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Carbon dioxide electroreduction facilitates the sustainable synthesis of fuels and chemicals 1 . Although Cu enables CO 2 -to-multicarbon product (C 2+ ) conversion, the nature of the active sites under operating conditions remains elusive 2 . Importantly, identifying active sites of high-performance Cu nanocatalysts necessitates nanoscale, time-resolved operando techniques 3 – 5 . Here, we present a comprehensive investigation of the structural dynamics during the life cycle of Cu nanocatalysts. A 7 nm Cu nanoparticle ensemble evolves into metallic Cu nanograins during electrolysis before complete oxidation to single-crystal Cu 2 O nanocubes following post-electrolysis air exposure. Operando analytical and four-dimensional electrochemical liquid-cell scanning transmission electron microscopy shows the presence of metallic Cu nanograins under CO 2 reduction conditions. Correlated high-energy-resolution time-resolved X-ray spectroscopy suggests that metallic Cu, rich in nanograin boundaries, supports undercoordinated active sites for C–C coupling. Quantitative structure–activity correlation shows that a higher fraction of metallic Cu nanograins leads to higher C 2+ selectivity. A 7 nm Cu nanoparticle ensemble, with a unity fraction of active Cu nanograins, exhibits sixfold higher C 2+ selectivity than the 18 nm counterpart with one-third of active Cu nanograins. The correlation of multimodal operando techniques serves as a powerful platform to advance our fundamental understanding of the complex structural evolution of nanocatalysts under electrochemical conditions. By investigation of structural dynamics during the life cycle of Cu nanocatalysts, correlation of multimodal operando techniques was found to serve as a powerful platform to advance understanding of their complex structural evolution.

Electrochemical CO 2 reduction (CO 2 R) to ethylene and ethanol enables the long-term storage of renewable electricity in valuable multi-carbon (C 2+ ) chemicals. However, carbon–carbon (C–C) coupling, the rate-determining step in CO 2 R to C 2+ conversion, has low efficiency and poor stability, especially in acid conditions. Here we find that, through alloying strategies, neighbouring binary sites enable asymmetric CO binding energies to promote CO 2 -to-C 2+ electroreduction beyond the scaling-relation-determined activity limits on single-metal surfaces. We fabricate experimentally a series of Zn incorporated Cu catalysts that show increased asymmetric CO* binding and surface CO* coverage for fast C–C coupling and the consequent hydrogenation under electrochemical reduction conditions. Further optimization of the reaction environment at nanointerfaces suppresses hydrogen evolution and improves CO 2 utilization under acidic conditions. We achieve, as a result, a high 31 ± 2% single-pass CO 2 -to-C 2+ yield in a mild-acid pH 4 electrolyte with >80% single-pass CO 2 utilization efficiency. In a single CO 2 R flow cell electrolyzer, we realize a combined performance of 91 ± 2% C 2+ Faradaic efficiency with notable 73 ± 2% ethylene Faradaic efficiency, 31 ± 2% full-cell C 2+ energy efficiency, and 24 ± 1% single-pass CO 2 conversion at a commercially relevant current density of 150 mA cm −2 over 150 h. CO 2 electroreduction to multi-carbon products in acids remains challenging due to the low efficiency and poor stability of C–C coupling. Here, the authors show that asymmetric CO binding at confined nanointerfaces enhances multi-carbon production, improves CO 2 utilization, and limits H 2 evolution.

Seawater electroreduction is attractive for future H 2 production and intermittent energy storage, which has been hindered by aggressive Mg 2+ /Ca 2+ precipitation at cathodes and consequent poor stability. Here we present a vital microscopic bubble/precipitate traffic system (MBPTS) by constructing honeycomb-type 3D cathodes for robust anti-precipitation seawater reduction (SR), which massively/uniformly release small-sized H 2 bubbles to almost every corner of the cathode to repel Mg 2+ /Ca 2+ precipitates without a break. Noticeably, the optimal cathode with built-in MBPTS not only enables state-of-the-art alkaline SR performance (1000-h stable operation at –1 A cm −2 ) but also is highly specialized in catalytically splitting natural seawater into H 2 with the greatest anti-precipitation ability. Low precipitation amounts after prolonged tests under large current densities reflect genuine efficacy by our MBPTS. Additionally, a flow-type electrolyzer based on our optimal cathode stably functions at industrially-relevant 500 mA cm −2 for 150 h in natural seawater while unwaveringly sustaining near-100% H 2 Faradic efficiency. Note that the estimated price (~1.8 US$/kg H2 ) is even cheaper than the US Department of Energy’s goal price (2 US$/kg H2 ). Seawater electroreduction is a promising technique for producing hydrogen, but it is hindered by cathodic Mg2 + /Ca2+ precipitation. Here, the authors propose a microscopic bubble/precipitate traffic system that releases small-sized bubbles across the cathode to repel Mg2 + /Ca2+ precipitates from almost the entire surface area of the catalyst.

The nitrate (NO 3 − ) electroreduction into ammonia (NH 3 ) represents a promising approach for sustainable NH 3 synthesis. However, the variation of adsorption configurations renders great difficulties in the simultaneous optimization of binding energy for the intermediates. Though the extensively reported Cu-based electrocatalysts benefit NO 3 − adsorption, one of the key issues lies in the accumulation of nitrite (NO 2 − ) due to its weak adsorption, resulting in the rapid deactivation of catalysts and sluggish kinetics of subsequent hydrogenation steps. Here we report a tandem electrocatalyst by combining Cu single atoms catalysts with adjacent Co 3 O 4 nanosheets to boost the electroreduction of NO 3 − to NH 3 . The obtained tandem catalyst exhibits a yield rate for NH 3 of 114.0 mg NH 3 h −1 cm −2 , which exceeds the previous values for the reported Cu-based catalysts. Mechanism investigations unveil that the combination of Co 3 O 4 regulates the adsorption configuration of NO 2 − and strengthens the binding with NO 2 − , thus accelerating the electroreduction of NO 3 − to NH 3 . An optimal catalyst for nitrate electroreduction should satisfy the simultaneously optimized adsorption of intermediates. Here, the authors report a tandem electrocatalyst by combining Cu single atoms with Co 3 O 4 nanosheets, enhancing the binding with NO 2 − , thus promoting nitrate electroreduction to NH 3 .

A very basic pathway from CO2 to ethyleneEthylene is an important commodity chemical for plastics. It is considered a tractable target for synthesizing renewable resources from carbon dioxide (CO2). The challenge is that the performance of the copper electrocatalysts used for this conversion under the required basic reaction conditions suffers from the competing reaction of CO2 with the base to form bicarbonate. Dinh et al. designed an electrode that tolerates the base by optimizing CO2 diffusion to the catalytic sites (see the Perspective by Ager and Lapkin). This catalyst design delivers 70% efficiency for 150 hours.Science, this issue p. 783; see also p. 707Carbon dioxide (CO2) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO2 to ethylene with 70% faradaic efficiency at a potential of −0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at −0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.

Electrocatalytic recycling of waste nitrate (NO 3 − ) to valuable ammonia (NH 3 ) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH 3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO 3 − -to-NH 3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuO x and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuO x phases preferentially catalyze NO 3 − reduction to NO 2 − , which is rapidly reduced to NH 3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO 3 − -to-NH 3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO 3 − concentrations at pH 13, a high NH 3 yield rate of 1.17 mmol cm −2 h −1 in 0.1 M NO 3 − at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports. Electrocatalytic recycling of waste nitrate to NH 3 under ambient conditions maybe an appealing alternative to the Haber−Bosch process. Here the authors report a tandem catalyst system involving cooperative adsorption of reaction intermediate on different transition metal active sites for nitrate electroreduction with high efficiency.

Electrochemical CO 2 reduction to multicarbon products faces challenges of unsatisfactory selectivity, productivity, and long-term stability. Herein, we demonstrate CO 2 electroreduction in strongly acidic electrolyte (pH ≤ 1) on electrochemically reduced porous Cu nanosheets by combining the confinement effect and cation effect to synergistically modulate the local microenvironment. A Faradaic efficiency of 83.7 ± 1.4% and partial current density of 0.56 ± 0.02 A cm −2 , single-pass carbon efficiency of 54.4%, and stable electrolysis of 30 h in a flow cell are demonstrated for multicarbon products in a strongly acidic aqueous electrolyte consisting of sulfuric acid and KCl with pH ≤ 1. Mechanistically, the accumulated species (e.g., K + and OH − ) on the Helmholtz plane account for the selectivity and activity toward multicarbon products by kinetically reducing the proton coverage and thermodynamically favoring the CO 2 conversion. We find that the K + cations facilitate C-C coupling through local interaction between K + and the key intermediate *OCCO. Attaining high selectivity for CO 2 electroreduction in acid is usually difficult due to competing hydrogen evolution. Here, the authors demonstrate efficient CO 2 reduction to multicarbon products in strongly acidic medium (pH ≤ 1) on a porous Cu catalyst by combining confinement and cation effects.

The mechanism of how interfacial wettability impacts the CO 2 electroreduction pathways to ethylene and ethanol remains unclear. This paper describes the design and realization of controllable equilibrium of kinetic-controlled *CO and *H via modifying alkanethiols with different alkyl chain lengths to reveal its contribution to ethylene and ethanol pathways. Characterization and simulation reveal that the mass transport of CO 2 and H 2 O is related with interfacial wettability, which may result in the variation of kinetic-controlled *CO and *H ratio, which affects ethylene and ethanol pathways. Through modulating the hydrophilic interface to superhydrophobic interface, the reaction limitation shifts from insufficient supply of kinetic-controlled *CO to that of *H. The ethanol to ethylene ratio can be continuously tailored in a wide range from 0.9 to 1.92, with remarkable Faradaic efficiencies toward ethanol and multi-carbon (C 2+ ) products up to 53.7% and 86.1%, respectively. A C 2+ Faradaic efficiency of 80.3% can be achieved with a high C 2+ partial current density of 321 mA cm −2 , which is among the highest selectivity at such current densities. The mechanism of how interfacial wettability impacts the CO 2 electcgq Herein, the authors describe the design and realization of controllable equilibrium of kinetic controlled *CO and *H to reveal its contribution to ethylene and ethanol pathways.

Efficient electroreduction of CO 2 to multi-carbon products is a challenging reaction because of the high energy barriers for CO 2 activation and C–C coupling, which can be tuned by designing the metal centers and coordination environments of catalysts. Here, we design single atom copper encapsulated on N-doped porous carbon (Cu-SA/NPC) catalysts for reducing CO 2 to multi-carbon products. Acetone is identified as the major product with a Faradaic efficiency of 36.7% and a production rate of 336.1 μg h −1 . Density functional theory (DFT) calculations reveal that the coordination of Cu with four pyrrole-N atoms is the main active site and reduces the reaction free energies required for CO 2 activation and C–C coupling. The energetically favorable pathways for CH 3 COCH 3 production from CO 2 reduction are proposed and the origin of selective acetone formation on Cu-SA/NPC is clarified. This work provides insight into the rational design of efficient electrocatalysts for reducing CO 2 to multi-carbon products. Efficient electroreduction of CO 2 to multi-carbon products is challenging. Here, the single atom Cu encapsulated on N-doped porous carbon catalysts are designed for reducing CO 2 to acetone at low overpotentials and the active sites are identified as Cu coordination with four pyrrole-N atoms.

Selective electroreduction of carbon dioxide (CO2RR) into ethanol at an industrially relevant current density is highly desired. However, it is challenging because the competing ethylene production pathway is generally more thermodynamically favored. Herein, we achieve a selective and productive ethanol production over a porous CuO catalyst that presents a high ethanol Faradaic efficiency (FE) of 44.1 ± 1.0% and an ethanol-to-ethylene ratio of 1.2 at a large ethanol partial current density of 501.0 ± 15.0 mA cm−2, in addition to an extraordinary FE of 90.6 ± 3.4% for multicarbon products. Intriguingly, we found a volcano-shaped relationship between ethanol selectivity and nanocavity size of porous CuO catalyst in the range of 0 to 20 nm. Mechanistic studies indicate that the increased coverage of surface-bounded hydroxyl species (*OH) associated with the nanocavity size-dependent confinement effect contributes to the remarkable ethanol selectivity, which preferentially favors the *CHCOH hydrogenation to *CHCHOH (ethanol pathway) via yielding the noncovalent interaction. Our findings provide insights in favoring the ethanol formation pathway, which paves the path toward rational design of ethanol-oriented catalysts.