements employed in the design of electrocatalysts of CO2RR. Therefore, the current approaches for the design of RE element-based electrocatalysts and their applications in CO2RR are thoroughly summarized in this review. The review starts by outlining the characteristics of CO2RR and RE elements, followed by a summary of design strategies and synthetic methods for RE element-based electrocatalysts. Finally, an overview of current limitations in research and an outline of the prospects for future investigations are proposed.

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.

Interfacial engineering of nickel selenide with CeO2 on N-doped carbon nanosheets for efficient methanol and urea electro-oxidation

The design of low cost, high efficiency electrocatalysts for methanol oxidation reactions (MOR) and urea oxidation reactions (UOR) is a pressing need to address the energy crisis and water pollution. In the present work, we developed Cerium dioxide (CeO2) and nickel selenide (Ni0.85Se) nanoparticles integrated into three-dimensional N-doped carbon nanosheets to be used as efficient and stable bifunctional electrocatalysts for MOR and UOR. By optimizing the selenization temperature, the CeO2-modified Ni0.85Se obtained at selenization temperature of 550 °C (CeO2-Ni0.85Se-550-NC) has the best MOR and UOR electrochemical performance. The CeO2-Ni0.85Se-550-NC potential only requires 1.309 V (MOR) and 1.294 V (UOR) to reach 10 mA cm-2, respectively. The DFT study reveals that CeO2-Ni0.85Se-550-NC has the best reaction path with the synergistic effect between CeO2 and Ni0.85Se. The outstanding catalytic performance of CeO2-Ni0.85Se-550-NC may be due to the cointeraction between CeO2 and Ni0.85Se, allowing more defects that function as catalytic sites while promoting fast electron transfer in the N-doped carbon substrate.

Directing the Selectivity of CO Electrolysis to Acetate by Constructing Metal-Organic Interfaces

Electrochemically converting CO2 to valuable chemicals holds great promise for closing the anthropogenic carbon cycle. Owing to complex reaction pathways and shared rate-determining steps, directing the selectivity of CO2 /CO electrolysis to a specific multicarbon product is very challenging. We report here a strategy for highly selective production of acetate from CO electrolysis by constructing metal-organic interfaces. We demonstrate that the Cu-organic interfaces constructed by in situ reconstruction of Cu complexes show very impressive acetate selectivity, with a high Faradaic efficiency of 84.2 % and a carbon selectivity of 92.1 % for acetate production, in an alkaline membrane electrode assembly electrolyzer. The maximum acetate partial current density and acetate yield reach as high as 605 mA cm-2 and 63.4 %, respectively. Thorough structural characterizations, control experiments, operando Raman spectroscopy measurements, and density functional theory calculation results indicate that the Cu-organic interface creates a favorable reaction microenvironment that enhances *CO adsorption, lowers the energy barrier for C-C coupling, and facilitates the formation of CH3 COOH over other multicarbon products, thus rationalizing the selective acetate production.

Curvature Effect of Pyridinic N-Modified Carbon Atom Sites for Electrocatalyzing CO2 Conversion to CO

Carbon material is considered a promising electrocatalyst for the CO2 reduction reaction (CO2RR); especially, N-doped carbon material shows high CO Faradic efficiency (FECO) when using pyridinic N species as the active site. However, in the past decade, more efforts were focused on the preparation of various carbon nanostructures containing abundant pyridinic N species and few researchers studied the electronic structure modulation of the pyridinic N site. The curvature of the carbon substrate is an easily controllable parameter for modulating the local electronic environment of catalytic sites. In this research, carbon nanotubes (CNTs) with different diameters are applied to modulate the electronic environment of pyridinic N by the curvature effect. The pyridinic N sites doped on CNTs with the average curvature of 0.04 show almost 100% FECO at the current density of 3 mA cm-2 at -0.6 V vs RHE and 91% FECO retention after 12 h test, which is superior to most of the carbon-based electrocatalysts. As demonstrated by density functional theory simulation, the pyridinic N site forms a strong local electric field around the nearby C active site and protrudes out of the curved CNT surface like a tip, which remarkably enriches the protons around the adsorbed CO2 molecule.

Modulation of *CHxO Adsorption to Facilitate Electrocatalytic Reduction of CO2 to CH4 over Cu-Based Catalysts

Copper (Cu) can efficiently catalyze the electrochemical CO₂ reduction reaction (CO₂RR) to produce value-added fuels and chemicals, among which methane (CH₄) has drawn attention due to its high mass energy density. However, the linear scaling relationship between the adsorption energies of *CO and *CH_xO on Cu restricts the selectivity toward CH₄. Alloying a secondary metal in Cu provides a new freedom to break the linear scaling relationship, thus regulating the product distribution. This paper describes a controllable electrodeposition approach to alloying Cu with oxophilic metal (M) to steer the reaction pathway toward CH₄. The optimized La₅Cu₉₅ electrocatalyst exhibits a CH₄ Faradaic efficiency of 64.5%, with the partial current density of 193.5 mA cm^-2. The introduction of oxophilic La could lower the energy barrier for *CO hydrogenation to *CH_xO by strengthening the M-O bond, which would also promote the breakage of the C-O bond in *CH₃O for the formation of CH₄. This work provides a new avenue for the design of Cu-based electrocatalysts to achieve high selectivity in CO₂RR through the modulation of the adsorption behaviors of key intermediates.

Defective Metal Oxides: Lessons from CO2 RR and Applications in NOx RR

Sluggish reaction kinetics and the undesired side reactions (hydrogen evolution reaction and self-reduction) are the main bottlenecks of electrochemical conversion reactions, such as the carbon dioxide and nitrate reduction reactions (CO₂ RR and NO₃ RR). To date, conventional strategies to overcome these challenges involve electronic structure modification and modulation of the charge-transfer behavior. Nonetheless, key aspects of surface modification, focused on boosting the intrinsic activity of active sites on the catalyst surface, are yet to be fully understood. Engingeering of oxygen vacancies (OVs) can tune surface/bulk electronic structure and improve surface active sites of electrocatalysts. The continuous breakthroughs and significant progress in the last decade position engineering of OVs as a potential technique for advancing electrocatalysis. Motivated by this, the state-of-the-art findings of the roles of OVs in both the CO₂ RR and the NO₃ RR are presented. The review starts with a description of approaches to constructing and techniques for characterizing OVs. This is followed by an overview of the mechanistic understanding of the CO₂ RR and a detailed discussion on the roles of OVs in the CO₂ RR. Then, insights into the NO₃ RR mechanism and the potential of OVs on NO₃ RR based on early findings are highlighted. Finally, the challenges in designing CO₂ RR/NO₃ RR electrocatalysts and perspectives in studying OV engineering are provided.

Leveraging Pd(100)/SnO2 interfaces for highly efficient electrochemical formic acid oxidation

The electrocatalytic formic acid oxidation (FAO) is the crucial anodic reaction of direct formic acid fuel cells (DFAFCs), but its activity remains to be largely improved in order to be practically viable. The rational development of enhanced catalysts requires thorough consideration of various contributing factors that are possibly integrated in composite systems. Here, we demonstrate that, Pd(100)/SnO₂ interfaces, provided being efficiently exploited, can significantly boost FAO activity by a factor of ∼10, compared with pure Pd(100) facets, with the mass activity reaching a record of 14.55 A mg_Pd^-1 at a 40 mV-lower peak potential. Unique Pd/SnO₂ nanocomposites with a myriad of Pd(100)/SnO₂ interfaces were obtained by a newly developed successive seeded growth strategy, wherein pre-formed SnO₂ nanospheres are used as seeds for two-round overgrowth of multitudinous Pd nanocubes. Using electron microscopic, electrochemical, spectroscopic and computational analyses, we found that the Pd(100)/SnO₂ interfaces induce lattice contraction and electron loss on Pd nanocubes, which optimize intermediate binding during FAO. Moreover, we showed that the good cubicity of the Pd nanocubes and the presence of SnO₂ nearby further promote the activity by facilitating the potential-determining step and the elimination of the poisoning CO intermediate, respectively. As such, the combined high intrinsic activity and number density of Pd(100)/SnO₂ interfaces enabled the superior activity of the Pd/SnO₂ nanocomposites. The composite material presented here holds promise for application in DFAFCs, but equally importantly, the insights regarding the structure-performance relationship would be beneficial for designing efficient metal/oxide composite catalysts for diverse electro- and photo-catalytic reactions.

Tuning the C1 /C2 Selectivity of Electrochemical CO2 Reduction on Cu-CeO2 Nanorods by Oxidation State Control

Ceria (CeO₂ ) is one of the most extensively used rare earth oxides. Recently, it has been used as a support material for metal catalysts for electrochemical energy conversion. However, to date, the nature of metal/CeO₂ interfaces and their impact on electrochemical processes remains unclear. Here, a Cu-CeO₂ nanorod electrochemical CO₂ reduction catalyst is presented. Using operando analysis and computational techniques, it is found that, on the application of a reductive electrochemical potential, Cu undergoes an abrupt change in solubility in the ceria matrix converting from less stable randomly dissolved single atomic Cu²⁺ ions to (Cu⁰ ,Cu¹⁺ ) nanoclusters. Unlike single atomic Cu, which produces C₁ products as the main product during electrochemical CO₂ reduction, the coexistence of (Cu⁰ ,Cu¹⁺ ) clusters lowers the energy barrier for C-C coupling and enables the selective production of C₂₊ hydrocarbons. As a result, the coexistence of (Cu⁰ ,Cu¹⁺ ) in the clusters at the Cu-ceria interface results in a C₂₊ partial current density/unit Cu weight 27 times that of a corresponding Cu-carbon catalyst under the same conditions.

Strain in Copper/Ceria Heterostructure Promotes Electrosynthesis of Multicarbon Products

Elastic strains in metallic catalysts induce enhanced selectivity for carbon dioxide reduction (CO₂R) toward valuable multicarbon (C₂₊) products. However, under working conditions, the structure of catalysts inevitably undergoes reconstruction, hardly retaining the initial strain. Herein, we present a metal/metal oxide synthetic strategy to introduce and maintain the tensile strain in a copper/ceria heterostructure, enabled by the presence of a thin interface layer of Cu₂O/CeO₂. The tensile strain in the copper domain and deficient electron environment around interfacial Cu sites resulted in strengthened adsorption of carbonaceous intermediates and promoted *CO dimerization. The strain effect in the copper/ceria heterostructure leads to an improved C₂₊ selectivity with a maximum Faradaic efficiency of 76.4% and a half-cell power conversion efficiency of 49.1%. The fundamental insights gained from this system can facilitate the rational design of heterostructure catalysts for CO₂R.

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

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

Precisely synthesized LiF-tipped CoF2-nanorod heterostructures improve energy storage capacities

CoF2, with a relatively high theoretical capacity (553 mA h g-1), has been attracting increasing attention in the energy storage field. However, a facile and controllable synthesis of monodispersed CoF2 and CoF2-based nano-heterostructures have been rarely reported. In this direction, an eco-friendly and precisely controlled colloidal synthesis strategy to grow uniformly sized CoF2 nanorods and LiF-tipped CoF2-nanorod heterostructures based on a seeded-growth method is established. The unveiled selective growth of LiF nanoparticles onto the two end tips of the CoF2 nanorods is associated with the higher energy of tips, which favors the nucleation of LiF nanocrystals. Notably, it was found that LiF could protect CoF2 from corrosion even after 9 months of aging. In addition, the as-obtained heterostructures were employed in supercapacitors and lithium sulfur batteries as cathode materials. The heterostructures consistently exhibited higher specific capacities than the corresponding two single components in both types of energy storage devices, making it a potential electrode material for energy storage applications.

Menezes L, Tittl A, Ren H, Maier SA. Optical Metasurfaces for Energy Conversion

Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light-matter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.

Highly efficient electrochemical N2 reduction over strongly coupled CeO2-Mo2C nanocomposites anchored by reduced graphene oxide

Electrocatalytic N₂ fixation has been considered a most promising approach for sustainably producing NH₃ under ambient conditions. However, owing to the strong chemical inertness of N₂, it is highly desired to explore efficient electrocatalysts for improving the yield and selectivity of nitrogen reduction. Herein, CeO₂ and Mo₂C nanoparticles embedded simultaneously in reduced graphene oxide nanosheets (CeO₂/Mo₂C@rGO) are successfully fabricated for catalyzing N₂ fixation. The as-obtained CeO₂/Mo₂C@rGO catalyst shows superior catalytic performance with an NH₃ yield of 22.3 μg h^-1 mg^-1 and a faradaic efficiency (FE) of 12.7% at -0.3 V vs. the RHE, distinctly outperforming the undoped Ce counterpart of Mo₂C@rGO. The experimental and DFT calculations reveal that the introduced Ce optimized the electronic structure, contributing to the improved NRR performance.

Vertically Oriented Metallic Heterodimer Array Semiembedded in Flat Conductive Carbon Film for Electrochemical Application

General synthesis of a highly oriented metallic heterodimer array based on a selective electrodeposition technique onto a metal nanoparticle-embedded carbon film is proposed, which enables the preparation of heterodimers with a wide variety of metal combinations. This method requires no surfactant, capping agent, organic solvent, or heat treatment. As a representative metal combination, a nickel (Ni)/palladium (Pd) heterodimer array was prepared by selective electrodeposition of Ni nanoparticles (Ni NPs) on top of partially exposed Pd NPs embedded in carbon film electrodes fabricated by a cosputtering technique. Such a selective electrodeposition becomes possible by utilizing the difference in electrodeposition overpotentials between carbon and Pd NP surfaces. X-ray photoelectron spectroscopy revealed a charge transfer from Ni NPs to Pd NPs, implying that the catalytic and optical properties can be expected to be controllable. The formed heterodimer array structure was mechanically stable against ultrasonication in ethanol for over 1 h because most parts of the Pd NPs were tightly embedded in the carbon film. After conversion from Ni to nickel hydroxide (Ni(OH)₂), the electrode showed high electrocatalytic activity toward glucose oxidation, with a higher turnover rate and lower overpotential compared to Ni(OH)₂ electrodeposited on pure carbon film electrodes.

Controlled Synthesis of Intermetallic Au2 Bi Nanocrystals and Au2 Bi/Bi Hetero-Nanocrystals with Promoted Electrocatalytic CO2 Reduction Properties

The electrocatalytic properties of metal nanoparticles (NPs) strongly depend on their compositions and structures. Rational design of alloys and/or heterostructures provides additional approaches to modifying their surface geometric and electronic structures for optimized electrocatalytic performance. Here, a solution synthesis of freestanding intermetallic Au₂ Bi NPs, the heterostructures of Au₂ Bi/Bi hetero-NPs, and their promoted electrocatalytic CO₂ reduction reaction (CO₂ RR) performances were reported. It was revealed that the formation and in-situ conversion of heterogeneous seeds (e. g., Au) were of vital importance for the formation of intermetallic Au₂ Bi and Au₂ Bi/Bi hetero-NPs. It was also found that the Au components would act as the structure promoter moderating the binding strength for key intermediates on Bi surfaces. The alloying of Bi with Au and the formation of heterogeneous Au₂ Bi/Bi interfaces would create more surface active sites with modulated electronic structures and stronger adsorption strengths for key intermediates, promoting the CO₂ -to-HCOOH conversion with high activity and selectivity. This work presents a novel route for preparing intermetallic nanomaterials with modulated surface geometric/electric structures and promoting their electrocatalytic activities with alloying effects and interfacial effects. Such strategy may find wide application in catalyst design and synthesis for more electrocatalytic reactions.

Enhanced electrocatalytic reduction of CO2 to formate via doping Ce in Bi2O3 nanosheets

Formate is considered as the most economically viable product of the prevalent electrochemical CO₂ reduction (ECR) products. However, most of the catalysts for ECR to formate in aqueous solution often suffer from low activity and limited selectivity. Herein, we report a novel Ce-doped Bi₂O₃ nanosheet (NS) electrocatalyst by a facile solvothermal method for highly efficient ECR to formate. The 5.04% Ce-doped Bi₂O₃ NSs exhibited a current density of 37.4 mA cm^-2 for the production of formate with a high formate faradaic efficiency (FE) of 95.8% at -1.12 V. The formate FE was stably maintained at about 90% in a wide potential range from -0.82 to -1.22 V. More importantly, density functional theory (DFT) calculations revealed that Ce doping can lead to a significant synergistic effect, which promotes the formation and the adsorption of the OCHO* intermediate for ECR, while significantly inhibiting the hydrogen evolution reaction via depressing the formation of *H, thus helping achieve high current density and FE. This work provides an effective and promising strategy to develop efficient electrocatalysts with heteroatom doping and new insights for boosting ECR into formate.

Cu Modified TiO2 Catalyst for Electrochemical Reduction of Carbon Dioxide to Methane

Electrochemical reduction of CO2 (ECO2R) is gaining attention as a promising approach to store excess or intermittent electricity generated from renewable energies in the form of valuable chemicals such as CO, HCOOH, CH4, and so on. Selective ECO2R to CH4 is a challenging target because the rate-determining step of CH4 formation, namely CO* protonation, competes with hydrogen evolution reaction and the C–C coupling toward the production of longer-chain chemicals. Herein, a Cu-TiO2 composite catalyst consisting of CuOx clusters or Cu nanoparticles (CuNPs), which are isolated on the TiO2 grain surface, was synthesized using a one-pot solvothermal method and subsequent thermal treatment. The Cu-TiO2 catalyst exhibited high selectivity for CH4, and the ratio of FE for CH4 to total FE for all products in ECO2R reached 70%.

Structure-Function Correlation and Dynamic Restructuring of Cu for Highly Efficient Electrochemical CO2 Conversion

The increasing global demand for sustainable energy sources and emerging environmental issues have pushed the development of energy conversion and storage technologies to the forefront of chemical research. Electrochemical carbon dioxide (CO₂ ) conversion provides an attractive approach to synthesizing fuels and chemical feedstocks using renewable energy. On the path to deploying this technology, basic and applied scientific hurdles remain. Copper, as the only metal catalyst that is capable to produce C₂₊ fuels from CO₂ reduction (CO₂ R), still faces challenges in the improvement of electrosynthesis pathways for highly selective fuel production. In this regard, mechanistically understanding CO₂ R on Cu-based electrocatalysts, particularly identifying the structure-function correlation, is crucial. Here, a broad view of the variable structural parameters and their complex interplay in CO₂ R catalysis on Cu was given, with the purpose of providing deep insights and guiding the future rational design of CO₂ R electrocatalysts. First, this Review described the progress and recent advances in the development of well-defined nanostructured catalysts and the mechanistic understanding on the influences from a particular structure of a catalyst, such as facet, defects, morphology, oxidation state, composition, and interface. Next, the in-situ dynamic restructuring of Cu was presented. The importance of operando characterization methods to understand the catalyst structure-sensitivity was also discussed. Finally, some perspectives on the future outlook for electrochemical CO₂ R were offered.

Metallic Copper-Containing Composite Photocatalysts: Fundamental, Materials Design, and Photoredox Applications

Semiconductor photocatalysis has long been regarded as a potential solution to tackle the energy and environmental challenges since the first discovery of water splitting by TiO₂ almost 50 years ago. The past few years have seen a tremendous flurry of research interest in the modification of semiconductors because of their shortcomings in the aspects of solar harvesting, electron-hole pairs separation, and utilization of photogenerated carriers. Among the various strategies, the introduction of metallic copper into the photocatalysis system can not only enhance the absorption of sunlight and the separation efficiency of photogenerated electrons and holes, but also increase the adsorption ability of substrate and the number of active sites, so as to realize the high solar to chemical energy conversion efficiency. This review focuses on the rational design of copper-based composites and their applications in photoredox catalysis. First, the preparation methods of metallic copper-containing composites are discussed. Then, the applications of different types of copper-based composites in the photocatalytic removal of pollutants, splitting of water to hydrogen production, reduction of carbon dioxide, and conversion of organic matter are introduced. Finally, the opportunities and challenges in the design and synthesis of copper-based composites and their applications in the photocatalysis are prospected.

Crystal-Phase Control of Ternary Metal Oxides by Solid-State Synthesis with Nanocrystals

Ternary metal oxides are materials of interest for many applications, from batteries to catalysis. Their crystalline structure and composition determine their properties, and thus it is important to achieve control over these features. Here, we demonstrate that solid-state chemistry among nanocrystalline precursors is a promising approach for their synthesis. We show that the crystalline phase of nanocrystal precursors direct that of the ternary reaction product. The combination of X-ray and electron microscopy techniques reveals that the spinel and rhombohedral phases of copper iron oxide are obtained by reacting copper nanocrystals with spinel γ-Fe₂O₃ and corundum α-Fe₂O₃ nanocrystals, respectively. Considering the available library of nanocrystals with tunable crystal phases, this discovery opens up an alternative pathway toward the synthesis of a wide variety of ternary and quaternary materials, including those with metastable phases.

Highly dispersed Cu nanoparticles on ceria for enhanced ethylene selectivity during electrochemical reduction of CO2

Strong interaction between Cu and CeO2 contributes to forming highly effective active sites for electroreduction of CO2 to ethylene.

Synergistic effect of Cu/Cu2O surfaces and interfaces for boosting electrosynthesis of ethylene from CO2 in a Zn–CO2 battery

We constructed Cu/Cu2O hybrid catalysts with highly active surfaces/interfaces to realize a synergistic effect, thus improving the selectivity and efficiency of C2H4 production.

One Pot-Synthesized Ag/Ag-Doped CeO2 Nanocomposite with Rich and Stable 3D Interfaces and Ce3+ for Efficient Carbon Dioxide Electroreduction

Electrochemical CO₂ reduction (ECR) technology is promising to produce value-added chemicals and alleviate the climate deterioration. Interface engineering is demonstrated to improve the ECR performance for metal and oxide composite catalysts. However, the approach to form a substantial interface is still limited. In this work, we report a facile one-pot coprecipitation method to synthetize novel silver and silver-doped ceria (Ag/CeO₂) nanocomposites. This catalyst provides a rich 3D interface and high Ce³⁺ concentration (33.6%), both of which are beneficial for ECR to CO. As a result, Ag/CeO₂ exhibits a 99% faradaic efficiency and 10.5 A g^-1 mass activity to convert CO₂ into CO at an overpotential of 0.83 V. The strong interfacial interaction between Ag and CeO₂ may enable the presence of surface Ce³⁺ and guarantee the improved durability during the electrolysis. We also develop numerical simulation to understand the local pH effect on the ECR performance and propose that the superior ECR performance of Ag/CeO₂ is mainly due to the accelerated CO formation rate rather than the suppressed hydrogen evolution reaction.

Improved electrochemical conversion of CO2 to multicarbon products by using molecular doping

The conversion of CO₂ into desirable multicarbon products via the electrochemical reduction reaction holds promise to achieve a circular carbon economy. Here, we report a strategy in which we modify the surface of bimetallic silver-copper catalyst with aromatic heterocycles such as thiadiazole and triazole derivatives to increase the conversion of CO₂ into hydrocarbon molecules. By combining operando Raman and X-ray absorption spectroscopy with electrocatalytic measurements and analysis of the reaction products, we identified that the electron withdrawing nature of functional groups orients the reaction pathway towards the production of C₂₊ species (ethanol and ethylene) and enhances the reaction rate on the surface of the catalyst by adjusting the electronic state of surface copper atoms. As a result, we achieve a high Faradaic efficiency for the C₂₊ formation of ≈80% and full-cell energy efficiency of 20.3% with a specific current density of 261.4 mA cm^-2 for C₂₊ products.

Elucidating the structure-dependent selectivity of CuZn towards methane and ethanol in CO2 electroreduction using tailored Cu/ZnO precatalysts

Understanding the catalyst compositional and structural features that control selectivity is of uttermost importance to target desired products in chemical reactions. In this joint experimental-computational work, we leverage tailored Cu/ZnO precatalysts as a material platform to identify the intrinsic features of methane-producing and ethanol-producing CuZn catalysts in the electrochemical CO2 reduction reaction (CO2RR). Specifically, we find that Cu@ZnO nanocrystals, where a central Cu domain is decorated with ZnO domains, and ZnO@Cu nanocrystals, where a central ZnO domain is decorated with Cu domains, evolve into Cu@CuZn core@shell catalysts that are selective for methane (∼52%) and ethanol (∼39%), respectively. Operando X-ray absorption spectroscopy and various microscopy methods evidence that a higher degree of surface alloying along with a higher concentration of metallic Zn improve the ethanol selectivity. Density functional theory explains that the combination of electronic and tandem effects accounts for such selectivity. These findings mark a step ahead towards understanding structure-property relationships in bimetallic catalysts for the CO2RR and their rational tuning to increase selectivity towards target products, especially alcohols.

Recent Advances in Interface Engineering for Electrocatalytic CO2 Reduction Reaction

Electrocatalytic CO₂ reduction reaction (CO₂RR) can store and transform the intermittent renewable energy in the form of chemical energy for industrial production of chemicals and fuels, which can dramatically reduce CO₂ emission and contribute to carbon-neutral cycle. Efficient electrocatalytic reduction of chemically inert CO₂ is challenging from thermodynamic and kinetic points of view. Therefore, low-cost, highly efficient, and readily available electrocatalysts have been the focus for promoting the conversion of CO₂. Very recently, interface engineering has been considered as a highly effective strategy to modulate the electrocatalytic performance through electronic and/or structural modulation, regulations of electron/proton/mass/intermediates, and the control of local reactant concentration, thereby achieving desirable reaction pathway, inhibiting competing hydrogen generation, breaking binding-energy scaling relations of intermediates, and promoting CO₂ mass transfer. In this review, we aim to provide a comprehensive overview of current developments in interface engineering for CO₂RR from both a theoretical and experimental standpoint, involving interfaces between metal and metal, metal and metal oxide, metal and nonmetal, metal oxide and metal oxide, organic molecules and inorganic materials, electrode and electrolyte, molecular catalysts and electrode, etc. Finally, the opportunities and challenges of interface engineering for CO₂RR are proposed.

Cation-Deficiency-Dependent CO2 Electroreduction over Copper-Based Ruddlesden-Popper Perovskite Oxides

We report an effective strategy to enhance CO₂ electroreduction (CER) properties of Cu-based Ruddlesden-Popper (RP) perovskite oxides by engineering their A-site cation deficiencies. With La_2-x CuO_4-δ (L_2-x C, x=0, 0.1, 0.2, and 0.3) as proof-of-concept catalysts, we demonstrate that their CER activity and selectivity (to C₂₊ or CH₄ ) show either a volcano-type or an inverted volcano-type dependence on the x values, with the extreme point at x=0.1. Among them, at -1.4 V, the L_1.9 C delivers the optimal activity (51.3 mA cm^-2 ) and selectivity (41.5 %) for C₂₊ , comparable to or better than those of most reported Cu-based oxides, while the L_1.7 C exhibits the best activity (25.1 mA cm^-2 ) and selectivity (22.1 %) for CH₄ . Such optimized CER properties could be ascribed to the favorable merits brought by the cation-deficiency-induced oxygen vacancies and/or CuO/RP hybrids, including the facilitated adsorption/activation of key reaction species and thus the manipulated reaction pathways.

Selective visible-light driven highly efficient photocatalytic reduction of CO2 to C2H5OH by two-dimensional Cu2S monolayers

Solar-driven highly-efficient photocatalytic reduction of CO2 into value-added fuels has been regarded as a promising strategy to assuage the current global warming and energy crisis, but developing highly product-selective, long-term stable and low-cost photocatalysts for C2 production remains a grand challenge. Herein, we demonstrate that two-dimensional β- and δ-phase Cu2S monolayers are promising photocatalysts for the reduction of CO2 into C2H5OH. The calculated potential-limiting steps for the CO2 reduction reaction (CO2RR) are less than 0.50 eV, while those for the hydrogen evolution reaction are as high as 1.53 and 0.87 eV. Most strikingly, the C-C coupling only needs to overcome an ultra-low kinetic barrier of ∼0.30 eV, half of that on the Cu surface, indicating that they can boost the C2H5OH conversion efficiency greatly. Besides, these catalysts also exhibit satisfactory band edge positions and suitable visible light absorption, rendering them ideal for the visible light driven CO2RR. Our work not only provides a promising photocatalyst for achieving the efficient and selective CO2RR, but also brings new opportunities for advanced sustainable C2H5OH product.

Noble-Metal-Free Multicomponent Nanointegration for Sustainable Energy Conversion

Global energy and environmental crises are among the most pressing challenges facing humankind. To overcome these challenges, recent years have seen an upsurge of interest in the development and production of renewable chemical fuels as alternatives to the nonrenewable and high-polluting fossil fuels. Photocatalysis, photoelectrocatalysis, and electrocatalysis provide promising avenues for sustainable energy conversion. Single- and dual-component catalytic systems based on nanomaterials have been intensively studied for decades, but their intrinsic weaknesses hamper their practical applications. Multicomponent nanomaterial-based systems, consisting of three or more components with at least one component in the nanoscale, have recently emerged. The multiple components are integrated together to create synergistic effects and hence overcome the limitation for outperformance. Such higher-efficiency systems based on nanomaterials will potentially bring an additional benefit in balance-of-system costs if they exclude the use of noble metals, considering the expense and sustainability. It is therefore timely to review the research in this field, providing guidance in the development of noble-metal-free multicomponent nanointegration for sustainable energy conversion. In this work, we first recall the fundamentals of catalysis by nanomaterials, multicomponent nanointegration, and reactor configuration for water splitting, CO₂ reduction, and N₂ reduction. We then systematically review and discuss recent advances in multicomponent-based photocatalytic, photoelectrochemical, and electrochemical systems based on nanomaterials. On the basis of these systems, we further laterally evaluate different multicomponent integration strategies and highlight their impacts on catalytic activity, performance stability, and product selectivity. Finally, we provide conclusions and future prospects for multicomponent nanointegration. This work offers comprehensive insights into the development of cost-competitive multicomponent nanomaterial-based systems for sustainable energy-conversion technologies and assists researchers working toward addressing the global challenges in energy and the environment.