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Transition metal carbides, especially Mo2C, are praised to be efficient electrocatalysts to reduce CO2 to valuable hydrocarbons. However, on Mo2C in an aqueous electrolyte, exclusively the competing hydrogen evolution reaction takes place, and this discrepancy to theory was traced back to the formation of a thin oxide layer at the electrode surface. Here, we study the CO2 reduction activity at Mo2C in a non-aqueous electrolyte to avoid such passivation and to determine products and the CO2 reduction reaction pathway. We find a tendency of CO2 to reduce to carbon monoxide. This process is inevitably coupled with the decomposition of acetonitrile to a 3-aminocrotonitrile anion. Furthermore, a unique behavior of the non-aqueous acetonitrile electrolyte is found, where the electrolyte, instead of the electrocatalyst, governs the catalytic selectivity of the CO2 reduction. This is evidenced by in situ electrochemical infrared spectroscopy on different electrocatalysts as well as by density functional theory calculations.

Based on the recent interest in oxy-carbide materials in catalysis, we employ a thin film model concept to highlight that variation of key reaction parameters in the reactive magnetron sputtering of zirconium carbide films (sputtering power, template temperature or reactive plasma environment) under realistic preparation and application conditions often results in zirconium oxy-carbide films of varying stoichiometry. The composition of the films grown on silicon wafers and in vacuo - cleaved NaCl (001) single crystal facets was confirmed by depth profiling X-ray photoelectron spectroscopy and electron microscopy analysis. A correlation between methane-to-argon ratio, excess carbon and template temperature with elemental composition emphasizes the exclusive presence of oxygen-containing zirconium carbides. To generalize the approach, we also show that embedding of highly ordered Cu particles with uniform sizes in zirconium oxy-carbide matrices yields well-defined metal / oxy-carbide interfaces. As the presence of an oxy-carbide and its reactivity has been inextricably linked to enhanced activity and selectivity in a variety of processes, including hydrogenation, oxidation or reduction reactions, our model thin film approach provides the necessary well-defined catalysts to derive mechanistic details and to study the decomposition/re-carburization cycles of oxy-carbides. We have exemplified the concept for zirconium oxy-carbide, but deliberate extension to similar systems is easily possible.

The hydrogen evolution reaction (HER) has been crucial for the development of fundamental knowledge on electrocatalysis and electrochemistry, in general. In alkaline media, many key questions concerning pH-dependent structure–activity relations and the underlying activity descriptors remain unclear. While the presence of Ni(OH)2 deposited on Pt(111) has been shown to highly improve the rate of the HER through the electrode’s bifunctionality, no studies exist on how low coverages of Ni(OH)2 influence the electrocatalytic behavior of Cu surfaces, which is a low-cost alternative to Pt. Here, we demonstrate that Cu(111) modified with 0.1 and 0.2 monolayers (ML) of Ni(OH)2 exhibits an unusual non-linear activity trend with increasing coverage. By combining in situ structural investigations with studies on the interfacial water orientation using electrochemical scanning tunneling microscopy and laser-induced temperature jump experiments, we find a correlation between a particular threshold of surface roughness and the decrease in the ordering of the water network at the interface. The highly disordered water ad-layer close to the onset of the HER, which is only present for 0.2 ML of Ni(OH)2, facilitates the reorganization of the interfacial water molecules to accommodate for charge transfer, thus enhancing the rate of the reaction. These findings strongly suggest a general validity of the interfacial water reorganization as an activity descriptor for the HER in alkaline media. A.A. is a recipient of a doctorate (DOC) Fellowship of the Austrian Academy of Sciences at the Institute of Physical Chemistry. C.G. thanks the Austrian Research Promotion Agency (FFG) for funding via the project number 870523. J.K.-L. acknowledges funding by the Austrian Science Fund (FWF) via grant I-4114-N37. J.M.F. and V.C. acknowledge financial support from Ministerio de Ciencia e Innovación (project PID2019-105653GB-100) and Generalitat Valenciana (project PROMETEO/2020/063).

Long term galvanostatic charge/discharge cycling of oxygen deficient, carburized and self‐organized titanium dioxide (TiO2) nanotubes (NTs) in sodium ion (Na) batteries (SIBs) are subject to a significant self‐improving charge storage behavior. Surface reactions upon sodiation of carburized NTs form acicular surface films that can be reversibly cycled. We show that, alongside organic species from the decomposition of the electrolyte, mainly inorganic compounds, such as Na2O2 and Na2CO3, are the main constituents. These components possess a characteristic acicular morphology. Na2O2 is found to form upon sodiation and converted to NaO2 upon desodiation. This, in combination with its pseudo‐capacitive charge storage characteristics, explains the excellent rate capability measured for TiO2‐x‐C NTs. The observed high reversibility of this surface chemistry is also essential for the fast kinetics and the high capacity retention found in the system. Our findings point to a more general Na‐ion storage mechanism, that is potentially relevant to other transition metal oxides also.

Compound materials, such as transition-metal (TM) carbides, are anticipated to be effective electrocatalysts for the carbon dioxide reduction reaction (CO2RR) to useful chemicals. This expectation is nurtured by density functional theory (DFT) predictions of a break of key adsorption energy scaling relations that limit CO2RR at parent TMs. Here, we evaluate these prospects for hexagonal Mo2C in aqueous electrolytes in a multimethod experiment and theory approach. We find that surface oxide formation completely suppresses the CO2 activation. The oxides are stable down to potentials as low as −1.9 V versus the standard hydrogen electrode, and solely the hydrogen evolution reaction (HER) is found to be active. This generally points to the absolute imperative of recognizing the true interface establishing under operando conditions in computational screening of catalyst materials. When protected from ambient air and used in nonaqueous electrolyte, Mo2C indeed shows CO2RR activity.

Following the need for an innovative catalyst and material design in catalysis, we provide a comparative approach using pure and Pd-doped LaCu

Copper (Cu) is a unique electrocatalyst, which is able to efficiently oxidize CO at very low overpotentials and reduce CO2 to valuable fuels with reasonable Faradaic efficiencies. Yet, knowledge of its electrochemical properties at the solid/liquid interface is still scarce. Here, we present the first two-stranded correlation of the potential of zero free charge (pzfc) of Cu(111) in alkaline electrolyte at different pH values through application of nanosecond laser pulses and the corresponding interfacial structure changes by in situ electrochemical scanning tunneling microscopy imaging. The pzfc of Cu(111) at pH 13 is identified at −0.73 VSHE in the apparent double layer region, prior to the onset of hydroxide adsorption. It shifts by (88 ± 4) mV to more positive potentials per decreasing pH unit. At the pzfc, Cu(111) shows structural dynamics at both pH 13 and pH 11, which can be understood as the onset of surface restructuring. At higher potentials, full reconstruction and electric field dependent OH adsorption occurs, which causes a remarkable decrease in the atomic density of the first Cu layer. The expansion of the Cu–Cu distance to 0.3 nm generates a hexagonal Moiré pattern, on which the adsorbed OH forms a commensurate (1 × 2) adlayer structure with a steady state coverage of 0.5 monolayers at pH 13. Our experimental findings shed light on the true charge distribution and its interrelation with the atomic structure of the electrochemical interface of Cu.

The development of low-temperature fuel cells for clean energy production is an appealing alternative to fossil-fuel technologies. CO is a key intermediate in the electro-oxidation of energy carrying fuels and, due to its strong interaction with state-of-the-art Pt electrodes, it is known to act as a poison. Here we demonstrate the ability of Earth-abundant Cu to electro-oxidize CO efficiently in alkaline media, reaching high current densities of ≥0.35 mA cm−2 on single-crystal Cu(111) model catalysts. Strong and continuous surface structural changes are observed under reaction conditions. Supported by first-principles microkinetic modelling, we show that the concomitant presence of high-energy undercoordinated Cu structures at the surface is a prerequisite for the high activity. Similar CO-induced self-activation has been reported for gas–surface reactions at coinage metals, demonstrating the strong parallels between heterogeneous thermal catalysis and heterogeneous electrocatalysis. CO is a key intermediate in the electro-oxidation of energy carrying fuels which typically acts as a poison. Here, the authors demonstrate that Cu is an efficient CO electro-oxidation catalyst in alkaline electrolyte due to the continuous formation of undercoordinated active Cu adatom sites in the presence of CO and OH.

In this work, we have investigated the influence of alkali metal cations on the electrical double-layer (EDL) properties for various metal electrodes. Using electrochemical impedance spectroscopy, ...

Developing sodium (Na)-ion batteries is highly appealing because they offer the potential to be made from raw materials, which hold the promise to be less expensive, less toxic, and at the same tim...

The electrocatalytic behavior of a tungsten carbide-supported Pt(3 wt %)Au(3 wt %)Sn(10 wt %) catalyst (PtAuSn/W2C) is investigated toward the oxidation of ethanol at temperatures below 70 °C. Vulc...

Tailoring electrocatalyst materials to the specific requirements of a certain reaction and to optimize activity or enhance selectivity is a key tactic for the development of low-temperature fuel and electrolyzer cells for clean energy production. Here, we demonstrate the modification of Cu(111) electrodes with different sub-monolayer coverages of foreign metals (Cd) and metal hydroxides (Co(OH)2 and Ni(OH)2) for application in the hydrogen evolution reaction (HER) in alkaline media. In situ electrochemical scanning tunneling microscopy (EC-STM) reveals that these modifications have a significant influence on the morphology and structure of the Cu(111) surface with its characteristics depending on both the nature and the amount of the adsorbed metal(hydroxide). Ni(OH)2 and Co(OH)2 on Cu(111) lead to a significant enhancement of the electrocatalytic activity towards the HER in alkaline electrolyte, whereas a decrease in activity is found for Cd modified Cu(111). These trends can be rationalized by considering the strength of the interfacial electric field and its influence on the specific interactions of the electrode with the water ad-layer close to the surface, as determined by laser-induced temperature jump measurements. This comparative study therefore provides valuable information on the structure-activity relation as well as insights on the interfacial characteristics of different bimetallic Cu electrocatalysts. A.A. is a recipient of a doctorate (DOC) Fellowship of the Austrian Academy of Sciences at the Institute of Physical Chemistry. C.G. thanks the Austrian Research Promotion Agency (FFG) for funding by the project number 870523. J.K-L. acknowledges funding by the Austrian Science Fund (FWF) via grant I-4114-N37. J.M.F and V.C. acknowledge financial support from Ministerio de Ciencia e Innovación (project PID2019-105653GB-100) and Generalitat Valenciana (project PROMETEO/2020/063).

A very important parameter for the electrocatalytic performance of a material is its potential of zero free charge (pzfc). For Cu(111) at pH 13 it was identified at −0.73 VSHE in the apparent double layer region. It shifts by (88±4) mV to more positive potentials per decreasing pH unit.1 At the pzfc, Cu(111) starts to restructure. At higher potentials, full reconstruction and electric field dependent OH adsorption occur, causing a remarkable decrease in the atomic density of the first Cu layer.1 It is this restructuring that enables Cu(111) to efficiently oxidize CO and to reduce water. Therefore, knowledge of the surface structure and the position of the pzfc is of paramount importance for the understanding of copper’s catalytic properties and for the rational design of electrocatalysts. CO is a key intermediate in the electro-oxidation of energy carrying fuels and known to act as a catalyst poison. Single-crystal Cu(111) model catalysts can efficiently electro-oxidize CO in alkaline media,2 where strong surface structural changes are observed under reaction conditions with electrochemical scanning tunneling microscopy (EC-STM). Supported by first-principles microkinetic modelling, we have shown that the concomitant presence of high-energy undercoordinated Cu structures at the surface is a prerequisite for the high activity. In water electrolyzers, it is possible to produce H2 in the course of the hydrogen evolution reaction (HER), which was studied with Ni(OH)2 and Co(OH)2 modified Cu(111) electrodes in alkaline media. 3 Strong morphological changes upon adatom modification lead to a significant HER rate enhancement. Intriguingly, this is induced through a decrease of the electric field strength negative of the pzfc. This implies an easier reorganization of the interfacial water molecules facilitating charge transfer through the double layer, and thus enhancing the efficiency of electrocatalytic reactions. The tendency of Cu(111) to restructure is found to dominate its electrochemical properties. The structural changes of the electrode surface are intimately related to the electric field at the solid/liquid interface and to its electrocatalytic activity, in general. References: [1] A. Auer, X. Ding, A. S. Bandarenka, J. Kunze-Liebhäuser, J. Phys. Chem. C 125 (2021) 5020. [2] A. Auer, M. Andersen, E.M. Wernig, N.G. Hörmann, N. Buller, K. Reuter, J. Kunze-Liebhäuser, Nature Catal. 3 (2020) 797. [3] A. Auer, F.J. Sarabia, D. Winkler, C. Griesser, V. Climent, J.M. Feliu, J. Kunze-Liebhäuser, ACS Catal. 11 (2021) 10324. Figure 1

Direct ethanol fuel cells are highly promising energy conversion devices, but the complete oxidation of ethanol to CO2 at low temperatures is still one of the main challenges. Titanium oxycarbide (TiO1-xCx) powder is investigated as stable and synergistic support for Pt nanoparticles during the ethanol oxidation reaction (EOR) in acidic electrolytes. EOR products are quantitatively detected online with differential electrochemical mass spectrometry. At room temperature, Pt/TiO1-xCx has a CO2 efficiency maximum of 8.9%, while only 1.7% are measured for Pt nanoparticles on Vulcan carbon (Pt/C). The reaction pathway is channeled towards the formation of C1 products, while C2 product formation is suppressed. This effect is expected to be much enhanced at elevated temperatures which makes TiO1-xCx a highly interesting catalyst support material in general.

The use of an activated carbon based quasi-reference electrode for in situ electrochemical scanning tunneling microscopy was found to allow investigations of electrode/electrolyte interfaces under realistic electrochemical reaction conditions. The implementation of purely inert porous carbon electrode materials, both as reference and counter electrode, ensures a stable reference electrode potential over a wide range of temperatures and in different electrolytes, which renders this electrode ‘universal’. Furthermore, the high surface area carbon can reduce and even eliminate contaminations that might be present in the electrolyte. Activated carbon electrodes can therefore generally contribute to more reliable electrochemical measurements when investigating electrochemical reactions under complex experimental conditions, where the use of classical secondary reference electrodes is impossible or impractical. This is often the case when electrochemistry is combined with in situ interface analytics. Keywords: Electrochemical scanning tunneling microscopy, Quasi-reference electrode, Activated carbon

We describe a new type of operando Fourier transform infrared (FTIR)–mass spectrometry setup for surface-chemical and reactivity characterization of heterogeneous catalysts. On the basis of a sophisticated all-quartz FTIR reactor cell, capable of operating between room temperature and 1000 °C in reactive gas atmospheres, the setup offers a unique opportunity to simultaneously collect and accordingly correlate FTIR surface-chemical adsorption data of the active catalyst state and FTIR gas phase data with complementary reactivity data obtained via mass spectrometry in situ. The full set of catalytic operation modes (recirculating static and flow reactor conditions) is accessible and can be complemented with a variety of temperature-programmed reaction modes or thermal desorption. Due to the unique transfer process involving a home-built portable glovebox to avoid air exposure, a variety of complementary quasi in situ characterization methods for the pre- and post-reaction catalyst states become accessible. We exemplify the capabilities for additional x-ray photoelectron spectroscopy characterization of surface-chemical states, highlighting the unique strength of combining adsorption, electronic structure, and reactivity data to gain detailed insight into the reactive state of a Cu/ZrO2 heterogeneous catalyst during methanol steam reforming operation.

Excellent chemical inertness, good conductivity and high overpotentials for water electrolysis make carbon fibres (CFS) an ideal electrode material for electrochemical applications. A customized design of three-dimensional (3D) carbon electrodes can be achieved by tailored fibre placement of carbon tows with textile production techniques like embroidery. After manufacturing of the 3D structure, appropriate removal of the polymer coating and oxidative activation is required to achieve low overpotentials and avoid thermal treatments of the carbon structure. For the electrolytes Na[FeIII-racEDDHA] and K4[FeII(CN)6] a sequential treatment by acetone extraction and anodic oxidation was identified to yield optimum surface activation. Electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy of activated fibres indicated complete removal of the coating layer without damage of the CFS. From electrochemical impedance spectroscopy (EIS) at the carbon tow electrodes, charge transfer resistances of

Spectroscopy with planar optical waveguides is still an active field of research for the quantitative analysis of various supramolecular surface architectures and processes, and for applications in integrated optical chip communication, direct chemical sensing, etc. In this contribution, we summarize some recent development in optical waveguide spectroscopy using nanoporous thin films as the planar substrates that can guide the light just as well as bulk thin films. This is because the nanoporosity is at a spacial length-scale that is far below the wavelength of the guided light; hence, it does not lead to an enhanced scattering or additional losses of the optical guided modes. The pores have mainly two effects: they generate an enormous inner surface (up to a factor of 100 higher than the mere geometric dimensions of the planar substrate) and they allow for the exchange of material and charges between the two sides of the solid thin film. We demonstrate this for several different scenarios including anodized aluminum oxide layers for the ultrasensitive determination of the refractive index of fluids, or the label-free detection of small analytes binding from the pore inner volume to receptors immobilized on the pore surface. Using a thin film of Ti metal for the anodization results in a nanotube array offering an even further enhanced inner surface and the possibility to apply electrical potentials via the resulting TiO2 semiconducting waveguide structure. Nanoporous substrates fabricated from SiNx thin films by colloid lithography, or made from SiO2 by e-beam lithography, will be presented as examples where the porosity is used to allow for the passage of ions in the case of tethered lipid bilayer membranes fused on top of the light-guiding layer, or the transport of protons through membranes used in fuel cell applications. The final example that we present concerns the replication of the nanopore structure by polymers in a process that leads to a nanorod array that is equally well suited to guide the light as the mold; however, it opens a totally new field for integrated optics formats for direct chemical and biomedical sensing with an extension to even molecularly imprinted structures. [Figure not available: see fulltext.] Fil: Knoll, Wolfgang. Competence Centre for Electrochemical Surface Technology; Austria. Austrian Institute of Technology; Austria Fil: Azzaroni, Omar. Competence Centre for Electrochemical Surface Technology; Austria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Duran, Hatice. University of Economics and Technology. Department of Materials Science and Nanotechnology Engineering; Austria Fil: Kunze Liebhäuser, Julia. Universidad de Innsbruck; Austria Fil: Lau, King Hang Aaron. University of Strathclyde; Reino Unido Fil: Reimhult, Erik. University of Natural Resources and Life Sciences. Department of Nanobiotechnology; Austria Fil: Yameen, Basit. Lahore University of Management Sciences. Syed Babar Ali School of Science and Engineering. Department of Chemistry and Chemical Engineering; Pakistán

Developing sodium (Na)-ion batteries is highly appealing because they offer the potential to be made from raw materials, which hold the promise to be less expensive, less toxic, and at the same time more abundant compared to state-of-the-art lithium (Li)-ion batteries. In this work, the Na-ion storage capability of nanostructured organic–inorganic polyaniline (PANI) titanium dioxide (TiO2) composite electrodes is studied. Self-organized, carbon-coated, and oxygen-deficient anatase TiO2–x-C nanotubes (NTs) are fabricated by a facile one-step anodic oxidation process followed by annealing at high temperatures in an argon–acetylene mixture. Subsequent electropolymerization of a thin film of PANI results in the fabrication of highly conductive and well-ordered, nanostructured organic–inorganic polyaniline-TiO2 composite electrodes. As a result, the PANI-coated TiO2–x-C NT composite electrodes exhibit higher Na storage capacities, significantly better capacity retention, advanced rate capability, and better Coulombic efficiencies compared to PANI-coated Ti metal and uncoated TiO2–x-C NTs for all current rates (C-rates) investigated.

The electrochemical lithiation/delithiation behavior of self-organized amorphous and anatase titanium dioxide (TiO2) nanotubes (NTs) is analyzed by means of electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The bulk lithiation properties are governed by the different phase transitions in amorphous and anatase TiO2. While in the case of amorphous nanotubes the phase transition only leads to a thermodynamic limitation of the bulk Li content, it additionally limits the lithiation kinetics for the anatase case. This kinetic constraint is found to originate from underlithiation of the anatase TiO2–x bulk caused by the instant first phase transition during lithium insertion. Together with the surface lithiation properties, it leads to different lithiation characteristics. Amorphous nanotubes are characterized by a reversible surface chemistry and thus pseudocapacitive lithiation/delithiation behavior. As a result, amorphous TiO2 nanotubes show higher overall capacities due...

X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy are used to investigate the electrochemical lithiation/delithiation behaviour of self-organized amorphous TiO2 and anatase TiO2 − x nanotubes. With proceeding bulk lithiation of the active material, surface films form on both nanotube arrays. Carbonates start forming with the beginning of the phase transitions and are reversibly desorbed upon delithiation, on both materials. LiF is found to mainly influence the lithiation/delithiation properties on amorphous nanotubes due to an important decrease of the surface film resistance and an increase of the surface film capacitance at potentials ≤ 2.0 V, where large amounts of LiF adsorb at the surface. Surface film formation is found to be completely reversible on amorphous nanotubes, while C O, C O and fluoride containing adsorbates partially stay adsorbed on anatase nanotubes. The higher reversibility of the surface chemistry on amorphous TiO2 nanotubes is therefore assumed to be essential for the higher rate capability, faster kinetics, and the higher capacity retention observed for amorphous TiO2 materials. This demonstrates that lithiation properties can be substantially altered through changes of the surface chemistry, which can be used to improve kinetics and cycling stability of titania based anode materials in general.

We report on the electrochemical characteristics of pristine and air aged carbon modified titania electrodes in acidic electrolyte, which find application as catalyst supports in electrocatalysis. Films of different chemical composition (including TiO2, TiOx, TiO, TiC, C) are synthesized through a carbothermal treatment of compact anodic TiO2 on Ti substrates at different temperatures, and analyzed with X-ray photoelectron spectroscopy. Their activity towards heterogeneous outer sphere electron transfer and their stability against passivation and corrosion under anodic polarization are investigated by means of electrochemical impedance spectroscopy. It is found that a high fraction of TiC in the pristine carburized films in combination with a thin TiO2 surface layer yields high electron transfer kinetics even after aging for ~9 months, and a high corrosion and passivation resistance until ~0.74VSHE. This finding is essential to the material's application as catalyst support in general.

Self-organized TiO2 nanotubes (NTs) with a preferential orientation along the [001] direction are anodically grown by controlling the water content in the fluoride-containing electrolyte. The intrinsic kinetic and thermodynamic properties of the Li intercalation process in the preferentially oriented (PO) TiO2 NTs and in a randomly oriented (RO) TiO2 NT reference are determined by combining complementary electrochemical methods, including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic cycling. PO TiO2 NTs demonstrate an enhanced performance as anode material in Li-ion batteries due to faster interfacial Li insertion/extraction kinetics. It is shown that the thermodynamic properties, which describe the ability of the host material to intercalate Li ions, have a negligible influence on the superior performance of PO NTs. This work presents a straightforward approach for gaining important insight into the influence of the crystallographic orientation on lithiation/de...

International audience; Mixtures or composites of titania and carbon have gained considerable research interest as innovative catalyst supports for low-and intermediate-temperature proton-exchange membrane fuel cells. For applications in electro-catalysis, variations in the local physicochemical properties of the employed materials can have significant effects on their behavior as catalyst supports. To assess microscopic hetero-geneities in composition, structure, and morphology, a microscopic multitechnique approach is required. In this work, compact anodic TiO 2 films on planar polycrystalline Ti substrates are converted into carbon/titania composites or multiphase titanium oxycarbides through carbothermal treatment in an acetylene/argon atmosphere in a flow reactor. The local chemical composition, structure, and morphology of the converted films are studied with scanning photoelectron microscopy, micro-Raman spectroscopy, and scanning electron microscopy and are related with the crystallographic orientations of the Ti substrate grains by means of electron backscatter diffraction. Different annealing temperatures, ranging from 550 to 850 °C, are found to yield different substrate grain-dependent chemical compositions, structures, and morphologies. The present study reveals individual time scales for the carbothermal conversion and subsequent surface re-oxidation on substrate grains of a given orientation. Furthermore, it demonstrates the power of a microscopic multitechnique approach for studying polycrystalline heterogeneous materials for electrocatalytic applications.

Nanostructuring of electrode materials is a promising approach to enhance the performance of next-generation, high-energy density lithium (Li)-ion batteries. Various experimental and theoretical approaches allow for a detailed understanding of solid-state or surface-controlled reactions that occur in nanoscaled electrode materials. While most techniques which are suitable for nanomaterial investigations are restricted to analysis widths of the order of A to some nm, they do not allow for characterization over the length scales of interest for electrode design, which is typically in the order of mm. In this work, three different self-organized anodic titania nanotube arrays, comprising as-grown amorphous titania nanotubes, carburized anatase titania nanotubes, and silicon coated carburized anatase titania nanotubes, have been synthesized and studied as model composite anodes for use in Li-ion batteries. Their 2D areal Li densities have been successfully reconstructed with a sub-millimeter spatial resolution over lateral electrode dimensions of 20 mm exploiting the 6Li(n,α)3H reaction, in spite of the extremely small areal Li densities (10-20 μg cm-2 Li) in the nanotubular active material. While the average areal Li densities recorded via triton analysis are found to be in good agreement with the electrochemically measured charges during lithiation, triton analysis revealed, for certain nanotube arrays, areas with a significantly higher Li content ('hot spots') compared to the average. In summary, the presented technique is shown to be extremely well suited for analysis of the lithiation behavior of nanostructured electrode materials with very low Li concentrations. Furthermore, identification of lithiation anomalies is easily possible, which allows for fundamental studies and thus for further advancement of nanostructured Li-ion battery electrodes.

A combined synthesis strategy involving a carbothermal reduction and gelation approach with glycine as gelating agent was used to obtain Zr-based (oxy)carbide materials with defined and controlled composition., A combined synthesis strategy involving a carbothermal reduction and gelation approach with glycine as gelating agent was used to obtain Zr-based (oxy)carbide materials with defined and controlled composition. A comparatively low temperature approach (1500 °C) allows exploration of the ZrC–ZrO2 phase diagram and reproducibly leads to zirconium (oxy)carbide phases with different C/Zr ratios, as confirmed by combined X-ray diffraction (XRD) and transmission electron microscopy (TEM) data. The latter also indicates a chemically very homogeneous distribution of oxygen and carbon throughout the sample bulk, a prerequisite for further characterization of its intrinsic physico-chemical properties. Due to the general variability of the synthesis procedure – variation of metal precursor, amount of gelating agent and carbon precursor source – it is expected that the method can be easily adapted and transferred to other metal – oxycarbide materials.

The actual energy demand and consumption issues make it necessary to critically discuss and compare different energy conversion and storage systems. At present, only one third of the primary energy is converted into end energy, for example, electrical energy. Losses are associated with a high consumption of fossil fuels and large CO2 emissions. They can be avoided by considering important electrochemical processes for energy conversion, using batteries, fuel cells, supercapacitors and electrochemical photovoltaics and by incorporating energy storage, employing rechargeable batteries, supercapacitors, generation of hydrogen via electrolysis, and generation of methanol.

Immobilization of high-potential multicopper oxidases like laccase from Trametes versicolor (TvLc) on cathode surfaces in an orientation that enables direct electron transfer (DET) to the active center allows to profit from the enzyme’s low overpotential towards the oxygen reduction reaction (ORR). In this work, TvLc is immobilized on mixed self-assembled monolayers (SAMs) of thiolates on Au(111). The SAMs consist of two species, a linker molecule, thiolated veratric acid (tVA) with a moiety similar to the enzyme’s natural substrates, and a diluent molecule, 3-mercaptopropionic acid (MPA), which increases the lateral distance between neighboring tVA molecules when incorporated between the linkers. In this work we study the effect of linker separation on enzyme activity. Electrochemical scanning tunneling microscopy (EC-STM) is used to determine the molecular arrangement of the two species in two different SAMs. After enzyme immobilization, negligible enzymatic activity is found on a monolayer, where a separation between tVA and MPA phases is observed. This is explained by the close packing of tVA linkers, which prevents access to the enzyme’s active center. Maximum bioelectrocatalytic currents at low overpotentials are measured on a SAM, where tVA and MPA homogeneously mix in a single phase. The increased distance between isolated linkers allows for induced-fit binding of TvLc to the linker moiety, which leads to a proper orientation of the enzyme and allows for DET from the electrode through the linker molecule to the enzyme’s active center.

To achieve complete oxidation of ethanol (EOR) to CO2, higher operating temperatures (often called intermediate-T, 150-200 °C) and appropriate catalysts are required. We examine here titanium oxycarbide (hereafter TiOxCy) as a possible alternative to standard carbon-based supports to enhance the stability of the catalyst/support assembly at intermediate-T. To test this material as electrocatalyst support, a systematic study of its behavior under electrochemical conditions was carried out. To have a clear description of the chemical changes of TiOxCy induced by electrochemical polarization of the material, a special setup that allows the combination of X-ray photoelectron spectroscopy and electrochemical measurements was used. Subsequently, an electrochemical study was carried out on TiOxCy powders, both at room temperature and at 150 °C. The present study has revealed that TiOxCy is a sufficiently conductive material whose surface is passivated by a TiO2 film under working conditions, which prevents the full oxidation of the TiOxCy and can thus be considered a stable electrode material for EOR working conditions. This result has also been confirmed through density functional theory (DFT) calculations on a simplified model system. Furthermore, it has been experimentally observed that ethanol molecules adsorb on the TiOxCy surface, inhibiting its oxidation. This result has been confirmed by using in situ Fourier transform infrared spectroscopy (FTIRS). The adsorption of ethanol is expected to favor the EOR in the presence of suitable catalyst nanoparticles supported on TiOxCy.

Self-organized TiO

Titanium oxide–titanium carbide (TiOxCy) hybrid materials have tunable electronic properties ranging from semiconductive to semimetallic. They can therefore be employed in solar energy conversion applications and as potential substitute for carbon based electrocatalyst supports for use in fuel cells. Understanding of the optical properties of semimetallic TiOxCy is of great importance. In this paper we report on the optical properties of compact TiOxCy in the mid-IR spectral region. TiOxCy reflects the IR light similarly to metals and is therefore suitable as a new substrate for molecular adsorption studies with infrared reflection absorption spectroscopy. For the first time polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) is applied to study quantitatively at the submolecular level the structure and orientation of fatty acid molecules in monolayers adsorbed on the TiOxCy surface. The analysis of the IR band intensities provides information on the structure, packing, and orie...

Self-organized anodic titania (TiO2) nanotube arrays are an interesting model anode material for use in Li-ion batteries owing to their excellent rate capability, their cycling stability and their enhanced safety compared to graphite. A composite material where carbothermally treated conductive TiO2nanotubes are used as support for a thin silicon film has been shown to have the additional advantage of high lithium storage capacity. This article presents a detailed comparison of the structure, surface and bulk morphology of self-organized conductive TiO2nanotube arrays, with and without silicon coating, using a combination of X-ray diffraction, X-ray reflectivity, grazing-incidence small-angle X-ray scattering (GISAXS) and time-of-flight grazing-incidence small-angle neutron scattering (TOF-GISANS) techniques. X-ray diffraction shows that the nanotubes crystallize in the anatase structure with a preferred (004) orientation. GISAXS and TOF-GISANS are used to study the morphology of the nanotube arrays, delivering values for the inner nanotube radius and intertubular distances with high statistical relevance because of the large probed volume. The analyses reveal the distinct signatures of a prominent lateral correlation of the TiO2nanotubes of ∼94 nm and a nanotube radius of ∼46 nm. The porosity averaged over the entire film using TOF-GISANS is 46%. The inner nanotube radius is reduced to half (∼23 nm) through the silicon coating, but the prominent lateral structure is preserved. Such in-depth morphological investigations over large sample volumes are useful towards development of more efficient battery electrode morphologies.