Stabilizing Cu2+ Ions by Solid Solutions to Promote CO2 Electroreduction to Methane

Dicopper(I) Sites Confined in a Single Metal-Organic Layer Boosting the Electroreduction of CO2 to CH4 in a Neutral Electrolyte

It is challenging and important to achieve high performance for an electrochemical CO2 reduction reaction (eCO2RR) to yield CH4 under neutral conditions. So far, most of the reported active sites for eCO2RR to yield CH4 are single metal sites; the performances are far below the commercial requirements. Herein, we reported a nanosheet metal-organic layer in single-layer, namely, [Cu2(obpy)2] (Cuobpy-SL, Hobpy = 1H-[2,2']bipyridinyl-6-one), possessing dicopper(I) sites for eCO2RR to yield CH4 in a neutral aqueous solution. Detailed examination of Cuobpy-SL revealed high performance for CH4 production with a faradic efficiency of 82(1)% and a current density of ∼90 mA cm-2 at -1.4 V vs. reversible hydrogen electrode (RHE). No obvious degradation was observed over 100 h of continuous operation, representing a remarkable performance to date. Mechanism studies showed that compared with the conventional single-copper sites and completely exposed dicopper(I) sites, the dicopper(I) sites in the confined space formed by the molecular stacking have a strong affinity to key C1 intermediates such as *CO, *CHO, and *CH2O to facilitate the CH4 production, yet inhibiting C-C coupling.

Restraining Interfacial Cu2+ by using Amorphous SnO2 as Sacrificial Protection Boosts CO2 Electroreduction

The electrochemical carbon dioxide reduction reaction (CO2 RR) to formate is of great interest in the field of electrochemical energy. Cu-based material is an appealing electrocatalyst for the CO2 RR. However, retaining Cu2+ under the high cathodic potential of CO2 RR remains a great challenge, leading to low electrocatalytic selectivity, activity, and stability. Herein, inspired by corrosion science, a sacrificial protection strategy to stabilize interfacial crystalline CuO through embedding of active amorphous SnO2 (c-CuO/a-SnO2 ) is reported, which greatly boosts the electrocatalytic sensitivity, activity, and stability for CO2 RR to formate. The as-made hybrid catalyst can achieve superior high selectivity for CO2 RR to formate with a remarkable Faradaic efficiency (FE) of 96.7%, and a superhigh current density of over 1 A cm-2 that far outperforms industrial benchmarks (FE > 90%, current density > 300 mA cm-2 ). In situ X-ray absorption spectroscopy (XAS) and X-ray diffractionexperimental and theoretical calculation results reveal that the broadened s-orbital in interfacial a-SnO2 offers the lower orbital for extra electrons than Cu2+ , which can effectively retain nearby Cu2+ , and the high active interface significantly lowers the energy barrier of the limited step (* CO2 → * HCOO) and enhances the selectivity and activity for CO2 RR to formate.

Ceo2 /Cus Nanoplates Electroreduce Co2 to Ethanol with Stabilized Cu+ Species

Copper-based electrocatalysts effectively produce multicarbon (C2+ ) compounds during the electrochemical CO2 reduction (CO2 RR). However, big challenges still remain because of the chemically unstable active sites. Here, cerium is used as a self-sacrificing agent to stabilize the Cu+ of CuS, due to the facile Ce3+ /Ce4+ redox. CeO2 -modified CuS nanoplates achieve high ethanol selectivity, with FE up to 54% and FEC2+ ≈ 75% in a flow cell. Moreover, in situ Raman spectroscopy and in situ Fourier-transform infrared spectroscopy indicate that the stable Cu+ species promote CC coupling step under CO2 RR. Density functional theory calculations further reveal that the stronger * CO adsorption and lower CC coupling energy, which is conducive to the selective generation of ethanol products. This work provides a facile strategy to convert CO2 into ethanol by retaining Cu+ species.

Operando Mössbauer Spectroscopic Tracking the Metastable State of Atomically Dispersed Tin in Copper Oxide for Selective CO2 Electroreduction

Metastable state is the most active catalyst state that dictates the overall catalytic performance and rules of catalytic behaviors; however, identification and stabilization of the metastable state of catalyst are still highly challenging due to the continuous evolution of catalytic sites during the reaction process. In this work, operando 119Sn Mössbauer measurements and theoretical simulations were performed to track and identify the metastable state of single-atom Sn in copper oxide (Sn1-CuO) for highly selective CO2 electroreduction to CO. A maximum CO Faradaic efficiency of around 98% at -0.8 V (vs. RHE) over Sn1-CuO was achieved at an optimized Sn loading of 5.25 wt. %. Operando Mössbauer spectroscopy clearly identified the dynamic evolution of atomically dispersed Sn4+ sites in the CuO matrix that enabled the in situ transformation of Sn4+-O4-Cu2+ to a metastable state Sn4+-O3-Cu+ under CO2RR conditions. In combination with quasi in situ X-ray photoelectron spectroscopy, operando Raman and attenuated total reflectance surface enhanced infrared absorption spectroscopies, the promoted desorption of *CO over the Sn4+-O3 stabilized adjacent Cu+ site was evidenced. In addition, density functional theory calculations further verified that the in situ construction of Sn4+-O3-Cu+ as the true catalytic site altered the reaction path via modifying the adsorption configuration of the *COOH intermediate, which effectively reduced the reaction free energy required for the hydrogenation of CO2 and the desorption of the *CO, thereby greatly facilitating the CO2-to-CO conversion. This work provides a fundamental insight into the role of single Sn atoms on in situ tuning the electronic structure of Cu-based catalysts, which may pave the way for the development of efficient catalysts for high-selectivity CO2 electroreduction.

Al-Doped Octahedral Cu2O Nanocrystal for Electrocatalytic CO2 Reduction to Produce Ethylene

Ethylene is an ideal CO2 product in an electrocatalytic CO2 reduction reaction (CO2RR) with high economic value. This paper synthesised Al-doped octahedral Cu2O (Al-Cu2O) nanocrystal by a simple wet chemical method. The selectivity of CO2RR products was improved by doping Al onto the surface of octahedral Cu2O. The Al-Cu2O was used as an efficient electrocatalyst for CO2RR with selective ethylene production. The Al-Cu2O exhibited a high % Faradic efficiency (FEC2H4) of 44.9% at -1.23 V (vs. RHE) in CO2 saturated 0.1 M KHCO3 electrolyte. Charge transfer from the Al atom to the Cu atom occurs after Al doping in Cu2O, optimizing the electronic structure and facilitating CO2RR to ethylene production. The DFT calculation showed that the Al-Cu2O catalyst could effectively reduce the adsorption energy of the *CHCOH intermediate and promote the mass transfer of charges, thus improving the FEC2H4. After Al doping into Cu2O, the center of d orbitals shift positively, which makes the d-band closer to the Fermi level. Furthermore, the density of electronic states increases due to the interaction between Cu atoms and intermediates, thus accelerating the electrochemical CO2 reduction process. This work proved that the metal doping strategy can effectively improve the catalytic properties of Cu2O, thus providing a useful way for CO2 cycling and green production of C2H4.

A Surfactant-Free and General Strategy for the Synthesis of Bimetallic Core-Shell Nanocrystals on Reduced Graphene Oxide through Targeted Photodeposition

Tunable physicochemical properties of bimetallic core-shell heterostructured nanocrystals (HNCs) have shown enormous potential in electrocatalytic reactions. In many cases, HNCs are required to load on supports to inhibit catalyst aggregation. However, the introduction of supports during the process of growing core-shell HNCs makes the synthesis much more complicated and difficult to control precisely. Herein, we reported a universal photochemical synthetic strategy for the controlled synthesis of well-defined surfactant-free core-shell metal HNCs on a reduced graphene oxide (rGO) support, which was assisted by the fine control of photogenerated electrons directly transferring to the targeted metal seeds via rGO and the precisely tuned adsorption capacity of the added second metal precursors. The surface photovoltage microscopy (SPVM) platform proved that photogenerated electrons flowed through rGO to Pd particles under illumination. We have successfully synthesized 24 different core-shell metal HNCs, i.,e., M_A@M_B (M_A = Pd, Au, and Pt; M_B = Au, Ag, Pt, Pd, Ir, Ru, Rh, Ni and Cu), on the rGO supports. The as-prepared Pd@Cu core-shell HNCs showed outstanding performance in the electrocatalytic reduction of CO₂ to CH₄. This work could shed light on the controlled synthesis of more functional bimetallic nanostructured materials on diverse supports for various applications.

Single-site decorated copper enables energy- and carbon-efficient CO2 methanation in acidic conditions

Renewable CH₄ produced from electrocatalytic CO₂ reduction is viewed as a sustainable and versatile energy carrier, compatible with existing infrastructure. However, conventional alkaline and neutral CO₂-to-CH₄ systems suffer CO₂ loss to carbonates, and recovering the lost CO₂ requires input energy exceeding the heating value of the produced CH₄. Here we pursue CH₄-selective electrocatalysis in acidic conditions via a coordination method, stabilizing free Cu ions by bonding Cu with multidentate donor sites. We find that hexadentate donor sites in ethylenediaminetetraacetic acid enable the chelation of Cu ions, regulating Cu cluster size and forming Cu-N/O single sites that achieve high CH₄ selectivity in acidic conditions. We report a CH₄ Faradaic efficiency of 71% (at 100 mA cm^-2) with <3% loss in total input CO₂ that results in an overall energy intensity (254 GJ/tonne CH₄), half that of existing electroproduction routes.

An Efficient Strategy for Electroreduction Reactor Outlet Fractioning into Valuable Products

In this work, two industrial dual-step pressure swing adsorption (PSA) processes were designed and simulated to obtain high-purity methane, CO₂, and syngas from a gas effluent of a CO₂ electroreduction reactor using different design configurations. Among the set of zeolites that was investigated using Monte Carlo and molecular dynamics simulations, NaX and MFI were the ones selected. The dual-PSA process for case study 1 is only capable of achieving a 90.5% methane purity with a 95.2% recovery. As for case study 2, methane is obtained with a 97.5% purity and 95.3% recovery. Both case studies can produce CO₂ with high purity and recovery (>97 and 95%, respectively) and syngas with a H₂/CO ratio above 4. Although case study 2 allows methane to be used as domestic gas, a much higher value for its energy consumption is observed compared to case study 1 (64.9 vs 29.8 W h mol_CH4^-1).

Dynamic Reconstitution Between Copper Single Atoms and Clusters for Electrocatalytic Urea Synthesis

Electrocatalytic CN coupling between carbon dioxide and nitrate has emerged to meet the comprehensive demands of carbon footprint closing, valorization of waste, and sustainable manufacture of urea. However, the identification of catalytic active sites and the design of efficient electrocatalysts remain a challenge. Herein, the synthesis of urea catalyzed by copper single atoms decorated on a CeO₂ support (denoted as Cu₁ -CeO₂ ) is reported. The catalyst exhibits an average urea yield rate of 52.84 mmol h^-1 g_cat. ^-1 at -1.6 V versus reversible hydrogen electrode. Operando X-ray absorption spectra demonstrate the reconstitution of copper single atoms (Cu₁ ) to clusters (Cu₄ ) during electrolysis. These electrochemically reconstituted Cu₄ clusters are real active sites for electrocatalytic urea synthesis. Favorable CN coupling reactions and urea formation on Cu₄ are validated using operando synchrotron-radiation Fourier transform infrared spectroscopy and theoretical calculations. Dynamic and reversible transformations of clusters to single-atom configurations occur when the applied potential is switched to an open-circuit potential, endowing the catalyst with superior structural and electrochemical stabilities.

Probing and Leveraging the Structural Heterogeneity of Nanomaterials for Enhanced Catalysis

The marriage between nanoscience and heterogeneous catalysis has introduced transformative opportunities for accessing better nanocatalysts. However, the structural heterogeneity of nanoscale solids stemming from distinct atomic configurations makes it challenging to realize atomic-level engineering of nanocatalysts in the way that is attained for homogeneous catalysis. Here, we discuss recent efforts in unveiling and exploiting the structural heterogeneity of nanomaterials for enhanced catalysis. Size and facet control of nanoscale domains produce well-defined nanostructures that facilitate mechanistic studies. Differentiation of surface and bulk characteristics for ceria-based nanocatalysts guides new thoughts toward lattice oxygen activation. Manipulating the compositional and species heterogeneity between local and average structures allows regulation of catalytically active sites via the ensemble effect. Studies on catalyst restructurings further highlight the necessity to assess the reactivity and stability of nanocatalysts under reaction conditions. These advances promote the development of novel nanocatalysts with expanded functionalities and bring atomistic insights into heterogeneous catalysis.

Charge-Separated Pdδ--Cuδ+ Atom Pairs Promote CO2 Reduction to C2

Positively charged Cu sites have been confirmed to significantly promote the production of multicarbon (C₂) products from an electrochemical CO₂ reduction reaction (CO₂RR). However, the positively charged Cu has difficulty in existing under a strong negative bias. In this work, we design a Pd^δ--Cu₃N catalyst containing charge-separated Pd^δ--Cu^δ+ atom pair that can stabilize the Cu^δ+ sites. In situ characterizations and density functional theory reveal that the first reported negatively charged Pd^δ- sites exhibited a superior CO binding capacity together with the adjacent Cu^δ+ sites, synergistically promoting the CO dimerization process to produce C₂ products. As a result, we achieve a 14-fold increase in the C₂ product Faradaic efficiency (FE) on Pd^δ--Cu₃N, from 5.6% to 78.2%. This work provides a new strategy for synthesizing negative valence atom-pair catalysts and an atomic-level modulation approach of unstable Cu^δ+ sites in the CO₂RR.

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.

Cu+-Mediated CO Coordination for Promoting C-C Coupling for CO2 and CO Electroreduction

Selective electrochemical upgrading of CO₂ to multicarbon (C₂₊) products requires a C-C coupling process, yet the underlying promoting mechanism of widely involved Cu oxidation states remains largely unclear, hindering the subtle design of efficient catalysts. Herein, we unveil the critical role of Cu⁺ in promoting C-C coupling via coordination with a CO intermediate during electrochemical CO₂ reduction. We find that, relative to other halogen anions, iodide (I^-) in HCO₃^- electrolytes accelerates the generation of strongly oxidative hydroxyl radicals that accounts for the formation of Cu⁺, which can be dynamically stabilized by I^- via the formation of CuI. The in situ generated CO intermediate strongly binds to CuI sites, forming nonclassical Cu(CO)_n⁺ complexes, leading to an approximately 3.0-fold increase of C₂₊ Faradaic efficiency at -0.9 V_RHE relative to that of I^--free Cu surfaces. Accordingly, a deliberate introduction of CuI into I^--containing HCO₃^- electrolytes for direct CO electroreduction brings about a 4.3-fold higher C₂₊ selectivity. This work provides insights into the role of Cu⁺ in C-C coupling and the enhanced C₂₊ selectivity for CO₂ and CO electrochemical reduction.

CeO2 Promotes CO2 Electroreduction to Formate on Bi2S3 via Tuning of the *OCHO Intermediate

Formate is identified as economically viable chemical fuel from electrochemical carbon dioxide reduction. However, the selectivity of current catalysts toward formate is limited by the competitive reaction such as HER. Herein, we propose a CeO₂ modification strategy to improve the selectivity of catalysts for formate through tuning of the *OCHO intermediate, which is important for formate production.

Alloying as a Strategy to Boost the Stability of Copper Nanocatalysts during the Electrochemical CO2 Reduction Reaction

Copper nanocatalysts are among the most promising candidates to drive the electrochemical CO₂ reduction reaction (CO₂RR). However, the stability of such catalysts during operation is sub-optimal, and improving this aspect of catalyst behavior remains a challenge. Here, we synthesize well-defined and tunable CuGa nanoparticles (NPs) and demonstrate that alloying Cu with Ga considerably improves the stability of the nanocatalysts. In particular, we discover that CuGa NPs containing 17 at. % Ga preserve most of their CO₂RR activity for at least 20 h while Cu NPs of the same size reconstruct and lose their CO₂RR activity within 2 h. Various characterization techniques, including X-ray photoelectron spectroscopy and operando X-ray absorption spectroscopy, suggest that the addition of Ga suppresses Cu oxidation at open-circuit potential (ocp) and induces significant electronic interactions between Ga and Cu. Thus, we explain the observed stabilization of the Cu by Ga as a result of the higher oxophilicity and lower electronegativity of Ga, which reduce the propensity of Cu to oxidize at ocp and enhance the bond strength in the alloyed nanocatalysts. In addition to addressing one of the major challenges in CO₂RR, this study proposes a strategy to generate NPs that are stable under a reducing reaction environment.

Electron-Rich Bi Nanosheets Promote CO2 ⋅- Formation for High-Performance and pH-Universal Electrocatalytic CO2 Reduction

Electrochemical CO₂ reduction reaction (CO₂ RR) to chemical fuels such as formate offers a promising pathway to carbon-neutral future, but its practical application is largely inhibited by the lack of effective activation of CO₂ molecules and pH-universal feasibility. Here, we report an electronic structure manipulation strategy to electron-rich Bi nanosheets, where electrons transfer from Cu donor to Bi acceptor in bimetallic Cu-Bi, enabling CO₂ RR towards formate with concurrent high activity, selectivity and stability in pH-universal (acidic, neutral and alkaline) electrolytes. Combined in situ Raman spectra and computational calculations unravel that electron-rich Bi promotes CO₂ ⋅^- formation to activate CO₂ molecules, and enhance the adsorption strength of *OCHO intermediate with an up-shifted p-band center, thus leading to its superior activity and selectivity of formate. Further integration of the robust electron-rich Bi nanosheets into III-V-based photovoltaic solar cell results in an unassisted artificial leaf with a high solar-to-formate (STF) efficiency of 13.7 %.

Rational design of atomic site catalysts for electrochemical CO2 reduction

Renewable-energy-powered electrochemical CO₂ reduction (ECR) is a promising way of transforming CO₂ to value-added products and achieving sustainable carbon recycling. By virtue of the extremely high exposure rate of active sites and excellent catalytic performance, atomic site catalysts (ASCs), including single-atomic site catalysts and diatomic site catalysts, have attracted considerable attention. In this feature article, we focus on the rational design strategies of ASCs developed in recent years for the ECR reaction. The influence of these strategies on the activity and selectivity of ASCs for ECR is further discussed in terms of electronic regulation, synergistic activation, microenvironmental regulation and tandem catalytic system construction. Finally, the challenges and future directions are indicated. We hope that this feature article will be helpful in the development of novel ASCs for ECR.

Catalysts Based on Ni(Mg)Al-Layered Hydroxides Prepared by Mechanical Activation for Furfural Hydrogenation

Ni(Mg)Al-layered hydroxides with molar ratios of (Ni + Mg)/Al = 2, 3, 4 and Ni/(Ni + Mg) = 0.1, 0.3, 0.5, 0.7 were synthesized by mechanochemical activation. It has been proven that the phase composition of the samples was presented by a single hydrotalcite phase up to Ni/(Ni + Mg) = 0.5. For the first time, catalysts based on Ni(Mg)Al-layered hydroxides prepared by a mechanochemical route have been studied in the reaction of furfural hydrogenation. The correlation between furfural conversion, the selectivity of the products, and the composition of the catalysts was established. The effect of phase composition, surface morphology, and microstructure on the activity of the catalysts was shown by XRD, SEM, and TEM. It was found that catalysts with Ni/(Ni + Mg) = 0.5 have the highest furfural conversion. Herewith, the product selectivity can be regulated by the (Ni + Mg)/Al ratio.

Highly Selective CO2 Electroreduction to C2+ Products over Cu2O-Decorated 2D Metal-Organic Frameworks with Rich Heterogeneous Interfaces

The electroreduction of carbon dioxide into high-value-added products is an effective approach to alleviating the energy crisis and pollution issues. However, there are still significant challenges for multicarbon (C₂₊) product production due to the lack of efficient catalysts with high selectivity. Herein, a Cu-rich electrocatalyst, where Cu₂O nanoparticles are decorated on two-dimensional (2D) Cu-BDC metal-organic frameworks (MOFs) with abundant heterogeneous interfaces, is synthesized for highly selective CO₂ electroreduction into C₂₊ products. A high C₂₊ Faradaic efficiency of 72.1% in an H-type cell and 58.2% in a flow cell are obtained, respectively. The heterogeneous interfaces of Cu₂O/Cu-BDC can optimize the adsorption energy of reaction intermediates during CO₂ electroreduction. An in situ infrared spectroscopy study indicates that the constructed interfaces can maintain the particular distribution of Cu valence states, where the C-C coupling is promoted to efficiently produce C₂₊ products owing to the stabilization of *CHO and *COH intermediates.

Wurtzite CuGaS2 with an In-Situ-Formed CuO Layer Photocatalyzes CO2 Conversion to Ethylene with High Selectivity

We present surface reconstruction-induced C-C coupling whereby CO₂ is converted into ethylene. The wurtzite phase of CuGaS_2. undergoes in situ surface reconstruction, leading to the formation of a thin CuO layer over the pristine catalyst, which facilitates selective conversion of CO₂ to ethylene (C₂ H₄ ). Upon illumination, the catalyst efficiently converts CO₂ to C₂ H₄ with 75.1 % selectivity (92.7 % selectivity in terms of R_electron ) and a 20.6 μmol g^-1  h^-1 evolution rate. Subsequent spectroscopic and microscopic studies supported by theoretical analysis revealed operando-generated Cu²⁺ , with the assistance of existing Cu⁺ , functioning as an anchor for the generated *CO and thereby facilitating C-C coupling. This study demonstrates strain-induced in situ surface reconstruction leading to heterojunction formation, which finetunes the oxidation state of Cu and modulates the CO₂ reduction reaction pathway to selective formation of ethylene.

Pushing the Performance Limit of Cu/CeO2 Catalyst in CO2 Electroreduction: A Cluster Model Study for Loading Single Atoms

Pushing the performance limit of catalysts is a major goal of CO₂ electroreduction toward practical application. A single-atom catalyst is recognized as a solution for achieving this goal, which is, however, a double-edged sword considering the limited loading amount and stability of single-atom sites. To overcome the limit, the loading of single atoms on supports should be well addressed, requiring a suitable model system. Herein, we report the model system of an ultrasmall CeO₂ cluster (2.4 nm) with an atomic precise structure and a high surface-to-volume ratio for loading Cu single atoms. The combination of multiple characterizations and theoretical calculations reveals the loading location and limit of Cu single atoms on CeO₂ clusters, determining an optimal configuration for CO₂ electroreduction. The optimal catalyst achieves a maximum Faradaic efficiency (FE) of 67% and a maximum partial current density of -364 mA/cm² for CH₄, and can maintain high CH₄ FE values over 50% in a wide range of applied current densities (-50 ∼ -600 mA/cm²), exceeding those of the reported catalysts.

Graphdiyne-Based Single-Atom Catalysts with Different Coordination Environments

As a special carbon material, graphdiyne (GDY) features the superiorities of incomplete charge transfer effect on the atomic level, tunable electronic structure and anchoring metal atoms directly with organometallic coordination bonds M (metal)-C (alkynyl carbon in GDY), providing it an ideal platform to construct single-atom catalysts (ACs). The coordination environment of single atoms anchored on GDY plays a key role in their catalytic performance. The mini-review highlights state-of-the-art progress in the rational design of GDY-based ACs and their applications, and mainly reveals the relationship between the coordination engineering of the GDY-based ACs and corresponding catalytic performance. Finally, some prospects concerning the future development of GDY-based ACs in energy conversion are also discussed.

Asymmetric Low-Frequency Pulsed Strategy Enables Ultralong CO2 Reduction Stability and Controllable Product Selectivity

Copper-based catalysts are widely explored in electrochemical CO₂ reduction (CO₂RR) because of their ability to convert CO₂ into high-value-added multicarbon products. However, the poor stability and low selectivity limit the practical applications of these catalysts. Here, we proposed a simple and efficient asymmetric low-frequency pulsed strategy (ALPS) to significantly enhance the stability and the selectivity of the Cu-dimethylpyrazole complex Cu₃(DMPz)₃ catalyst in CO₂RR. Under traditional potentiostatic conditions, Cu₃(DMPz)₃ exhibited poor CO₂RR performance with the Faradaic efficiency (FE) of 34.5% for C₂H₄ and FE of 5.9% for CH₄ as well as the low stability for less than 1 h. We optimized two distinguished ALPS methods toward CH₄ and C₂H₄, correspondingly. The high selectivities of catalytic product CH₄ (FE_CH4 = 80.3% and above 76.6% within 24 h) and C₂H₄ (FE_C2H4 = 70.7% and above 66.8% within 24 h) can be obtained, respectively. The ultralong stability for 300 h (FE_CH4 > 60%) and 145 h (FE_C2H4 > 50%) was also recorded with the ALPS method. Microscopy (HRTEM, SAED, and HAADF) measurements revealed that the ALPS method in situ generated and stabilized extremely dispersive and active Cu-based clusters (∼2.7 nm) from Cu₃(DMPz)₃. Meanwhile, ex situ spectroscopies (XPS, AES, and XANES) and in situ XANES indicated that this ALPS method modulated the Cu oxidation states, such as Cu(0 and I) with C₂H₄ selectivity and Cu(I and II) with CH₄ selectivity. The mechanism under the ALPS methods was explored by in situ ATR-FTIR, in situ Raman, and DFT computation. The ALPS methods provide a new opportunity to boost the selectivity and stability of CO₂RR.

Atomically Incorporating Ni into Mesoporous CeO2 Matrix via Synchronous Spray-Pyrolysis as Efficient Noble-Metal-Free Catalyst for Low-Temperature CO Oxidation

Low-temperature catalytic CO oxidation is an important chemical process in versatile applications, such as the H₂ utilization for low-temperature H₂ air fuel cells. Pt-group metal catalysts are efficient but highly cost-consuming. This work demonstrates an excellent and sixpenny catalyst with earth-abundant Ni and Ce, in which Ni ions are atomically incorporated into the CeO₂ matrix (Ni-Ce-O_x) by synchronous spray-pyrolysis (SSP) of mixture nitrates of Ni and Ce. The Ni-Ce-O_x catalyst presents a mesoporous structure. Revealed by a model reaction of 1% CO, 1% O₂, and 98% balance He at a space velocity of 13,200 mL/g_cat/h, Ni-Ce-O_x catalysts display a typical volcano-shaped relationship between reactivity and Ni incorporation amount. The optimized Ni incorporation appears with a high Ni/Ce atomic ratio of 0.25, endowing the T₅₀ (temperature corresponding to a CO conversion of 50%), which is lower-shifted by 165 °C than that of pristine CeO₂ (266 °C). The density functional theory (DFT) calculations further indicate that the much-reduced oxygen vacancy formation energy at Ni-Ce single-atom sites boosted the adsorption activation of the CO molecule and therefore promoted the CO oxidation process. Besides, the₂ Ni-Ce-O_x from the SSP method presents better performance than the counterparts from immersion and hydrothermal methods. This work paves a way to access efficient noble-metal-free catalysts for low-temperature CO oxidation.

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.

Demystifying the roles of single metal site and cluster in CO2 reduction via light and electric dual-responsive polyoxometalate-based metal-organic frameworks

Photo- or electroreduction of carbon dioxide into highly valued products offers a promising strategy to achieve carbon neutrality. Here, a series of polyoxometalate-based metal-organic frameworks (M-POMOFs) were constructed by metalloporphyrins [tetrakis(4-carboxyphenyl)-porphyrin-M (M-TCPPs)] and reductive POM for photo- and electrocatalytic carbon dioxide reductions (PCR and ECR, respectively), and the mysteries between the roles of single metal site and cluster in catalysis were disclosed. Iron-POMOF exhibited an excellent selectivity (97.2%) with high methane production of 922 micromoles per gram in PCR, together with superior Faradaic efficiency for carbon dioxide to carbon monoxide (92.1%) in ECR. The underlying mechanisms were further clarified. Photogenerated electrons transferred from iron-TCPP to the POM cluster for methane generation under irradiation, while the abundant electrons flowed to the center of iron-TCPP for carbon monoxide formation under the applied electric field. The specific multielectron products generated on iron-POMOF through switching driving forces to control electron flow direction between single metal site and cluster catalysis.

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.

Sn Dopants with Synergistic Oxygen Vacancies Boost CO2 Electroreduction on CuO Nanosheets to CO at Low Overpotential

Using the electrochemical CO₂ reduction reaction (CO₂RR) with Cu-based electrocatalysts to achieve carbon-neutral cycles remains a significant challenge because of its low selectivity and poor stability. Modulating the surface electron distribution by defects engineering or doping can effectively improve CO₂RR performance. Herein, we synthesize the electrocatalyst of V_o-CuO(Sn) nanosheets containing oxygen vacancies and Sn dopants for application in CO₂RR-to-CO. Density functional theory calculations confirm that the incorporation of oxygen vacancies and Sn atoms substantially reduces the energy barrier for *COOH and *CO intermediate formation, which results in the high efficiency, low overpotential, and superior stability of the CO₂RR to CO conversion. This electrocatalyst possesses a high Faraday efficiency (FE) of 99.9% for CO at a low overpotential of 420 mV and a partial current density of up to 35.22 mA cm^-2 at -1.03 V versus reversible hydrogen electrode (RHE). The FE_CO of V_o-CuO(Sn) could retain over 95% within a wide potential area from -0.48 to -0.93 V versus RHE. Moreover, we obtain long-term stability for more than 180 h with only a slight decay in its activity. Therefore, this work provides an effective route for designing environmentally friendly electrocatalysts to improve the selectivity and stability of the CO₂RR to CO conversion.

Tuning the Micro-coordination Environment of Al in Dealumination Y Zeolite to Enhance Electron Transfer at the Cu-Mn Oxides Interface for Highly Efficient Catalytic Ozonation of Toluene at Low Temperatures

The development of stable, highly active, and inexpensive catalysts for the ozone catalytic oxidation of volatile organic compounds (VOCs) is challenging but of great significance. Herein, the micro-coordination environment of Al in commercial Y zeolite was regulated by a specific dealumination method and then the dealuminated Y zeolite was used as the support of Cu-Mn oxides. The optimized catalyst Cu-Mn/DY exhibited excellent performance with around 95% of toluene removal at 30 °C. Besides, the catalyst delivered satisfactory stability in both high-humidity conditions and long-term reactions, which is attributed to more active oxygen vacancies and acidic sites, especially the strong Lewis acid sites newly formed in the catalyst. The decrease in the electron cloud density around aluminum species enhanced electron transfer at the interface between Cu-Mn oxides. Moreover, extra-framework octahedrally coordinated Al in the support promoted the electronic metal-support interaction (EMSI). Compared with single Mn catalysts, the incorporation of the Cu component changed the degradation pathway of toluene. Benzoic acid, as the intermediate of toluene oxidation, can directly ring-open on Cu-doped catalysts rather than being further oxidized to other byproducts, which increased the rate of the catalytic reaction. This work provides a new insight and theoretical guidance into the rational design of efficient catalysts for the catalytic ozonation of VOCs.

Emerging Applications of Synchrotron Radiation X-Ray Techniques in Single Atomic Catalysts

Single atom catalysts (SACs) can achieve a maximum atom utilization efficiency of 100%, which provides significantly increased active sites compared with traditional catalysts during catalytic reactions. Synchrotron radiation technology is an important characterization method for identifying single-atom catalysts. Several types of internal information, such as the coordination number, bond length and electronic structure of metals, can all be analyzed. This review will focus on the introduction of synchrotron radiation techniques and their applications in SACs. First, the fundamentals of synchrotron radiation and the corresponding techniques applied in characterization of SACs will be briefly introduced, such as X-ray absorption near edge spectroscopy and extended X-ray absorption fine structure spectroscopy and in situ techniques. The detailed information obtained from synchrotron radiation X-ray characterization is described through four routes: 1) the local environment of a specific atom; 2) the oxidation state of SACs; 3) electronic structures at different orbitals; and 4) the in situ structure modification during catalytic reaction. In addition, a systematic summary of synchrotron radiation X-ray characterization on different types of SACs (noble metals and transition metals) will be discussed.

In situ resource utilization of lunar soil for highly efficient extraterrestrial fuel and oxygen supply

Building up a lunar settlement is the ultimate aim of lunar exploitation. Yet, limited fuel and oxygen supplies restrict human survival on the Moon. Herein, we demonstrate the in situ resource utilization of lunar soil for extraterrestrial fuel and oxygen production, which may power up our solely natural satellite and supply respiratory gas. Specifically, the lunar soil is loaded with Cu species and employed for electrocatalytic CO₂ conversion, demonstrating significant production of methane. In addition, the selected component in lunar soil (i.e. MgSiO₃) loaded with Cu can reach a CH₄ Faradaic efficiency of 72.05% with a CH₄ production rate of 0.8 mL/min at 600 mA/cm². Simultaneously, an O₂ production rate of 2.3 mL/min can be achieved. Furthermore, we demonstrate that our developed process starting from catalyst preparation to electrocatalytic CO₂ conversion is so accessible that it can be operated in an unmmaned manner via a robotic system. Such a highly efficient extraterrestrial fuel and oxygen production system is expected to push forward the development of mankind's civilization toward an extraterrestrial settlement.

Bicarbonate Rebalances the *COOH/*OCO- Dual Pathways in CO2 Electrocatalytic Reduction: In Situ Surface-Enhanced Raman Spectroscopic Evidence

Understanding the reactive site/CO₂/electrolyte interfacial behaviors is very crucial for the design of an advantageous CO₂ electrocatalytic reduction (CO₂ER) system. One important but unrevealed question is how the CO₂ER process is influenced by the high concentration of HCO₃^-, which is deliberately added as electrolyte or from the inevitable reaction between dissolved CO₂ and OH^-. Here, we provide unambiguous in situ spectroscopic evidence that on Ag-based catalysts, HCO₃^- is apt to facilitate *OCO^- generation and therefore rebalances CO₂ER pathways. By employing an alternative acid electrolyte to restrict the exchange between CO₂ and HCO₃^- and eliminating the effect of solution pH, we reveal that HCO₃^- can decrease the onset potential of *OCO^- and promote further formate production. Theoretical calculations indicate HCO₃^- can stabilize the adsorption of *OCO^- instead of *COOH. The renewed understanding of the role of HCO₃^- could facilitate the judicious selection of electrolytes to regulate the CO₂ER pathway and product distribution.

Electrocatalytic CO2-to-C2+ with Ampere-Level Current on Heteroatom-Engineered Copper via Tuning *CO Intermediate Coverage

An ampere-level current density of CO₂ electrolysis is critical to realize the industrial production of multicarbon (C₂₊) fuels. However, under such a large current density, the poor CO intermediate (*CO) coverage on the catalyst surface induces the competitive hydrogen evolution reaction, which hinders CO₂ reduction reaction (CO₂RR). Herein, we report reliable ampere-level CO₂-to-C₂₊ electrolysis by heteroatom engineering on Cu catalysts. The Cu-based compounds with heteroatom (N, P, S, O) are electrochemically reduced to heteroatom-derived Cu with significant structural reconstruction under CO₂RR conditions. It is found that N-engineered Cu (N-Cu) catalyst exhibits the best CO₂-to-C₂₊ productivity with a remarkable Faradaic efficiency of 73.7% under -1100 mA cm^-2 and an energy efficiency of 37.2% under -900 mA cm^-2. Particularly, it achieves a C₂₊ partial current density of -909 mA cm^-2 at -1.15 V versus reversible hydrogen electrode, which outperforms most reported Cu-based catalysts. In situ spectroscopy indicates that heteroatom engineering adjusts *CO adsorption on Cu surface and alters the local H proton consumption in solution. Density functional theory studies confirm that the high adsorption strength of *CO on N-Cu results from the depressed HER and promoted *CO adsorption on both bridge and atop sites of Cu, which greatly reduces the energy barrier for C-C coupling.

Electrochemical Reduction of CO2 With Good Efficiency on a Nanostructured Cu-Al Catalyst

Carbon monoxide (CO) and formic acid (HCOOH) are suggested to be the most convenient products from electrochemical reduction of CO2 according to techno-economic analysis. To date, tremendous advances have been achieved in the development of catalysts and processes, which make this research topic even more interesting to both academic and industrial sectors. In this work, we report nanostructured Cu-Al materials that are able to convert CO2 to CO and HCOOH with good efficiency. The catalysts are synthesized via a green microwave-assisted solvothermal route, and are composed of Cu2O crystals modified by Al. In KHCO3 electrolyte, these catalysts can selectively convert CO2 to HCOOH and syngas with H2/CO ratios between 1 and 2 approaching one unit faradaic efficiency in a wide potential range. Good current densities of 67 and 130 mA cm−2 are obtained at −1.0 V and −1.3 V vs. reversible hydrogen electrode (RHE), respectively. When switching the electrolyte to KOH, a significant selectivity up to 20% is observed for C2H4 formation, and the current densities achieve 146 and 222 mA cm−2 at −1.0 V and −1.3 V vs. RHE, respectively. Hence, the choice of electrolyte is critically important as that of catalyst in order to obtain targeted products at industrially relevant current densities.

In situ probing the dynamic reconstruction of copper-zinc electrocatalysts for CO2 reduction

Unravelling the dynamic characterization of electrocatalysts during the electrochemical CO₂ reduction reaction (CO₂RR) is a critical factor to improve the production efficiency and selectivity, since most pre-electrocatalysts undergo structural reconstruction and surface rearrangement under working conditions. Herein, a series of pre-electrocatalysts including CuO, ZnO and two different ratios of CuO/ZnO were systematically designed by a sputtering process to clarify the correlation of the dynamic characterization of Cu sites in the presence of Zn/ZnO and the product profile. The evidence provided by in situ X-ray absorption spectroscopy (XAS) indicated that appropriate Zn/ZnO levels could induce a variation in the coordination number of Cu sites via reversing Ostwald ripening. Specifically, the recrystallized Cu site with a lower coordination number exhibited a preferential production of methane (CH₄). More importantly, our findings provide a promising approach for the efficient production of CH₄ by in situ reconstructing Cu-based binary electrocatalysts.

In Situ Electrochemical Reconstitution of CF-CuO/CeO2 for Efficient Active Species Generation

Achievement of the intrinsic activity by in situ electrochemical reconstruction has been becoming a great challenge for designing a catalyst. Herein, an effective electrochemical strategy is proposed to reconstruct the surface of the CF-CuO/CeO₂ precursor. Under the stimulation of oxidative/reductive potential, abundant active sites were successfully generated on the surface of CF-CuO/CeO₂. Remarkably, the implantation of oxygen vacancy-rich CeO₂ synergistically optimizes the chemical composition and electronic structure of CF-CuO/CeO₂, greatly promoting the generation of active species. Systematic electrochemical experiments indicate that the superior catalytic performance of reconstructed CF-CuO/CeO₂ could be attributed to CuOOH/CeO₂ and Cu₂O/Ce₂O₃ active species, respectively. The oxidative-/reductive-activated CF-CuO/CeO₂ was further employed in a paired cell for the synergistic catalysis of hydroxymethylfurfural oxidation with 4-nitrophenol hydrogenation. As a result, nearly 100% Faraday efficiency for furandicarboxylic acid/4-aminophenol production was achieved in the paired system (-0.9 V vs Ag/AgCl, 1.5 h). Therefore, the electrochemical reconstruction via oxidative/reductive activation has been confirmed as a feasible approach to significantly excite the intrinsic activity of a catalyst.

Surface Modification of 2D Photocatalysts for Solar Energy Conversion

2D materials show many particular properties, such as high surface-to-volume ratio, high anisotropic degree, and adjustable chemical functionality. These unique properties in 2D materials have sparked immense interest due to their applications in photocatalytic systems, resulting in significantly enhanced light capture, charge-transfer kinetics, and surface reaction. Herein, the research progress in 2D photocatalysts based on varied compositions and functions, followed by specific surface modification strategies, is introduced. Fundamental principles focusing on light harvesting, charge separation, and molecular adsorption/activation in the 2D-material-based photocatalytic system are systemically explored. The examples described here detail the use of 2D materials in various photocatalytic energy-conversion systems, including water splitting, carbon dioxide reduction, nitrogen fixation, hydrogen peroxide production, and organic synthesis. Finally, by elaborating the challenges and possible solutions for developing these 2D materials, the review is expected to provide some inspiration for the future research of 2D materials used on efficient photocatalytic energy conversions.