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We report an in situ catalyst regeneration strategy that can extend the operation time of Cu-based catalysts for electrochemical CO2 reduction many times.

Upgrading carbon dioxide/monoxide to multi-carbon C

Electrochemical CO

The electrochemical reduction of carbon dioxide (CO2) to chemicals is gaining great attention as a pragmatic solution for greenhouse gas mitigation and for the utilization of CO2 to produce useful fuels and chemical feedstocks using intermittent renewable energy sources. In recent years, strategies to design electrocatalysts for CO2 reduction to ethanol, a valuable liquid fuel, have been increasingly reported. The mechanistic understanding providing insights into steps of the reduction process has allowed for further development of highly efficient and selective catalysts. Several significant breakthroughs have been made; however, the door toward industrial-scale production of ethanol from CO2 is still wide open as most electrocatalytic systems reported so far are still suffering from low energy efficiency, inferior stability, and discouraging selectivity. Inspired by recent advances in the field, we herein provide a review of fundamental and material advances of the electrochemical CO2 reduction to ethanol. First, we discuss the pathways and the effects of reaction-environment factors on the formation of ethanol from both theoretical and spectroscopic points of view. We then give an overview of different strategies to design electrocatalysts for this reaction. Finally, we discuss the remaining challenges and propose promising future research directions, with the aim to bring this technology closer to practical applications.

As renewable electricity prices continue to decline, interest grows in alternative routes for the synthesis of sustainable fuels and chemicals, including ammonia. Considering demand for fertilizers, as well as its future potential as a dispatchable energy vector, sustainable synthesis of ammonia is being explored as an alternative to the capital- and carbon-intensive fossil-fuel-driven Haber–Bosch process. Here we assess stages along a transition to the sustainable synthesis of ammonia, looking at economic feasibility and climate impacts compared to the incumbent Haber–Bosch without and with CO2 capture. This analysis enables us to suggest technological thresholds for sustainable synthesis of ammonia to become economically and environmentally favourable. When driven by renewable energy sources, the water electrolyzer (near $400 per kW) coupled Haber–Bosch process will reach cost parity near 2.5 cents per kWh electricity. In the case of direct electrochemical ammonia synthesis, achieving cost-parity using the same 2.5 cents per kWh electricity will rely on achieving major advances in performance: an electrolysis full-cell energy efficiency exceeding 40% at a current density of 0.5 A cm−2. Once this operating performance is reached, electrically-powered ammonia synthesis will bring climate benefits when coupled with low-carbon electricity (

This work was supported by MOST (grant no. 2016YFA0203302), NSFC (grant nos. 21875042, 21634003 and 51573027), STCSM (grant nos. 16JC1400702 and 18QA1400800), SHMEC (grant no. 2017-01-07-00-07-E00062) and Yanchang Petroleum Group. This work was also supported by The Programme for Professor of Eastern Scholar at Shanghai Institutions of Higher Learning. This work was supported by the Ontario Research Fund—Research Excellence Program, NSERC and the CIFAR Bio-Inspired Solar Energy program. This work has also benefited from the use of the SGM beamlines at Canadian Light Source; the 1W1B and 4B9B beamlines at the Beijing Synchrotron Radiation Facility; the BL14W1, BL08U1-A beamline at Shanghai Synchrotron Radiation Facility; and the 44A beamline at Taiwan Photon Source (TPS). Mossbauer spectroscopy measurements were conducted at the Advanced Photon Source, a Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. We acknowledge the Paul Scherrer Institut, Villigen, Switzerland, for provision of synchrotron radiation beamtime at the beamline SuperXAS of the SLS and would like to thank M. Nachtegaal for assistance. We thank M. Garcia-Melchor and Y. Zhang for discussions on DFT calculations. We thank J. Wu for the assistance with the TEM measurements. We thank R. Wolowiec and D. Kopilovic for their assistance. For computer time, this research used the resources of the Supercomputing Laboratory at KAUST.

The electrochemical reduction of CO2 to methane is a promising method to store intermittent renewable energy. Previous research reporting high methane selectivity has relied on H-cells, and total c...

Electrochemical carbon dioxide (CO2) reduction powered by renewable electricity offers a path to produce valuable products from CO2 —this earth-scale human waste— and to store intermittent renewable energy in the form of chemical fuels. Recently, single metal atoms (SMAs) immobilized on a conductive substrate have been shown as effective catalysts for the electrochemical CO2 reduction, opening the door to a new generation of low-cost and high-performance catalysts for fuel and chemical production. The unique physical and chemical properties of a single-atomic structure, the homogeneity of the active sites, combined with tunable coordination environment are essential for realizing highly active and selective catalysts. In this review, we focus on the structure-performance relationship in SMA catalysts for CO2 reduction from both theoretical and experimental aspects. We discuss why SMA catalysts exhibit distinct catalytic performance compared to their counterpart nanoparticles. Recent strategies for improving the CO2 reduction selectivity and activity by tuning the nature and coordination environment of SMA active sites are described. Finally, we highlight potential applications of SMA catalysts in practical CO2 reduction conditions, critical challenges and the path toward efficient electrochemical CO2 reduction catalysis based on SMAs.

The rapid increase in global energy demand and the need to replace carbon dioxide (CO2)-emitting fossil fuels with renewable sources have driven interest in chemical storage of intermittent solar and wind energy1,2. Particularly attractive is the electrochemical reduction of CO2 to chemical feedstocks, which uses both CO2 and renewable energy3–8. Copper has been the predominant electrocatalyst for this reaction when aiming for more valuable multi-carbon products9–16, and process improvements have been particularly notable when targeting ethylene. However, the energy efficiency and productivity (current density) achieved so far still fall below the values required to produce ethylene at cost-competitive prices. Here we describe Cu-Al electrocatalysts, identified using density functional theory calculations in combination with active machine learning, that efficiently reduce CO2 to ethylene with the highest Faradaic efficiency reported so far. This Faradaic efficiency of over 80 per cent (compared to about 66 per cent for pure Cu) is achieved at a current density of 400 milliamperes per square centimetre (at 1.5 volts versus a reversible hydrogen electrode) and a cathodic-side (half-cell) ethylene power conversion efficiency of 55 ± 2 per cent at 150 milliamperes per square centimetre. We perform computational studies that suggest that the Cu-Al alloys provide multiple sites and surface orientations with near-optimal CO binding for both efficient and selective CO2 reduction17. Furthermore, in situ X-ray absorption measurements reveal that Cu and Al enable a favourable Cu coordination environment that enhances C–C dimerization. These findings illustrate the value of computation and machine learning in guiding the experimental exploration of multi-metallic systems that go beyond the limitations of conventional single-metal electrocatalysts. Machine learning predicts Cu-Al electrocatalysts provide better efficiency and productivity than copper when using intermittent renewable electricity to convert carbon dioxide to useful chemicals and fuels.

The carbon dioxide electroreduction reaction (CO2RR) provides ways to produce ethanol but its Faradaic efficiency could be further improved, especially in CO2RR studies reported at a total current density exceeding 10 mA cm−2. Here we report a class of catalysts that achieve an ethanol Faradaic efficiency of (52 ± 1)% and an ethanol cathodic energy efficiency of 31%. We exploit the fact that suppression of the deoxygenation of the intermediate HOCCH* to ethylene promotes ethanol production, and hence that confinement using capping layers having strong electron-donating ability on active catalysts promotes C–C coupling and increases the reaction energy of HOCCH* deoxygenation. Thus, we have developed an electrocatalyst with confined reaction volume by coating Cu catalysts with nitrogen-doped carbon. Spectroscopy suggests that the strong electron-donating ability and confinement of the nitrogen-doped carbon layers leads to the observed pronounced selectivity towards ethanol. The electroreduction of CO2 to ethanol could enable the clean production of fuels using renewable power. This study shows how confinement effects from nitrogen-doped carbon layers on copper catalysts enable selective ethanol production from CO2 with a Faradaic efficiency of up to 52%.

Graceful choreography for CO 2 and H 2 O One challenge for efficient electrochemical reduction of carbon dioxide (CO 2 ) is that the gas is hydrophobic, but many of its desirable reactions require water (H 2 O). García de Arquer et al. addressed this problem by combining a copper electrocatalyst with an ionomer assembly that intersperses sulfonate-lined paths for the H 2 O with fluorocarbon channels for the CO 2 . The electrode architecture enables production of two-carbon products such as ethylene and ethanol at current densities just over an ampere per square centimeter. Science , this issue p. 661

There is significant interest in developing efficient electrochemical processes for commodity chemical manufacturing, all directly powered by renewable electricity. A vital chemical is ethylene glycol, with an annual consumption of around 20 million tonnes due to its use as antifreeze and as a polymer precursor. Here we report a one-step electrochemical route at ambient temperature and pressure in aqueous media to the selective partial oxidation of ethylene to ethylene glycol. Tuning of the catalyst OH binding energy was hypothesized to be crucial for facilitating the transfer of OH to *C2H4OH to form ethylene glycol. Computational studies suggested that a gold-doped palladium catalyst could perform this step efficiently, and experimentally we found it to exhibit an approximate 80% Faradaic efficiency to ethylene glycol, retaining its performance for 100 hours of continuous operation. These findings represent a significant advance in the development of selective anodic partial oxidation reactions in aqueous media under mild conditions. Ethylene glycol is a commodity chemical with an annual consumption of 20 million tonnes. Its production generates 1.6 tonnes of CO2 per tonne of ethylene glycol. To reduce these CO2 emissions, the authors report a one-step electrochemical route to selectively convert ethylene to ethylene glycol at ambient temperature and pressure in aqueous media.

The electroreduction of carbon dioxide (CO2) to C2 products is a promising approach to divert and utilize CO2 emissions. However, the requirement of a purified CO2 feedstock decreases the economic feasibility of CO2 electrolysis. Direct utilization of industrial flue gas streams is encumbered by low CO2 concentrations and reactive oxygen (O2) impurities. We demonstrate that pressurization enables efficient CO2 electroreduction of dilute CO2 streams (15% v/v); however, with the inclusion of O2 (4% v/v), the oxygen reduction reaction (ORR) displaces CO2 reduction and consumes up to 99% of the applied current in systems based on previously-reported catalysts. We develop a hydrated ionomer catalyst coating strategy that selectively slows O2 transport and stabilizes the copper catalyst. Applying this strategy, we convert an O2-containing flue gas to C2 products at a faradaic efficiency (FE) of 68% and a non-iR-corrected full cell energetic efficiency (EE) of 26%.

Electrochemical conversion of CO2 into liquid fuels, powered by renewable electricity, offers one means to address the need for the storage of intermittent renewable energy. Here we present a cooperative catalyst design of molecule–metal catalyst interfaces with the goal of producing a reaction-intermediate-rich local environment, which improves the electrosynthesis of ethanol from CO2 and H2O. We implement the strategy by functionalizing the copper surface with a family of porphyrin-based metallic complexes that catalyse CO2 to CO. Using density functional theory calculations, and in situ Raman and operando X-ray absorption spectroscopies, we find that the high concentration of local CO facilitates carbon–carbon coupling and steers the reaction pathway towards ethanol. We report a CO2-to-ethanol Faradaic efficiency of 41% and a partial current density of 124 mA cm−2 at −0.82 V versus the reversible hydrogen electrode. We integrate the catalyst into a membrane electrode assembly-based system and achieve an overall energy efficiency of 13%. Electrochemical conversion of CO2 into liquid fuels, powered by renewable electricity, offers one means to address the need for the storage of intermittent renewable energy. Now, Sargent and co-workers present a cooperative catalyst design of molecule–metal interfaces to improve the electrosynthesis of ethanol from CO2 by producing a reaction-intermediate-rich local environment.

The electrosynthesis of C2+ hydrocarbons from CO2 has attracted recent attention in light of the relatively high market price per unit energy input. Today’s low selectivities and stabilities towards C2+ products at high current densities curtail system energy efficiency, which limits their prospects for economic competitiveness. Here we present a materials processing strategy based on in situ electrodeposition of copper under CO2 reduction conditions that preferentially expose and maintain Cu(100) facets, which favour the formation of C2+ products. We observe capping of facets during catalyst synthesis and achieve control over faceting to obtain a 70% increase in the ratio of Cu(100) facets to total facet area. We report a 90% Faradaic efficiency for C2+ products at a partial current density of 520 mA cm−2 and a full-cell C2+ power conversion efficiency of 37%. We achieve nearly constant C2H4 selectivity over 65 h operation at 350 mA cm−2 in a membrane electrode assembly electrolyser. Electrocatalytic reduction of CO2 to multicarbon products is useful for producing high-value chemicals and fuels. Here the authors present a strategy that is based on the in situ electrodeposition of copper under CO2 reduction conditions that preferentially expose and maintain Cu(100) facets, which favour the formation of C2+ products.

The availability of inexpensive industrial CO gas streams motivates efficient electrocatalytic upgrading of CO to higher-value feedstocks such as ethylene. However, the electrosynthesis of ethylene by the CO reduction reaction (CORR) has suffered from low selectivity and energy efficiency. Here we find that the recent strategy of increasing performance through use of highly alkaline electrolyte—which is very effective in CO2RR—fails in CORR and drives the reaction to acetate. We then observe that ethylene selectivity increases when we constrain (decrease) CO availability. Using density functional theory, we show how CO coverage on copper influences the reaction pathways of ethylene versus oxygenate: lower CO coverage stabilizes the ethylene-relevant intermediates whereas higher CO coverage favours oxygenate formation. We then control local CO availability experimentally by tuning the CO concentration and reaction rate; we achieve ethylene Faradaic efficiencies of 72% and a partial current density of >800 mA cm−2. The overall system provides a half-cell energy efficiency of 44% for ethylene production. The electrocatalytic upgrading of CO to higher-value feedstocks provides a promising route to multicarbon products. Here, the authors show that high ethylene selectivity can be achieved by constraining CO availability on copper, with an ethylene Faradaic efficiency of 72% and a partial current density of >800 mA cm−2.

Summary Electrochemical carbon dioxide (CO2) reduction is a promising strategy to synthesize valuable multi-carbon products (C2+) while sequestering CO2 and utilizing intermittent renewable electricity. For industrial deployment, CO2 electrolyzers must remain stable while selectively producing concentrated C2+ products at high rates with modest cell voltages. Here, we present a membrane electrode assembly (MEA) electrolyzer that converts CO2 to C2+ products. We perform side-by-side comparisons of state-of-the-art electrolyzer systems and find that the MEA provides the most stable cell voltage and product selectivity. We then demonstrate an approach to release concentrated gas and liquid products from the cathode outlet. This strategy achieves ∼50% and ∼80% Faradaic efficiency for ethylene and C2+ products, respectively, with cathode outlet concentrations of ∼30% ethylene and the direct production of ∼4 wt % ethanol. We characterize stability by operating continuously for 100 h, the longest stable ethylene production at current densities >100 mA cm−2 among reported CO2 electrolyzers.

The electroreduction of C1 feedgas to high-energy-density fuels provides an attractive avenue to the storage of renewable electricity. Much progress has been made to improve selectivity to C1 and C2 products, however, the selectivity to desirable high-energy-density C3 products remains relatively low. We reason that C3 electrosynthesis relies on a higher-order reaction pathway that requires the formation of multiple carbon-carbon (C-C) bonds, and thus pursue a strategy explicitly designed to couple C2 with C1 intermediates. We develop an approach wherein neighboring copper atoms having distinct electronic structures interact with two adsorbates to catalyze an asymmetric reaction. We achieve a record n-propanol Faradaic efficiency (FE) of (33 ± 1)% with a conversion rate of (4.5 ± 0.1) mA cm−2, and a record n-propanol cathodic energy conversion efficiency (EEcathodic half-cell) of 21%. The FE and EEcathodic half-cell represent a 1.3× improvement relative to previously-published CO-to-n-propanol electroreduction reports., Catalysts for CO electroreduction have focused on Cu, and their main products have been C2 chemicals. Here authors use the concept of asymmetric active sites to develop a class of doped Cu catalysts for C-C coupling, delivering record selectivity to n-propanol.

Summary Defect sites are often proposed as key active sites in the design of catalysts. A promising strategy for improving activity is to achieve a high density of homogeneously dispersed atomic defects; however, this is seldom accomplished in metals. We hypothesize that vacancy-rich catalysts could be obtained through the synthesis of quantum dots (QDs) and their electrochemical reduction during the CO2 reduction reaction (CO2RR). Here, we report that QD-derived catalysts (QDDCs) with up to 20 vol % vacancies achieve record current densities of 16, 19, and 25 mAcm−2 with high faradic efficiencies in the electrosynthesis of formate, carbon monoxide, and ethylene at low potentials of –0.2, –0.3, and –0.9 V versus reversible hydrogen electrode (RHE), respectively. The materials are stable after 80 hr of CO2RR. These CO2RR performances in aqueous solution surpass those of previously reported catalysts by 2×. Together, X-ray absorption spectroscopy and computational studies reveal that the vacancies produce a local atomic and electronic structure that enhances CO2RR.

Electrochemical carbon dioxide recycling provides an attractive approach to synthesizing fuels and chemical feedstocks using renewable energy. On the path to deploying this technology, basic and applied scientific hurdles remain. Integrating catalytic design with mechanistic understanding yields scientific insights and progresses the technology towards industrial relevance. Catalysts must be able to generate valuable carbon-based products with better selectivity, lower overpotentials and improved current densities with extended operation. Here, we describe progress and identify mechanistic questions and performance metrics for catalysts that can enable carbon-neutral renewable energy storage and utilization. Electrochemical carbon dioxide reduction is an attractive approach for obtaining fuels and chemical feedstocks using renewable energy. In this Review, the authors describe progress so far, identify mechanistic questions and performance metrics, and discuss design principles for improved activity and selectivity.

The process of CO2 valorization—from capture of CO2 to its electrochemical upgrade—requires significant inputs in each of the capture, upgrade, and separation steps. Here we report an electrolyzer ...

The electrochemical reduction of CO2 has seen many record-setting advances in C2 productivity in recent years. However, the selectivity for ethanol, a globally significant commodity chemical, is still low compared to the selectivity for products such as ethylene. Here we introduce diverse binding sites to a Cu catalyst, an approach that destabilizes the ethylene reaction intermediates and thereby promotes ethanol production. We develop a bimetallic Ag/Cu catalyst that implements the proposed design toward an improved ethanol catalyst. It achieves a record Faradaic efficiency of 41% toward ethanol at 250 mA/cm2 and -0.67 V vs RHE, leading to a cathodic-side (half-cell) energy efficiency of 24.7%. The new catalysts exhibit an in situ Raman spectrum, in the region associated with CO stretching, that is much broader than that of pure Cu controls, a finding we account for via the diversity of binding configurations. This physical picture, involving multisite binding, accounts for the enhanced ethanol production for bimetallic catalysts, and presents a framework to design multimetallic catalysts to control reaction paths in CO2 reductions toward desired products.

Magic-number gold nanoclusters are atomically precise nanomaterials that have enabled unprecedented insight into structure-property relationships in nanoscience. Thiolates are the most common ligand, binding to the cluster via a staple motif in which only central gold atoms are in the metallic state. The lack of other strongly bound ligands for nanoclusters with different bonding modes has been a significant limitation in the field. Here, we report a previously unknown ligand for gold(0) nanoclusters-N-heterocyclic carbenes (NHCs)-which feature a robust metal-carbon single bond and impart high stability to the corresponding gold cluster. The addition of a single NHC to gold nanoclusters results in significantly improved stability and catalytic properties in the electrocatalytic reduction of CO2. By varying the conditions, nature and number of equivalents of the NHC, predominantly or exclusively monosubstituted NHC-functionalized clusters result. Clusters can also be obtained with up to five NHCs, as a mixture of species.

The renewable-energy-powered electrocatalytic conversion of carbon dioxide and carbon monoxide into carbon-based fuels provides a means for the storage of renewable energy. We sought to convert carbon monoxide—an increasingly available and low-cost feedstock that could benefit from an energy-efficient upgrade in value—into n-propanol, an alcohol that can be directly used as engine fuel. Here we report that a catalyst consisting of highly fragmented copper structures can bring C1 and C2 binding sites together, and thereby promote further coupling of these intermediates into n-propanol. Using this strategy, we achieved an n-propanol selectivity of 20% Faradaic efficiency at a low potential of −0.45 V versus the reversible hydrogen electrode (ohmic corrected) with a full-cell energetic efficiency of 10.8%. We achieved a high reaction rate that corresponds to a partial current density of 8.5 mA cm–2 for n-propanol. The upgrade of carbon monoxide to higher alcohols offers a route to renewable fuels. Now, Sinton, Sargent and co-workers report a highly fragmented, copper-based catalyst with engineered interfaces between the (111) and (100) facets that promote the coupling of C1 and C2 species, leading to enhanced production of n-propanol.

High-performance hydrogen evolution reaction (HER) catalysts are compelling for the conversion of renewable electricity to fuels and feedstocks. The best HER catalysts rely on the use of platinum and show the highest performance in acidic media. Efficient HER catalysts based on inexpensive and Earth-abundant elements that operate in neutral (hence biocompatible) media could enable low-cost direct seawater splitting and the realization of bio-upgraded chemical fuels. In the challenging neutral-pH environment, water splitting is a multistep reaction. Here we present a HER catalyst comprising Ni and CrOx sites doped onto a Cu surface that operates efficiently in neutral media. The Ni and CrOx sites have strong binding energies for hydrogen and hydroxyl groups, respectively, which accelerates water dissociation, whereas the Cu has a weak hydrogen binding energy, promoting hydride coupling. The resulting catalyst exhibits a 48 mV overpotential at a current density of 10 mA cm−2 in a pH 7 buffer electrolyte. These findings suggest design principles for inexpensive, efficient and biocompatible catalytic systems. Integrating electrocatalytic H2 production with biological H2-fed systems for CO2 upgrading requires H2 generation to occur in biocompatible media—typically with neutral pH. Here, the authors design multi-site H2 evolution catalysts that minimize the water dissociation barrier and promote hydride coupling in neutral media.

In hydrogen production, the anodic oxygen evolution reaction (OER) limits the energy conversion efficiency and also impacts stability in proton-exchange membrane water electrolyzers. Widely used Ir-based catalysts suffer from insufficient activity, while more active Ru-based catalysts tend to dissolve under OER conditions. This has been associated with the participation of lattice oxygen (lattice oxygen oxidation mechanism (LOM)), which may lead to the collapse of the crystal structure and accelerate the leaching of active Ru species, leading to low operating stability. Here we develop Sr-Ru-Ir ternary oxide electrocatalysts that achieve high OER activity and stability in acidic electrolyte. The catalysts achieve an overpotential of 190 mV at 10 mA cm-2 and the overpotential remains below 225 mV following 1,500 h of operation. X-ray absorption spectroscopy and 18O isotope-labeled online mass spectroscopy studies reveal that the participation of lattice oxygen during OER was suppressed by interactions in the Ru-O-Ir local structure, offering a picture of how stability was improved. The electronic structure of active Ru sites was modulated by Sr and Ir, optimizing the binding energetics of OER oxo-intermediates.

Carbon dioxide electroreduction (CO

Potassium helps CO 2 compete in acid Electrochemical reduction of carbon dioxide (CO 2 ) is a promising means of converting this greenhouse gas into valuable fuels and chemicals. However, two competing reactions restrict the efficiency of this process. In base, much of the CO 2 is trapped as carbonate before reduction; in acid, protons outpace CO 2 at catching electrons from the cathode. Huang et al. report that a high dose of potassium ions can help to solve the latter problem. By concentrating potassium ions at the electrode, high selectivity toward CO 2 reduction at high current in acid is possible, which the authors attribute to electrostatic stabilization of the desired adsorbates. Science , abg6582, this issue p. 1074

Anthropogenic carbon dioxide (CO2) emissions contribute to the greenhouse effect and global warming, which can lead to undesirable climate change and extinction of species. Besides the ongoing efforts to develop environmentally benign sources of energy and to advance technologies for the capture and sequestration of CO2, the transformation of emitted CO2 into valuable products is a pragmatic solution to curb its accumulation in the atmosphere. In this regard, electrochemical CO2 reduction (ECR) powered by renewable electricity provides an attractive approach because it not only converts CO2 to valuable fuels and chemicals but also offers a solution for the long-term storage of intermittent renewable energies. In ECR, the gas diffusion electrode (GDE) is the most critical component and has been the subject of intensive research in the last few years. This tutorial review provides an insightful guide to developing GDEs with high activity, selectivity, and stability, the three important performance metrics in ECR. First, we introduce critical fundamentals of ECR, including the chemical and physical phenomena at the electrodes as well as the electrochemical cell configurations. Next, we discuss recent advances in GDE design, focusing on their structure-performance correlation and fabrication techniques for each component of GDEs. Finally, we discuss the remaining challenges and propose promising research directions for the design of efficient GDEs. This review aims at promoting the development of industrially relevant ECR systems to bring this technology to practical applications.

Electrochemical conversion of nitrate (NO3-) into ammonia (NH3) recycles nitrogen and offers a route to the production of NH3, which is more valuable than dinitrogen gas. However, today's development of NO3- electroreduction remains hindered by the lack of a mechanistic picture of how catalyst structure may be tuned to enhance catalytic activity. Here we demonstrate enhanced NO3- reduction reaction (NO3-RR) performance on Cu50Ni50 alloy catalysts, including a 0.12 V upshift in the half-wave potential and a 6-fold increase in activity compared to those obtained with pure Cu at 0 V vs reversible hydrogen electrode (RHE). Ni alloying enables tuning of the Cu d-band center and modulates the adsorption energies of intermediates such as *NO3-, *NO2, and *NH2. Using density functional theory calculations, we identify a NO3-RR-to-NH3 pathway and offer an adsorption energy-activity relationship for the CuNi alloy system. This correlation between catalyst electronic structure and NO3-RR activity offers a design platform for further development of NO3-RR catalysts.

The electrocatalytic reduction of carbon dioxide, powered by renewable electricity, to produce valuable fuels and feedstocks provides a sustainable and carbon-neutral approach to the storage of energy produced by intermittent renewable sources1. However, the highly selective generation of economically desirable products such as ethylene from the carbon dioxide reduction reaction (CO2RR) remains a challenge2. Tuning the stabilities of intermediates to favour a desired reaction pathway can improve selectivity3–5, and this has recently been explored for the reaction on copper by controlling morphology6, grain boundaries7, facets8, oxidation state9 and dopants10. Unfortunately, the Faradaic efficiency for ethylene is still low in neutral media (60 per cent at a partial current density of 7 milliamperes per square centimetre in the best catalyst reported so far9), resulting in a low energy efficiency. Here we present a molecular tuning strategy—the functionalization of the surface of electrocatalysts with organic molecules—that stabilizes intermediates for more selective CO2RR to ethylene. Using electrochemical, operando/in situ spectroscopic and computational studies, we investigate the influence of a library of molecules, derived by electro-dimerization of arylpyridiniums11, adsorbed on copper. We find that the adhered molecules improve the stabilization of an ‘atop-bound’ CO intermediate (that is, an intermediate bound to a single copper atom), thereby favouring further reduction to ethylene. As a result of this strategy, we report the CO2RR to ethylene with a Faradaic efficiency of 72 per cent at a partial current density of 230 milliamperes per square centimetre in a liquid-electrolyte flow cell in a neutral medium. We report stable ethylene electrosynthesis for 190 hours in a system based on a membrane-electrode assembly that provides a full-cell energy efficiency of 20 per cent. We anticipate that this may be generalized to enable molecular strategies to complement heterogeneous catalysts by stabilizing intermediates through local molecular tuning. Electrocatalytic reduction of CO2 over copper can be made highly selective by ‘tuning’ the copper surface with adsorbed organic molecules to stabilize intermediates for carbon-based fuels such as ethylene

The electrosynthesis of higher-order alcohols from carbon dioxide and carbon monoxide addresses the need for the long-term storage of renewable electricity; unfortunately, the present-day performance remains below what is needed for practical applications. Here we report a catalyst design strategy that promotes C3 formation via the nanoconfinement of C2 intermediates, and thereby promotes C2:C1 coupling inside a reactive nanocavity. We first employed finite-element method simulations to assess the potential for the retention and binding of C2 intermediates as a function of cavity structure. We then developed a method of synthesizing open Cu nanocavity structures with a tunable geometry via the electroreduction of Cu2O cavities formed through acidic etching. The nanocavities showed a morphology-driven shift in selectivity from C2 to C3 products during the carbon monoxide electroreduction, to reach a propanol Faradaic efficiency of 21 ± 1% at a conversion rate of 7.8 ± 0.5 mA cm−2 at −0.56 V versus a reversible hydrogen electrode. The production of higher alcohols is very valuable because of their high volumetric energy density. Now, Sargent, Sinton and co-workers report the design of copper nanoparticles with tailored nanocavities that promote n-propanol formation by the coupling of C2 and C1 intermediates inside the cavity.

The electroreduction of carbon dioxide (CO2) to chemicals such as carbon monoxide (CO) shows great potential for renewable fuel and chemical production. Significant progress in individual performance metrics such as reaction rate, selectivity, and stability has been achieved, yet the simultaneous achievement of each of these key metrics within a single system, and in a wide range of operating conditions, has yet to be demonstrated. Here we report a composite multilayered porous electrode consisting of a polytetrafluoroethylene gas distribution layer, a conformal Ag catalyst, and a carbon current distributor. Separating the gas and current distribution functions provides endurance, and further reconstructing the catalyst to carbonate-derived Ag provides flexibility in terms of electrolyte. The resulting electrodes reduce CO2 to CO with a Faradaic efficiency over 90% at current densities above 150 mA/cm2, in both neutral and alkaline media for over 100 h of operation. This represents an important step towar...

Producing liquid fuels such as ethanol from CO2, H2O, and renewable electricity offers a route to store sustainable energy. The search for efficient electrocatalysts for the CO2 reduction reaction relies on tuning the adsorption strength of carbonaceous intermediates. Here, we report a complementary approach in which we utilize hydroxide and oxide doping of a catalyst surface to tune the adsorbed hydrogen on Cu. Density functional theory studies indicate that this doping accelerates water dissociation and changes the hydrogen adsorption energy on Cu. We synthesize and investigate a suite of metal-hydroxide-interface-doped-Cu catalysts, and find that the most efficient, Ce(OH)x-doped-Cu, exhibits an ethanol Faradaic efficiency of 43% and a partial current density of 128 mA cm−2. Mechanistic studies, wherein we combine investigation of hydrogen evolution performance with the results of operando Raman spectroscopy, show that adsorbed hydrogen hydrogenates surface *HCCOH, a key intermediate whose fate determines branching to ethanol versus ethylene., Producing ethanol from carbon dioxide, water, and renewable electricity offers a route to sustainable energy. Here, the authors enhance electrocatalytic activity for carbon dioxide reduction by tuning adsorbed hydrogen in a class of copper catalysts with oxide- and hydroxide-modified surfaces.

The electrochemical carbon dioxide reduction reaction (CO2RR) produces diverse chemical species. Cu clusters with a judiciously controlled surface coordination number (CN) provide active sites that simultaneously optimize selectivity, activity, and efficiency for CO2RR. Here we report a strategy involving metal–organic framework (MOF)-regulated Cu cluster formation that shifts CO2 electroreduction toward multiple-carbon product generation. Specifically, we promoted undercoordinated sites during the formation of Cu clusters by controlling the structure of the Cu dimer, the precursor for Cu clusters. We distorted the symmetric paddle-wheel Cu dimer secondary building block of HKUST-1 to an asymmetric motif by separating adjacent benzene tricarboxylate moieties using thermal treatment. By varying materials processing conditions, we modulated the asymmetric local atomic structure, oxidation state and bonding strain of Cu dimers. Using electron paramagnetic resonance (EPR) and in situ X-ray absorption spectros...