Reduction Of CuO Research Articles

Self-Inhibition Phenomena in Cu3Pt Oxidation by CO2.

This study investigates the oxidation behavior of Cu3Pt(100) in CO2 using a combination of ambient-pressure X-ray photoelectron spectroscopy, mass spectroscopy, and density functional theory modeling. Our in situ measurements reveal the simultaneous oxidation and reduction of Cu2O due to the opposing effects of atomic oxygen and CO generated from dissociative CO2 adsorption, leading to a dynamic equilibrium state of simultaneously occurring redox reactions. Complementary atomistic calculations elucidate the inhibitory effects of subsurface Pt enrichment and the counteracting roles of CO2 and CO in surface oxidation and reduction. These results provide mechanistic insights into the dissociative pathway of CO2 molecules and dynamic evolution of surface composition and reactivity of Cu-based alloy catalysts in CO2-rich environments, with broader implications for tuning gas-surface reactions by manipulating gas reactants or solid surface composition.

Role of Structural and Compositional Changes of Cu2O Nanocubes in Nitrate Electroreduction to Ammonia.

Nitrate electroreduction reaction (NO3RR) to ammonia (NH3) still faces fundamental and technological challenges. While Cu-based catalysts have been widely explored, their activity and stability relationship are still not fully understood. Here, we systematically monitored the dynamic alterations in the chemical and morphological characteristics of Cu2O nanocubes (NCs) during NO3RR in an alkaline electrolyte. In 1 h of electrolysis from -0.10 to -0.60 V vs RHE, the electrocatalyst achieved the maximum NH3 faradaic efficiency (FE) and yield rate at -0.3 V (94% and 149 μmol h-1 cm-2, respectively). Similar efficiency could be found at a lower overpotential (-0.20 V vs RHE) in long-term electrolysis. At -0.20 V vs RHE, the catalyst FE increased from 73% in the first 2 h to ∼90% in 10 h of electrolysis. Electron microscopy revealed the loss of the cubic shape with the formation of sintered domains. In situ Raman, X-ray diffraction (XRD), and in situ Cu K-edge X-ray absorption near-edge spectroscopy (XANES) indicated the reduction of Cu2O to oxide-derived Cu0 (OD-Cu). Nevertheless, a remaining Cu2O phase was noticed after 1 h of electrolysis at -0.3 V vs RHE. This observation indicates that the activity and selectivity of the initially well-defined Cu2O NCs are not solely dependent on the initial structure. Instead, it underscores the emergence of an OD-Cu-rich surface, evolving from near-surface to underlying layers over time and playing a crucial role in the reaction pathways. By employing online differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIR), we experimentally probed the presence of key intermediates (NO and NH2OH) and byproducts of NO3RR (N2 and N2H x ) for NH3 formation. These results show a complex relationship between activity and stability of the nanostructured Cu2O oxide catalyst for NO3RR.

Exploring the influence of cell configurations on Cu catalyst reconstruction during CO2 electroreduction

Membrane electrode assembly (MEA) cells incorporating Cu catalysts are effective for generating C2+ chemicals via the CO2 reduction reaction (CO2RR). However, the impact of MEA configuration on the inevitable reconstruction of Cu catalysts during CO2RR remains underexplored, despite its considerable potential to affect CO2RR efficacy. Herein, we demonstrate that MEA cells prompt a unique reconstruction of Cu, in contrast to H-type cells, which subsequently influences CO2RR outcomes. Utilizing three Cu-based catalysts, specifically engineered with different nanostructures, we identify contrasting selectivity trends in the production of C2+ chemicals between H-type and MEA cells. Operando X-ray absorption spectroscopy, alongside ex-situ analyses in both cell types, indicates that MEA cells facilitate the reduction of Cu2O, resulting in altered Cu surfaces compared to those in H-type cells. Time-resolved CO2RR studies, supported by Operando analysis, further highlight that significant Cu reconstruction within MEA cells is a primary factor leading to the deactivation of CO2RR into C2+ chemicals.

Stabilization of Cu2O catalyst via strong electronic interaction for selective electrocatalytic CO2 reduction to ethanol

While cuprous oxide (Cu2O) remains the most efficient and viable electrocatalyst for the electrochemical conversion of CO2 to ethanol, its reduction to Cu during the catalytic CO2RR process poses a barrier to its industrial application. To address this challenge, we have reported a highly stable Cu2O-based catalyst by introducing pseudo-capacitive NiCo2O4 intermediate layers. The current densities observed on the surface of the prepared NF@NiCo2O4@Cu2O remained consistent over a 15-hour stability test, demonstrating excellent durability that exceeds that of the NF@Cu2O electrode by more than 200 %. Experimental characterization and DFT analysis indicate that the exceptional stability is primarily attributed to the pseudo-capacitive NiCo2O4 interlayer with cyclic charge–discharge properties, where NiCo2O4 can capture and eliminate accumulated reduced electrons around Cu2O under strong electronic interactions and release electrons through catalytic reduction to produce hydrogen. Furthermore, the NiCo2O4@Cu2O (111) heterostructure significantly reduces the Gibbs free energy (ΔG) required for C-C coupling of *CO intermediates compared to Cu2O (111). This mechanism establishes a cyclic charge–discharge process in order to prevent reduction of Cu2O into copper monomers. As a result, NF@NiCo2O4@Cu2O demonstrates a C2H5OH faradaic efficiency of 56.9 % at −0.5 V vs. RHE, surpassing many other Cu-based catalytic electrodes. This work provides new insights into studying strong electronic interaction structures to eliminate electron enrichment at the catalytic site for stabilizing catalysts and also offers an effective strategy for designing catalysts that maintain long-term stability in industrial applications.

Anticancer, antimicrobial and antioxidant activity of CuO–ZnO bimetallic nanoparticles: green synthesised from Eryngium foetidum leaf extract

In the present study, green synthetic pathway was adapted to synthesize CuO–ZnO bimetallic nanoparticles (BNPs) using Eryngium foetidum leaf extract and their anti-cancer activity against MCF7 breast cancer cell lines, anti-microbial activity and in vitro anti-oxidant activity were evaluated. Various bio-active compounds present in leaf extract were responsible for the reduction of CuO–ZnO NPs from respective Cu2+ and Zn2+ metal precursors. In the present study, the involvement of bio-active compounds present in E. foetidum extract before and after green synthesis of BNPs were evaluated for the first time. Rod-shaped and spherical structural morphology of synthesized BNPs were revealed by using FESEM, TEM, and XRD analysis with particle size ranged from 7 to 23 nm with an average size of 16.49 nm. The distribution of Cu and Zn were confirmed by elemental mapping. The green synthesized CuO–ZnO NPs showed significant cytotoxic effect with the inhibition rate 89.20 ± 0.03% at concentration of 500 μg/mL. Again, good antioxidant activity with IC50; 0.253 mg/mL and antimicrobial activity of BNPs were also evaluated with the increasing order of MIC; E. coli (7.81 μg/mL) < B. subtilis (62.5 μg/mL) < S. aureus (31.25 μg/mL).

Investigating the reaction mechanism of zirconium as a fuel in reactive multilayer films via multimodal analysis

In this report, we examine the intricate details of the mechanism driving Zr/CuO thermite system, shedding new light on the exceptional reactivity of Zr fuel with oxygen. Magnetron-sputtered Zr/CuO reactive multilayers were deposited, and thermo-physical techniques were employed to characterize the progression of the chemical reaction upon heating. Unlike commonly used Al fuel, Zr/CuO exhibited 100% heat release below 500 °C, contrasting with the ∼5% observed for conventional Al/CuO system. This enhanced reactivity at low temperature is attributed to the rapid oxygen consumption behavior of Zr, due to the poor barrier of ZrOx to oxygen diffusion. The oxidizing behavior of Zr was quantitatively analyzed using electron microscopy and spectroscopy. Our observations reveal a three-step process of Zr oxidation facilitated by a rapid reduction of CuO to metallic Cu accompanied by the formation of an intermediate Cu2O phase: (i) a preliminary low-temperature mass transport initiating at 275 °C, (ii) partial Zr oxidation forming ZrO2 and oxygen enriched Zr and finally (iii) complete conversion to zirconia at 450 °C. Finally, Zr/CuO reactive thin-films demonstrated a very high reactivity with an ignition delay time of 0.04 ± 0.016 ms and a burn rate of 3.5 m.s−1, in stark contrast to the same volume of Al/CuO, which failed to ignite and burn altogether. This study not only deepens our comprehension of Zr-based thermite system but also underscores its potential for diverse applications in energetic materials.

Highly efficient and selective hydrogenation of furfural to furfuryl alcohol and cyclopentanone over Cu-Ni bimetallic Catalysts: The crucial role of CuNi alloys and Cu+ species

The selective hydrogenation of furfural derived from biomass is of significant importance in the synthesis of valuable chemical compounds. In this work, Cu-Ni bimetallic catalysts with varying metal ratios were effectively synthesized using the urea deposition method and employed in catalytic hydrogenation of furfural (FA) to furfuryl alcohol (FOL) and cyclopentanone (CPO) in different solvents. The study revealed that the synergistic interaction between Cu and Ni favors the formation of CuNi alloys, thereby facilitating the reduction of CuO and NiO and resulting in larger amount of metallic species (Cu0/+ and Ni0), and promoting the formation of highly dispersed nanoparticles. Moreover, the formed Cu+ species can serve as Lewis acid sites and improve the adsorption of polarized C = O, thus significantly enhancing the selectivity to FOL. More importantly, the cooperation between Cu+ species and water can promote the aqueous-phase hydrogenation-rearrangement (AP-HR) of FA to CPO. Also, in-situ/on-line DRIFTS shows that Cu3Ni1/SiO2 preferentially adsorbs and activates C = O and prefers to form 4-hydroxy-2-cyclopentenone (HCP), which is the key intermediate to form CPO. DFT calculations agree with the in-situ/on-line DRIFTS, showing that Cu3Ni1 (111) crystal surface with the lowest d-band center and the strongest electronic effects presents the highest adsorption energies of H2, H2O, and FA, the lowest adsorption energies of H*, FOL, and CPO, and the lowest energy barriers of Piancatelli rearrangement of FOL to HCP. Under the optimum conditions, Cu3Ni1/SiO2 gives 99.9 % yield to FOL at 333 K in isopropanol and 96.7 % yield to CPO at 413 K in water. The low cost and high activity of Cu3Ni1/SiO2 make it a potential catalyst for the green production of FOL and CPO in industry.

Correlative In Situ Spectro-Microscopy of Supported Single CuO Nanoparticles: Unveiling the Relationships between Morphology and Chemical State during Thermal Reduction.

The activity, selectivity, and lifetime of nanocatalysts critically depend on parameters such as their morphology, support, chemical composition, and oxidation state. Thus, correlating these parameters with their final catalytic properties is essential. However, heterogeneity across nanoparticles (NPs) is generally expected. Moreover, their nature can also change during catalytic reactions. Therefore, investigating these catalysts in situ at the single-particle level provides insights into how these tunable parameters affect their efficiency. To unravel this question, we applied spectro-microscopy to investigate the thermal reduction of SiO2-supported copper oxide NPs in ultrahigh vacuum. Copper was selected since its oxidation state and morphological transformations strongly impact the product selectivity of many catalytic reactions. Here, the evolution of the NPs' chemical state was monitored in situ during annealing and correlated with their morphology in situ. A reaction front was observed during the reduction of CuO to Cu2O. From the temperature dependence of this front, the activation energy was extracted. Two parameters were found to strongly influence the NP reduction: the initial nanoparticle size and the chemical state of the SiO2. substrate. The CuOx reduction was found to be completed first on smaller NPs and was also favored over partially reduced SiOx regions that resulted from X-ray beam irradiation. This methodology with single-particle level spectro-microscopy resolution provides a way of isolating the influence of diverse morphologic, electronic, and chemical influences on a chemical reaction. The knowledge gained is crucial for the future design of more complex multimetallic catalytic systems.

Cu2O photocathodes prepared by thermal reduction of CuO: Influence of O2 concentration on photocurrent stability

Copper oxide (CuO and Cu2O) p-type semiconducting photocathodes have gained attention for hydrogen production (proton reduction), due to their appropriate conduction band potentials and light sensitivity in the visible. However, photocorrosion is the main handicap for both compounds. In this work, the transformation of CuO layers deposited via spray pyrolysis on conductive FTO (fluorine doped tin oxide on glass) into Cu2O via thermal reduction was studied. Optimal conditions for obtaining Cu2O were found by in situ temperature-controlled XRD. Synthesis of Cu2O films was finally carried out under moderate temperature and vacuum conditions (380 °C, 1·10−2 mbar). The influence of 3 different oxygen concentration in the electrolyte on the stability of the Cu2O electrodes under light and electrical bias was studied, and it was found that the O2 content had a high impact on the photoelectrochemical performance of Cu2O electrodes. The stability of the electrodes against self-reduction was demonstrated.

Cu metallization of Al2O3 ceramics via CuO reduction: Role of SiO2 additive and sintering atmosphere

A Cu-coated Al2O3 substrates which can be used for power modules are prepared via sintering and reduction of CuO–SiO2 film onto the surface of Al2O3 ceramic without precious metal brazing filler or high-vacuum equipment. This method has a significant cost advantage over the existing technology. Effects of oxygen partial pressure from sintering atmosphere and SiO2 content on microstructure and mechanical properties of Cu/Al2O3 interface are systematically investigated. Phase compositions and morphologies of sintered Cu2O layer, reduced Cu layer and reactive layer are characterized via X-ray diffraction and scanning electron microscopy. In addition, physicochemical changes within CuO–SiO2 during sintering are characterized by thermogravimetry-differential scanning calorimeter. It is found that oxygen and SiO2 can promote the generation of Cu2O–CuO–SiO2 eutectic phase with low melting point upon sintering, which increases the thickness of reaction layer and the densification of Cu layer. The shear strength between the Cu layer and the Al2O3 substrate is enhanced with the increase in Cu layer densification degree, while varying in irregular manner with the thickness of reaction layer. In particular, the highest shear strength of 62.70 MPa is obtained at oxygen partial pressure of 0.02 atm and SiO2 content of 1.5 wt%.

The Preparation of an Ultrafine Copper Powder by the Hydrogen Reduction of an Ultrafine Copper Oxide Powder and Reduction Kinetics.

Ultrafine copper powders were prepared by the air-jet milling of copper oxide (CuO) powders and a subsequent hydrogen (H2) reduction. After milling, the particle size and grain size of CuO powders decreased, while the specific surface area and structural microstrain increased, thereby improving the reaction activity. In a pure H2 atmosphere, the process of CuO reduction was conducted in one step, and followed a pseudo-first-order kinetics model. The smaller CuO powders after milling exhibited higher reduction rates and lower activation energies compared with those without milling. Based on the unreacted shrinking core model, the reduction of CuO powders via H2 was controlled by the interface reaction at the early stage, whereas the latter was limited by the diffusion of H2 through the solid product layer. Additionally, the scanning electron microscopy (SEM) indicated that copper powders after H2 reduction presented a spherical-like shape, and the sintering and agglomeration between particles occurred after 300 °C, which led to a moderate increase in particle size. The preparing parameters (at 400 °C for 180 min) were preferred to obtain ultrafine copper powders with an average particle size in the range of 5.43-6.72 μm and an oxygen content of less than 0.2 wt.%.

Hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol over in-situ reduced CuO/Al2O3 catalysts under mild conditions

A new method for the hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol (MMP) by in-situ reduced CuO/Al2O3 catalysts was developed. The CuO/Al2O3 catalysts with different CuO contents were prepared by simple wet impregnation and could provide complete vanillin conversion with 99 % MMP selectivity under mild conditions (120 °C, 0.5 MPa H2, 8 h). The results from XPS and H2-TPR characterizations of the CuO/Al2O3 catalysts suggested that CuO species had a strong interaction with the Al2O3 support, which was beneficial for the in-situ reduction of CuO to Cu+ and Cu0 species during the hydrodeoxygenation reaction. The synergistic effect of Cu+ and Cu0 species was believed to promote the hydrodeoxygenation of vanillin, in which Cu0 accounts for the hydrogenation reaction, while Cu+ is responsible for the adsorption of vanillin and 4-hydroxy-3-methoxybenzyl alcohol to facilitate the further dehydration of 4-hydroxy-3-methoxybenzyl alcohol. In addition, the CuO/Al2O3 catalyst could maintain high catalytic activity after three reaction cycles and showed versatility for various lignin derivatives. The development of this in-situ reduceable catalyst could provide a cost-effective approach for the upgrading of biomass derived products.

The reduction of copper in LaFeO3, La2CuO4 and CuO three-phase system improves the efficiency of NO removal: Experimental and density functional theory calculation

Hollow spherical LaCu0.5Fe0.5O3 (LCF) and La0.8Ce0.1Cu0.5Fe0.5O3 (LCCF) catalysts are synthesized by solvothermal method, and CuO is reduced in two samples, so that the two corresponding multiphase catalysts (R-LCF and R-LCCF) were prepared and used for the selective catalytic reduction of NO with CO (CO-SCR). The results show that the balance of Ce3++Cu2+↔Cu++Ce4+ between Ce and Cu ions promotes the reduction of CuO in the Ce-doped LCCF catalyst more obviously. In addition, the reduction of Ce and Cu in R-LCCF generates more oxygen vacancies, which leads to more surface adsorbed oxygen species, thus facilitating the conversion of more NO to NOx species. Besides, the presence of reduced Cu is highly active and can inhibit the production of carbonates occupying the active site. The ability to activate both CO and NO after the evolution of Cu0 to the key species Cu+ leads to a rapid reaction between Cu+-CO and NOx species. These are the key factors for the significant increase in catalytic activity at low temperatures. It is worth noting that the CO-SCR reaction on the R-LCCF catalyst corresponds to the Langmuir-Hinshlwood (L-H) and Eley-Rideal (E-R) mechanisms at different temperature windows, respectively.

Graphene oxide-induced CuO reduction in TiO2/CaTiO3/Cu2O/Cu composites for photocatalytic degradation of drugs via peroxymonosulfate activation

Contamination of water bodies is a global environmental and human health issue. Conventional water treatment systems cannot efficiently eliminate organic contaminants, particularly drugs. Photocatalysis is a promising, environmentally friendly oxidation process for the removal of such compounds. A key point is the choice of material to be used as photocatalyst. Here, TiO2/CaTiO3/Cu2O/Cu composites were fabricated by adding different amounts (x) of graphene oxide (GO) (x wt% = 1, 3, and 5 %) to CaCu3Ti4O12 powder using the solid-state synthesis method. The produced pellets were sintered under inert nitrogen atmosphere at 1100 °C for 3 h. X-ray diffraction analysis showed that the Cu metal amount was increased upon GO addition, and the UV–Vis diffuse reflectance spectroscopy showed that the spectral response was extended to the visible range. Then, high performance liquid chromatography assessment of paracetamol degradation by a photocatalytic cell using TiO2/CaTiO3/Cu2O/Cu composites with different GO amounts showed that the removal efficiency was increased upon introduction of 0.5 mM peroxymonosulfate (PMS) as active component to generate SO4‾ radicals. After 3 h under visible light, 96 % of 10 ppm paracetamol was degraded by the composite with 3 % of GO (1 cm2 surface photocatalyst) compared with 50 % by the composite without GO in the same experimental conditions (PMS in 210 mL of aqueous solution). Free radical trapping and the acute toxicity of potential degradation by-products were also investigated. Our results indicate that TiO2/CaTiO3/Cu2O/Cu with 3 % GO displays long-term stability and durability for the photocatalytic removal of pharmaceutical pollutants from wastewater.

Single-crystal Cu(1 1 1) foil preparation by direct bonding technology

Considering the significant advantages of single-crystal Cu(111) in the synthesis of 2D materials and many other fields, its controllable preparation has attracted widespread attention. However, the formation of a single-crystal Cu foil has always been hindered by competition among grains with different orientations. Herein, single-crystal Cu(111) was prepared on the basis of the traditional direct bonding copper method. Cu foil and c-plane sapphire substrate were bonded through Cu2O at high temperature. After the reduction of Cu2O by H2, the surface crystal structure of sapphire will guide Cu to form single-crystal Cu(111). The single-crystallinity of Cu(111) and the specific orientation relationship between Cu(111) and sapphire were confirmed by LEED and XRD. Furthermore, the growth of high-quality single-crystal graphene was performed on single-crystal Cu(111). This work not only facilitates the mass production of 2D materials such as single-crystal graphene, but also provides greater application potential to the direct bonding copper technology and single-crystal Cu.

Dual mechanisms in hydrogen reduction of copper oxide: surface reaction and subsurface oxygen atom transfer.

The study of the reduction of copper oxide (CuO) by hydrogen (H2) is helpful in elucidating the reduction mechanism of oxygen carriers. In this study, the reduction mechanism of CuO by H2 and the process of oxygen atom transfer were investigated through the density functional theory (DFT) method and thermodynamic calculation. DFT calculation results showed that during the reaction between H2 and the surface of CuO, Cu underwent a Cu2+ → Cu1+ → Cu0 transformation, the Cu-O bond (-IpCOHP = 2.41) of the Cu2O phase was more stable than that (-IpCOHP = 1.94) of the CuO phase, and the reduction of Cu2O by H2 was more difficult than the reduction of CuO. As the surface oxygen vacancy concentration increased, it was more likely that the subsurface O atoms transfer to the surface at zero H2 coverage (no H2 molecule on the surface), allowing the surface to maintain a stable Cu2O phase. However, when the H2 coverage was 0.25 monolayer (ML) (one H2 molecule every four surface Cu atoms), the presence of H atoms on the surface made the upward transfer of O atoms from the subsurface more difficult. The rate of consuming surface O atoms in the reduction reaction was greater than the rate of subsurface O atom transfer induced by the reduction reaction and the surface Cu2O phase could not be maintained stably. Through thermodynamic analysis, at high H2 concentration, the reaction between H2 and CuO was more likely to generate Cu, while at low H2 concentration, it was more likely to generate Cu2O. In summary, the valence state of Cu in the reaction process between CuO and H2 depended on the concentration of H2.

Atomic Dynamics of Multi-Interfacial Migration and Transformations.

Redox-induced interconversions of metal oxidation states typically result in multiple phase boundaries that separate chemically and structurally distinct oxides and suboxides. Directly probing such multi-interfacial reactions is challenging because of the difficulty in simultaneously resolving the multiple reaction fronts at the atomic scale. Using the example of CuO reduction in H2 gas, a reaction pathway of CuO → monoclinic m-Cu4 O3 → Cu2 O is demonstrated and identifies interfacial reaction fronts at the atomic scale, where the Cu2 O/m-Cu4 O3 interface shows a diffuse-type interfacial transformation; while the lateral flow of interfacial ledges appears to control the m-Cu4 O3 /CuO transformation. Together with atomistic modeling, it is shown that such a multi-interface transformation results from the surface-reaction-induced formation of oxygen vacancies that diffuse into deeper atomic layers, thereby resulting in the formation of the lower oxides of Cu2 O and m-Cu4 O3 , and activate the interfacial transformations. These results demonstrate the lively dynamics at the reaction fronts of the multiple interfaces and have substantial implications for controlling the microstructure and interphase boundaries by coupling the interplay between the surface reaction dynamics and the resulting mass transport and phase evolution in the subsurface and bulk.

Plasma-catalytic CO2 hydrogenation to methanol over CuO-MgO/Beta catalyst with high selectivity

Herein, we report a CuO-MgO/Beta catalyst, which exhibits 72.0% methanol selectivity with 8.5% CO2 conversion in plasma-catalytic CO2 hydrogenation at ambient conditions (30 °C and 0.1 MPa). The catalysts have been systematically characterized by XRD, H2-TPR, HRTEM, STEM, XPS, CO2-TPD and NH3-TPD to study the interaction between CuO and MgO, as well as physicochemical properties of the catalysts. Furthermore, in-situ Optical Emission Spectroscopy (OES) and in-situ Fourier Transform Infrared Spectroscopy (FTIR) were employed to investigate the active species in gas-phase and on catalyst surface. The excellent selectivity of the CuO-MgO/Beta catalyst is attributed to synergy between MgO and CuO species. The strong interaction between CuO and MgO leads to electron transfer from MgO to CuO, which is favorable for partially reduction of CuO to form Cu2O active sites. Furthermore, MgO strongly adsorb CO2 to form formate species, which suppresses CO generation and leads to CO2 hydrogenation through Formate pathway for CH3OH production.

Designed Synthesis of Cu2O Quantum Dots/TiO2 Nanotubes Heterostructure as a Photocatalyst for Converting CO2 to CH4

Herein, H+ in oxalic acid is used instead of Na+ to obtain titanate nanosheets through P200 hydrolysis, which further curls to form a multilayer TiO2 nanotubes (NTs) structure. Then, Cu2O quantum dots (QDs) are successfully loaded on TiO2 NTs via a hydrothermal method using fructose as a reducing agent. The optical, impedance, and photocurrent tests indicate that the composite structure improves its optoelectronic performance. The photocatalytic H2 production and CO2 reduction efficiency of Cu2O QDs/TiO2 NTs are lower than those of TiO2 NTs. However, the molar ratio of CH4 to CO produced by CO2 reduction of Cu2O QDs/TiO2 NTs composite catalyst is greater than that of pure TiO2 NTs. The CH4 production accounts for 97%, indicating that the composite catalyst has a high CH4 selectivity. The experimental and density functional theory calculation results prove that the Z‐scheme heterojunction accelerates the separation and transfer of photogenerated carriers, and broadens the absorption range of visible light.

Mechanistic investigation on Ag-Cu2O in electrocatalytic CO2 to CH4 by in situ/operando spectroscopic and theoretical analysis

Silver-copper electrocatalysts have demonstrated effectively catalytic performance in electroreduction CO2 toward CH4, yet a revealing insight into the reaction pathway and mechanism has remained elusive. Herein, we construct chemically bonded Ag-Cu2O boundaries, in which the complete reduction of Cu2O to Cu has been strongly impeded owing to the presence of surface Ag shell. The interfacial confinement effect helps to maintain Cu+ sites at the Ag-Cu2O boundaries. Using in situ/operando spectroscopy and theoretical simulations, it is revealed that CO2 is enriched at the Ag-Cu2O boundaries due to the enhanced physisorption and chemisorption to CO2, activating CO2 to form the stable intermediate *CO. The boundaries between Ag shell and the Cu2O mediate local *CO coverage and promote *CHO intermediate formation, consequently facilitating CO2-to-CH4 conversion. This work not only reveals the structure-activity relationships but also offers insights into the reaction mechanism on Ag-Cu catalysts for efficient electrocatalytic CO2 reduction.