Spillover Of CO Research Articles

Insights into the Structure and Activity of Bimetallic Au/Cu2O Catalysts during CO2 Electroreduction to C2 products

Despite its promising performance for C2+ product formation in electrochemical reduction of CO2 (CO2RR), Cu-based catalysts exhibit a relatively poor selectivity towards important chemical intermediates such as ethylene and ethanol. Up to 16 different products can typically be formed during CO2RR.1 Cu is the only element that can form C-C bonds at an appreciable rate.2 Therefore, it is critical to better understand the active sites of Cu-based electrocatalysts, as it can lead to better catalyst design with improved selectivity towards desired products. A common approach is to investigate the reactivity of well-defined surface terminations of Cu, which can be achieved by employing shape-controlled (nano)particles.3 Here, we expanded on such studies by evaluating the impact of Au on well-defined Cu2O surfaces for the electrochemical reduction of CO2. This promoter metal was chosen, because it can reduce CO2 to CO, which is widely accepted as the key intermediate for C-C coupling.2,4 In this study, 40 nm Cu2O nanocubes that predominantly expose the (100) facet were synthesized with a ligand-free method. The (100) facet is more active in the production of ethylene at the expense of unwanted methane formation, which takes place predominantly at the (111) facet.3 The surface of the nanocubes was decorated with Au nanoparticles by a galvanic replacement reaction. HAADF-STEM images of the catalysts with various Au loadings are shown in Figure 1a-d. After addition of Au nanoparticles, the shape of the Cu2O nanocubes was preserved. However, the Au nanoparticles were highly dispersed at low loadings (1 mol % Au) whereas Au clusters were observed at higher loadings (10 mol % Au). This result was in line with synchrotron X-ray diffraction (XRD) results, whereby the Au(111) reflection appears for the 10Au/Cu2O sample. Besides, the formation of a Au-Cu alloy and CuO phase was confirmed as well. The highly dispersed nature of the Au nanoparticles at low loadings was further established by Au 4f X-ray photoelectron spectroscopy (XPS), whereby a shift towards higher binding energies was observed as compared to the samples with higher Au loadings. The electrocatalytic performance of the catalysts was assessed over a range of potentials in neutral electrolyte (0.1 M KHCO3) in H-cell configuration. With highly dispersed Au as promotor, we found that the formation of ethylene and ethanol was significantly enhanced (Figure 1e-f). More specifically, the Faradaic effiency towards ethanol increased by roughly 1.5 times by introducing 1 mol % Au to the Cu2O nanocubes. Surprisingly, the 10Au/Cu2O sample displayed the lowest Faradaic efficiency for C2 products. We believe that the dispersion of Au on the Cu2O surface plays an important role in the product formation, whereby CO can be formed at Au sites and diffuse to Cu sites in proximity for further reduction to C2 products (CO spillover). To further study structure-activity relationships, we performed in-situ X-ray absorption spectroscopy (XAS) measurements. Figure 1g shows the normalized Cu K-edge X-ray absorption near-edge structure (XANES) of the Cu2O and Au/Cu2O samples in the final state. The evolution of the Cu(0), Cu(I) and Cu(II) fractions was followed by Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) analysis. This analysis revealed that the final oxidation state of the catalysts is different. The Cu(I)/Cu(0) ratio shows the following trend 1Au/Cu2O > 5Au/Cu2O > Cu2O > 10Au/Cu2O. Based on these observations, we hypothesize that the oxidation state of Cu affects the product distribution and in particular, the formation of oxygenates. The presence of Cu(I) species and the formation of Cu(0) species during CO2 electroreduction was further confirmed with in-situ XRD measurements. Finally, we performed quasi in-situ XPS measurements to study the reduction of the surface of the catalysts. Acknowledgements This publication is part of the research programme 'Reversible Large-scale Energy Storage' (RELEASE) with project number 17621 which is financed by the Dutch Research Council (NWO).

Influence of TiO2 coverage on activity and stability of Pd-TiO2/MWCNT-supported catalysts used in direct formic acid fuel cells

Pd and TiO2 supported on functionalized multiwall carbon nanotubes (f-MWCNTs) catalysts were investigated in formic acid electrooxidation reaction in direct formic acid fuel cell. TiO2 (5–60 wt.% loading) on f-MWCNTs was deposited using microwave-assisted hydrothermal method. 20 wt.% of Pd was deposited on TiO2/f-MWCNTs by reduction of palladium (II) chloride salt with sodium borohydride. Catalysts’ structure and composition were characterized by XRD, STEM, HR-TEM, TGA, XPS/XAES (Pd, Ti, O spectra features, density of valence states, Auger parameters). Average crystallite size of Pd and TiO2 from XRD (3–4 nm) agrees with those by HR-TEM (3–5 nm). Low TiO2 coverages (below 32wt.%) show smaller crystallites due to increased surface hydrophilicity, higher amount of TiO2 oxygen vacancies with attached Pd nanoparticles, increased density of valence states of strong Pd–TiO2 interface. In contrary, the higher coverages indicate lower amount of Pd–O–Ti, Ti–O–C, Pd–O–C interfaces, with electron charge transfer from TiO2 to f-MWCNTs, and to Pd. Catalysts activity (40–106 mWmgPd−1) and stability (5–240 h) are enhanced at low TiO2 coverages (4–8 wt.%) due to a strong Pd-TiO2 interface on oxygen vacancies, improved electron transport and a high active surface area. Oscillatory self-cleaning mechanism of Pd is due to oxidation by -OH groups (TiO2, f-MWCNTs), and hydrogen and CO spillover.

Prussian blue analogs photocatalyst promote the evolution of value‐added platform compounds via CoCNZn covalent bonds

AbstractValue‐added conversion of lignocellulose is a sustainable approach. Photo‐refining biomass is in line with current environmental protection strategies. However, photo‐reforming biomass suffers from poor catalyst stability and low conversion efficiency. Here, we designed fructose as a lignocellulosic model. The heterogeneous structure of Prussian blue coating was constructed with a special covalent bond structure of CoCNZn. This structure has a catalytic conversion mechanism that can accelerate electron transfer. Fructose was simultaneously converted to value‐added platform compounds (5‐HMF and formic acid) and gaseous fuels (CO, CH4) with a conversion rate of up to 92.5%, which is more than 1.7 times than that of catalysts without adding Prussian blue. Hydrogen transfer and carbon transfer on the carbon atoms of fructose facilitates the production and accelerates the spillover of CO from formic acid. This work provides new ideas for the development of Prussian blue catalysts and the conversion of pentose.image

Insight into the Formation and Catalytic Mechanism of “CO Pool” during Electrocatalytic Conversion of CO2

The OC-CO coupling reaction, requiring pairs of *CO or *CHO intermediates absorbed on adjacent Cu sites, is the key elementary reaction during the electrocatalytic conversion of CO2 towards C2 products, where the harsh demand of adjacent *CO cause the transmission and preservation of CO species become the critical step of CO coupling reaction. Among the reported M-Cu (M=Ag, Au, Zn, etc....) tandem catalysts and Cu+-Cu sites, CO goes through the route of “generation-desorption-transmission-deeply reduction” over the catalytic surface. Despite the in-depth studies of the various site’s composition, morphological structures, and catalytic sites arrangement on Cu-based catalysts, the migratory manner on the electrode surface and the concentration and reactivity of CO in the double layer is still obscure, which are essential steps for CO spillover on the surface of Cu-based catalysts and further coupling reactions, as well as the underlying causes of the poor selectivity of CO/C2 products. At the same time, in situtechniques with temporal resolution are still lacking for probing the overflow and inter-diffusion of CO in the double layer.In this study, based on the rotating disk electrode, we developed an effective means for in situ monitoring of the transport and electrochemical properties of CO in the diffusion layer. Based on theoretical analysis of the electrochemical interface CO species transfer path and time-resolved RRDE techniques, we proved that most of the CO intermediates are favorable to transferred and then reserved in the diffusion layer, leading to an enhanced concentration of CO over equilibrium concentration, and finally benefitted the transmission and reactivity of CO species. By analyzing the reaction chain, combined with in situ ATR-SEIRAS monitor and theoretic calculation, the chemical potential was proved to be enhanced by introducing the “CO pool”, which could be resonated in the reaction chain, raised an increased entropy production and finally led to a resonance-enhanced concentration of by-intermediates, finally strengthening the activity of whole chain-system. Figure 1

*CO spillover induced by bimetallic xZnO@yCuO active centers for enhancing C–C coupling over electrochemical CO2 reduction

Cu-based catalysts attaining high catalytic activity and selectivity towards C2+ product remains a major obstacle, which has garnered significant attention. *CO plays a key role as an intermediate in the next process of C–C dimerization. In this study, we devise a novel approach for generating *CO in situ and facilitating its spillover to neighboring dandelion-liked CuO active sites, utilizing flower-shaped ZnO as a source of *CO intermediate. Consequently, the Zn-rich 3ZnO@CuO catalyst shows the highest Faraday efficiency of CO (FECO) is 89.94 % at −1.2 V vs. RHE. Additionally, a remarkable C2H4 selectivity of 46.37 % for ZnO@CuO at a more positive potential of −1.1 V vs. RHE is achieved. In-situ ATR-SEIRAS also unveils that *CO spillover increases the surface coverage of *CO on the catalyst, ultimately improving the selectivity for C–C coupling and C2H4 production. The relationship between structure and performance will offer guidance for the design of Cu-based catalysts with superior efficiency in CO2 reduction.

How *CO spill-over affects C–C coupling on amorphous Cu for converting CO2 to multi-carbon products

Cu-based catalysts, especially oxide-derived Cu, exhibit high multi-carbon product selectivity, thus showing excellent industrialization prospects. Although the mechanism for the superiority is debatable, both experimental and calculation results indicate that the more disordered crystal structure is better for C–C coupling. Herein, we build an amorphous Cu model by making oxygen doping and disordered morphology to approach the actual condition. The oxygen atoms in the subsurface would diffuse to the surface, creating a vacancy that would break the C–C bond. Besides, only limited sites on the amorphous surface with low coordination number and stepped morphology are conducive to the occurrence of CO–CO coupling. Furthermore, we find that the spill-over effect on the amorphous Cu surface could promote the coupling of two *CO intermediates by reducing the reaction energy barrier rather than 50 % of the C–C coupling process on stationary positions. This beneficial strategy encourages the synthesis of C2+ products.

Cold plasma-activated Cu-Co catalysts with CN vacancies for enhancing CO2 electroreduction to low-carbon alcohol

Electrocatalytic CO2 reduction reaction to low-carbon alcohol is a challenging task, especially high selectivity for ethanol, which is mainly limited by the regulation of reaction intermediates and subsequent C–C coupling. A Cu-Co bimetallic catalyst with CN vacancies is successfully developed by H2 cold plasma toward a high-efficiency CO2RR into low-carbon alcohol. The Cu-Co PBA-VCN (Prussian blue analogues with CN vacancies) electrocatalyst yields methanol and ethanol as major products with a total low-carbon alcohol FE of 83.8% (methanol: 39.2%, ethanol: 44.6%) at −0.9 V vs. RHE, excellent durability (100 h) and a small onset potential of −0.21 V. ATR-SEIRAS (attenuated total internal reflection surface enhanced infrared absorption spectroscopy) and DFT (density functional theory) reveal that the steric hindrance of VCN can enhance the CO generation from *COOH, and the C–C coupling can also be increased by CO spillover on uniformly dispersed Cu atoms. This work provides a strategy for the design and preparation of electrocatalysts for CO2RR into low-carbon alcohol products and highlights the impact of catalyst steric hindrance to catalytic performance.

Boosting CO Catalytic Oxidation Performance via Highly Dispersed Copper Atomic Clusters: Regulated Electron Interaction and Reaction Pathways.

Copper-loaded ceria (Cu/CeO2) catalysts have become promising for the catalytic oxidation of industrial CO emissions. Since their superior redox property mainly arises from the synergistic effect between Cu and the CeO2 support, the dispersion state of Cu species may dominate the catalytic performance of Cu/CeO2 catalysts: the extremely high or low dispersity is disadvantageous for the catalytic performance. The nanoparticle catalysts usually present few contact sites, while the single-atom catalysts tend to be passivated due to their relatively single valence state. To achieve a suitable dispersion state, we synthesized a superior Cu/CeO2 catalyst with Cu atomic clusters, realizing high atomic exposure and unit atomic activity simultaneously via favorable electron interaction and an anchoring effect. The catalyst reaches a 90% CO conversion at 130 °C, comparable to noble-metal catalysts. According to combined in situ spectroscopy and density functional theory calculations, the superior CO oxidation performance of the Cu atomic cluster catalyst results from the joint efforts of effective adsorption of CO at the electrophilic sites, the CO spillover phenomenon, and the efficient bicarbonate pathway triggered by hydroxyl. By providing a superior atomic cluster catalyst and uncovering the catalytic oxidation mechanism of Cu-Ce dual-active sites, our work may enlighten future research on industrial gaseous pollutant removal.

Probing the redox capacity of Pt–CeO2 model catalyst for low-temperature CO oxidation

The redox activity of the Pt–CeO2 catalysts is controlled by CO spillover in the low-temperature region and by Mars–van Krevelen mechanism in the high-temperature region.

Role of CeO2 in promoting the spillover in CO oxidation reaction over platinum nanoparticle-supported CeO2 catalyst

CeO2 has been extensively studied as a support material for platinum group metals because of the high catalytic activity of CeO2-supported catalysts in oxidation reactions. In particular, it has been reported that the Pt/CeO2 catalyst exhibits high CO oxidation activity after reductive treatment, thereby lowering the temperature of 50 % CO conversion to 150 ℃ or less. Such high activity of Pt/CeO2 has been attributed to the formation of active sites at the interface between the Pt nanoparticles (NP) and CeO2 surface. In this study, we attempt to deepen our understanding of the catalytic activity of Pt/CeO2 by studying the spillover of CO and O species at the interface. Combined kinetics and in situ CO-diffuse reflectance infrared Fourier transform spectroscopy studies reveal that CO spills over from Pt NPs to the CeO2 surface; this contributes to circumventing Pt poisoning by CO at low temperatures. Moreover, the CO oxidation activity of the Pt/CeO2 catalyst was considerably enhanced by simply mixing CeO2 particles with the Pt/CeO2 catalyst. This is explained by the formation of more reactive O atoms on the CeO2 surface after the reductive treatment. This study demonstrates that understanding the dynamic mobility of reactants is vital for discerning catalyst activity and designing more reactive catalysts.

Boosting the Electroreduction of CO2 to Ethanol via the Synergistic Effect of Cu–Ag Bimetallic Catalysts

Electroreduction of CO2 to ethanol remains a formidable challenge due to the unsatisfactory efficiency of the C–C coupling process and the demand for complex oxygen-containing intermediates, thus resulting in poor selectivity and electrocatalytic activity. Cu–Ag bimetallic materials with adjustable electronic structures and active site exposure are promising catalysts to electrochemically convert CO2 to ethanol. Herein, we report Ag-decorated Cu2O materials to promote the catalytic performance of CO2 electroreduction to ethanol. The as-prepared CuAg-0.75% catalyst exhibited an improved ethanol Faradaic efficiency of 21.0% at −0.71 V (vs reversible hydrogen electrode (RHE)) and a maximum ethanol partial current density of 214.4 mA cm–2 at −0.74 V (vs RHE), which were ca. 2 times those of the counterpart without Ag decoration. Density functional theory (DFT) calculations revealed that the adsorption intensity of CO on Ag-decorated Cu surface was stronger than that on Ag surface; hence, the *CO spillover from Ag sites to Cu sites could be promoted, leading to a higher *CO coverage than that on pure Cu surface to facilitate the C–C coupling process. The evenly distributed Ag atoms provided abundant Ag sites for CO formation and a short CO transfer distance. Furthermore, the free energy of formation of key intermediates toward ethanol pathway was lower on the Ag-doped sample, which led to enhanced ethanol selectivity. Both the improved CO spillover process and the optimization of free energy on the Ag-decorated sample resulted in a better catalytic performance toward ethanol.

Atomically dispersed chromium coordinated with hydroxyl clusters enabling efficient hydrogen oxidation on ruthenium

Overcoming the sluggish kinetics of alkaline hydrogen oxidation reaction (HOR) is challenging but is of critical importance for practical anion exchange membrane fuel cells. Herein, abundant and efficient interfacial active sites are created on ruthenium (Ru) nanoparticles by anchoring atomically isolated chromium coordinated with hydroxyl clusters (Cr1(OH)x) for accelerated alkaline HOR. This catalyst system delivers 50-fold enhanced HOR activity with excellent durability and CO anti-poisoning ability via switching the active sites from Ru surface to Cr1(OH)x-Ru interface. Fundamentally different from the conventional mechanism merely focusing on surface metal sites, the isolated Cr1(OH)x could provide unique oxygen species for accelerating hydrogen or CO spillover from Ru to Cr1(OH)x. Furthermore, the original oxygen species from Cr1(OH)x are confirmed to participate in hydrogen oxidation and H2O formation. The incorporation of such atomically isolated metal hydroxide clusters in heterostructured catalysts opens up new opportunities for rationally designing advanced electrocatalysts for HOR and other complex electrochemical reactions. This work also highlights the importance of size effect of co-catalysts, which should also be paid substantial attention to in the catalysis field.

Catalytic activity of bimetallic Rh/Rh-M nanosheets governed by CO spillover

In this issue of Chem Catalysis , Huang and co-workers constructed a series of Rh/Rh-M (M = Co, Mn, Fe, and Ni) catalysts with unique nanosheet structure, exhibiting superior anti-CO poisoning and ethanol oxidation reaction activity. This study opens a promising path to manipulating the intermediate species via CO spillover. In this issue of Chem Catalysis , Huang and co-workers constructed a series of Rh/Rh-M (M = Co, Mn, Fe, and Ni) catalysts with unique nanosheet structure, exhibiting superior anti-CO poisoning and ethanol oxidation reaction activity. This study opens a promising path to manipulating the intermediate species via CO spillover.

CO spillover on ultrathin bimetallic Rh/Rh-M nanosheets

Rh has been regarded as a promising catalyst for ethanol-oxidation reaction (EOR). Nevertheless, Rh is vulnerable to CO poisoning. In this work, we demonstrate a facile strategy for constructing a unique class of ultrathin Rh/Rh-M nanosheets, on which CO can diffuse from the Rh site to the M site. Detailed experiments, characterizations, and theoretical simulations have been conducted to validate the CO spillover effects on Rh/Rh-M nanosheets (NSs). Moreover, the significance of the CO spillover effect has been demonstrated by catalyzing the EOR, where Rh/Rh-M NSs with CO spillover display much higher activity, higher CO 2 selectivity, and stronger resistance to CO poisoning compared with pure Rh NSs. Consequently, the Faraday efficiencies (FEs) of CO 2 of the optimal catalyst (e.g., Rh 79 Co 21 NSs) are 70.3% and 75.5% at 0.7 and 0.8 V RHE , respectively, and these are much higher than those of Rh NSs (62.0% and 64.3% at 0.7 and 0.8 V RHE , respectively). • A versatile strategy for the fabrication of Rh/Rh-M nanosheets • CO can spill from Rh-site to M-site Rh/Rh-M nanosheets • CO spillover effect enhances the stability of Rh to CO poisoning • Rh-Co nanosheets display promising performance for ethanol oxidation Noble metals generally suffer from deactivation due to their strong adsorption abilities to some poisoning intermediates, such as CO. Despite great efforts that have been devoted to the modification of noble-metal catalysts to regulate their surface properties to prevent them from being poisoned, it is challenging to balance the activity, selectivity, and stability of noble-metal catalysts. In this work, we have successfully fabricated a unique class of ultrathin Rh/Rh-M (M = Co, Mn, Fe, and Ni) nanosheets with a strong CO spillover effect for enhanced catalysis. Benefitting from the specific structures of Rh/Rh-M nanosheets (NSs), CO can spill from Rh sites of ultrathin Rh nanosheets to M sites of RhM nanoparticles, which leads to the weakened CO adsorption on Rh sites and strengthened CO adsorption on M sites. This work provides a facile strategy for strengthening the resistance to CO poisoning through the CO spillover effects, which may attract great interests of researchers in diverse fields. A facile strategy for fabricating the ultrathin Rh/Rh-M (M = Co, Mn, Fe, and Ni) nanosheets were proposed. Owing to the unique structures, CO can spillover from the Rh site to the M site on ultrathin Rh/Rh-M nanosheets, leading to significantly strengthened resistance to CO poisoning and enhanced ethanol-oxidation reaction performance.

Seeded Growth of Gold-Copper Janus Nanostructures as a Tandem Catalyst for Efficient Electroreduction of CO2 to C2+ Products.

Gold-copper (Au-Cu) Janus nanostructures (Au-Cu Janus NSs) are successfully prepared using N-oleyl-1,3-propanediamine as capping agent and Cu(acac)2 as the precursor in a typical seeded growth strategy. By preferably depositing Cu atoms on one side of concave cubic Au seeds, the Cu part gradually grows larger as more Cu precursors are added, making the size tuning feasible in the range of 74-156nm. When employed as an electrocatalyst for electrochemical CO2 reduction (CO2 RR), the Au-Cu Janus NSs display superior performance to Au@Cu core-shell NSs and Cu NPs in terms of C2+ products selectivity (67%) and C2+ partial current density (-0.29Acm-2 ). Combined experimental verification and theoretical simulations reveal that CO spillover from Au sites to the nearby Cu counterparts would enhance CO coverage and thus promote C-C coupling, highlighting the unique structural advantages of the Au-Cu Janus NSs toward deep reduction of CO2 . The current work provides a facile strategy to fabricate tandem catalyst with a Janus structure and validates its structural advantages toward CO2 RR, which are of critical importance for the rational design of efficient CO2 RR catalyst.

Electroreduction of carbon dioxide to multi-electron reduction products using poly(ionic liquid)-based Cu-Pd catalyst

Electrocatalytic reduction of CO2 (CO2RR) to multi-electron (> 2e–) products provides a green and sustainable route for producing fuels and chemicals. Introducing the second metal element is a feasible strategy for "managing" the key intermediate on Cu-based materials to further improve the CO2RR catalytic performance. In this work, palladium, which promises the generation of CO, was introduced into the poly(ionic liquid)-based copper hybrid (Cu@PIL) to construct a novel Cu-Pd bimetallic electrocatalyst (Cu@PIL@Pd). Remarkably, with a small dosage of palladium (2.0 mol% compared with Cu), a high faradaic efficiency (FE) for C2+ products (68.7%) was achieved at –1.01 V (with respect to the reversible hydrogen electrode (RHE), the same below) with a high partial current density of 178.3 mA cm–2. Meanwhile, high selectivity towards CH4 (FE = 42.5%) and corresponding partial current density of 172.8 mA cm–2 were obtained on the same catalyst at –1.24 V, signifying a significant potential-dependent selectivity. Mechanistic studies reveal that both copper and palladium oxides are reduced to metallic states during the CO2RR. The presence of the adjoint copper phase and the highly dispersed electrostatic layer promote the generation of CO on the palladium components (both the PdO2 phase and the Pd(II) site). Besides, the local CO* was enriched by the significant diffusion resistance of CO in the PIL layer. The spillover of CO* from Pd sites to the adjoint Cu sites, accompanied by the increased local concentration of CO* around Cu sites, accounted for the observed good CO2RR catalytic performance, especially the high C2+ product selectivity.

In-Situ generation of surface-active HCo(CO)y like intermediate from gold supported on ion-promoted Co3O4 for induced hydroformylation-hydrogenation of alkenes to alcohols

In this study, a greener and stable surface-active cobalt-carbonyl like specie [HCo(CO)y] was generated via H2 and CO spillover by gold on ion-promoted cobalt oxide. The supports and catalysts syntheses were based on inverse micelle and deposition-precipitation methods, respectively. The temperature-programmed reduction was used for optimization to obtain the best supports. The catalysts with activity (Co3O4 < Cs-Co3O4 < Au/Cs-Co3O4 and Au loadings 10 % < 2 % < 5 %) were evaluated for the hydroformylation-hydrogenation of alkenes to alcohols, with the 5 % Au/Cs-Co3O4 catalyst more active than the others and displayed excellent alcohol chemoselectivity with varying regioselectivity under milder reaction conditions. The reaction was assumed to take place via the formation of [HCo(CO)y] specie, as the active catalytic site of the catalyst. The enhanced catalytic performance was also ascribed to the low-temperature reducibility and surface basicity of the nanomaterials. The stability of the catalyst was evaluated by recycling, with its mesostructure retained after four cycles.

Thermodynamically Controlled Microstructure of Binary Alloy for Efficient Electrochemical Conversion of CO2 to C2H4

Since the first development of synthetic plastics, people have been getting a variety of plastics mainly from petroleum, which drove modern civilization. Typically, polyethylene is the most frequently and widely used plastic. But the depletion of fossil fuels and the simultaneous increase in the concentration of carbon dioxide(CO2), which is at a dangerous level, have led to the need to reduce petroleum use and to reduce CO2. The conversion of CO2 to ethylene, the raw material for polyethylene, is a very promising strategy for achieving that. Electrochemically, ethylene can be obtained by reducing CO2 using sustainable electricity. Cu is reported to be the only single element catalyst that is capable of producing hydrocarbons with more than one carbon such as ethylene(C2H4) from CO2. It is because Cu has moderate intermediate binding energy. However, pure Cu catalyst represents poor C2H4 production efficiency because of the activity and selectivity problem. Therefore, alloying Cu with other elements can be one of the best strategy to enhance the activity and selectivity of the catalysis. However, conventional strategy to alloy Cu with other elements and modify the d-orbital energy failed to enhance selectivity for C2H4 because of the scaling relationship between binding energy of intermediates. In this work, controlled microstructure of binary alloy was investigated as a new strategy for selective C2H4 production. Based on the thermodynamic database, the microstructure of Cu-X alloy was carefully designed. By adopting the terminal solid solution system, in which phase segregation take place, unlike conventional homogeneous solid solution system, the microstructure of the alloy consisting of lamellar structure could be controlled. In that system, different binding affinities with intermediates of segregated phases were taken advantage of. The synergetic effect between different phases was investigated by controlling the density of phase boundaries based on the understanding on metallurgy of alloy system. As the result, the selectivity for C2H4 increased with the increase of the density of phase boundary, which suggests the CO spillover between CO-selective phase and Cu and the following CO-CO dimerization. This work provided new catalyst design strategy for efficient electrochemical CO2 conversion to targeted chemicals.

Evidences of CO spillover at a Pt/Pd bimetallic interface during the formic acid oxidation reaction

The surface diffusion (spillover) through the intermetallic Pt/Pd junction of adsorbed CO (COad) during the formic acid electrooxidation reaction (FAO) was analyzed on a bimetallic Pt/Pd electrode by chronoamperometry followed by stripping voltammetry. An ordered matrix of equally spaced square palladium islands on a platinum substrate was prepared by the Mask-Assisted E-Beam (MAEB) method in order to have a large interface length/area relationship. Potential steps were applied in 0.5 M HCOOH + 0.5 M H2SO4 solution (0.2 V ≤ Es vs. RHE ≤ 0.5 V) during times t ≤ 500 s in a flow cell. After changing solution to 0.5 M H2SO4, the amount of COad on Pt and Pd were measured by voltammetric stripping. Under these experimental conditions, the pure metals show the presence of COad on Pt but not on Pd. The results obtained on the bimetallic electrode demonstrate the COad spillover from Pt towards Pd through the heterometallic junction.

Experimental and Theoretical Investigation of the Restructuring Process Induced by CO at Near Ambient Pressure: Pt Nanoclusters on Graphene/Ir(111).

The adsorption of CO on Pt nanoclusters grown in a regular array on a template provided by the graphene/Ir(111) Moiré was investigated by means of infrared-visible sum frequency generation vibronic spectroscopy, scanning tunneling microscopy, X-ray photoelectron spectroscopy from ultrahigh vacuum to near-ambient pressure, and ab initio simulations. Both terminally and bridge bonded CO species populate nonequivalent sites of the clusters, spanning from first to second-layer terraces to borders and edges, depending on the particle size and morphology and on the adsorption conditions. By combining experimental information and the results of the simulations, we observe a significant restructuring of the clusters. Additionally, above room temperature and at 0.1 mbar, Pt clusters catalyze the spillover of CO to the underlying graphene/Ir(111) interface.