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In alkaline and neutral MEA CO 2 electrolyzers, CO 2 rapidly converts to (bi)carbonate, imposing a significant energy penalty arising from separating CO 2 from the anode gas outlets. Here we report a CO 2 electrolyzer uses a bipolar membrane (BPM) to convert (bi)carbonate back to CO 2 , preventing crossover; and that surpasses the single-pass utilization (SPU) limit (25% for multi-carbon products, C 2+ ) suffered by previous neutral-media electrolyzers. We employ a stationary unbuffered catholyte layer between BPM and cathode to promote C 2+ products while ensuring that (bi)carbonate is converted back, in situ, to CO 2 near the cathode. We develop a model that enables the design of the catholyte layer, finding that limiting the diffusion path length of reverted CO 2 to ~10 μm balances the CO 2 diffusion flux with the regeneration rate. We report a single-pass CO 2 utilization of 78%, which lowers the energy associated with downstream separation of CO 2 by 10× compared with past systems. In the carbon dioxide (CO 2 ) to multicarbon electrolysis, the crossover CO 2 to the oxygen-rich anodic gas stream add a further energy-intensive chemical separation step. Here, the authors demonstrate a bipolar membrane-based electrolyzer design that eliminates the crossover CO2.

The electrochemical conversion of CO 2 to methane provides a means to store intermittent renewable electricity in the form of a carbon-neutral hydrocarbon fuel that benefits from an established global distribution network. The stability and selectivity of reported approaches reside below technoeconomic-related requirements. Membrane electrode assembly-based reactors offer a known path to stability; however, highly alkaline conditions on the cathode favour C-C coupling and multi-carbon products. In computational studies herein, we find that copper in a low coordination number favours methane even under highly alkaline conditions. Experimentally, we develop a carbon nanoparticle moderator strategy that confines a copper-complex catalyst when employed in a membrane electrode assembly. In-situ XAS measurements confirm that increased carbon nanoparticle loadings can reduce the metallic copper coordination number. At a copper coordination number of 4.2 we demonstrate a CO 2 -to-methane selectivity of 62%, a methane partial current density of 136 mA cm −2 , and > 110 hours of stable operation. Electrochemical conversion of carbon dioxide to methane can store intermittent renewable electricity in a staple of global energy. Here, the authors develop a moderator strategy to maintain the catalyst in a low coordination state, thereby enabling stable and selective electrochemical methanation.

Electrochemical conversion of CO 2 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 CO 2 and H 2 O. We implement the strategy by functionalizing the copper surface with a family of porphyrin-based metallic complexes that catalyse CO 2 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 CO 2 -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 CO 2 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 CO 2 by producing a reaction-intermediate-rich local environment.

Multi-carbon alcohols such as ethanol are valued as fuels in view of their high energy density and ready transport. Unfortunately, the selectivity toward alcohols in CO 2 /CO electroreduction is diminished by ethylene production, especially when operating at high current densities (>100 mA cm −2 ). Here we report a metal doping approach to tune the adsorption of hydrogen at the copper surface and thereby promote alcohol production. Using density functional theory calculations, we screen a suite of transition metal dopants and find that incorporating Pd in Cu moderates hydrogen adsorption and assists the hydrogenation of C 2 intermediates, providing a means to favour alcohol production and suppress ethylene. We synthesize a Pd-doped Cu catalyst that achieves a Faradaic efficiency of 40% toward alcohols and a partial current density of 277 mA cm −2 from CO electroreduction. The activity exceeds that of prior reports by a factor of 2. The electrocatalytic upgrading of CO to higher-value fuels provides a promising route to multi-carbon alcohol products. Here, the authors show that high alcohol selectivity and activity can be achieved by incorporating palladium in copper.

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 CO 2 RR—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 .

The electroreduction of C 1 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 C 1 and C 2 products, however, the selectivity to desirable high-energy-density C 3 products remains relatively low. We reason that C 3 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 C 2 with C 1 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 (EE cathodic half-cell ) of 21%. The FE and EE cathodic 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 C 2 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.

Reactive capture of carbon dioxide (CO 2 ) offers an electrified pathway to produce renewable carbon monoxide (CO), which can then be upgraded into long-chain hydrocarbons and fuels. Previous reactive capture systems relied on hydroxide- or amine-based capture solutions. However, selectivity for CO remains low (<50%) for hydroxide-based systems and conventional amines are prone to oxygen (O 2 ) degradation. Here, we develop a reactive capture strategy using potassium glycinate (K-GLY), an amino acid salt (AAS) capture solution applicable to O 2 -rich CO 2 -lean conditions. By employing a single-atom catalyst, engineering the capture solution, and elevating the operating temperature and pressure, we increase the availability of dissolved in-situ CO 2 and achieve CO production with 64% Faradaic efficiency (FE) at 50 mA cm −2 . We report a measured CO energy efficiency (EE) of 31% and an energy intensity of 40 GJ t CO −1 , exceeding the best hydroxide- and amine-based reactive capture reports. The feasibility of the full reactive capture process is demonstrated with both simulated flue gas and direct air input. The electrosynthesis of CO via integrated capture and conversion of dilute CO 2 suffers from low energy efficiency. Here, the authors report an amino acid salt-based system that employs a single-atom catalyst and operates at an elevated temperature and pressure, which enables efficient CO production.

Electrocatalysis offers a promising route to convert CO 2 into alcohols, which is most efficient in a two-step cascade reaction with CO 2 -to-CO followed by CO-to-alcohol. However, current alcohol-producing CO 2 /CO electrolyzers suffer from low selectivity or alcohol crossover, resulting in alcohol concentrations of less than 1%, which are further diluted in downstream cold-traps. As a result, electrocatalytic alcohol production has yet to be scaled beyond the lab (1-10 cm 2 ). Here, we reverse the electroosmotic drag of water using a cation exchange membrane assembly, enabling the recovery of over 85% of alcohol products at a concentration of 6 wt.%. We develop a multi-step condenser strategy to separate the produced alcohols from the effluent gas stream without dilution. Scaling up this approach to an 800 cm 2 cell resulted in an output of 200 mL alcohol/day. The electrocatalytic upgrading of CO 2 /CO provides a promising route to produce carbon-neutral alcohols but suffers from product loss to crossover and dilution. Here, the authors report on a CO reduction electrolyzer that recovers over 85% of alcohol without dilution, which is then scaled to 800 cm 2 .

The upgrading of CO 2 /CO feedstocks to higher-value chemicals via energy-efficient electrochemical processes enables carbon utilization and renewable energy storage. Substantial progress has been made to improve performance at the cathodic side; whereas less progress has been made on improving anodic electro-oxidation reactions to generate value. Here we report the efficient electroproduction of value-added multi-carbon dimethyl carbonate (DMC) from CO and methanol via oxidative carbonylation. We find that, compared to pure palladium controls, boron-doped palladium (Pd-B) tunes the binding strength of intermediates along this reaction pathway and favors DMC formation. We implement this doping strategy and report the selective electrosynthesis of DMC experimentally. We achieve a DMC Faradaic efficiency of 83 ± 5%, fully a 3x increase in performance compared to the corresponding pure Pd electrocatalyst. The electro-oxidative synthesis of valued chemicals offers to enhance the overall efficiency and economic viability of renewable electrosynthesis systems. Here, the authors use dopant-tuned catalysts to promote the electrosynthesis of dimethyl carbonate from CO and methanol via oxidative carbonylation.

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 sources 1 . However, the highly selective generation of economically desirable products such as ethylene from the carbon dioxide reduction reaction (CO 2 RR) remains a challenge 2 . Tuning the stabilities of intermediates to favour a desired reaction pathway can improve selectivity 3 – 5 , and this has recently been explored for the reaction on copper by controlling morphology 6 , grain boundaries 7 , facets 8 , oxidation state 9 and dopants 10 . 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 far 9 ), 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 CO 2 RR 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 arylpyridiniums 11 , 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 CO 2 RR 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 CO 2 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