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A Cu-based tandem catalyst shows high ethylene selectivity from the electrochemical CO2 reduction reaction. In the catalyst, high-concentration CO is generated at one site and then converted with low energy barrier to ethylene at another site.

We focus on the new horizons in operando/in situ characterisation techniques in electrocatalysis, providing a critical analysis of how advanced in situ techniques help us to deepen our understanding of reaction mechanisms and material evolution.

CsPbBr3/NiFe-LDH heterostructure photocatalysts are developed with tuneable Z-scheme reduction capability for efficient CO2 reduction performance.

A benzenethiol molecule modulates the electronic structure of copper surfaces and thus tunes the coverage of key reaction intermediates, boosting electrochemical CO2 methanation.

Direct electrochemical conversion of CO

Upgrading carbon dioxide/monoxide to multi-carbon C

High-rate conversion of carbon dioxide (CO

CO2 electroreduction powered by renewable electricity represents a promising method to enclose anthropogenic carbon cycle. Current catalysts display high selectivity toward the desired product only over a narrow potential window due primarily to unoptimized intermediate binding. Here, we report a functional ligand modification strategy in which palladium nanoparticles are encapsulated inside metal–organic frameworks with 2,2′-bipyridine organic linkers to tune intermediate binding and thus to sustain a highly selective CO2-to-CO conversion over widened potential window. The catalyst exhibits CO faradaic efficiency in excess of 80% over a potential window from −0.3 to −1.2 V and reaches the maxima of 98.2% at −0.8 V. Mechanistic studies show that the 2,2′-bipyridine on Pd surface reduces the binding strength of both *H and *CO, a too strong binding of which leads to competing formate production and CO poison, respectively, and thus enhances the selectivity and stability of CO product.

The electrochemical CO2 reduction reaction (eCO2RR) has been regarded as a promising means to store renewable electricity in the form of value-added chemicals or fuels. However, most of the present eCO2RR studies focus on the conversion of pure CO2. The CO2 valorisation chain – from CO2 capture to the eCO2RR – requires significant energy and capital inputs in each of the capture, purification, conversion, and product separation steps. The integration of upstream CO2 capture and downstream electrochemical conversion by direct electrolysis of capture media, such as amine and carbonate salts, offers a potential solution to energy- and cost-efficient utilisation of CO2. In this perspective, we first summarise the present advances in the direct eCO2RR from CO2-capture media. We then focus on potential development directions of materials and systems that boost the process to a phase of high selectivity towards valuable products (e.g., syngas, ethylene, and ethanol). We conclude by highlighting the major challenges and emerging opportunities in the area of integrated electrochemical CO2 utilisation systems.

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.

In the electrochemical CO2 reduction reaction (CO2RR), control over the binding of intermediates is key for tuning product selectivity and catalytic activity. Here we report the use of reticular chemistry to control the binding of CO2RR intermediates on metal catalysts encapsulated inside metal-organic frameworks (MOFs), thereby allowing us to improve CO2RR electrocatalysis. By varying systematically both the organic linker and the metal node in a face-centered cubic (fcu) MOF, we tune the adsorption of CO2, pore openness, and Lewis acidity of the MOFs. Using operando X-ray absorption spectroscopy (XAS) and in situ Raman spectroscopy, we reveal that the MOFs are stable under operating conditions and that this tuning plays the role of optimizing the *CO binding mode on the surface of Ag nanoparticles incorporated inside the MOFs with the increase of local CO2 concentration. As a result, we improve the CO selectivity from 74% for Ag/Zr-fcu-MOF-1,4-benzenedicarboxylic acid (BDC) to 94% for Ag/Zr-fcu-MOF-1,4-naphthalenedicarboxylic acid (NDC). The work offers a further avenue to utilize MOFs in the pursuit of materials design for CO2RR.

CO2 capture technologies based on chemisorption present the potential to lower net emissions of CO2 into the atmosphere. The electrochemical upgrade of captured CO2 to value-added products would be particularly convenient. Here we find that this goal is curtailed when the adduct of the capture molecule with CO2 fails to place the CO2 sufficiently close to the site of the heterogeneous reaction. We investigate tailoring the electrochemical double layer to achieve the valorization of chemisorbed CO2 in an aqueous monoethanolamine electrolyte. We reveal, using electrochemical studies and in situ surface-enhanced Raman spectroscopy, that a smaller double layer distance correlates with improved activity for CO2 to CO from amine solutions. With the aid of an alkali cation and accelerated mass transport by system design—temperature and concentration—we demonstrate amine–CO2 conversion to CO with 72% Faradaic efficiency at 50 mA cm–2. Electrochemical conversion of CO2 into high-value products is attractive for lowering net carbon emissions. Lee et al. present the valorization of chemisorbed CO2 to CO in an aqueous monoethanolamine electrolyte via tailoring of the electrochemical double layer, with 72% Faradaic efficiency at 50 mA cm–2.

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...

Charging into epoxides Ethylene oxide is a strained, reactive molecule produced on a vast scale as a plastics precursor. The current method of synthesis involves the direct reaction of ethylene and oxygen at high temperature, but the original protocol relied on the reduction of chlorine to produce a chlorohydrin intermediate. Leow et al. report a room temperature method that returns to the chlorine route but uses electrochemistry to generate it catalytically from chloride (see the Perspective by Barton). This efficient process uses water in place of oxygen and can be integrated with the electrochemical generation of ethylene from carbon dioxide. Propylene oxide can be produced using the same method. Science , this issue p. 1228 ; see also p. 1181

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%.

Electrochemical CO2 reduction is a potential approach to manufacture carbon-neutral fuels and chemicals. To deploy CO2 electrolysis in the practical production of fuels and chemicals, energetically efficient electrolyzers are required. However, carbonate formation and the consequent CO2 crossover from cathodes to anodes cause unacceptable energy consumption, making the cost of CO2 electroreduction lower than the threshold for economic viability. Herein, we provide quantitative analyses of the impact of carbonate formation on the product costs of CO2 electroreduction products. Using the electrosynthesis of alcohols and ethylene as examples, we conducted techno-economic assessments (TEAs), and found that carbonate formation impacts the production costs of alcohols and ethylene by altering the costs of electrolyzer, CO2, and separation. Solving the carbonate formation issue reduces the production cost by 744-1696 USD per tonne, nearly equal to the market prices of the products. Finally, we conclude that inhibiting carbonate formation, together with improving reaction selectivity and productivity, would decrease the production costs by more than 90%.

Electrochemical CO

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

The electroreduction of carbon dioxide (CO2RR) to valuable chemicals is a promising avenue for the storage of intermittent renewable electricity. Renewable methane, obtained via CO2RR using renewable electricity as energy input, has the potential to serve as a carbon-neutral fuel or chemical feedstock, and it is of particular interest in view of the well-established infrastructure for its storage, distribution, and utilization. However, CO2RR to methane still suffers from low selectivity at commercially relevant current densities (>100 mA cm-2). Density functional theory calculations herein reveal that lowering *CO2 coverage on the Cu surface decreases the coverage of the *CO intermediate, and then this favors the protonation of *CO to *CHO, a key intermediate for methane generation, compared to the competing step, C-C coupling. We therefore pursue an experimental strategy wherein we control local CO2 availability on a Cu catalyst by tuning the concentration of CO2 in the gas stream and regulate the reaction rate through the current density. We achieve as a result a methane Faradaic efficiency (FE) of (48 ± 2)% with a partial current density of (108 ± 5) mA cm-2 and a methane cathodic energy efficiency of 20% using a dilute CO2 gas stream. We report stable methane electrosynthesis for 22 h. These findings offer routes to produce methane with high FE and high conversion rate in CO2RR and also make direct use of dilute CO2 feedstocks.

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 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.

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 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.

Two-dimensional (2D) materials are attractive catalysts for the electrochemical reduction of carbon dioxide reaction (eCO2 RR) by virtue of their tunable atomic structures, abundant active sites, enhanced conductivity, suitable binding affinity to carbon dioxide and/or reaction intermediates, and intrinsic scalability. Herein, recent advances in 2D catalysts for the eCO2 RR are reviewed. Structural features and properties of 2D materials that contribute to their advanced electrocatalytic properties are summarized, and strategies for enhancing their activity and selectivity for the eCO2 RR are reviewed. Prospects and challenges of applications of 2D catalysts for the eCO2 RR on an industrial scale are highlighted.

A simple one-pot method has been developed to synthesize a palladium/cuprous oxide-copper (Pd/Cu2 O-Cu) material with a well-defined structure, by modification of Cu2 O-Cu with Pd through a galvanic replacement reaction. Compared with the well-known copper/cuprous oxide (Cu/Cu2 O) catalysts, the Pd/Cu2 O-Cu material can catalyze the electroreduction of CO2 into C1 products with much higher faradaic efficiencies at lower overpotentials in a CO2 -saturated 0.5 m NaHCO3 solution. In particular, the highest faradaic efficiencies of 92 % for formate and 30 % for methane were achieved at -0.25 and -0.65 V (vs. the reversible hydrogen electrode), respectively. The improvement is suggested to be the result of a synergistic effect between PdH and the catalytically active copper sites during electrochemical CO2 reduction.

Uniting the advantages of molecular and heterogeneous catalysts, a continuing effort in heterogeneous catalysis, has often proved to be challenging. This work introduces a facile strategy to obtain molybdenum-oxo functional groups strongly anchored on metallic copper support through in situ electrochemical reduction of a cuprous oxomolybdate thin film resulting from electroless plating. The oxomolybdate modified copper electrode exhibits enzyme-like activity and excellent stability for the hydrogen evolution reaction over the entire pH range, together with excellent mechanical properties and cost effectiveness that are needed for commercial applications, including seawater electrolysis. In situ Fourier transformed ac voltammetric study revealed two underlying MoIV/III and MoIII/II processes that are responsible for the high catalytic activity of the material. This study opens up a new avenue for designing advanced heterogeneous catalysts for a greener future using a broad range of oxometalates.

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.

CO

2D bismuth nanosheets are a promising layered material for formate-producing via electrocatalytic CO