Cu(111) single crystal electrodes: Modifying interfacial properties to tailor electrocatalysis

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)

Interfacial Water Structure as a Descriptor for Its Electro-Reduction on Ni(OH)2-Modified Cu(111)

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)

A universal quasi-reference electrode for in situ EC-STM

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 carbo

Carbon Doping: In‐Situ Carbon Doping of TiO2 Nanotubes Via Anodization in Graphene Oxide Quantum Dot Containing Electrolyte and Carburization to TiOxCy Nanotubes (Adv. Mater. Interfaces 5/2015)

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Hexaethylguanidinium tetrakis(trimethylsilylethynyl)borate diethyl ether monosolvate

The solvated molecular salt, C13H30N3+·C20H36BSi4−·C4H10O, was obtained by the reaction of trimethylsilylethyne with boron trichloride in the presence of tert-butyllithium, followed by ion metathesis. The cation exhibits positional disorder and one of the Me3Si groups shows rotational disorder. No significant directional intermolecular interactions are observed

An ultra-flexible modular high vacuum setup for thin film deposition

A modular high vacuum chamber dedicated to thin film deposition is presented. We detail the vacuum and gas infrastructure required to operate two highly flexible chambers simultaneously, with a focus on evaporation techniques (thermal and electron beam) and magnetron sputtering, including baking equipment to remove residual water from the chamber. The use of O-ring-sealed flat flanges allows a tool-free assembly process, in turn enabling rapid changes of the whole setup. This leads to a high flexibility regarding the deposition techniques as the chamber can be adapted to different sources within minutes, permitting the formation of multilayer systems by consecutive depositions onto the same substrate. The central piece of the chamber is a flat flange ground glass tube or cross. The glass recipient permits optical monitoring of the deposition process. Further equipment, such as for the introduction of gases, additional pressure gauges, or evaporators, can be incorporated via specifically designed stainless steel/aluminum interconnectors and blank flanges. In the end, we demonstrate the preparation of an unsupported thin film system consisting of electron-beam-evaporated platinum nanoparticles embedded in magnetron-sputtered zirconia (ZrO2), deposited onto NaCl single crystals, which subsequently can be removed by dissolution. These films are further analyzed by means of transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy.(VLID)3593621Accepted versio

What is limiting the potential window in aqueous sodium‐ion batteries? Online study of the hydrogen‐, oxygen‐ and CO2‐evolution reactions at NaTi2(PO4)3 and Na0.44MnO2 electrodes

Abstract NaTi2(PO4)3 (NTP) and Na0.44MnO2 (NMO), and their derivatives, have emerged as the most promising materials for aqueous Na‐ion batteries. For both, NTP and NMO, avoiding the evolution of hydrogen and oxygen is found to be mandatory in order to mitigate material dissolution. Intriguingly, however, no direct determination of the hydrogen and oxygen evolution reactions (HER and OER) has yet been carried out. Using differential electrochemical mass spectrometry (DEMS) we directly identify the onset potentials for the HER and OER. Surprisingly, the potential window is found to be significantly smaller than suggested by commonly employed cyclic voltammetry measurements. CO2 evolution, upon decomposition of carbon black, is observed at an onset potential of 1.61 VRHE, which is 0.25 V more cathodic than the OER for the NMO electrode. Our results show that the state‐of‐the‐art carbon additive plays a crucial role in the stability of the positive NMO electrode in the ion battery

Lab‐based electrochemical X‐ray photoelectron spectroscopy for in‐situ probing of redox processes at the electrified solid/liquid interface

Abstract A profound understanding of the solid/liquid interface is central in electrochemistry and electrocatalysis, as the interfacial properties ultimately determine the electro‐reactivity of a system. Although numerous electrochemical methods exist to characterize this interface under operating conditions, tools for the in‐situ observation of the surface chemistry, that is, chemical composition and oxidation state, are still scarce, and currently exclusively available at synchrotron facilities. Here, we demonstrate the ability of laboratory‐based near‐ambient pressure X‐ray photoelectron spectroscopy to track changes in oxidation states in‐situ with respect to the applied potential. In this proof‐of‐principle study with polycrystalline gold (Au) as the best‐studied electrochemical standard, we show that during the oxygen evolution reaction (OER), at high OER overpotentials, Au3+ governs the interfacial chemistry, while, at lower overpotentials, Au+ dominates

TiO2 Nanotubes: Interdependence of Substrate Grain Orientation and Growth Rate

International audienceHighly ordered arrays of TiO2 nanotubes can be produced by self-organized anodic growth. It is desirable to identify key parameters playing a role in the maximization of the surface area, growth rate, and nanotube lengths. In this work, the role of the crystallographic orientation of the underlying Ti substrate on the growth rate of anodic self-organized TiO2 nanotubes in viscous organic electrolytes in the presence of small amounts of fluorides is studied. A systematic analysis of cross sections of the nanotubular oxide films on differently oriented substrate grains was conducted by a combination of electron backscatter diffraction and scanning electron microscopy. The characterization allows for a correlation between TiO2 nanotube lengths and diameters and crystallographic parameters of the underlying Ti metal substrate, such as planar surface densities. It is found that the growth rate of TiO2 nanotubes gradually increases with the decreasing planar atomic density of the titanium substrate. Anodic TiO2 nanotubes with the highest aspect ratio form on Ti(-151) [which is close to Ti(010)], whereas nanotube formation is completely inhibited on Ti(001). In the thin compact oxide on Ti(001), the electron donor concentration and electronic conductivity are higher, which leads to a competition between oxide growth and other electrochemical oxidation reactions, such as the oxygen evolution reaction, upon anodic polarization. At grain boundaries between oxide films on Ti(hk0), where nanotubes grow, and Ti(001), where thin compact oxide films are formed, the length of nanotubes decreases most likely because of lateral electron migration from TiO2 on Ti(001) to TiO2 on Ti(hk0)