Electrochemically converting carbon monoxide to liquid fuels by directing selectivity with electrode surface area

High yield electrosynthesis of oxygenates from CO using a relay Cu-Ag co-catalyst system

As a sustainable alternative to fossil fuel-based manufacture of bulk oxygenates, electrochemical synthesis using CO and H2O as raw materials at ambient conditions offers immense appeal. However, the upscaling of the electrosynthesis of oxygenates encounters kinetic bottlenecks arising from the competing hydrogen evolution reaction with the selective production of ethylene. Herein, a catalytic relay system that can perform in tandem CO capture, activation, intermediate transfer and enrichment on a Cu-Ag composite catalyst is used for attaining high yield CO-to-oxygenates electrosynthesis at high current densities. The composite catalyst Cu/30Ag (molar ratio of Cu to Ag is 7:3) enables high efficiency CO-to-oxygenates conversion, attaining a maximum partial current density for oxygenates of 800 mA cm-2 at an applied current density of 1200 mA cm-2, and with 67 % selectivity. The ability to finely control the production of ethylene and oxygenates highlights the principle of efficient catalyst design based on the relay mechanism.

Small molecule activation by sila/germa boryne species

The inability of p-block elements to participate in π-backbonding restricts them from activating small molecules like CO, H2 , and so forth. However, the development of the main group metallomimetics became a new pathway, where the main-group elements like boron can bind and activate small molecules like CO and H2 . The concept of the frustrated Lewis pair, Boron-Boron multiple bonds, and borylene are previously illustrated. Some of these reported classes of boron species can mimic the jobs of the metal complexes. Hence, we have theoretically studied the binding of CO/N2 molecules at B-center of elusive species like sila/germa boryne stabilized by donor base ligands (cAAC)BE(Me)(L), where E  Si, L  cAACMe , NHCMe , PMe3 , E  Ge, L  cAACMe and (NHCMe )BE(Me)(cAACMe )). The substitutional analogues of (cAACR )BSiR1 (cAAC) and E  P, L  cAACMe ) have been studied by density functional theory (DFT), natural bond orbital, QTAIM calculations and energy decomposition analysis (EDA) coupled with natural orbital for chemical valence (NOCV) analyses. The computed bond dissociation energy and inner stability analyses by the EDA-NOCV method showed that the CO molecule can bind at the B-center of the above-mentioned species due to stronger σ-donor ability while binding of N2 has been theoretically predicted to be weak. The energy barrier for the CO binding is estimated to be 13-14 kcal/mol by transition state calculation. The change of partial triple bond character to single bond nature of the BSi bond and the bending of CBSi bond angle of sila-boryne species are the reason for the activation energy. Our study reveals the ability of such species to bind and activate the CO molecule to mimic the transition metal-containing complexes. We have additionally shown that binding of Fe(CO)4 and Ni(CO)3 is feasible at Si-center after binding of CO at the B-center.

Ligand-modified nanoparticle surfaces influence CO electroreduction selectivity

Improving the kinetics and selectivity of CO2/CO electroreduction to valuable multi-carbon products is a challenge for science and is a requirement for practical relevance. Here we develop a thiol-modified surface ligand strategy that promotes electrochemical CO-to-acetate. We explore a picture wherein nucleophilic interaction between the lone pairs of sulfur and the empty orbitals of reaction intermediates contributes to making the acetate pathway more energetically accessible. Density functional theory calculations and Raman spectroscopy suggest a mechanism where the nucleophilic interaction increases the sp2 hybridization of CO(ad), facilitating the rate-determining step, CO* to (CHO)*. We find that the ligands stabilize the (HOOC-CH2)* intermediate, a key intermediate in the acetate pathway. In-situ Raman spectroscopy shows shifts in C-O, Cu-C, and C-S vibrational frequencies that agree with a picture of surface ligand-intermediate interactions. A Faradaic efficiency of 70% is obtained on optimized thiol-capped Cu catalysts, with onset potentials 100 mV lower than in the case of reference Cu catalysts.

Enhancing Cu-ligand interaction for efficient CO2 reduction towards multi-carbon products

Electrochemical CO2 reduction (CO2R) to valuable products provides a promising strategy to enable CO2 utilization sustainably. Here, we report the strategy of using Cu-DAT (3,5-diamino-1,2,4-triazole) as a catalyst precursor for efficient CO2 reduction, demonstrating over 80% selectivity towards multicarbon products at 400 mA cm-2, with intrinsic activity over 19 times higher than that of Cu nanoparticles. The catalyst's active phase is determined to be metallic copper wrapped with the DAT ligand. We attribute this enhanced CO2R performance to the accelerated steps of *CO adsorption and C-C coupling induced by the closely cooperated DAT ligand.

Tuning the Catalytic Selectivity Toward C2+ Oxygenate Products by Manipulating Cu Oxidation States in CO Electroreduction

Enhancing the reaction selectivity for multicarbon products (C2+) is an important goal for the electrochemical CO(2) reduction (ECO(2)R) process. Cuprous compounds have demonstrated promising C2+ selectivity in the ECO(2)R process, but further investigation is necessary to thoroughly elucidate their catalytic behavior toward C2+ oxygenate production. In this study, copper nitride-based materials with varying reduction rates were employed as precatalysts. Consequently, a relationship between the selectivity toward C2+ oxygenates and the Cu oxidation state during the ECOR process is established. Results of theoretical and experimental analyses reveal that the Cu0/Cu+ interface plays a key role in enhancing *CO adsorption while lowering the formation energy of *CH2CO, thereby promoting acetate production. This work highlights the significance of the Cu0/Cu+ interface in the regulation of C2+ oxygenate production and paves the way for the development of highly selective catalysts in the future.

Screening Efficient C-N Coupling Catalysts for Electrosynthesis of Acetamide and Output Ammonia through a Cascade Strategy of Electrochemical CO2 and N2 Reduction Using Cu-Based Nitrogen-Carbon Nanosheets

Due to the limitation of the high-value-added products obtained from electrocatalytic CO2 reduction within an acid environment, introducing additional elements can expand the diversity of the products obtained during the CO2 reduction reaction (CO2RR) and nitrogen reduction reaction (NRR). Thus, coelectroreduction of CO2 and N2 is a new strategy for producing acetamide (CH3CONH2) via both C-C and C-N bond coupling using Cu-based nitrogen-carbon nanosheets. CO2 can reduce to CO, and a key ketene (*C═C═O) can be generated from *CO*CO dimerization; this ketene is postulated as an intermediate in the formation of acetamide. However, most studies focus on promoting the C-C bond formation. Here, we propose that C-N bond coupling can form acetamide through the interaction of *C═C═O with NH3. The acetamide is formed via a nucleophilic attack between *NH3 and the *C═C═O intermediate. The C-N coupling mechanism was successfully applied to expand the variety of nitrogen-containing products obtained from CO2 and N2 coreduction. Thus, we successfully screened Cu2-based graphite and Cu-based C3N4 as catalysts that can produce C2+ compounds by integrating CO dimerization with acetamide synthesis. In addition, we observed that Cu2-based C2N and Cu-based C3N4 catalysts are suitable for the NRR. Cu-based C3N4 showed high CO2RR and NRR activities with small negative limiting potential (UL) values of -0.83 and -0.58 V compared to those of other candidates, respectively. The formation of *COHCOH from *COHCO was considered the rate-determining step (RDS) during acetamide electrosynthesis. The limiting potential value of Cu2-based C2N was only -0.46 V for NH3 synthesis, and the formation of *NNH was via the RDS via an alternating path. The adsorption energy difference analysis both CO2 and N2 compare with the hydrogen evolution reaction (HER), suggesting that Cu2-based C2N exhibited the highest CO2RR and NRR selectivity among the 13 analyzed catalysts. The results of this study provide innovative insights into the design principle of Cu-based nitrogen-carbon electrocatalysts for generating highly efficient C-N coupling products.

Nanocurvature-induced field effects enable control over the activity of single-atom electrocatalysts

Tuning interfacial electric fields provides a powerful means to control electrocatalyst activity. Importantly, electric fields can modify adsorbate binding energies based on their polarizability and dipole moment, and hence operate independently of scaling relations that fundamentally limit performance. However, implementation of such a strategy remains challenging because typical methods modify the electric field non-uniformly and affects only a minority of active sites. Here we discover that uniformly tunable electric field modulation can be achieved using a model system of single-atom catalysts (SACs). These consist of M-N4 active sites hosted on a series of spherical carbon supports with varying degrees of nanocurvature. Using in-situ Raman spectroscopy with a Stark shift reporter, we demonstrate that a larger nanocurvature induces a stronger electric field. We show that this strategy is effective over a broad range of SAC systems and electrocatalytic reactions. For instance, Ni SACs with optimized nanocurvature achieved a high CO partial current density of ~400 mA cm-2 at >99% Faradaic efficiency for CO2 reduction in acidic media.

Steering the Reconstruction of Oxide-Derived Cu by Secondary Metal for Electrosynthesis of n-Propanol from CO

As fuel and an important chemical feedstock, n-propanol is highly desired in electrochemical CO2/CO reduction on Cu catalysts. However, the precise regulation of the Cu localized structure is still challenging and poorly understood, thus hindering the selective n-propanol electrosynthesis. Herein, by decorating Au nanoparticles (NPs) on CuO nanosheets (NSs), we present a counterintuitive transformation of CuO into undercoordinated Cu sites locally around Au NPs during CO reduction. In situ spectroscopic techniques reveal the Au-steered formation of abundant undercoordinated Cu sites during the removal of oxygen on CuO. First-principles accuracy molecular dynamic simulation demonstrates that the localized Cu atoms around Au tend to rearrange into disordered layer rather than a Cu (111) close-packed plane observed on bare CuO NSs. These Au-steered undercoordinated Cu sites facilitate CO binding, enabling selective electroreduction of CO into n-propanol with a high Faradaic efficiency of 48% in a flow cell. This work provides new insight into the regulation of the oxide-derived catalysts reconstruction with a secondary metal component.

Gas-induced controllable synthesis of the Cu(100) crystal facet for the selective electroreduction of CO2 to multicarbon products

Electrocatalytic CO2 reduction (ECR) to high value-added chemicals is an excellent method to attenuate the impact of greenhouse effect caused by CO2. At the same time, multicarbon products (C2+) get extensive attention in view of their relatively high energy density and market price. At present, Cu is an important metal electrocatalyst to convert CO2 into multicarbon products (e.g. ethylene, ethanol, and n-propanol); however, its poor selectivity impedes its practical application. It is well-known that the Cu(100) crystal facet can enhance the selectivity toward multicarbon products among different Cu crystal facets. Herein, the Cu nanoparticles were firstly prepared using the inductive effect of different gases (CO2, CO, Ar, N2, and air) during the Cu electrodeposition processes, in which the CO2-induced Cu catalyst (Cu-CO2) showed the largest normalized content of the Cu(100) crystal facet and the highest C2+ faradaic efficiency of 69% at a current density of 80 mA cm-2 in ECR. Subsequently, the different CO2 pressures during the Cu electrodepositions were studied to reveal the optimal CO2 pressure in the CO2-induced Cu synthesis for improved Cu(100) content as well as C2+ faradaic efficiency. Finally, density functional theory (DFT) calculations confirmed that CO2 molecules preferred to get adsorbed on the Cu(100) crystal facet, which resulted in not only the presence of dominant Cu(100) during the CO2-induced Cu synthesis but also the good electrocatalytic performance in ECR.

Site-selective protonation enables efficient carbon monoxide electroreduction to acetate

Electrosynthesis of acetate from CO offers the prospect of a low-carbon-intensity route to this valuable chemical--but only once sufficient selectivity, reaction rate and stability are realized. It is a high priority to achieve the protonation of the relevant intermediates in a controlled fashion, and to achieve this while suppressing the competing hydrogen evolution reaction (HER) and while steering multicarbon (C2+) products to a single valuable product--an example of which is acetate. Here we report interface engineering to achieve solid/liquid/gas triple-phase interface regulation, and we find that it leads to site-selective protonation of intermediates and the preferential stabilization of the ketene intermediates: this, we find, leads to improved selectivity and energy efficiency toward acetate. Once we further tune the catalyst composition and also optimize for interfacial water management, we achieve a cadmium-copper catalyst that shows an acetate Faradaic efficiency (FE) of 75% with ultralow HER (<0.2% H2 FE) at 150 mA cm-2. We develop a high-pressure membrane electrode assembly system to increase CO coverage by controlling gas reactant distribution and achieve 86% acetate FE simultaneous with an acetate full-cell energy efficiency (EE) of 32%, the highest energy efficiency reported in direct acetate electrosynthesis.

Cu-based catalyst designs in CO2 electroreduction: precise modulation of reaction intermediates for high-value chemical generation

The massive emission of excess greenhouse gases (mainly CO2) have an irreversible impact on the Earth's ecology. Electrocatalytic CO2 reduction (ECR), a technique that utilizes renewable energy sources to create highly reduced chemicals (e.g. C2H4, C2H5OH), has attracted significant attention in the science community. Cu-based catalysts have emerged as promising candidates for ECR, particularly in producing multi-carbon products that hold substantial value in modern industries. The formation of multi-carbon products involves a range of transient intermediates, the behaviour of which critically influences the reaction pathway and product distribution. Consequently, achieving desirable products necessitates precise regulation of these intermediates. This review explores state-of-the-art designs of Cu-based catalysts, classified into three categories based on the different prospects of the intermediates' modulation: heteroatom doping, morphological structure engineering, and local catalytic environment engineering. These catalyst designs enable efficient multi-carbon generation in ECR by effectively modulating reaction intermediates.

Silver and Copper Nitride Cooperate for CO Electroreduction to Propanol

The need of carbon sources for the chemical industry, alternative to fossil sources, has pointed to CO2 as a possible feedstock. While CO2 electroreduction (CO2 R) allows production of interesting organic compounds, it suffers from large carbon losses, mainly due to carbonate formation. This is why, quite recently, tandem CO2 R, a two-step process, with first CO2 R to CO using a solid oxide electrolysis cell followed by CO electroreduction (COR), has been considered, since no carbon is lost as carbonate in either step. Here we report a novel copper-based catalyst, silver-doped copper nitride, with record selectivity for formation of propanol (Faradaic efficiency: 45 %), an industrially relevant compound, from CO electroreduction in gas-fed flow cells. Selective propanol formation occurs at metallic copper atoms derived from copper nitride and is promoted by silver doping as shown experimentally and computationally. In addition, the selectivity for C2+ liquid products (Faradaic efficiency: 80 %) is among the highest reported so far. These findings open new perspectives regarding the design of catalysts for production of C3 compounds from CO2 .

Direct Electroreduction of Carbonate to Formate

A cause of losses in energy and carbon conversion efficiencies during the electrochemical CO2 reduction reaction (eCO2RR) can be attributed to the formation of carbonates (CO32-), which is generally considered to be an electrochemically inert species. Herein, using in situ Raman spectroscopy, liquid chromatography, 1H nuclear magnetic resonance spectroscopy, 13C and deuterium isotope labeling, and density functional theory simulations, we show that carbonate intermediates are adsorbed on a copper electrode during eCO2RR in KHCO3 electrolyte from 0.2 to -1.0 VRHE. These intermediates can be reduced to formate at -0.4 VRHE and more negative potentials. This finding is supported by our observation of formate from the reduction of Cu2(CO3)(OH)2. Pulse electrolysis on a copper electrode immersed in a N2-purged K2CO3 electrolyte was also performed. We found that the carbonate anions therein could be first adsorbed at -0.05 VRHE and then directly reduced to formate at -0.5 VRHE (overpotential of 0.28 V) with a Faradaic efficiency of 0.61%. The nature of the active sites generating the adsorbed carbonate species and the mechanism for the pulse-enabled reduction of carbonate to formate were elucidated. Our findings reveal how carbonates are directly reduced to a high-value product such as formate and open a potential pathway to mitigate carbonate formation during eCO2RR.

Dynamic Surface Reconstruction of Amphoteric Metal (Zn, Al) Doped Cu2 O for Efficient Electrochemical CO2 Reduction to C2+ Products

The recognition of the surface reconstruction of the catalysts during electrochemical CO2 reduction (CO2RR) is essential for exploring and comprehending active sites. Although the superior performance of Cu-Zn bimetallic sites toward multicarbon C2+ products has been established, the dynamic surface reconstruction has not been fully understood. Herein, Zn-doped Cu2 O nano-octahedrons are used to investigate the effect of the dynamic stability by the leaching and redeposition on CO2RR. Correlative characterizations confirm the Zn leaching from Zn-doped Cu2 O, which is redeposited at the surface of the catalysts, leading to dynamic stability and abundant Cu-Zn bimetallic sites at the surface. The reconstructed Zn-doped Cu2 O catalysts achieve a high Faradaic efficiency (FE) of C2+ products (77% at -1.1 V versus reversible hydrogen electrode (RHE)). Additionally, similar dynamic stability is also discovered in Al-doped Cu2 O for CO2RR, proving its universality in amphoteric metal-doped catalysts. Mechanism analyses reveal that the OHC-CHO pathway can be the C-C coupling processes on bare Cu2 O and Zn-doped Cu2 O, and the introduction of Zn to Cu can efficiently lower the energy barrier for CO2RR to C2 H4 . This research provides profound insight into unraveling surface dynamic reconstruction of amphoteric metal-containing electrocatalysts and can guide rational design of the high-performance electrocatalysts for CO2RR.

Steering the Dynamics of Reaction Intermediates and Catalyst Surface during Electrochemical Pulsed CO2 Reduction for Enhanced C2+ Selectivity

Developing alternative electrolysis techniques is crucial for advancing electrocatalysis in addition to tremendous efforts of material developments. Recently, pulse electrochemical CO2 reduction reaction (CO2RR) has demonstrated dramatic selectivity improvement toward multicarbon (C2+) products compared to potentiostatic electrochemical CO2RR, yet the underlying mechanisms remain little understood. Herein, we develop a fast time-resolved in situ Raman spectroscopic method with a time resolution of 0.25 s. We reveal that pulse electrolysis improves the C2+ selectivity of CO2RR through dynamic controls of the surface CuxO/Cu composition that would be unachievable under potentiostatic electrolysis. The population of the surface-adsorbed CO intermediate (COads) is characterized to be the determining factor in controlling reaction selectivity, which depicts the C2+/C1 selectivity of CO2RR under pulse conditions. Meanwhile, the vibrational character of COads, despite transforming dynamically between the low-frequency and high-frequency modes is characterized not to be the key factor in controlling the reaction selectivity. Such an active control of catalyst surface compositions and reaction intermediates enabled by pulse electrolysis offer a general way of regulating the electrocatalysis performance of broad electrochemical reactions beyond CO2RR.

Metal-Organic Framework Derived Cu-Ag Interface for Selective Carbon Monoxide Electroreduction to Acetate

Electrochemical carbon monoxide reduction reaction (CORR) is a potential way to obtain high-value multi-carbon (C2+ ) products. However, achieving high selectivity to acetate is still a challenge. Herein, we develop a two-dimensional Ag-modified Cu metal-organic framework (Ag0.10 @CuMOF-74) that demonstrates Faradaic efficiency (FE) for C2+ products up to 90.4 % at 200 mA cm-2 and an acetate FE of 61.1 % with a partial current density of 122.2 mA cm-2 . Detailed investigations show that the introduction of Ag on CuMOF-74 favors the generation of abundant Cu-Ag interface sites. In situ attenuated total reflection surface enhanced infrared absorption spectroscopy confirms that these Cu-Ag interface sites improve the coverage of *CO and *CHO and the coupling between each other and stabilize key intermediates *OCCHO and *OCCH2 , thus significantly promoting to the acetate selectivity on Ag0.10 @CuMOF-74. This work provides a high-efficiency pathway for CORR to C2+ products.

In-situ spectroscopic probe of the intrinsic structure feature of single-atom center in electrochemical CO/CO2 reduction to methanol

While exploring the process of CO/CO₂ electroreduction (CO_xRR) is of great significance to achieve carbon recycling, deciphering reaction mechanisms so as to further design catalytic systems able to overcome sluggish kinetics remains challenging. In this work, a model single-Co-atom catalyst with well-defined coordination structure is developed and employed as a platform to unravel the underlying reaction mechanism of CO_xRR. The as-prepared single-Co-atom catalyst exhibits a maximum methanol Faradaic efficiency as high as 65% at 30 mA/cm² in a membrane electrode assembly electrolyzer, while on the contrary, the reduction pathway of CO₂ to methanol is strongly decreased in CO₂RR. In-situ X-ray absorption and Fourier-transform infrared spectroscopies point to a different adsorption configuration of *CO intermediate in CORR as compared to that in CO₂RR, with a weaker stretching vibration of the C-O bond in the former case. Theoretical calculations further evidence the low energy barrier for the formation of a H-CoPc-CO^- species, which is a critical factor in promoting the electrochemical reduction of CO to methanol.

Cu+-Mediated CO Coordination for Promoting C-C Coupling for CO2 and CO Electroreduction

Selective electrochemical upgrading of CO₂ to multicarbon (C₂₊) products requires a C-C coupling process, yet the underlying promoting mechanism of widely involved Cu oxidation states remains largely unclear, hindering the subtle design of efficient catalysts. Herein, we unveil the critical role of Cu⁺ in promoting C-C coupling via coordination with a CO intermediate during electrochemical CO₂ reduction. We find that, relative to other halogen anions, iodide (I^-) in HCO₃^- electrolytes accelerates the generation of strongly oxidative hydroxyl radicals that accounts for the formation of Cu⁺, which can be dynamically stabilized by I^- via the formation of CuI. The in situ generated CO intermediate strongly binds to CuI sites, forming nonclassical Cu(CO)_n⁺ complexes, leading to an approximately 3.0-fold increase of C₂₊ Faradaic efficiency at -0.9 V_RHE relative to that of I^--free Cu surfaces. Accordingly, a deliberate introduction of CuI into I^--containing HCO₃^- electrolytes for direct CO electroreduction brings about a 4.3-fold higher C₂₊ selectivity. This work provides insights into the role of Cu⁺ in C-C coupling and the enhanced C₂₊ selectivity for CO₂ and CO electrochemical reduction.

Analysis of the Scale of Global Human Needs and Opportunities for Sustainable Catalytic Technologies

We analyzed the enormous scale of global human needs, their carbon footprint, and how they are connected to energy availability. We established that most challenges related to resource security and sustainability can be solved by providing distributed, affordable, and clean energy. Catalyzed chemical transformations powered by renewable electricity are emerging successor technologies that have the potential to replace fossil fuels without sacrificing the wellbeing of humans. We highlighted the technical, economic, and societal advantages and drawbacks of short- to medium-term decarbonization solutions to gauge their practicability, economic feasibility, and likelihood for widespread acceptance on a global scale. We detailed catalysis solutions that enhance sustainability, along with strategies for catalyst and process development, frontiers, challenges, and limitations, and emphasized the need for planetary stewardship. Electrocatalytic processes enable the production of solar fuels and commodity chemicals that address universal issues of the water, energy and food security nexus, clothing, the building sector, heating and cooling, transportation, information and communication technology, chemicals, consumer goods and services, and healthcare, toward providing global resource security and sustainability and enhancing environmental and social justice.

Oxidation of metallic Cu by supercritical CO2 and control synthesis of amorphous nano-metal catalysts for CO2 electroreduction

Amorphous nano-metal catalysts often exhibit appealing catalytic properties, because the intrinsic linear scaling relationship can be broken. However, accurate control synthesis of amorphous nano-metal catalysts with desired size and morphology is a challenge. In this work, we discover that Cu(0) could be oxidized to amorphous Cu_xO species by supercritical CO₂. The formation process of the amorphous Cu_xO is elucidated with the aid of machine learning. Based on this finding, a method to prepare Cu nanoparticles with an amorphous shell is proposed by supercritical CO₂ treatment followed by electroreduction. The unique feature of this method is that the size of the particles with amorphous shell can be easily controlled because their size depends on that of the original crystal Cu nanoparticles. Moreover, the thickness of the amorphous shell can be easily controlled by CO₂ pressure and/or treatment time. The obtained amorphous Cu shell exhibits high selectivity for C2+ products with the Faradaic efficiency of 84% and current density of 320 mA cm^-2. Especially, the FE of C2+ oxygenates can reach up to 65.3 %, which is different obviously from the crystalline Cu catalysts.

Surface-Dependent Hydrogen Evolution Activity of Copper Foil

Single-crystal planes are ideal platforms for catalytic research. In this work, rolled copper foils with predominantly (220) planes were used as the starting material. By using temperature gradient annealing, which caused grain recrystallization in the foils, they were transformed to those with (200) planes. In acidic solution, the overpotential of such a foil (10 mA cm^-2) was found to be 136 mV lower than that of a similar rolled copper foil. The calculation results show that hollow sites formed on the (200) plane have the highest hydrogen adsorption energy and are active centers for hydrogen evolution. Thus, this work clarifies the catalytic activity of specific sites on the copper surface and demonstrates the critical role of surface engineering in designing catalytic properties.

Weak CO binding sites induced by Cu-Ag interfaces promote CO electroreduction to multi-carbon liquid products

Electrochemical reduction of carbon monoxide to high-value multi-carbon (C₂₊) products offers an appealing route to store sustainable energy and make use of the chief greenhouse gas leading to climate change, i.e., CO₂. Among potential products, C₂₊ liquid products such as ethanol are of particular interest owing to their high energy density and industrial relevance. In this work, we demonstrate that Ag-modified oxide-derive Cu catalysts prepared via high-energy ball milling exhibit near 80% Faradaic efficiencies for C₂₊ liquid products at commercially relevant current densities (>100 mA cm^-2) in the CO electroreduction in a microfluidic flow cell. Such performance is retained in an over 100-hour electrolysis in a 100 cm² membrane electrode assembly (MEA) electrolyzer. A method based on surface-enhanced infrared absorption spectroscopy is developed to characterize the CO binding strength on the catalyst surface. The lower C and O affinities of the Cu-Ag interfacial sites in the prepared catalysts are proposed to be responsible for the enhanced selectivity for C₂₊ oxygenates, which is the experimental verification of recent computational predictions.

Surface Water as an Initial Proton Source for the Electrochemical CO Reduction Reaction on Copper Surfaces

We have employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) and density functional theory (DFT) calculations to study the CO reduction reaction (CORR) on Cu single-crystal surfaces under various conditions. Coadsorbed and structure-/potential-dependent surface species, including *CO, Cu-O_ad , and Cu-OH_ad , were identified using electrochemical spectroscopy and isotope labeling. The relative abundance of *OH follows a "volcano" trend with applied potentials in aqueous solutions, which is yet absent in absolute alcoholic solutions. Combined with DFT calculations, we propose that the surface H₂ O can serve as a strong proton donor for the first protonation step in both the C₁ and C₂ pathways of CORR at various applied potentials in alkaline electrolytes, leaving adsorbed *OH on the surface. This work provides fresh insights into the initial protonation steps and identity of key interfacial intermediates formed during CORR on Cu surfaces.

Identifying an Interfacial Stabilizer for Regeneration-Free 300 h Electrochemical CO2 Reduction to C2 Products

The electrochemical CO₂ reduction reaction (CO₂RR) to produce high value-added hydrocarbons and oxygenates presents a sustainable and compelling approach toward a carbon-neutral society. However, uncontrollable migration of active sites during the electrochemical CO₂RR limits its catalytic ability to simultaneously achieve high C₂ selectivity and ultradurability. Here, we demonstrate that the generated interfacial CuAlO₂ species can efficiently stabilize the highly active sites over the Cu-CuAlO₂-Al₂O₃ catalyst under harsh electrochemical conditions without active sites regeneration for a long-term test. We show that this unique Cu-CuAlO₂-Al₂O₃ catalyst exhibits ultradurable electrochemical CO₂RR performance with an 85% C₂ Faradaic efficiency for a 300 h test. Such a simple interfacial engineering design approach unveiled in this work would be adaptable to develop various ultradurable catalysts for industrial-scale electrochemical CO₂RR.

Functionalized Ag with Thiol Ligand to Promote Effective CO2 Electroreduction

It is challenging while critical to develop efficient catalysts that can achieve both high current density and high energy efficiency for electrocatalytic CO₂ reduction (CO₂R). Herein, we report a strategy of tailoring the surface electronic structure of an Ag catalyst via thiol ligand modification to improve its intrinsic activity, selectivity, and further energy efficiency toward CO₂R. Specifically, interconnected Ag nanoparticles with residual thiol ligands on the surface were prepared through electrochemical activation of a thiol-ligand-based Ag complex. When it was used as a catalyst for CO₂R, the thiol-ligand modified Ag exhibited high CO selectivity (>90%) throughout a wide electrode-potential range; furthermore, high cathodic energy efficiencies of >90% and >70% were obtained for CO formation at high current densities of 150 and 750 mA cm^-2, respectively, outperforming the state-of-the-art Ag-based electrocatalysts for CO₂ to CO conversion. The first-principle calculations on the reaction energetics suggest that the binding energies of the key intermediate -*COOH on Ag are optimized by the adsorbed thiol ligand, thus favoring CO formation while suppressing the competing H₂ evolution. Our findings provide a rational design strategy for CO₂ reduction electrocatalyst by electronic modulation through surface-adsorbed ligands.

Selective Ethylene Production from CO2 and CO Reduction via Engineering Membrane Electrode Assembly with Porous Dendritic Copper Oxide

Gas-fed zero-gap electrolyzers have recently emerged as attractive systems for limiting ohmic losses and costs associated with electrolytes and for optimizing energy efficiencies. Here, we report that using a dendritic Cu oxide (D-CuO) material deposited on a gas diffusion layer as the cathode of a gas-fed zero-gap membrane electrode assembly (MEA) system results in a very selective conversion of CO to ethylene. More specifically, CO reduction yielded ethylene with an FE up to 68% at 100-125 mA·cm^-2 with H₂ as the only other gaseous product and the electrolysis could be carried out for several hours with good stability. Ethylene was also the major product during CO₂ electrolysis (FE = 41%) at 125-150 mA·cm^-2, reflecting the high selectivity of D-CuO for ethylene production. Such systems are relevant for tandem CO₂ electroreduction processes, allowing energy efficiencies above 30%.

Directing the Architecture of Surface-Clean Cu2O for CO Electroreduction

Tailoring the morphology of nanocrystals is a promising way to enhance their catalytic performance. In most previous shape-controlled synthesis strategies, surfactants are inevitable due to their capability to stabilize different facets. However, the adsorbed surfactants block the intrinsic active sites of the nanocrystals, reducing their catalytic performance. For now, strategies to control the morphology without surfactants are still limited but necessary. Herein, a facile surfactant-free synthesis method is developed to regulate the morphology of Cu₂O nanocrystals (e.g., solid nanocube, concave nanocube, cubic framework, branching nanocube, branching concave nanocube, and branching cubic framework) to enhance the electrocatalytic performance for the conversion of CO to n-propanol. Specifically, the Cu₂O branching cubic framework (BCF-Cu₂O), which is difficult to fabricate using previous surfactant-free methods, is fabricated by combining the concentration depletion effect and the oxidation etching process. More significantly, the BCF-Cu₂O-derived catalyst (BCF) presents the highest n-propanol current density (-0.85 mA cm^-2) at -0.45 V versus the reversible hydrogen electrode (V_RHE), which is fivefold higher than that of the surfactant-coated Cu₂O nanocube-derived catalyst (SFC, -0.17 mA cm^-2). In terms of the n-propanol Faradaic efficiency in CO electroreduction, that of the BCF exhibits a 41% increase at -0.45 V_RHE as compared with SFC. The high catalytic activity of the BCF that results from the clean surface and the coexistence of Cu(100) and Cu(110) in the lattice is well-supported by density functional theory calculations. Thus, this work presents an important paradigm for the facile fabrication of surface-clean nanocrystals with an enhanced application performance.

Effects of the Catalyst Dynamic Changes and Influence of the Reaction Environment on the Performance of Electrochemical CO2 Reduction

Electrochemical reduction of carbon dioxide (CO₂ ) is substantially researched due to its potential for storing intermittent renewable electricity and simultaneously helping mitigating the pressing CO₂ emission concerns. The major challenge of electrochemical CO₂ reduction lies on having good controls of this reaction due to its complicated reaction networks and its unusual sensitivity to the dynamic changes of the catalyst structure (chemical states, compositions, facets and morphology, etc.), and to the non-catalyst components at the electrode/electrolyte interface, in another word the reaction environments. To date, a comprehensive analysis on the interplays between the above catalyst-dynamic-changes/reaction environments and the CO₂ reduction performance is rare, if not none. In this review, the catalyst dynamic changes observed during the catalysis are discussed based on the recent reports of electrochemical CO₂ reduction. Then, the above dynamic changes are correlated to their effects on the catalytic performance. The influences of the reaction environments on the performance of CO₂ reduction are also discussed. Finally, some perspectives on future investigations are offered with the aim of understanding the origins of the effects from the catalyst dynamic changes and the reaction environments, which will allow one to better control the CO₂ reduction toward the desired products.

Revealing the Nature of C-C Coupling Sites on a Cu Surface for CO2 Reduction

Electrochemical CO₂ reduction technology plays an important role in reducing CO₂ into valuable chemical fuels. Therein, Cu-based catalysts show superior performance for producing high-value C₂₊ products. Here, we illustrate the ascendency of high-index facets of Cu catalysts in producing C₂₊ products and find that two kinds of sites favor C-C coupling on the surface. One is prone to adsorb the C-C coupling structure by spanning stepped coppers with different coordination numbers. The other is to embed the structure along two columns of Cu with similar characteristics through O and C adsorbed simultaneously. Within all research surfaces, the coupling energy barrier is lowest on the Cu(911) facet, which is consistent with the experiment. The less charged sites promote the stabilization of the CO-CO structure as determined by charge analysis. Furthermore, our results suggest that the high selectivity for C₂₊ products on a Cu surface could significantly come from the contribution of the high-index facet.

In situ formed N-containing copper nanoparticles: a high-performance catalyst toward carbon monoxide electroreduction to multicarbon products with high faradaic efficiency and current density

Developing efficient catalysts for electrochemical carbon monoxide reduction (ECOR) with high faradaic efficiency (FE) and current density is highly desirable. In this work, we demonstrate that the N-containing Cu nanoparticles formed in situ by the reconstruction of cuprous 7,7,8,8-tetracyanoquinodimethane possess high-performance ECOR ability. Impressively, the N-containing Cu nanoparticle catalyst presented the highest FE of 81.31% towards multicarbon products with a high commercial-grade partial current density of 162.62 mA cm^-2, which is among the best of the reported Cu-based ECOR catalysts at -0.69 V versus the reversible hydrogen electrode. The retained ligand on the formed catalyst via the convenient in situ formation is crucial for the selectivity of multicarbon products. This work will arouse enthusiasm for the utilization of reconstruction features for designing ligand-containing catalysts with enhanced artificial carbon fixation ability.

Selective, Stable Production of Ethylene Using a Pulsed Cu-Based Electrode

Ethylene (C₂H₄) is an important product in carbon dioxide electroreduction (CO₂RR) because of the essential role it plays in chemical industry. While several strategies have been proposed to tune the selectivity of Cu-based catalysts in order to achieve high C₂H₄ faradaic efficiency, maintaining high selectivity toward C₂H₄ in CO₂RR remains an unresolved problem hampering the deployment of CO₂ conversion technology due to the lack of stable electrocatalysts. Here, we develop a facile method to deposit a layer of Cu₂O on Cu foil by an electrochemical pulsed potential treatment. This method is capable to easily scale up and synthesize multiple electrodes in one step. After the synthesis, the pulsed copper foil, denoted as P-Cu, exhibits good C₂H₄ faradaic efficiency of ∼50% in CO₂RR at a potential around -1.0 V vs. RHE. The C₂H₄ selectivity is also found to be quantitatively correlated with the roughness factor (RF) of Cu-based catalysts. More importantly, for the first time, we demonstrate that the P-Cu electrode is quite durable in CO₂RR to produce C₂H₄ for more than 6 months.

Trends in oxygenate/hydrocarbon selectivity for electrochemical CO(2) reduction to C2 products

The electrochemical conversion of carbon di-/monoxide into commodity chemicals paves a way towards a sustainable society but it also presents one of the great challenges in catalysis. Herein, we present the trends in selectivity towards specific dicarbon oxygenate/hydrocarbon products from carbon monoxide reduction on transition metal catalysts, with special focus on copper. We unveil the distinctive role of electrolyte pH in tuning the dicarbon oxygenate/hydrocarbon selectivity. The understanding is based on density functional theory calculated energetics and microkinetic modeling. We identify the critical reaction steps determining selectivity and relate their transition state energies to two simple descriptors, the carbon and hydroxide binding strengths. The atomistic insight gained enables us to rationalize a number of experimental observations and provides avenues towards the design of selective electrocatalysts for liquid fuel production from carbon di-/monoxide.

Exposing Cu(100) Surface via Ion-Implantation-Induced Oxidization and Etching for Promoting Hydrogen Evolution Reaction

Metallic materials with unique surface structure have attracted much attention due to their unique physical and chemical properties. However, it is hard to prepare bulk metallic materials with special crystal faces, especially at the nanoscale. Herein, we report an efficient method to adjust the surface structure of a Cu plate which combines ion implantation technology with the oxidation-etching process. The large number of vacancies generated by ion implantation induced the electrochemical oxidation of several atomic layers in depth; after chemical etching, the Cu(100) planes were exposed on the surface of the Cu plate. As a catalyst for acid hydrogen evolution reaction, the Cu plate with (100) planes merely needs 273 mV to deliver a current density of 10 mA/cm² because the high-energy (100) surface has moderate hydrogen adsorption and desorption capability. This work provides an appealing strategy to engineer the surface structure of bulk metallic materials and improve their catalytic properties.

Epitaxial Growth of High-Energy Copper Facets for Promoting Hydrogen Evolution Reaction

Copper is known as a conductive metal but an inert catalyst for the hydrogen evolution reaction due to its inappropriate electronic structure. In this work, an active copper catalyst is prepared with high-energy surfaces by adopting the friction stir welding (FSW) technique. FSW can mix the immiscible Fe and Cu materials homogenously and heat them to a high temperature. Resultantly, α-Fe transforms into γ-Fe, and low-energy γ-Fe (100) and (110) surfaces induce the epitaxial growth of high-energy Cu (110) and (100) planes, respectively. After the removal of γ-Fe by acid etching, the copper electrode exposes high-energy surface and exhibits excellent acidic HER activity, even being superior to Pt foil at high current densities (>66 mA cm^-2 ). Density functional theory calculation reveals that the high-energy surface favors the adsorption of hydrogen intermediate, thus accelerating the hydrogen evolution reaction. The epitaxial growth induced by FSW opens a new avenue toward engineering high-performance catalysts. In addition, FSW makes it possible to massively fabricate low-cost catalyst, which is advantageous to industrial application.

Scalable Gas Diffusion Electrode Fabrication for Electrochemical CO2 Reduction Using Physical Vapor Deposition Methods

Electrochemical CO₂ reduction (ECR) promises the replacement of fossil fuels as the source of feedstock chemicals and seasonal storage of renewable energy. While much progress has been made in catalyst development and electrochemical reactor design, few studies have addressed the effect of catalyst integration on device performance. Using a microfluidic gas diffusion electrolyzer, we systematically studied the effect of thickness and the morphology of electron beam (EB) and magnetron-sputtered (MS) Cu catalyst coatings on ECR performance. We observed that EB-Cu outperforms MS-Cu in current density, selectivity, and energy efficiency, with 400 nm thick catalyst coatings performing the best. The superior performance of EB-Cu catalysts is assigned to their faceted surface morphology and sharper Cu/gas diffusion layer interface, which increases their hydrophobicity. Tests in a large-scale zero-gap electrolyzer yielded similar product selectivity distributions with an ethylene Faradaic efficiency of 39% at 200 mA/cm², demonstrating the scalability for industrial ECR applications.

Photocatalytic turnover of CO2 under visible light by [Re(CO)3(1-(1,10) phenanthroline-5-(4-nitro-naphthalimide))Cl] in tandem with the sacrificial donor BIH

Optimized photocatalytic conversion of CO₂ requires new potent catalysts that can absorb visible light. The photocatalytic reduction of CO₂ using rhenium(i) has been demonstrated but suffers from low turnover. Herein, we describe a [Re(CO)₃(1-(1,10)phenanthroline-5-(4-nitro-naphthalimide))Cl] photocatalyst, which when combined with the sacrificial donor 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole, results in selective production of formic acid and a high turnover number of 533 and turnover frequency of 356 h⁻¹. Single-crystal X-ray diffraction and DFT studies are also discussed.

Rhenium based photocatalytic conversion CO₂ to formate in the visible region with excellent turnover.

In Situ Analysis of the Facets of Cu-Based Electrocatalysts in Alkaline Media Using Pb Underpotential Deposition

Establishing relationships between the surface atomic structure and activity of Cu-based electrocatalysts for CO₂ and CO reduction is hindered by probable surface restructuring under working conditions. Insights into these structural evolutions are scarce as techniques for monitoring the surface facets in conventional experimental designs are lacking. To directly correlate surface reconstructions to changes in selectivity or activity, the development of surface-sensitive, electrochemical probes is highly desirable. Here, we report the underpotential deposition of lead over three low index Cu single crystals in alkaline media, the preferred electrolyte for CO reduction studies. We find that underpotential deposition of Pb onto these facets occurs at distinct potentials, and we use these benchmarks to probe the predominant facet of polycrystalline Cu electrodes in situ. Finally, we demonstrate that Cu and Pb form an irreversible surface alloy during underpotential deposition, which limits this method to investigating the surface atomic structure after reaction.