Theoretical Investigation of the Adsorbate and Potential-Induced Stability of Cu Facets During Electrochemical CO2 and CO Reduction.

The activity and product selectivity of electrocatalysts for reactions like the carbon dioxide reduction reaction (CO2RR) are intimately dependent on the catalyst's structure and composition. While engineering catalytic surfaces can improve performance, discovering the key sets of rational design principles remains challenging due to limitations in modeling catalyst stability under operating conditions. Herein, we perform first-principles density functional calculations adopting implicit solvation methods with potential control to study the influence of adsorbates and applied potential on the stability of different facets of model Cu electrocatalysts. Using coverage dependencies extracted from microkinetic models, we describe an approach for calculating potential and adsorbate-dependent contributions to surface energies under reaction conditions, where Wulff constructions are used to understand the morphological evolution of Cu electrocatalysts under CO2RR conditions. We identify that CO*, a key reaction intermediate, exhibits higher kinetically and thermodynamically accessible coverages on (100) relative to (111) facets, which can translate into an increased relative stabilization of the (100) facet during CO2RR. Our results support the known tendency for increased (111) faceting of Cu nanoparticles under more reducing conditions and that the relative increase in (100) faceting observed under CO2RR conditions is likely attributed to differences in CO* coverage between these facets.

Enhanced Catalytic Oxidation Reactivity over Atomically Dispersed Pt/CeO2 Catalysts by CO Activation.

The elevation of the low-temperature oxidation activity for Pt/CeO2 catalysts is challenging to meet the increasingly stringent requirements for effectively eliminating carbon monoxide (CO) from automobile exhaust. Although reducing activation is a facile strategy for boosting reactivity, past research has mainly concentrated on applying H2 as the reductant, ignoring the reduction capabilities of CO itself, a prevalent component of automobile exhaust. Herein, atomically dispersed Pt/CeO2 was fabricated and activated by CO, which could lower the 90% conversion temperature (T90) by 256 °C and achieve a 20-fold higher CO consumption rate at 200 °C. The activated Pt/CeO2 catalysts showed exceptional catalytic oxidation activity and robust hydrothermal stability under the simulated working conditions for gasoline or diesel exhausts. Characterization results illustrated that the CO activation triggered the formation of a large portion of Pt0 terrace sites, acting as inherent active sites for CO oxidation. Besides, CO activation weakened the Pt-O-Ce bond strength to generate a surface oxygen vacancy (Vo). It served as the oxygen reservoir to store the dissociated oxygen and convert it into active dioxygen intermediates. Conversely, H2 activation failed to stimulate Vo, but triggered a deactivating transformation of the Pt nanocluster into inactive PtxOy in the presence of oxygen. The present work offers coherent insight into the upsurging effect of CO activation on Pt/CeO2, aiming to set up a valuable avenue in elevating the efficiency of eliminating CO, C3H6, and NH3 from automobile exhaust.

Direct and continuous generation of pure acetic acid solutions via electrocatalytic carbon monoxide reduction.

Electrochemical CO2 or CO reduction to high-value C2+ liquid fuels is desirable, but its practical application is challenged by impurities from cogenerated liquid products and solutes in liquid electrolytes, which necessitates cost- and energy-intensive downstream separation processes. By coupling rational designs in a Cu catalyst and porous solid electrolyte (PSE) reactor, here we demonstrate a direct and continuous generation of pure acetic acid solutions via electrochemical CO reduction. With optimized edge-to-surface ratio, the Cu nanocube catalyst presents an unprecedented acetate performance in neutral pH with other liquid products greatly suppressed, delivering a maximal acetate Faradaic efficiency of 43%, partial current of 200 mA⋅cm-2, ultrahigh relative purity of up to 98 wt%, and excellent stability of over 150 h continuous operation. Density functional theory simulations reveal the role of stepped sites along the cube edge in promoting the acetate pathway. Additionally, a PSE layer, other than a conventional liquid electrolyte, was designed to separate cathode and anode for efficient ion conductions, while not introducing any impurity ions into generated liquid fuels. Pure acetic acid solutions, with concentrations up to 2 wt% (0.33 M), can be continuously produced by employing the acetate-selective Cu catalyst in our PSE reactor.

In situ/Operando Synchrotron Radiation Analytical Techniques for CO2/CO Reduction Reaction: From Atomic Scales to Mesoscales.

Electrocatalytic carbon dioxide/carbon monoxide reduction reaction (CO(2)RR) has emerged as a prospective and appealing strategy to realize carbon neutrality for manufacturing sustainable chemical products. Developing highly active electrocatalysts and stable devices has been demonstrated as effective approach to enhance the conversion efficiency of CO(2)RR. In order to rationally design electrocatalysts and devices, a comprehensive understanding of the intrinsic structure evolution within catalysts and micro-environment change around electrode interface, particularly under operation conditions, is indispensable. Synchrotron radiation has been recognized as a versatile characterization platform, garnering widespread attention owing to its high brightness, elevated flux, excellent directivity, strong polarization and exceptional stability. This review systematically introduces the applications of synchrotron radiation technologies classified by radiation sources with varying wavelengths in CO(2)RR. By virtue of in situ/operando synchrotron radiationanalytical techniques, we also summarize relevant dynamic evolution processes from electronic structure, atomic configuration, molecular adsorption, crystal lattice and devices, spanning scales from the angstrom to the micrometer. The merits and limitations of diverse synchrotron characterization techniques are summarized, and their applicable scenarios in CO(2)RR are further presented. On the basis of the state-of-the-art fourth-generation synchrotron facilities, a perspective for further deeper understanding of the CO(2)RR process using synchrotron radiation analytical techniques is proposed.

Photoelectrocatalytic Synthesis of Urea from Carbon Dioxide and Nitrate over a Cu2O Photocathode.

Transformation of carbon dioxide and nitrate ions into urea offers an attractive route for both nitrogen fertilizer production and environmental remediation. However, achieving this transformation under mild conditions remains challenging. Herein, we report an efficient photoelectrochemical method for urea synthesis by co-reduction of carbon dioxide and nitrate ion over a Cu2O photocathode, delivering urea formation rate of 29.71±2.20 µmol g-1 h-1 and Faradaic efficiency (FE) of 12.90±1.15 % at low external potential (-0.017 V vs. reversible hydrogen electrode). Experimental data combined with theoretical calculations suggest that the adsorbed CO* and NO2* species are the key intermediates, and associated C-N coupling is the rate-determining step. This work demonstrates that Cu2O is an efficient catalyst to drive co-reduction of CO2 and NO3 - to urea under light irradiation with low external potential, showing great opportunity of photoelectrocatalysis as a sustainable tool for value-added chemical synthesis.

Selective reduction of CO to acetaldehyde with CuAg electrocatalysts.

Electrochemical CO reduction can serve as a sequential step in the transformation of CO2 into multicarbon fuels and chemicals. In this study, we provide insights on how to steer selectivity for CO reduction almost exclusively toward a single multicarbon oxygenate by carefully controlling the catalyst composition and its surrounding reaction conditions. Under alkaline reaction conditions, we demonstrate that planar CuAg electrodes can reduce CO to acetaldehyde with over 50% Faradaic efficiency and over 90% selectivity on a carbon basis at a modest electrode potential of -0.536 V vs. the reversible hydrogen electrode. The Faradaic efficiency to acetaldehyde was further enhanced to 70% by increasing the roughness factor of the CuAg electrode. Density functional theory calculations indicate that Ag ad-atoms on Cu weaken the binding energy of the reduced acetaldehyde intermediate and inhibit its further reduction to ethanol, demonstrating that the improved selectivity to acetaldehyde is due to the electronic effect from Ag incorporation. These findings will aid in the design of catalysts that are able to guide complex reaction networks and achieve high selectivity for the desired product.

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-Oad , and Cu-OHad , 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.

Sustainable and High-Rate Electrosynthesis of Nitrogen Fertilizer.

The conventional industrial production of nitrogen-containing fertilizers, such as urea and ammonia, relies heavily on energy-intensive processes, accounting for approximately 3 % of global annual CO2 emissions. Herein, we report a sustainable electrocatalytic approach that realizes direct and selective synthesis of urea and ammonia from co-reduction of CO2 and nitrates under ambient conditions. With the assistance of a copper (Cu)-based salphen organic catalyst, outstanding urea (3.64 mg h-1 mgcat -1 ) and ammonia (9.73 mg h-1 mgcat -1 ) yield rates are achieved, in addition to a remarkable Faradaic efficiency of 57.9±3 % for the former. This work proposes an appealing sustainable route to converting greenhouse gas and waste nitrates by renewable energies into value-added fertilizers.

High-Pressure CO Electroreduction at Silver Produces Ethanol and Propanol.

Reducing CO2 to long-chain carbon products is attractive considering such products are typically more valuable than shorter ones. However, the best electrocatalyst for making such products from CO2 , copper, lacks selectivity. By studying alternate C2+ producing catalysts we can increase our mechanistic understanding, which is beneficial for improving catalyst performance. Therefore, we investigate CO reduction on silver, as density functional theory (DFT) results predict it to be good at forming ethanol. To address the current disagreement between DFT and experimental results (ethanol vs. no ethanol), we investigated CO reduction at higher surface coverage (by increasing pressure) to ascertain if desorption effects can explain the discrepancy. In terms of product trends, our results agree with the DFT-proposed acetaldehyde-like intermediate, yielding ethanol and propanol as C2+ products-making the CO2 electrochemistry of silver very similar to that of copper at sufficiently high coverage.

Flow Electrolyzer Mass Spectrometry with a Gas-Diffusion Electrode Design.

Operando mass spectrometry is a powerful technique to probe reaction intermediates near the surface of catalyst in electrochemical systems. For electrochemical reactions involving gas reactants, conventional operando mass spectrometry struggles in detecting reaction intermediates because the batch-type electrochemical reactor can only handle a very limited current density due to the low solubility of gas reactant(s). Herein, we developed a new technique, namely flow electrolyzer mass spectrometry (FEMS), by incorporating a gas-diffusion electrode design, which enables the detection of reactive volatile or gaseous species at high operating current densities (>100 mA cm-2 ). We investigated the electrochemical carbon monoxide reduction reaction (eCORR) on polycrystalline copper and elucidated the oxygen incorporation mechanism in the acetaldehyde formation. Combining FEMS and isotopic labelling, we showed that the oxygen in the as-formed acetaldehyde intermediate originates from the reactant CO, while ethanol and n-propanol contained mainly solvent oxygen. The observation provides direct experimental evidence of an isotopic scrambling mechanism.

Probing CO2 Conversion Chemistry on Nanostructured Surfaces with Operando Vibrational Spectroscopy.

With the rising emphasis on renewable energy research, the field of electrocatalytic CO2 conversion to fuels has grown tremendously in recent years. Advances in nanomaterial synthesis and characterization have enabled researchers to screen effects of elemental composition, size, and surface chemistry on catalyst performance. However, direct links from structure and active state to catalytic function are difficult to establish. To this end, operando spectroscopic techniques, those conducted simultaneously as catalysts operate, can provide key complementary information by investigating electrocatalysis under turnover conditions. In particular, Raman and infrared spectroscopy have the potential to reveal the identity of surface-bound intermediates, catalyst active state, and possible reaction sites to supplement the insights extracted from conventional electrochemistry. Such research aims to work in tandem synthetic and catalytic efforts to guide the development of next-generation CO2 electrocatalytic systems through rational design. In this Mini Review, we examine the latest developments in the operando probing of electrochemical CO2 reduction on nanostructured electrocatalysts and detail how this research accelerates the advancement of this field.

CO Binding to the FeV Cofactor of CO-Reducing Vanadium Nitrogenase at Atomic Resolution.

Nitrogenases reduce N2 , the most abundant element in Earth's atmosphere that is otherwise resistant to chemical conversions due to its stable triple bond. Vanadium nitrogenase stands out in that it additionally processes carbon monoxide, a known inhibitor of the reduction of all substrates other than H+ . The reduction of CO leads to the formation of hydrocarbon products, holding the potential for biotechnological applications in analogy to the industrial Fischer-Tropsch process. Here we report the most highly resolved structure of vanadium nitrogenase to date at 1.0 Šresolution, with CO bound to the active site cofactor after catalytic turnover. CO bridges iron ions Fe2 and Fe6, replacing sulfide S2B, in a binding mode that is in line with previous reports on the CO complex of molybdenum nitrogenase. We discuss the structural consequences of continued turnover when CO is removed, which involve the replacement of CO possibly by OH- , the movement of Q176D and K361D , the return of sulfide and the emergence of two additional water molecules that are absent in the CO-bound state.

Highly Selective Production of Ethylene by the Electroreduction of Carbon Monoxide.

Conversion of carbon monoxide to high value-added ethylene with high selectivity by traditional syngas conversion process is challenging because of the limitation of Anderson-Schulz-Flory distribution. Herein we report a direct electrocatalytic process for highly selective ethylene production from CO reduction with water over Cu catalysts at room temperature and ambient pressure. An unprecedented 52.7 % Faradaic efficiency of ethylene formation is achieved through optimization of cathode structure to facilitate CO diffusion at the surface of the electrode and Cu catalysts to enhance the C-C bond coupling. The highly selective ethylene production is almost without other carbon-based byproducts (e.g. C1 -C4 hydrocarbons and CO2 ) and avoids the drawbacks of the traditional Fischer-Tropsch process that always delivers undesired products. This study provides a new and promising strategy for highly selective production of ethylene from the abundant industrial CO.

Hydroxide Is Not a Promoter of C2+ Product Formation in the Electrochemical Reduction of CO on Copper.

Highly alkaline electrolytes have been shown to improve the formation rate of C2+ products in the electrochemical reduction of carbon dioxide (CO2 ) and carbon monoxide (CO) on copper surfaces, with the assumption that higher OH- concentrations promote the C-C coupling chemistry. Herein, by systematically varying the concentration of Na+ and OH- at the same absolute electrode potential, we demonstrate that higher concentrations of cations (Na+ ), rather than OH- , exert the main promotional effect on the production of C2+ products. The impact of the nature and the concentration of cations on the electrochemical reduction of CO is supported by experiments in which a fraction or all of Na+ is chelated by a crown ether. Chelation of Na+ leads to drastic decrease in the formation rate of C2+ products. The promotional effect of OH- determined at the same potential on the reversible hydrogen electrode scale is likely caused by larger overpotentials at higher electrolyte pH.

Electrochemically reduced graphene oxide and gold nanoparticles on an indium tin oxide electrode for voltammetric sensing of dopamine.

The authors describe an electrochemical dopamine sensor that is based on the use of electrochemically co-reduced graphene oxide (Er-GO) and gold nanoparticles (AuNPs) on an indium-tin oxide (ITO) electrode. The synergistic effects of Er-GO and Er-AuNPs promote electron transport in the modified ITO. This results in an excellent performance for voltammetric sensing of dopamine (DA). Under the optimum conditions and a typical working potential of -0.05 V (vs. Ag/AgCl), the ITO electrode has a linear response in the 0.02-200 µM DA concentration range and a low detection limit of 15 nM. The sensor also showed a good selectivity over ascorbic acid and uric acid. The feasibility of the method was studied by analyzing DA in cerebrospinal fluid of rats. Graphical abstract Schematic presentation of one-step electrochemical co-reduction of graphene oxide (GO) and gold nanoparticles (AuNPs) on an ITO electrode for voltammetric sensing of dopamine.

Amperometric determination of nitrite by using a nanocomposite prepared from gold nanoparticles, reduced graphene oxide and multi-walled carbon nanotubes.

A nanocomposite consisting of gold nanoparticles (AuNP), reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) was synthesized using a co-reduction strategy in ethylene glycol using sodium citrate as the reducing agent. The nanocomposite was successfully characterized using X-ray powder diffraction, scanning electron microscopy and electrochemical methods. The material was deposited on a glassy carbon electrode and then was found to have high electrocatalytic capability for the electrode process of nitrite. This is attributed to the synergic actions of rGO, MWCNTs and AuNPs. Based on this, an amperometric nitrite sensing scheme was worked out that had attractive features: (a) a wide linear range that extends from 50 nM to 2.2 mM, (b) a working potential of 0.80 V (vs.SCE) at pH 5.0, (c) a 14 nM detection limit (at an SNR of 3), and (d) an electrochemical sensitivity of 1201 µA·mM-1·cm-2. The sensor was successfully applied to the determination of nitrite in the local river water. Graphical abstract Schematic presentation of the fabrication of the AuNPs-rGO-MWCNTs composite modified electrode and its application for the nitrite electrochemical sensing.

Preparation of the Borane (Fmes)BH2 and its Utilization in the FLP Reduction of Carbon Monoxide and Carbon Dioxide.

Treatment of 1,3,5-tris(trifluoromethyl)benzene with n-BuLi, followed by H3 B⋅SMe2 and subsequent hydride removal gave the (Fmes)BH2 reagent, which was isolated as a SMe2 stabilized monomer or a ligand free (µ-H)2 -bridged dimer. Reaction with Mes2 P(vinyl) gave the respective ethylene-bridged P/B(Fmes)H FLP. It reduced carbon monoxide to the formyl stage and carbon dioxide to the formaldehyde oxidation state. Most new compounds were characterized by X-ray diffraction.

Evaluation of the Catalytic Relevance of the CO-Bound States of V-Nitrogenase.

Binding and activation of CO by nitrogenase is a topic of interest because CO is isoelectronic to N2 , the physiological substrate of this enzyme. The catalytic relevance of one- and multi-CO-bound states (the lo-CO and hi-CO states) of V-nitrogenase to C-C coupling and N2 reduction was examined. Enzymatic and spectroscopic studies demonstrate that the multiple CO moieties in the hi-CO state cannot be coupled as they are, suggesting that C-C coupling requires further activation and/or reduction of the bound CO entity. Moreover, these studies reveal an interesting correlation between decreased activity of N2 reduction and increased population of the lo-CO state, pointing to the catalytic relevance of the belt Fe atoms that are bridged by the single CO moiety in the lo-CO state. Together, these results provide a useful framework for gaining insights into the nitrogenase-catalyzed reaction via further exploration of the utility of the lo-CO conformation of V-nitrogenase.

Tuning Electron Flux through Nitrogenase with Methanogen Iron Protein Homologues.

Nitrogenase uses a reductase component called Fe protein to deliver electrons to its catalytic partner for substrate reduction. The essential role of Fe protein in catalysis makes it an ideal target for regulating the electron flux and enzymatic activity of nitrogenase without perturbing the cofactor site. This work reports that hybrids between the Fe protein homologs of Methanosarcina acetivorans and the catalytic components of Azotobacter vinelandii can trap substrate CO through reduced electron fluxes. In addition, homology modeling/in silico docking is used to define markers for binding energy and specificity between the component proteins that correlate with the experimentally determined activities. This homologue-based approach could be further developed to allow identification or design of hybrids between homologous nitrogenase components for mechanistic investigations of nitrogenase through capture of substrates/ intermediates or for transgenic expression of nitrogenase through synthetic biology.

The Chemistry of a Non-Interacting Vicinal Frustrated Phosphane/Borane Lewis Pair.

The dimesitylphosphinocyclopentene/HB(C6 F5 )2 -derived vicinal trans-1,2-P/B frustrated Lewis pair (FLP) 4 shows no direct phosphane-borane interaction. Toward some reagents it behaves similar to an intermolecular FLP; it cleaves dihydrogen, deprotonates terminal alkynes, and adds to organic carbonyl compounds including CO2 . It shows typical intramolecular FLP reaction modes (cooperative 1,1-additions) to mesityl azide, to carbon monoxide, and to NO. The latter reaction yields a persistent P/B FLPNO nitroxide radical, which undergoes H-atom abstraction reactions. The FLP 4 serves as a template for the CO reduction by [HB(C6 F5 )2 ] to generate a FLP-η2 -formylborane. The formylborane moiety is removed from the FLP template by reaction with pyridine to yield a genuine pyridine stabilized formylborane that undergoes characteristic borane carbaldehyde reactions (Wittig olefination, imine formation). Most new products were characterized by X-ray diffraction.