Copper Electrocatalyst Research Articles

Sulfonate-Functionalized Metal-Organic Framework as a Porous "Proton Reservoir" for Boosting Electrochemical Reduction of Nitrate to Ammonia.

The electrochemical reduction reaction of nitrate (NO3RR) is an attractive route to produce ammonia at ambient conditions, but the conversion from nitrate to ammonia, which requires nine protons, has to compete with both the two-proton process of nitrite formation and the hydrogen evolution reaction. Extensive research efforts have thus been made in recent studies to develop electrocatalysts for the NO3RR facilitating the production of ammonia. Rather than designing another better electrocatalyst, herein, we synthesize an electrochemically inactive, porous, and chemically robust zirconium-based metal-organic framework (MOF) with enriched intraframework sulfonate groups, SO3-MOF-808, as a coating deposited on top of the catalytically active copper-based electrode. Although both the overall reaction rate and electrochemically active surface area of the electrode are barely affected by the MOF coating, with negatively charged sulfonate groups capable of enriching more protons near the electrode surface, the MOF coating significantly promotes the selectivity of the NO3RR toward the production of ammonia. In contrast, the use of MOF coating with positively charged trimethylammonium groups to repulse protons strongly facilitates the conversion of nitrate to nitrite, with selectivity of more than 90% at all potentials. Under the optimal operating conditions, the copper electrocatalyst with SO3-MOF-808 coating can achieve a Faradaic efficiency of 87.5% for ammonia production, a nitrate-to-ammonia selectivity of 95.6%, and an ammonia production rate of 97 μmol/cm2 h, outperforming all of those achieved by both the pristine copper (75.0%; 93.9%; 87 μmol/cm2 h) and copper with optimized Nafion coating (83.3%; 86.9%; 64 μmol/cm2 h). Findings here suggest the function of MOF as an advanced alternative to the commercially available Nafion to enrich protons near the surface of electrocatalyst for NO3RR, and shed light on the potential of utilizing such electrochemically inactive MOF coatings in a range of proton-coupled electrocatalytic reactions.

Atomically Dispersed High-Active Site Density Copper Electrocatalyst for the Reduction of Oxygen

Enlarging the M-Nx active-site density is an effective route to enhance the ORR performance of M-N-C catalysts. In this work, a single-atom catalyst Cu–N@Cu–N–C with enlarged Cu–N4 active site density was prepared by the second doping and pyrolysis (SDP) of Cu–N–C derived from Cu-doped zeolite imidazole frameworks. The half-wave potentials of Cu–N@Cu–N–C were measured as 0.85 V in alkaline electrolyte and 0.75 V in acidic media, which was 50 mV and 60 mV higher than that of Cu–N–C, respectively. N2 adsorption–desorption isotherm curves and corresponding pore distribution analysis were used to verify the successful filling of additional Cu and N in micropores of Cu–N–C after SDP. The obvious increase in Cu contents for Cu–N@Cu–N–C (1.92 wt%) compared with Cu–N–C (0.88 wt%) tested by ICP demonstrated the successful doping of Cu into Cu–N–C. XAFS analysis confirmed the presence of Cu–N4 single-atom active centers in Cu–N@Cu–N–C. The N 1 s high-resolution XPS results proved a great increase in Cu–N4 contents from 13.15% for Cu–N–C to 18.36% for Cu–N@Cu–N–C. The enhanced ORR performance of Cu–N@Cu–N–C was attributed to the enlargement of Cu–N4 active site density, providing an effective route for the preparation of efficient and low-cost ORR catalysts.

Copper Electrocatalyst Produced by Cu2(OH)2CO3-Mediated In Situ Deposition for Diluted CO2 Reduction to Multicarbon Products.

Pure CO2 is commonly used in most of the current studies for electrochemical CO2 reduction which will need a further cost of gas purification and separation. However, the limited works on diluted CO2 reduction are focused on CO or CH4 production other than C2 products. In this work, copper electrocatalysts were prepared by Cu2(OH)2CO3-mediated in situ deposition for diluted CO2 reduction to multicarbon products. Using in situ Raman spectroscopy, constant amounts of CO and OH* were observed on the catalyst surface, which could effectively suppress the high kinetics of hydrogen evolution and promote C-C coupling, especially under the condition of diluted CO2 reduction. The optimized Cu catalyst achieves a C2 Faradaic efficiency as high as 60.72% in the presence of merely 25% CO2, which is almost equivalent to that observed with pure CO2.

Molecular Cu Electrocatalyst Escalates Ambient Perfluorooctanoic Acid Degradation.

Groundwater reservoirs contaminated with perfluoroalkyl and polyfluoroalkyl substances (PFASs) need purifying remedies. Perfluorooctanoic acid (PFOA) is the most abundant PFAS in drinking water. Although different degradation strategies for PFOA have been explored, none of them disintegrates the PFOA backbone rapidly under mild conditions. Herein, we report a molecular copper electrocatalyst that assists in the degradation of PFOA up to 93% with a 99% defluorination rate within 4 h of cathodic controlled-current electrolysis. The current-normalized pseudo-first-order rate constant has been estimated to be quite high for PFOA decomposition (3.32 L h-1 A-1), indicating its fast degradation at room temperature. Furthermore, comparatively, rapid decarboxylation over the first 2 h of electrolysis has been suggested to be the rate-determining step in PFOA degradation. The related Gibbs free energy of activation has been calculated as 22.6 kcal/mol based on the experimental data. In addition, we did not observe the formation of short-alkyl-chain PFASs as byproducts that are typically found in chain-shortening PFAS degradation routes. Instead, free fluoride (F-), trifluoroacetate (CF3COO-), trifluoromethane (CF3H), and tetrafluoromethane (CF4) were detected as fragmented PFOA products along with the evolution of CO2 using gas chromatography (GC), ion chromatography (IC), and gas chromatography-mass spectrometry (GC-MS) techniques, suggesting comprehensive cleavage of C-C bonds in PFOA. Hence, this study presents an effective method for the rapid degradation of PFOA into small ions/molecules.

Bifunctional TEMPO-electrocatalysts enabled enantioselective oxidative lactonization of 1,4-diols

Asymmetric electrocatalysis is poised to provide a unique avenue for access to enantioenriched molecules that are difficult to obtain through more conventional approaches, but the development of efficient electrocatalysts capable of highly enantioselective transformations remains elusive. Towards this enviable end, bifunctional electrocatalyst capable of both redox mediation and delivery of high stereocontrol is needed. Here we disclose a novel TEMPO-BOX-ligated copper electrocatalyst that enables oxidative kinetic resolution of racemic 1,4-diols, affording diverse chiral 1,4-diols and γ-lactones with good or excellent chemo-, regio, and enantioselectivity. We also show that this cooperative Cu/TEMPO-BOX catalytic strategy is applicable to the electro-oxidative kinetic resolution of 1,2- and 1,3-amino alcohols. This work demonstrates the potential of bifunctional electrocatalysis for asymmetric synthetic methods and we anticipate that it will spur the development of new hybrid electrocatalysts to realize novel asymmetric electrocatalytic methods.

Spatiotemporal Mapping of Local Heterogeneities during Electrochemical Carbon Dioxide Reduction.

The activity and selectivity of a copper electrocatalyst during the electrochemical CO2 reduction reaction (eCO2RR) are largely dominated by the interplay between local reaction environment, the catalyst surface, and the adsorbed intermediates. In situ characterization studies have revealed many aspects of this intimate relationship between surface reactivity and adsorbed species, but these investigations are often limited by the spatial and temporal resolution of the analytical technique of choice. Here, Raman spectroscopy with both space and time resolution was used to reveal the distribution of adsorbed species and potential reaction intermediates on a copper electrode during eCO2RR. Principal component analysis (PCA) of the in situ Raman spectra revealed that a working electrocatalyst exhibits spatial heterogeneities in adsorbed species, and that the electrode surface can be divided into CO-dominant (mainly located at dendrite structures) and C-C dominant regions (mainly located at the roughened electrode surface). Our spectral evaluation further showed that in the CO-dominant regions, linear CO was observed (as characterized by a band at ∼2090 cm-1), accompanied by the more classical Cu-CO bending and stretching vibrations located at ∼280 and ∼360 cm-1, respectively. In contrast, in the C-C directing region, these three Raman bands are suppressed, while at the same time a band at ∼495 cm-1 and a broad Cu-CO band at ∼2050 cm-1 dominate the Raman spectra. Furthermore, PCA revealed that anodization creates more C-C dominant regions, and labeling experiments confirmed that the 495 cm-1 band originates from the presence of a Cu-C intermediate. These results indicate that a copper electrode at work is very dynamic, thereby clearly displaying spatiotemporal heterogeneities, and that in situ micro-spectroscopic techniques are crucial for understanding the eCO2RR mechanism of working electrocatalyst materials.

Synergistic effect of Polydopamine incorporated Copper electrocatalyst by dopamine oxidation for efficient hydrogen production

Tuning the metal-support interaction in electrocatalysts has been proposed as a viable method for manipulating the electronic structure and catalytic activity. In this work, inspired by natural hydrogenase enzyme, electrocatalysts with a hybrid metal-matrix complex using polydopamine (PDA) as a supporting matrix were synthesized for efficient green hydrogen production. Among the various Metal-PDA electrocatalysts, Cu-PDA shows outstanding catalytic activity (low overpotential (ƞ) of 104 mV at 10 mA cm−2 and small Tafel slope of 60.67 mV dec-1) with high stability at neutral pH. Also, the electrochemical impedance spectroscopy analysis verified the fast charge transfer properties of Cu-PDA (2.8 Ω cm2) than PDA (26 Ω cm2), indicating a faster proton-coupled electron transfer process in Cu-PDA electrocatalyst. Therefore, emerging nature inspired organic ligand-transition metal ion complexes can be extensively encouraged as a prospective HER electrocatalyst under neutral conditions.

Use of Chitosan as Copper Binder in the Continuous Electrochemical Reduction of CO2 to Ethylene in Alkaline Medium.

This work explores the potential of novel renewable materials in electrode fabrication for the electrochemical conversion of carbon dioxide (CO2) to ethylene in alkaline media. In this regard, the use of the renewable chitosan (CS) biopolymer as ion-exchange binder of the copper (Cu) electrocatalyst nanoparticles (NPs) is compared with commercial anion-exchange binders Sustainion and Fumion on the fabrication of gas diffusion electrodes (GDEs) for the electrochemical reduction of carbon dioxide (CO2R) in an alkaline medium. They were tested in membrane electrode assemblies (MEAs), where selectivity to ethylene (C2H4) increased when using the Cu:CS GDE compared to the Cu:Sustainion and Cu:Fumion GDEs, respectively, with a Faradaic efficiency (FE) of 93.7% at 10 mA cm−2 and a cell potential of −1.9 V, with a C2H4 production rate of 420 µmol m−2 s−1 for the Cu:CS GDE. Upon increasing current density to 90 mA cm−2, however, the production rate of the Cu:CS GDE rose to 509 µmol/m2s but the FE dropped to 69% due to increasing hydrogen evolution reaction (HER) competition. The control of mass transport limitations by tuning up the membrane overlayer properties in membrane coated electrodes (MCE) prepared by coating a CS-based membrane over the Cu:CS GDE enhanced its selectivity to C2H4 to a FE of 98% at 10 mA cm−2 with negligible competing HER. The concentration of carbon monoxide was below the experimental detection limit irrespective of the current density, with no CO2 crossover to the anodic compartment. This study suggests there may be potential in sustainable alernatives to fossil-based or perfluorinated materials in ion-exchange membrane and electrode fabrication, which constitute a step forward towards decarbonization in the circular economy perspective.

Anchoring Ionic Liquid in Copper Electrocatalyst for Improving CO2 Conversion to Ethylene.

Electrochemical conversion of CO2 to valuable fuels is appealing for CO2 fixation and energy storage. The Cu-based catalysts feature unique superiorities, but achieving high ethylene selectivity is still restricted. In this study, we propose the anchoring of an ionic liquid (IL) on a Cu electrocatalyst for improving the electrochemical CO2 reduction to ethylene. In a water-based electrolyte and a commonly used H-type cell, a high ethylene Faradaic efficiency of 77.3 % was achieved at -1.49 V (vs. RHE). Experimental and theoretical studies reveal that an IL can modify the electronic structure of a Cu catalyst through its interaction with Cu, making it more conducive to *CO dimerization for ethylene formation.

Anchoring Ionic Liquid in Copper Electrocatalyst for Improving CO2 Conversion to Ethylene

AbstractElectrochemical conversion of CO2 to valuable fuels is appealing for CO2 fixation and energy storage. The Cu‐based catalysts feature unique superiorities, but achieving high ethylene selectivity is still restricted. In this study, we propose the anchoring of an ionic liquid (IL) on a Cu electrocatalyst for improving the electrochemical CO2 reduction to ethylene. In a water‐based electrolyte and a commonly used H‐type cell, a high ethylene Faradaic efficiency of 77.3 % was achieved at −1.49 V (vs. RHE). Experimental and theoretical studies reveal that an IL can modify the electronic structure of a Cu catalyst through its interaction with Cu, making it more conducive to *CO dimerization for ethylene formation.

Highly Selective Atomically Dispersed Copper Electrocatalyst for CO2 Reduction to Ethanol

Introduction Ethanol has been extensively blended in gasoline as fuel to improve the combustion efficiency. Electrochemical CO2 reduction reaction (CO2RR) to ethanol and other value-added chemicals offers a promising “carbon-neutral” or even “carbon-negative” strategy1 when combined with renewable electricity, making the approach not only environmentally sound but also economically attractive. A key challenge for CO2RR is the lack of electrocatalyst that is capable of converting CO2 to a single product with high current efficiency, i.e. Faradaic efficiency (FE), low overpotentials and high durability2. Here, we report the preparation of commercial carbon-supported Cu SA catalysts by an amalgamated Cu–Li method. The catalysts demonstrated highly selective CO2-to-ethanol conversion with FE reaching ~91% at -0.7 V versus RHE and an onset potential as low as -0.4 V with FE of ~15%. The FE of the catalysts maintained at roughly 90% without degradation for 16 h. The CO2-to-ethanol FE is favored by high initial dispersion of single Cu atoms. Operando synchrotron X-ray absorption spectroscopy revealed that such dispersion played a critical role in a reversible transformation between Cu SA and Cu n (n= 3 and 4) as the active sites during the electrocatalytic reaction. Materials and Methods Preparing single atom catalyst starts with melting metal in liquid lithium in an Ar-filled glovebox. Lithium was heated to 200 °C, then the target metal (Cu in this case) was simultaneously added and kept for 4 h. The Li-Cu solid solutions were removed from the glovebox. The prepared amalgamated Cu-Li was oxidized to LiOH and mixed with carbon support materials before the LiOH was leached out with copious amounts of DI water, leaving the metal single atoms imbedded in the carbon support. Results and Discussion High-angle annular dark-field and aberration-corrected scanning transmission electron microscopy (HAADF-STEM), and X-ray absorption spectrum (XAS) are used to characterize the resulting samples. Fig. 1a shows a HAADF-STEM image of the atomically disperse Cu in sample Cu/C-0. Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) are used to characterize the coordination structures and the electronic structure of the Cu atoms. Based on these XAS techniques, the Cu atoms are identified as being coordinated with four oxygens (Figure 1b). Figure 1c shows the FEs and CO2RR product distributions as the function of applied potentials from -0.4 V to -1.2 V over Cu/C-0.4. We detected the active potential for ethanol formation as low as -0.4 V with a decent FE of ~ 15%. The peak FE for ethanol is ~91% at a low potential of only -0.6 V and -0.7 V. To our knowledge, this value represents the highest FE for direct electrocatalytic CO2-to-ethanol conversion among Cu-based catalysts. The Cu/C-0.4 catalyst over a 16-hour span at -0.7 V showed an excellent stability in both current density and FE of CO2-to-ethanol over Cu/C-0.4 (Fig. 1d). Fig. 1e shows the FEs of the ethanol formation at different potentials obtained from individual catalyst studied. For Cu/C-0.1, Cu/C-0.4 and Cu/C-0.8, the FE for ethanol formation followed nearly identical profile with the active potential starting at as low as -0.4 V and reaching peak value > 90% at -0.7 V. Once the Cu loading reached to 1.6 wt.% or higher, however, the ethanol FE profile underwent a drastic reduction. Operando XAS study under the reaction conditions revealed a crucial dynamic catalytic mechanism, a reversible transformation between atomically dispersed Cu to Cun (n=3 or 4) clusters (Fig. 1f).Fig 1 (a) Representative HAADF-STEM images of Cu/C-0.4 showing the presence of isolated Cu species; (b) Fourier transform of k2-weighted R-space χ EXAFS data of the catalysts plus Cu(AcAc)2 as reference; (c) FE and the product distribution at different polarization potentials. The data were averaged over three repeated measurements with the standard deviations marked by black error bar for ethanol and red error bar for the total products; (d) FE and current density as the function of time during chronoamperometric electrolysis at -0.6 V; (e) FE of CO2-to-ethanol at different potentials over catalysts of different Cu loadings. (f) The hypothesised reaction mechanism suggested by the operando measurements. Significance Understanding the role of metal single atoms on the CO2 electrochemical reduction reaction is fundamentally important in designing new CO2RR catalyst for the large-scale production of value-added liquid fuels and chemicals. Reference 1 Xu, H. P. et al Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically-dispersed copper, Nature Energy, 2020, 5, 623-632.2 Zhou, Y. S. et al Dopant-induced electron localization drives CO2 reduction to C2 hydrocarbons. Nature Chemistry, 2018, 10, 974–980. Figure 1

Highly Selective Atomically Dispersed Copper Electrocatalyst for CO2 Reduction to Ethanol

Introduction Ethanol has been extensively blended in gasoline as fuel to improve the combustion efficiency. Electrochemical CO2 reduction reaction (CO2RR) to ethanol and other value-added chemicals offers a promising “carbon-neutral” or even “carbon-negative” strategy1 when combined with renewable electricity, making the approach not only environmentally sound but also economically attractive. A key challenge for CO2RR is the lack of electrocatalyst that is capable of converting CO2 to a single product with high current efficiency, i.e. Faradaic efficiency (FE), low overpotentials and high durability2. Here, we report the preparation of commercial carbon-supported Cu SA catalysts by an amalgamated Cu–Li method. The catalysts demonstrated highly selective CO2-to-ethanol conversion with FE reaching ~91% at -0.7 V versus RHE and an onset potential as low as -0.4 V with FE of ~15%. The FE of the catalysts maintained at roughly 90% without degradation for 16 h. The CO2-to-ethanol FE is favored by high initial dispersion of single Cu atoms. Operando synchrotron X-ray absorption spectroscopy revealed that such dispersion played a critical role in a reversible transformation between Cu SA and Cu n (n= 3 and 4) as the active sites during the electrocatalytic reaction. Materials and Methods Preparing single atom catalyst starts with melting metal in liquid lithium in an Ar-filled glovebox. Lithium was heated to 200 °C, then the target metal (Cu in this case) was simultaneously added and kept for 4 h. The Li-Cu solid solutions were removed from the glovebox. The prepared amalgamated Cu-Li was oxidized to LiOH and mixed with carbon support materials before the LiOH was leached out with copious amounts of DI water, leaving the metal single atoms imbedded in the carbon support. Results and Discussion High-angle annular dark-field and aberration-corrected scanning transmission electron microscopy (HAADF-STEM), and X-ray absorption spectrum (XAS) are used to characterize the resulting samples. Figure. 1a shows a HAADF-STEM image of the atomically disperse Cu in sample Cu/C-0. Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) are used to characterize the coordination structures and the electronic structure of the Cu atoms. Based on these XAS techniques, the Cu atoms are identified as being coordinated with four oxygens (Figure 1b). Figure 1c shows the FEs and CO2RR product distributions as the function of applied potentials from -0.4 V to -1.2 V over Cu/C-0.4. We detected the active potential for ethanol formation as low as -0.4 V with a decent FE of ~ 15%. The peak FE for ethanol is ~91% at a low potential of only -0.6 V and -0.7 V. To our knowledge, this value represents the highest FE for direct electrocatalytic CO2-to-ethanol conversion among Cu-based catalysts. The Cu/C-0.4 catalyst over a 16-hour span at -0.7 V showed an excellent stability in both current density and FE of CO2-to-ethanol over Cu/C-0.4 (Figure. 1d). Figure. 1e shows the FEs of the ethanol formation at different potentials obtained from individual catalyst studied. For Cu/C-0.1, Cu/C-0.4 and Cu/C-0.8, the FE for ethanol formation followed nearly identical profile with the active potential starting at as low as -0.4 V and reaching peak value > 90% at -0.7 V. Once the Cu loading reached to 1.6 wt.% or higher, however, the ethanol FE profile underwent a drastic reduction. Operando XAS study under the reaction conditions revealed a crucial dynamic catalytic mechanism, a reversible transformation between atomically dispersed Cu to Cun (n=3 or 4) clusters (Figure. 1f).Figure 1. (a) Representative HAADF-STEM images of Cu/C-0.4 showing the presence of isolated Cu species; (b) Fourier transform of k2-weighted R-space χ EXAFS data of the catalysts plus Cu(AcAc)2 as reference; (c) FE and the product distribution at different polarization potentials. The data were averaged over three repeated measurements with the standard deviations marked by black error bar for ethanol and red error bar for the total products; (d) FE and current density as the function of time during chronoamperometric electrolysis at -0.6 V; (e) FE of CO2-to-ethanol at different potentials over catalysts of different Cu loadings. (f) The hypothesised reaction mechanism suggested by the operando measurements. Significance Understanding the role of metal single atoms on the CO2 electrochemical reduction reaction is fundamentally important in designing new CO2RR catalyst for the large-scale production of value-added liquid fuels and chemicals.

Efficient carboxylation of styrene and carbon dioxide by single-atomic copper electrocatalyst

Electrocarboxylation of olefins with carbon dioxide (CO2) is a potential approach to produce carboxylates as synthetic intermediates of polymer and pharmaceuticals. Nonetheless, due to the intrinsic inertness of CO2 at ambient conditions, the electrocarboxylation efficiency has been quite limited, typically with high applied potentials and low current densities. In this work, we demonstrate that nitrogen-coordinated single-atomic copper sites on carbon framework (Cu/NC) served as an excellent electrocatalyst for electrocarboxylation of styrene with CO2. The Cu/NC catalyst allowed to efficiently activate CO2, followed by nucleophilic attack to carboxylate styrene to produce phenylsuccinic acid, thus leading the reaction toward the CO2 activation pathway. The enhanced CO2 activation capability enabled increased selectivity and activity for electrocarboxylation of styrene. The Faradaic efficiency of electrocarboxylation was 92%, suggesting most of the activated CO2 proceeded to react with styrene rather than direct reduction to CO or CH4. The electrocarboxylation exhibited almost 100% product selectivity toward phenylsuccinic acid, with a high partial current density of 58 mA·cm−2 at −2.2 V (vs. Ag/AgI), corresponding to an outstanding production rate of 216 mg·cm−2·h−1, substantially exceeding previously reported works. Our work suggests an exciting perspective in electrocarboxylation of olefins by rational design of CO2 activation electrocatalysts.

Catalytic Cooperation between a Copper Oxide Electrocatalyst and a Microbial Community for Microbial Electrosynthesis.

Electrocatalytic metals and microorganisms can be combined for CO2 conversion in microbial electrosynthesis (MES). However, a systematic investigation on the nature of interactions between metals and MES is still lacking. To investigate this nature, we integrated a copper electrocatalyst, converting CO2 to formate, with microorganisms, converting CO2 to acetate. A co-catalytic (i. e. metabolic) relationship was evident, as up to 140 mg L-1 of formate was produced solely by copper oxide, while formate was also evidently produced by copper and consumed by microorganisms producing acetate. Due to non-metabolic interactions, current density decreased by over 4 times, though acetate yield increased by 3.3 times. Despite the antimicrobial role of copper, biofilm formation was possible on a pure copper surface. Overall, we show for the first time that a CO2 -reducing copper electrocatalyst can be combined with MES under biological conditions, resulting in metabolic and non-metabolic interactions.

Residual Chlorine Induced Cationic Active Species on a Porous Copper Electrocatalyst for Highly Stable Electrochemical CO2 Reduction to C2.

Electrochemical carbon dioxide (CO2 ) reduction reaction (CO2 RR) is an attractive approach to deal with the emission of CO2 and to produce valuable fuels and chemicals in a carbon-neutral way. Many efforts have been devoted to boost the activity and selectivity of high-value multicarbon products (C2+ ) on Cu-based electrocatalysts. However, Cu-based CO2 RR electrocatalysts suffer from poor catalytic stability mainly due to the structural degradation and loss of active species under CO2 RR condition. To date, most reported Cu-based electrocatalysts present stabilities over dozens of hours, which limits the advance of Cu-based electrocatalysts for CO2 RR. Herein, a porous chlorine-doped Cu electrocatalyst exhibits high C2+ Faradaic efficiency (FE) of 53.8 % at -1.00 V versus reversible hydrogen electrode (VRHE ). Importantly, the catalyst exhibited an outstanding catalytic stability in long-term electrocatalysis over 240 h. Experimental results show that the chlorine-induced stable cationic Cu0 /Cu+ species and the well-preserved structure with abundant active sites are critical to the high FE of C2+ in the long-term run of electrochemical CO2 reduction.

Residual Chlorine Induced Cationic Active Species on a Porous Copper Electrocatalyst for Highly Stable Electrochemical CO2 Reduction to C2+

AbstractElectrochemical carbon dioxide (CO2) reduction reaction (CO2RR) is an attractive approach to deal with the emission of CO2 and to produce valuable fuels and chemicals in a carbon‐neutral way. Many efforts have been devoted to boost the activity and selectivity of high‐value multicarbon products (C2+) on Cu‐based electrocatalysts. However, Cu‐based CO2RR electrocatalysts suffer from poor catalytic stability mainly due to the structural degradation and loss of active species under CO2RR condition. To date, most reported Cu‐based electrocatalysts present stabilities over dozens of hours, which limits the advance of Cu‐based electrocatalysts for CO2RR. Herein, a porous chlorine‐doped Cu electrocatalyst exhibits high C2+ Faradaic efficiency (FE) of 53.8 % at −1.00 V versus reversible hydrogen electrode (VRHE). Importantly, the catalyst exhibited an outstanding catalytic stability in long‐term electrocatalysis over 240 h. Experimental results show that the chlorine‐induced stable cationic Cu0/Cu+ species and the well‐preserved structure with abundant active sites are critical to the high FE of C2+ in the long‐term run of electrochemical CO2 reduction.

(Energy Technology Division Supramaniam Srinivasan Young Investigator Award Address) Using Mechanistic Understanding of Electrocatalytic CO2 and CO Reduction to Guide Catalyst Discovery

Many technical challenges remain for the implementation of CO2 electrolysis as a practical means for CO2 utilization. A key challenge in heterogeneous catalysis has been developing technologies that can selectively convert CO2 or CO into short‐chain multi‐carbon oxygenates due to complex reaction networks.1 I will first discuss how CO reduction can be used as a means to understand how the electrochemical potential, electrolyte pH, and Cu electrode morphology impact product selectivity.2 Proper use of these design principles on high roughness factor Cu electrodes enabled 100% selectivity for CO reduction to multi-carbon oxygenates at low overpotentials.3 Next, I will discuss how engineering the surface structure of Cu electrocatalysts led to the discovery of structure-reactivity relationships.4 Using a combination of electrocatalysis experiments and in situ surface probe microscopy, we demonstrate that undercoordinated sites are selective motifs for oxygenates and C-C coupling. By comparing these results with state-of-the-art Cu electrocatalysts from the literature, we show that different morphologies have similar intrinsic activities for CO2 reduction. Afterwards, I will discuss a tandem catalysis approach for improving upon these normalized CO2 reduction activities, which is enabled by utilizing bimetallic electrodes consisting of Au nanoparticles on polycrystalline Cu (Au/Cu).5 At low overpotentials, the Au/Cu electrocatalyst has a synergistic catalytic activity superior to that of either Cu or Au, indicating that tandem catalysis mechanisms can be used to increase the energy efficiency for alcohol production. By comparing Au/Cu to Cu, I will highlight common potential-driven trends in the selectivity to oxygenated and multi-carbon products. Combined, all of these findings outline key principles for designing electrocatalytic systems that are able to produce valuable chemicals and fuels from CO2 or CO with high energy efficiency. Finally, I will conclude the presentation with our perspective on key research opportunities for the design and implementation of CO2 vapor-feed reactors, a necessary endeavor to achieve the performances required for practical implementation.6,7 Nitopi, S. et al. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chemical Reviews 119, 7610-7672 (2019).Wang, L. et al. Electrochemical Carbon Monoxide Reduction on Polycrystalline Copper: Effects of Potential, Pressure, and pH on Selectivity toward Multicarbon and Oxygenated Products. ACS Catalysis 8, 7445-7454 (2018).Wang, L. et al. Electrochemically converting carbon monoxide to liquid fuels by directing selectivity with electrode surface area. Nature Catalysis 2, 702-708 (2019).Hahn, C., Hatsukade, T., Kim, Y.-G., Vailionis, A., Baricuatro, J.H., Higgins, D.C., Nitopi, S.A., Soriaga, M.P. & Jaramillo, T.F. Engineering Cu surfaces for the electrocatalytic conversion of CO2: Controlling selectivity toward oxygenates and hydrocarbons. Proceedings of the National Academy of Sciences 114, 5918 (2017).Morales-Guio, C.G. et al. Improved CO2 reduction activity towards C2+ alcohols on a tandem gold on copper electrocatalyst. Nature Catalysis 1, 764-771 (2018).De Luna, P., Hahn, C., Higgins, D., Jaffer, S.A., Jaramillo, T.F. & Sargent, E.H. What would it take for renewably powered electrosynthesis to displace petrochemical processes? Science 364, eaav3506 (2019).Higgins, D., Hahn, C., Xiang, C., Jaramillo, T.F. & Weber, A.Z. Gas-Diffusion Electrodes for Carbon Dioxide Reduction: A New Paradigm. ACS Energy Letters 4, 317-324 (2019).

Operando time-resolved X-ray absorption spectroscopy reveals the chemical nature enabling highly selective CO2 reduction

Copper electrocatalysts have been shown to selectively reduce carbon dioxide to hydrocarbons. Nevertheless, the absence of a systematic study based on time-resolved spectroscopy renders the functional agent—either metallic or oxidative Copper—for the selectivity still undecidable. Herein, we develop an operando seconds-resolved X-ray absorption spectroscopy to uncover the chemical state evolution of working catalysts. An oxide-derived Copper electrocatalyst is employed as a model catalyst to offer scientific insights into the roles metal states serve in carbon dioxide reduction reaction (CO2RR). Using a potential switching approach, the model catalyst can achieve a steady chemical state of half-Cu(0)-and-half-Cu(I) and selectively produce asymmetric C2 products - C2H5OH. Furthermore, a theoretical analysis reveals that a surface composed of Cu-Cu(I) ensembles can have dual carbon monoxide molecules coupled asymmetrically, which potentially enhances the catalyst’s CO2RR product selectivity toward C2 products. Our results offer understandings of the fundamental chemical states and insights to the establishment of selective CO2RR.

CO2 Conversion by Combining a Copper Electrocatalyst and Wild‐type Microorganisms

AbstractCarbon dioxide (CO2) can be converted to valuable products using different catalysts, including metal or biological catalysts (e. g. microorganisms). Some products formed by metal electrocatalysts can be further utilized by microorganisms, and therefore catalytic cooperation can be envisioned. To prevent cumbersome separations, it is beneficial when both catalyst work under the same conditions, or at least in the same reaction medium. Here, we will show that a formate‐producing copper electrocatalyst can function in a biological medium. Furthermore, we will show that the effluent of the copper‐containing reactor can be used without purification as the sole medium for a bio‐reactor, inoculated with a mixed culture of microorganisms. In that second reactor, formate, H2 and CO2 are consumed by the microorganisms, forming acetate and methane. Compared to simple buffer electrolyte, catalytic activity of copper was improved in the presence of microbial growth medium, likely due to EDTA (Ethylenediaminetetraacetic acid) present in the latter.

(Energy Technology Division Supramaniam Srinivasan Young Investigator Award Address) Using Mechanistic Understanding of Electrocatalytic CO2 and CO Reduction to Guide Catalyst Discovery

Many technical challenges remain for the implementation of CO2 electrolysis as a practical means for CO2 utilization. A key challenge in heterogeneous catalysis has been developing technologies that can selectively convert CO2 or CO into short‐chain multi‐carbon oxygenates due to complex reaction networks.1 I will first discuss how CO reduction can be used as a means to understand how the electrochemical potential, electrolyte pH, and Cu electrode morphology impact product selectivity.2 Proper use of these design principles on high roughness factor Cu electrodes enabled 100% selectivity for CO reduction to multi-carbon oxygenates at low overpotentials.3 Next, I will discuss how engineering the surface structure of Cu electrocatalysts led to the discovery of structure-reactivity relationships.4 Using a combination of electrocatalysis experiments and in situ surface probe microscopy, we demonstrate that undercoordinated sites are selective motifs for oxygenates and C-C coupling. By comparing these results with state-of-the-art Cu electrocatalysts from the literature, we show that different morphologies have similar intrinsic activities for CO2 reduction. Afterwards, I will discuss a tandem catalysis approach for improving upon these normalized CO2 reduction activities, which is enabled by utilizing bimetallic electrodes consisting of Au nanoparticles on polycrystalline Cu (Au/Cu).5 At low overpotentials, the Au/Cu electrocatalyst has a synergistic catalytic activity superior to that of either Cu or Au, indicating that tandem catalysis mechanisms can be used to increase the energy efficiency for alcohol production. By comparing Au/Cu to Cu, I will highlight common potential-driven trends in the selectivity to oxygenated and multi-carbon products. Combined, all of these findings outline key principles for designing electrocatalytic systems that are able to produce valuable chemicals and fuels from CO2 or CO with high energy efficiency. Finally, I will conclude the presentation with our perspective on key research opportunities for the design and implementation of CO2 vapor-feed reactors, a necessary endeavor to achieve the performances required for practical implementation.6,7 1. Nitopi, S. et al. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chemical Reviews 119, 7610-7672 (2019).2. Wang, L. et al. Electrochemical Carbon Monoxide Reduction on Polycrystalline Copper: Effects of Potential, Pressure, and pH on Selectivity toward Multicarbon and Oxygenated Products. ACS Catalysis 8, 7445-7454 (2018).3. Wang, L. et al. Electrochemically converting carbon monoxide to liquid fuels by directing selectivity with electrode surface area. Nature Catalysis 2, 702-708 (2019).4. Hahn, C., Hatsukade, T., Kim, Y.-G., Vailionis, A., Baricuatro, J.H., Higgins, D.C., Nitopi, S.A., Soriaga, M.P. & Jaramillo, T.F. Engineering Cu surfaces for the electrocatalytic conversion of CO2: Controlling selectivity toward oxygenates and hydrocarbons. Proceedings of the National Academy of Sciences 114, 5918 (2017).5. Morales-Guio, C.G. et al. Improved CO2 reduction activity towards C2+ alcohols on a tandem gold on copper electrocatalyst. Nature Catalysis 1, 764-771 (2018).6. De Luna, P., Hahn, C., Higgins, D., Jaffer, S.A., Jaramillo, T.F. & Sargent, E.H. What would it take for renewably powered electrosynthesis to displace petrochemical processes? Science 364, eaav3506 (2019).7. Higgins, D., Hahn, C., Xiang, C., Jaramillo, T.F. & Weber, A.Z. Gas-Diffusion Electrodes for Carbon Dioxide Reduction: A New Paradigm. ACS Energy Letters 4, 317-324 (2019).