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Among the electrolyzers under development for CO2 electroreduction at practical reaction rates, gas-fed approaches that use gas diffusion electrodes (GDEs) as cathodes are the most promising. Howev...

Deep eutectic solvents (DESs) were applied to the electrochemical CO2 reduction reaction (CO2 RR). Choline-based DESs represent a non-toxic and inexpensive alternative to room-temperature ionic liquids (RTILs) as additives to the system or as electrolyte. Following the study on choline-based DESs this approach was generalized and simple and organic-soluble systems were devised based on the combination of organic chloride salts with ethylene glycol (EG), allowing the chlorides to be readily used as cocatalysts in the CO2 RR. This approach negates the need for anion exchange and, because the chloride salt is usually the least expensive one, substantially reduces the cost of the electrolyte and opens the way for high-throughput experimentation.

Rare-earth elements (REEs) are one of the most important raw materials and are of vast significance for the modern hi-tech industry. Electrochemical deposition of REE-containing materials can provide a real alternative to currently used high-temperature processes of molten salt electrolysis. Here we study the process of Eu electrodeposition from 1‑butyl‑1-methylpyrrolidinium dicyanamide IL, [BMP][DCA], containing controlled amount of water. The Eu deposition is performed on Pt(111) single crystal as well as on Au(111) and glassy carbon electrodes. We show that addition of water (up to 3.092 M) to a [BMP][DCA] solution promotes the electroreduction of Eu ions to Eu(0) shifting the potential of Eu deposition in the positive direction. The potential shift is already pronounced after addition of a moderate water amount and is equal to ~0.28 V upon increase in cH2O from 0.012 to 0.167 M. Microscopic and X-ray spectroscopic analyses of the electrodes after potentiostatic polarization confirm the formation of Eu deposit, however Eu in the deposit is mainly in the oxidized form. The oxidation of electrochemically deposited Eu(0) can occur simultaneously with the electrodeposition process in the chemical reaction with residual or added water. Furthermore, the electrode material is found to affect the overpotential of Eu deposition, and the deposition accelerates in the order of GC

International audience; Strategies for the conversion of CO2 to valuable products are paramount for reducing the environmental risks associated with high levels of this greenhouse gas and offer unique opportunities for transforming waste into useful products. While catalysts based on nickel as an Earth-abundant metal for the sustainable reduction of CO2 are known, the vast majority produce predominantly CO as a product. Here, efficient and selective CO2 reduction to formate as a synthetically valuable product has been accomplished with novel nickel complexes containing a tailored C,O-bidentate chelating mesoionic carbene ligand. These nickel(II) complexes are easily accessible and show excellent catalytic activity for electrochemical H+ reduction to H2 (from HOAc in MeCN), and CO2 reduction (from CO2-saturated MeOH/MeCN solution) with high faradaic efficiency to yield formate exclusively as an industrially and synthetically valuable product from CO2. The most active catalyst precursor features the 4,6-di-tert-butyl substituted phenolate triazolylidene ligand, tolerates different proton donors including water, and reaches an unprecedented faradaic efficiency of 83% for formate production, constituting the most active and selective Ni-based system known to date for converting CO2 into formate as an important commodity chemical.

We present a comprehensive study on the initial stages of silver electrodeposition on Pt (111), Au (111), and Au (100) single crystal surfaces in low-viscosity ionic liquids (ILs) containing dicyanamide anions: 1-butyl-1-methylpyrrolidinium dicyanamide [BMP][DCA] and 1-butyl-3-methylimidazolium dicyanamide [BMIm][DCA]. Electrochemical methods in combination with in situ scanning tunneling microscopy (STM) and ex situ atomic force microscopy (AFM) are employed to explore the Ag underpotential (upd) and overpotential (opd) deposition processes as well as the stability of the single crystal electrode surfaces in the absence of Ag+ ions. The substrate material is shown to significantly affect the mechanism of Ag deposit nucleation and growth in the ILs. While no Ag upd is detected on Pt (111), the formation of a Ag upd monolayer on a Au (111) electrode in both ILs is clearly visualized by in situ STM. The Ag adlayer formation on the Au electrodes in the underpotential regime facilitates Ag opd, which starts on Au (111) and Au (100) at much less negative potentials than on Pt (111). There is an excellent agreement between the electrochemical (voltammetry and chronoamperometry), AFM and STM data, demonstrating the nucleation and growth of individual Ag crystallites on Pt (111) according to the Volmer–Weber mechanism and the layer–by–layer growth of Ag deposit on Au (111) and Au (100). Only at high overpotentials, the Ag growth on the gold electrodes switches to the Stranski-Krastanov mode involving the appearance of 3D crystallites.

The data on the rate constants for ferrocene/ferrocenium (Fc/Fc + ) electron transfer in ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF 4 ]) are reported for a series of -S-(CH 2 ) n -Fc adlayers (n = 8…16) on polycrystalline gold. The values and trends are compared to the previously published data for similar series in aqueous medium, as well as to the results for ‘free’ Fc at -S-(CH 2 ) n − 1 -CH 3 modified gold in the same ionic liquid. For the latter case, the trend is opposite as compared to that in the available aqueous series (attached and ‘free’ ruthenium ammine complex): the ratio of rate constants for attached and ‘free’ reactants decreases with electrode-reactant distance in the former case, and increases in the latter. The presented comparison discovers the role of reactant and product work terms, which are essential for attached reactants as well because of conformational diversity. Corresponding contributions are estimated from molecular modeling and considered in terms of reaction volume.

In this work, electroreduction of nitrate anions on bare and copper-modified platinum nanoparticles (Pt NPs) supported on glassy carbon is studied using cyclic voltammetry. Two types of Pt NPs are chosen for this purpose: unshaped (polyoriented) NPs and cubic NPs displaying the preferential (100) orientation of faces. The modification of cubic and polyoriented Pt NPs by copper adatoms with submonolayer coverages is performed in a controlled way in solutions containing small concentrations of Cu 2 + ions, 10 − 5 M. Nitrate reduction is studied first in copper-free solutions and then in the presence of 10 − 5 M Cu 2 + . The transmission electron microscopy and voltammetric measurements of the cubic NPs indicate the presence of a significant amount of Pt(100) terraces on the surface of these NPs. In perchloric acid solutions containing 0.02 M NaNO 3 and 10 − 5 M Cu 2 + , accumulation of copper adatoms on the NPs results in a fast increase in the currents of nitrate electroreduction. These reduction currents on the cubic NPs are up to three times higher than on the polyoriented NPs at Cu coverages of 0.20–0.35. The comparison of the data on Pt NPs with the data for single crystal electrodes with (100) terraces of different width (Pt(610), Pt(210)) shows that the behavior of NPs can be simulated on the basis of the data for single crystal faces with wide (cubic NPs) and narrow (unshaped NPs) (100) terraces. Thus, cubic NPs manifest rather a high electrocatalytic activity in the studied reaction of nitrate anion electroreduction, which is typical for single crystal surfaces with relatively wide Pt(100) terraces. At the same time, in comparison with macro single crystalline electrodes, these NPs are characterized by sufficiently higher stability, larger specific surface area, and flexibility in application.

Room-temperature ionic liquids (RTILs) are promising new electrolytes for efficient carbon dioxide reduction. However, due to their high viscosity, the mass transport of CO2 in RTILs is typically slow, at least one order of magnitude slower than in aqueous systems. One possibility to improve mass transport in RTILs is to decrease their viscosity through dilution with water. Herein, defined amounts of water are added to 1-butyl-3methylimidazolium tetrafluoroborate ([BMIm][BF4 ]), which is a hydrophilic RTIL. Electrochemical measurements on quiescent and hydrodynamic systems both indicate enhanced CO2 electroreduction. This enhancement has its origin in thermodynamic/kinetic effects (the addition of water increases the availability of H+ , which is a reaction partner of CO2 electroreduction) and in an increased rate of transport due to lower viscosity. Electrochemically determined diffusion coefficients for CO2 in [BMIm][BF4 ]/water systems agree well with values determined by NMR spectroscopy.

The full understanding of an electrode/ionic liquid (IL) interface is crucial for the use of ILs as electrolytes in applications for energy conversion and storage. Scanning probe microscopy (SPM) has proved to be a very powerful method to probe the local structure of this interface and obtain real-time and real-space images with an atomic resolution. Herein we present the recent advances in SPM studies on the electrode/IL interface and emphasize the aspects that are most important in our opinion. We finish with some thoughts on future research directions in the field.

Pyrazolium ionic liquids (Pz ILs) were employed as co-catalysts for electrochemical conversion of CO2 to CO on a silver disk electrode, leading to a significant decrease in the onset potential for the reduction (ca. 500 mV). The electrochemical conversion of CO2 to CO proceeds in acetonitrile-based electrolytes containing Pz IL co-catalysts with Faradaic efficiencies (FEs) of nearly 100% over a range of at least 0.5 V, and the Pz cations remain intact over prolonged CO2 electrolysis. The impact of alkyl substituents on the Pz ring and the influence of water on the process are also discussed.

The promoting effect of water on the electrochemical reduction of carbon dioxide (CO2) from non-aqueous solvents has been studied by means of cyclic voltammetry and in-situ surface-enhanced infrared absorption spectroscopy (SEIRAS). CO2 electroreduction on gold is known to be highly selective towards CO formation in aqueous and in non-aqueous media. The use of non-aqueous solvents is advantageous due to the significantly increased solubility of CO2 compared to aqueous systems. However, in the absence of any proton source, extremely high overpotentials are required for the CO2 electroreduction. In this work, we demonstrate for the first time a tremendous accelerating effect of water additives on the electroreduction of CO2 taking place at gold/acetonitrile interfaces. Already moderate amounts of water, in the concentration range of 0.5 to 0.7 M, are sufficient to decrease significantly the overpotential of CO2 reduction while keeping the CO2 concentration as high as in the pure acetonitrile. The effect of water additives on the mechanism of CO2 electroreduction on gold is discussed on the basis of electrochemical and IR spectroscopic data. The results obtained from gold are compared to analogue experiments carried out on platinum.

Bejarano, Francesc et al., Organic paramagnetic and electroactive molecules are attracting interest as core components of molecular electronic and spintronic devices. Currently, further progress is hindered by the modest stability and reproducibility of the molecule/electrode contact. We report the synthesis of a persistent organic radical bearing one and two terminal alkyne groups to form Au-C σ bonds. The formation and stability of self-assembled monolayers and the electron transport through single-molecule junctions at room temperature have been studied. The combined analysis of both systems demonstrates that this linker forms a robust covalent bond with gold and a better-defined contact when compared to traditional sulfur-based linkers. Density functional theory and quantum transport calculations support the experimental observation highlighting a reduced variability of conductance values for the C-Au based junction. Our findings advance the quest for robustness and reproducibility of devices based on electroactive molecules., We acknowledge Dr. G. Sauthier from the ICN2 for the XPS measurements, Prof. Carlos Gomez from IcMOL for the SQUID measurements, A. Bernabé and Dr. V. Lloveras from ICMAB for the LDI-ToF and EPR measurements, respectively. This work was supported by FET ACMOL project (GA no. 618082), CIBER-BBN, the DGI (Spain) project FANCY CTQ2016-80030-R, the Generalitat de Catalunya (2014-SGR-17) and the MINECO, through the “Severo Ochoa” Programme for Centers of Excel-lence in R&D (SEV-2015-0496). F.B he is enrolled in the Materi-als Science Ph.D. program of UAB. We thank the Dutch science foundation NWO/FOM for financial support.

Molecular electronics aims to construct functional molecular devices at the single-molecule scale. One of the major challenges is to construct a single-molecule junction and to further manipulate the charge transport through the molecular junction. Break junction techniques, including STM break junctions and mechanically controllable break junctions are considered as testbed to investigate and control the charge transport on a single-molecule scale. Moreover, additional electrochemical gating provides a unique opportunity to manipulate the energy alignment and molecular redox processes for a single-molecule junction. In this review, we start from the technical aspects of the break junction technique, then discuss the molecular structure-conductance correlation derived from break junction studies, and, finally, emphasize electrochemical gating as a promising method for the functional molecular devices.

Electrochemical methods are combined with shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) for a comprehensive study of pyridine adsorption on Au(111), Au(100) and Au(110) single crystal electrode surfaces. The effects of crystallographic orientation, pyridine concentration, and applied potential are elucidated, and the formation of a second pyridine adlayer on Au(111) is observed spectroscopically for the first time. Electrochemical and SHINERS results correlate extremely well throughout this study, and we demonstrate the potential of EC-SHINERS for thorough characterization of processes occurring on single crystal surfaces. Our method is expected to open up many new possibilities in surface science, electrochemistry and catalysis. Analytical figures of merit are discussed.

The controlled arraying of DNA strands on adaptive polymeric platforms remains a challenge. Here, the noncovalent synthesis of DNA-grafted supramolecular polymers from short chimeric oligomers is presented. The oligomers are composed of an oligopyrenotide strand attached to the 5'-end of an oligodeoxynucleotide. The supramolecular polymerization of these oligomers in an aqueous medium leads to the formation of one-dimensional (1D) helical ribbon structures. Atomic force and transmission electron microscopy show rod-like polymers of several hundred nanometers in length. DNA-grafted polymers of the type described herein will serve as models for the development of structurally and functionally diverse supramolecular platforms with applications in materials science and diagnostics.

Graphene is a promising candidate for an ideal membrane material. Its ultralow (one-atomic) thickness potentially provides high permeation and at the same time high selectivity. Here, it is shown that these properties can be used to create a confined, two-dimensional electrochemical environment between a graphene layer and a single-crystal Pt(111) surface. The well-defined fingerprint voltammetric characteristics of Pt(111) provide an immediate information about the penetration and intercalation of ions into the confined space. These processes are shown to be highly selective.

Herein, we present a study on the initial stages of chromium electrodeposition on platinum and gold single-crystal surfaces from an ionic liquid containing dicyanamide anions. We employed conventional electrochemical techniques in combination with in situ and ex situ scanning probe microscopy (in situ scanning tunneling microscopy (STM), ex situ atomic force microscopy (AFM)) and ex situ X-ray photoemission spectroscopy (XPS). Cr electrodeposition was carried out from Cr(II) and Cr(III) solutions of low (10 mM) and high (250 mM) Cr concentrations. The microscopic and spectroscopic approaches clearly demonstrate the formation of a Cr deposit, although the voltammetric responses are difficult to interpret. The absence of a pronounced Cr dissolution peak in the backward scan of the cyclic voltammograms and a relatively low amount of Cr deposit (as confirmed by AFM) suggest the passivation of Cr and the substrate during deposition, thus hindering both further deposition of Cr and its anodic dissolution.

The understanding of the charge transport through single molecule junctions is a prerequisite for the design and building of electronic circuits based on single molecule junctions. However, reliable and robust formation of such junctions is a challenging task to achieve. In this topical review, we present a systematic investigation of the anchoring group effect on single molecule junction conductance by employing two complementary techniques, namely scanning tunneling microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques, based on the studies published in the literature and important results from our own work. We compared conductance studies for conventional anchoring groups described earlier with the molecular junctions formed through π-interactions with the electrode surface (Au, Pt, Ag) and we also summarized recent developments in the formation of highly conducting covalent Au-C σ-bonds using oligophenyleneethynylene (OPE) and an alkane molecular backbone. Specifically, we focus on the electron transport properties of diaryloligoyne, oligophenyleneethynylene (OPE) and/or alkane molecular junctions composed of several traditional anchoring groups, (dihydrobenzo[b]thiophene (BT), 5-benzothienyl analogue (BTh), thiol (SH), pyridyl (PY), amine (NH2), cyano (CN), methyl sulphide (SMe), nitro (NO2)) and other anchoring groups at the solid/liquid interface. The qualitative and quantitative comparison of the results obtained with different anchoring groups reveals structural and mechanistic details of the different types of single molecular junctions. The results reported in this prospective may serve as a guideline for the design and synthesis of molecular systems to be used in molecule-based electronic devices.

Perchlorate adsorption on Au(1 1 1) was investigated by cyclic voltammetry and surface-enhanced infrared absorption spectroscopy. We found that the electrosorption valency of ClO4− on Au(1 1 1) is ∼ 0.6 and the total coverage of ClO4− on Au(1 1 1) is higher (∼ 0.15) than previously estimated (∼ 0.04). Based on the experimental adsorption isotherms obtained from infrared spectra and the reconstruction-free cyclic voltammograms, we proposed a mechanism for the ClO4− adsorption on Au(1 1 1).

Reading the bands: Amphiphilic pyrene trimers self-assemble into two-dimensional, supramolecular polymers in aqueous medium. Folding and aggregation processes are accompanied by simultaneous development of J- and H-bands and significant changes in the fluorescence properties. The formation of sheet-like nano-structures is confirmed by AFM.

A novel, persistent, electrochemically active perchlorinated triphenylmethyl (PTM) radical with a diazonium functionality has been covalently attached to highly ordered pyrolytic graphite (HOPG) by electrografting in a single-step process. Electrochemical scanning tunneling microscopy (EC-STM) and Raman spectroscopy measurements revealed that PTM molecules had a higher tendency to covalently react at the HOPG step edges. The cross-section profiles from EC-STM images showed that there was current enhancement at the functionalized areas, which could be explained by redox-mediated electron tunneling through surface-confined redox-active molecules. Cyclic voltammetry clearly demonstrated that the intrinsic properties of the organic radical were preserved upon grafting and DFT calculations also revealed that the magnetic character of the PTM radical was preserved., We acknowledgeGuillaume Sauthier from the Ca talan Ins tituteof Nanoscience and Nanotechnology (ICN2) for XPS measure-ments.This work was supported by ACMOL (GA no. 618082),the Swiss National Science Foundation (grant no. 200020-144471), ERC StG 2012-306826 e-GAMES,ITN iSwitch (642196)project, the Networking Research Center of Bioengineering,Biomaterials and Nanomedicine(CIBER-BBN), the DGI (Spain)with project BE-WELL CTQ2013-40480-R, and the Generalitatde Catalunya with project 2014-SGR-17. N.C acknowledges theRyC program. We also acknowledge financial suppo rt from theSpanishMinistry of Economyand Competitiveness, throughthe “Severo Ochoa” Programme for Centres of Excellence inR&D (SEV-2015-0496).

Charge transport by tunnelling is one of the most ubiquitous elementary processes in nature. Small structural changes in a molecular junction can lead to significant difference in the single-molecule electronic properties, offering a tremendous opportunity to examine a reaction on the single-molecule scale by monitoring the conductance changes. Here, we explore the potential of the single-molecule break junction technique in the detection of photo-thermal reaction processes of a photochromic dihydroazulene/vinylheptafulvene system. Statistical analysis of the break junction experiments provides a quantitative approach for probing the reaction kinetics and reversibility, including the occurrence of isomerization during the reaction. The product ratios observed when switching the system in the junction does not follow those observed in solution studies (both experiment and theory), suggesting that the junction environment was perturbing the process significantly. This study opens the possibility of using nano-structured environments like molecular junctions to tailor product ratios in chemical reactions., The conductance across single-molecule junctions is highly dependent on the electronic properties of the molecule in question. Here the authors use this fact to monitor a photo-thermal reaction by analysing break junction data, and observe significant differences compared to solution state behaviour.

A series of dicyanobiphenyl-cyclophanes 1-6 with various pi-backbone conformations and characteristic n-type semiconductor properties is presented. Their synthesis, optical, structural, electrochemical, spectroelectrochemical, and packing properties are investigated. The X-ray crystal structures of all n-type rods allow the systematic correlation of structural features with physical properties. In addition, the results are supported by quantum mechanical calculations based on density functional theory. A two-step reduction process is observed for all n-type rods, in which the first step is reversible. The potential gap between the reduction processes depends linearly on the cos(2) value of the torsion angle phi between the pi-systems. Similarly, optical absorption spectroscopy shows that the vertical excitation energy of the conjugation band correlates with the cos(2) value of the torsion angle phi. These correlations demonstrate that the fixed intramolecular torsion angle phi is the dominant factor determining the extent of electron delocalization in these model compounds, and that the angle phi measured in the solid-state structure is a good proxy for the molecular conformation in solution. Spectroelectrochemical investigations demonstrate that conformational rigidity is maintained even in the radical anion form. In particular, the absorption bands corresponding to the SOMO-LUMO+i transitions are shifted bathochromically, whereas the absorption bands corresponding to the HOMO-SOMO transition are shifted hypsochromically with increasing torsion angle phi.

A redox-active persistent perchlorotriphenylmethyl (PTM) radical chemically linked to gold exhibits stable electrochemical activity in ionic liquids. Electrochemical tunnelling spectroscopy in this medium demonstrates that the PTM radical shows a highly effective redox-mediated current enhancement, demonstrating its applicability as an active nanometer-scale electronic component., We acknowledge the financial support from the EU projects ACMOL (FET Young Explorers, GA no. 618082), ERC StG 2012- 306826 e-GAMES, ITN iSwitch (GA no. 642196), COST Action TD1002, the Swiss National Science Foundation (Grant No. 200020- 144471), the Networking Research Center of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) with project BE-WELL CTQ2013-40480-R, the Generalitat de Catalunya with project 2014-SGR-17, and the Severo Ochoa program. N. C acknowledges the RyC program. C. F. is enrolled in the Materials Science PhD program of UAB., We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

Controlling charge transport through a single molecule connected to metallic electrodes remains one of the most fundamental challenges of nanoelectronics. Here we use electrochemical gating to reversibly tune the conductance of two different organic molecules, both containing anthraquinone (AQ) centers, over >1 order of magnitude. For electrode potentials outside the redox-active region, the effect of the gate is simply to shift the molecular energy levels relative to the metal Fermi level. At the redox potential, the conductance changes abruptly as the AQ unit is oxidized/reduced with an accompanying change in the conjugation pattern between linear and cross conjugation. The most significant change in conductance is observed when the electron pathway connecting the two electrodes is via the AQ unit. This is consistent with the expected occurrence of destructive quantum interference in that case. The experimental results are supported by an excellent agreement with ab initio transport calculations.

Interface engineering to attain a uniform and compact self-assembled monolayer at atomically flat surfaces plays a crucial role in the bottom-up fabrication of organic molecular devices. Here we report a promising and operationally simple approach for modification/functionalization not only at ultraflat single-crystal metal surfaces, M(111) (M=Au, Pt, Pd, Rh and Ir) but also at the highly oriented pyrolytic graphite surface, upon efficient in situ cleavage of trimethylsilyl end groups of the molecules. The obtained self-assembled monolayers are ultrastable within a wide potential window. The carbon–surface bonding on various substrates is confirmed by shell-isolated nanoparticle-enhanced Raman spectroscopy. Application of this strategy in tuning surface wettability is also demonstrated. The most valuable finding is that a combination of the desilylation with the click chemistry represents an efficient method for covalent and tailor-made functionalization of diverse surfaces., Formation of stable and uniform self-assembled monolayers on surfaces is a prerequisite for bottom-up fabrication of many organic molecular devices. Here, the authors present a fabrication approach based on desilylation chemistry for modification and functionalization on various metal and carbon surfaces.

Room temperature molecular electronics get one step closer to reality by exploiting chemical contacts between a single molecule and graphite., An open challenge for single-molecule electronics is to find stable contacts at room temperature with a well-defined conductance. Common coinage metal electrodes pose fabrication and operational problems due to the high mobility of the surface atoms. We demonstrate how molecules covalently grafted onto mechanically robust graphite/graphene substrates overcome these limitations. To this aim, we explore the effect of the anchoring group chemistry on the charge transport properties of graphite-molecule contacts by means of the scanning tunneling microscopy break-junction technique and ab initio simulations. Molecules adsorbed on graphite only via van der Waals interactions have a conductance that decreases exponentially upon stretching the junctions, whereas the molecules bonded covalently to graphite have a single well-defined conductance and yield contacts of unprecedented stability at room temperature. Our results demonstrate a strong bias dependence of the single-molecule conductance, which varies over more than one order of magnitude even at low bias voltages, and show an opposite rectification behavior for covalent and noncovalent contacts. We demonstrate that this bias-dependent conductance and opposite rectification behavior is due to a novel effect caused by the nonconstant, highly dispersive density of states of graphite around the Fermi energy and that the direction of rectification is governed by the detailed nature of the molecule/graphite contact. Combined with the prospect of new functionalities due to a strongly bias-dependent conductance, these covalent contacts are ideal candidates for next-generation molecular electronic devices.