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Enzymes feature the concerted operation of multiple components around an active site, leading to exquisite catalytic specificity. Realizing such configurations on synthetic catalyst surfaces remains elusive. Here, we report a nanoparticle/ordered-ligand interlayer that contains a multi-component catalytic pocket for high-specificity CO 2 electrocatalysis. The nanoparticle/ordered-ligand interlayer comprises a metal nanoparticle surface and a detached layer of ligands in its vicinity. This interlayer possesses unique pseudocapacitive characteristics where desolvated cations are intercalated, creating an active-site configuration that enhances catalytic turnover by two orders and one order of magnitude against a pristine metal surface and nanoparticle with tethered ligands, respectively. The nanoparticle/ordered-ligand interlayer is demonstrated across several metals with up to 99% CO selectivity at marginal overpotentials and onset overpotentials of as low as 27 mV, in aqueous conditions. Furthermore, in a gas-diffusion environment with neutral media, the nanoparticle/ordered-ligand interlayer achieves nearly unit CO selectivity at high current densities (98.1% at 400 mA cm −2 ). The complex, multi-component environments found in enzymes induce high catalytic specificity, but are difficult to achieve in synthetic catalysts. Now, researchers report a catalyst comprising a dynamic, ordered layer of ligands above a nanoparticle surface that creates a pocket to facilitate CO 2 electroreduction.

The biggest challenge of exploring the catalytic properties of under-coordinated nanoclusters is the issue of stability. We demonstrate herein that chemical dopants on sulfur-doped graphene (S-G) can be utilized to stabilize ultrafine (sub-2 nm) Au 25 (PET) 18 clusters to enable stable nitrogen reduction reaction (NRR) without significant structural degradation. The Au 25 @S-G exhibits an ammonia yield rate of 27.5 μg NH 3 ⋅ mg Au − 1 ⋅ h − 1 at −0.5 V with faradic efficiency of 2.3%. More importantly, the anchored clusters preserve ∼ 80% NRR activity after four days of continuous operation, a significant improvement over the 15% remaining ammonia production rate for clusters loaded on undoped graphene tested under the same conditions. Isotope labeling experiments confirmed the ammonia was a direct reaction product of N 2 feeding gas instead of other chemical contaminations. Ex-situ X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy of post-reaction catalysts reveal that the sulfur dopant plays a critical role in stabilizing the chemical state and coordination environment of Au atoms in clusters. Further ReaxFF molecular dynamics (RMD) simulation confirmed the strong interaction between Au nanoclusters (NCs) and S-G. This substrate-anchoring process could serve as an effective strategy to study ultrafine nanoclusters’ electrocatalytic behavior while minimizing the destruction of the under-coordinated surface motif under harsh electrochemical reaction conditions.

Promotion of C–C bonds is one of the key fundamental questions in the field of CO2 electroreduction. Much progress has occurred in developing bulk-derived Cu-based electrodes for CO2-to-multicarbons (CO2-to-C2+), especially in the widely studied class of high-surface-area “oxide-derived” copper. However, fundamental understanding into the structural characteristics responsible for efficient C–C formation is restricted by the intrinsic activity of these catalysts often being comparable to polycrystalline copper foil. By closely probing a Cu nanoparticle (NP) ensemble catalyst active for CO2-to-C2+, we show that bias-induced rapid fusion or “electrochemical scrambling” of Cu NPs creates disordered structures intrinsically active for low overpotential C2+ formation, exhibiting around sevenfold enhancement in C2+ turnover over crystalline Cu. Integrating ex situ, passivated ex situ, and in situ analyses reveals that the scrambled state exhibits several structural signatures: a distinct transition to single-crystal Cu2O cubes upon air exposure, low crystallinity upon passivation, and high mobility under bias. These findings suggest that disordered copper structures facilitate C–C bond formation from CO2 and that electrochemical nanocrystal scrambling is an avenue toward creating such catalysts.

SignificanceThe electroconversion of CO2 to value-added products is a promising path to sustainable fuels and chemicals. However, the microenvironment that is created during CO2 electroreduction near the surface of heterogeneous Cu electrocatalysts remains unknown. Its understanding can lead to the development of ways to improve activity and selectivity toward multicarbon products. This work introduces a method called on-stream substitution of reactant isotope that provides quantitative information of the CO intermediate species present on Cu surfaces during electrolysis. An intermediary CO reservoir that contains more CO molecules than typically expected in a surface adsorbed configuration was identified. Its size was shown to be a factor closely associated with the formation of multicarbon products. Despite the importance of the microenvironment in heterogeneous electrocatalysis, its role remains unclear due to a lack of suitable characterization techniques. Multistep reactions like the electroconversion of CO2 to multicarbons (C2+) are especially relevant considering the potential creation of a unique microenvironment as part of the reaction pathway. To elucidate the significance of the microenvironment during CO2 reduction, we develop on-stream substitution of reactant isotope (OSRI), a method that relies on the subsequent introduction of CO2 isotopes. Combining electrolytic experiments with a numerical model, this method reveals the presence of a reservoir of CO molecules concentrated near the catalyst surface that influences C2+ formation. Application of OSRI on a Cu nanoparticle (NP) ensemble and an electropolished Cu foil demonstrates that a CO monolayer covering the surface does not provide the amount of CO intermediates necessary to facilitate C-C coupling. Specifically, the C2+ turnover increases only after reaching a density of ∼100 CO molecules per surface Cu atom. The Cu NP ensemble satisfies this criterion at an overpotential 100 mV lower than the foil, making it a better candidate for efficient C2+ formation. Furthermore, given the same reservoir size, the ensemble’s intrinsically higher C-C coupling ability is highlighted by the fourfold higher C2+ turnover it achieves at a more positive potential. The OSRI method provides an improved understanding of how the presence of CO intermediates in the microenvironment impacts C2+ formation during the electroreduction of CO2 on Cu surfaces.

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.

C–C coupling is a critical step of CO 2 fixation in constructing the carbon skeleton of value-added multicarbon products. The Wood–Ljungdahl pathway is an efficient natural process through which microbes transform CO 2 into methyl and carbonyl groups and subsequently couple them together. This asymmetric coupling mechanism remains largely unexplored in inorganic CO 2 electroreduction. Here we experimentally validate the asymmetric coupling pathway through isotope-labelled co-reduction experiments on a Cu surface where 13 CH 3 I and 12 CO are co-fed externally as the methyl and the carbonyl source, respectively. Isotope-labelled multicarbon oxygenates were detected, which confirms an electrocatalytic asymmetric coupling on the Cu surface. We further employed tandem Cu–Ag nanoparticle systems in which *CH x and *CO intermediates can be generated to achieve asymmetric C–C coupling for a practical CO 2 electroreduction. We found that the production of multicarbon oxygenates is correlated with the generation rate of two intermediate indicators, CH 4 and CO. By aligning their rates, the oxygenates generation rate can be maximized. An asymmetric C–C coupling (Wood–Ljungdahl) pathway has long been known in biological carbon fixation, whereas its occurrence in inorganic systems has remained unclear. In this study, the coupling of *CO and *CH x intermediates to form multicarbon oxygenates has been experimentally observed on Cu electrodes.

Despite the importance of the microenvironment in heterogeneous electrocatalysis, its role remains unclear due to a lack of suitable characterization techniques. Multistep reactions like the electroconversion of CO₂ to multicarbons (C2+) are especially relevant considering the potential creation of a unique microenvironment as part of the reaction pathway. To elucidate the significance of the microenvironment during CO₂ reduction, we develop on-stream substitution of reactant isotope (OSRI), a method that relies on the subsequent introduction of CO₂ isotopes. Combining electrolytic experiments with a numerical model, this method reveals the presence of a reservoir of CO molecules concentrated near the catalyst surface that influences C2+ formation. Application of OSRI on a Cu nanoparticle (NP) ensemble and an electropolished Cu foil demonstrates that a CO monolayer covering the surface does not provide the amount of CO intermediates necessary to facilitate C-C coupling. Specifically, the C2+ turnover increases only after reaching a density of ∼100 CO molecules per surface Cu atom. The Cu NP ensemble satisfies this criterion at an overpotential 100 mV lower than the foil, making it a better candidate for efficient C2+ formation. Furthermore, given the same reservoir size, the ensemble’s intrinsically higher C-C coupling ability is highlighted by the four-fold higher C2+ turnover it achieves at a more positive potential. The OSRI method provides an improved understanding of how the presence of CO intermediates in the microenvironment impacts C2+ formation during the electroreduction of CO₂ on Cu surfaces.

The electroconversion of CO 2 to value-added products is a promising path to sustainable fuels and chemicals. However, the microenvironment that is created during CO 2 electroreduction near the surface of heterogeneous Cu electrocatalysts remains unknown. Its understanding can lead to the development of ways to improve activity and selectivity toward multicarbon products. This work introduces a method called on-stream substitution of reactant isotope that provides quantitative information of the CO intermediate species present on Cu surfaces during electrolysis. An intermediary CO reservoir that contains more CO molecules than typically expected in a surface adsorbed configuration was identified. Its size was shown to be a factor closely associated with the formation of multicarbon products. Despite the importance of the microenvironment in heterogeneous electrocatalysis, its role remains unclear due to a lack of suitable characterization techniques. Multistep reactions like the electroconversion of CO 2 to multicarbons (C 2+ ) are especially relevant considering the potential creation of a unique microenvironment as part of the reaction pathway. To elucidate the significance of the microenvironment during CO 2 reduction, we develop on-stream substitution of reactant isotope (OSRI), a method that relies on the subsequent introduction of CO 2 isotopes. Combining electrolytic experiments with a numerical model, this method reveals the presence of a reservoir of CO molecules concentrated near the catalyst surface that influences C 2+ formation. Application of OSRI on a Cu nanoparticle (NP) ensemble and an electropolished Cu foil demonstrates that a CO monolayer covering the surface does not provide the amount of CO intermediates necessary to facilitate C-C coupling. Specifically, the C 2+ turnover increases only after reaching a density of ∼100 CO molecules per surface Cu atom. The Cu NP ensemble satisfies this criterion at an overpotential 100 mV lower than the foil, making it a better candidate for efficient C 2+ formation. Furthermore, given the same reservoir size, the ensemble’s intrinsically higher C-C coupling ability is highlighted by the fourfold higher C 2+ turnover it achieves at a more positive potential. The OSRI method provides an improved understanding of how the presence of CO intermediates in the microenvironment impacts C 2+ formation during the electroreduction of CO 2 on Cu surfaces.

The CO2 carbon building block is essential to sustain life on Earth. However, its excessive emissions driven by anthropological activity have irreversibly affected the environment. Therefore, closing the carbon cycle loop through CO2 recycling using renewably sourced electricity not only addresses the growing threat of climate change but is also a powerful way to synthesize the chemicals necessary for the development of present and future generations. Specifically, the combination of CO2, protons, and electrons into value-added products enables the upcycling of CO2 while storing energy into chemical bonds. Given CO2 worldwide availability on Earth as well as in outer space (e.g., Mars), CO2 will always be a relevant feedstock in the future development of chemicals electrosynthesis. In this thesis, I present the prospects of catalyst materials design targeted for improving the utilization of CO2 through electrocatalysis.I introduce in Chapter 1 the current challenges we face for the CO2 electroreduction reaction to have a sizeable impact. There, I specifically discuss within the field of heterogeneous electrocatalysis the various strengths and drawbacks of utilizing nanomaterials to optimize CO2 electroconversion. Nanomaterials are the preferred platform to achieve catalyst fine-tuning that is essential to the CO2 electroconversion to higher-order products. However, in spite of the specific structural design accessible through their synthesis, nanomaterials’ high surface energy makes their structure and resulting properties especially prone to transformation when subject to external activation. The applied bias and reaction environment necessary to electrocatalysis induce in fact great change to such materials. In Chapter 2, I show that although often associated with the degradation of the catalyst surface and thus activity, the structural dynamics in nanocatalysts simultaneously introduces the possibility to design an incredible variety of catalysts constructed in operando. Furthermore, I present in Chapter 3 how the activity of nanocatalysts is not only driven by their surface properties, but also by the reaction environment formed near their surface during the reaction. The unique physicochemical landscape created at this interface can be exploited to tune the progress of complex reactions such as the electrochemical CO2 reduction reaction (CO2RR). Understanding the driving forces behind the formation of such an interface is therefore crucial in guiding the outcome of CO2RR in a controlled manner. I discuss the tools that can be employed to obtain such insights in Chapter 4, including powerful characterization techniques and the fine tuning catalyst structural properties. I emphasize there the importance of in situ and operando characterization techniques to accurately probe the dynamics of nanocatalysts. In addition, I highlight the synthetic advantages intrinsic to utilizing nanomaterials which can help isolate the driving parameters behind their structural evolution during electrolysis. While CO2 electroreduction is a close parallel to photosynthesis, there is a long way to go before it can replicate its selectivity and produce molecules as complex. In Chapter 5, I introduce a first attempt to bridge the synthetic gap between CO2 and sugars in an abiological catalytic process. I conclude this thesis in the last and 6th chapter with an overview of the breadth of advances done on the CO2 valuation through heterogeneous catalysis approaches.

The electrocatalytic conversion of CO 2 to value-added products, especially valuable multicarbon products, is a pathway toward sustainable formation of chemicals and fuels typically derived from fossil fuels, while mitigating CO 2 emissions. Fundamental understanding and development of more efficient catalysts for this reaction require deep investigation into structures with high intrinsic activity, which are limited at present. This work comprehensively investigates a dynamic copper nanoparticle ensemble catalyst that significantly improves intrinsic activity of copper for multicarbon formation. Through concerted ex situ and in situ characterization techniques, it illustrates an electrochemically induced fusion of copper nanoparticles that result in a catalytically active disordered structure, motivating closer study of disordered metal nanostructures for C–C coupling electrocatalysis. Promotion of C–C bonds is one of the key fundamental questions in the field of CO 2 electroreduction. Much progress has occurred in developing bulk-derived Cu-based electrodes for CO 2 -to-multicarbons (CO 2 -to-C 2+ ), especially in the widely studied class of high-surface-area “oxide-derived” copper. However, fundamental understanding into the structural characteristics responsible for efficient C–C formation is restricted by the intrinsic activity of these catalysts often being comparable to polycrystalline copper foil. By closely probing a Cu nanoparticle (NP) ensemble catalyst active for CO 2 -to-C 2+ , we show that bias-induced rapid fusion or “electrochemical scrambling” of Cu NPs creates disordered structures intrinsically active for low overpotential C 2+ formation, exhibiting around sevenfold enhancement in C 2+ turnover over crystalline Cu. Integrating ex situ, passivated ex situ, and in situ analyses reveals that the scrambled state exhibits several structural signatures: a distinct transition to single-crystal Cu 2 O cubes upon air exposure, low crystallinity upon passivation, and high mobility under bias. These findings suggest that disordered copper structures facilitate C–C bond formation from CO 2 and that electrochemical nanocrystal scrambling is an avenue toward creating such catalysts.