Ulrich Stimming - Academia.edu (original) (raw)

Papers by Ulrich Stimming

Journal of Physical Chemistry C, Mar 7, 2008

The redox metalloprotein yeast cytochrome c was directly selfchemisorbed on ™bare∫ gold electrode... more The redox metalloprotein yeast cytochrome c was directly selfchemisorbed on ™bare∫ gold electrodes through the free sulfurcontaining group Cys102. Topological, spectroscopic, and electron transfer properties of the immobilised molecules were investigated by in situ scanning probe microscopy and cyclic voltammetry. Atomic force and scanning tunnelling microscopy revealed individual protein molecules adsorbed on the gold substrate, with no evidence of aggregates. The adsorbed proteins appear to be firmly bound to gold and display dimensions in good agreement with crystallographic data. Cyclic voltammetric analysis showed that up to 84 % of the electrode surface is functionalised with electroactive proteins whose measured redox midpoint potential is in good agreement with the formal potential. Our results clearly indicate that this variant of cytochrome c is adsorbed on bare gold electrodes with preservation of morphological properties and redox functionality.

Journal of The Electrochemical Society, 2018

The development of high performance electrodes for Na-ion batteries requires a fundamental unders... more The development of high performance electrodes for Na-ion batteries requires a fundamental understanding of the electrode electrochemistry. In this work, the effect of the morphology of vanadium oxide on battery performance is investigated. First, the phase transitions upon sodiation/de-sodiation of Na x V 2 O 5 cathodes in standard battery solvents are explored by cyclic voltammetry and X-Ray diffraction. At potentials 1.5 V positive of Na/Na + the insertion of the first Na + into pristine V 2 O 5 is completed and α'-NaV 2 O 5 is formed. A discharge to 1.0 V results in the introduction of a second Na + and after a deep discharge to 0 V a third Na + is intercalated. When cycled as an intercalation electrode, the Na-content x in Na x V 2 O 5 varies between x = 1 (charged) and x = 2 (discharged). For studying the effect of electrode morphology on the battery performance, several types of V 2 O 5 (hollow V 2 O 5 microspheres, V 2 O 5 nanobundles and V 2 O 5 nanobundles blended with 10% wt TiO 2) were prepared and compared to a commercially available V 2 O 5-micropowder. The nanobundles were prepared by a facile sonochemical process. In comparison to the microsized V 2 O 5 morphologies, the potential plateaus in the charge/discharge curves of the V 2 O 5 nanobundles are at more positive potentials and the capacity loss in the first cycle is suppressed. The V 2 O 5 nanobundles showed the best battery performance with a reversible capacity of 209.2 mAh g −1 and an energy density of 571.2 mWh kg −1 (2 nd cycle). After an initial capacity fading, which can be slightly suppressed by blending the V 2 O 5 with TiO 2 , the pure V 2 O 5 nanobundles have a practical capacity of 85 mAh g −1 , an operation potential of 2.4 V, an energy density of 266.5 mWh kg −1 and a capacity retention of 83% after 100 cycles. The best battery performance of the nanomaterial is ascribed in this study to the amorphous character of the electrode, favoring faster electrode kinetics due to a (pseudo-) capacity dominated charging/discharging, reducing diffusion lengths and preventing further amorphization, which all is beneficial in terms of lifetime, capacity, operation voltage, energy density and energy efficiency.

Recent advances in electrochemistry show that nanostructuring surfaces with a rational design of ... more Recent advances in electrochemistry show that nanostructuring surfaces with a rational design of metallic catalysts can enhance their electrocatalytic activity. This can be advantageous for various applications such as fuel cells and electrolyzers, since it can improve their performance with simultaneously decreasing the amount of precious metal catalyst used. Previous work on Pd decorated Au(111) surfaces showed that by decreasing the Pd amount on Au(111), an increase of the activity for hydrogen evolution reaction (HER) occurred for small coverages 1. A similar trend was observed for the case of Pt nanostructured Au(111) surfaces 2 but for even smaller coverages of Pt. It was reported that a possible explanation of this increase could be attributed to an effect of the substrate material. Hammer et al. 3 and Eikerling et al. 4 showed that the choice of substrate material can affect the performance of the catalyst system by the so-called strain and spill-over effects. However the choice of substrate material is only one parameter. There are other parameters such as the morphology of the catalyst particles (e.g. particle size, particle height, inter-particle distance) and the choice of catalyst material. In order to get a deeper understanding of how different parameters affect the electrocatalytic activity, we investigated hydrogen related reactions such as HER and HOR on three different catalyst systems. These systems are all based on Pt as the catalyst material and Au(111), Cu and highly oriented pyrolytic graphite (HOPG) as the substrate materials. The influence of different parameters on the above mentioned reactions (HOR and HER) is investigated by using electrochemical methods (e.g. potentiostatic pulse techniques). The morphological and structural properties of the model catalysts is studied by electrochemical atomic force microscopy (EC-AFM) and scanning tunneling microscopy (EC-STM). Therefore, we can develop pathways to optimize the design and suggest catalyst structures that will have the potential for a high and efficient electrocatalytic activity.

The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggesstions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports,

Electrochimica Acta, 2017

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 Intern... more This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence Newcastle University ePrints-eprint.ncl.ac.uk

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1984

Iron(III)-txtanlum(IV)-oxades of the general composmon FexT11 _xOy were prepared in the compositi... more Iron(III)-txtanlum(IV)-oxades of the general composmon FexT11 _xOy were prepared in the composition range x = 0-0.9 by thermal decomposition of the corresponding metal salt solutions. For a medium range of composition, 0.1 _< x _< 0 7, amorphous orades were formed under the gwen conditions of preparation. Electrochemacal properUes such as reduction and re-oradatlon of the orade, electrode capacity behavlour, oxygen evolution and reduction and the redox reaction, FeE+/Fe3+, were lnvesUgated Photoelectrochemlcal properties were obtamed from photocurrent spectra and the dependence on potential of the photocurrent. Anneahng experiments showed that crystallization yields lower photocurrents and a shaft of the photocurrents spectra to shorter wavelengths Thus, amorphous semaconductors seem worth being investigated for a possible application in electrochermcal solar cells. An attempt is made to describe the impact of non-crystalhnlty on the photoelectrochemlcal behavlour of sermconductors. A model of the oxade is proposed to explain the electrochermcal and photoelectrochemical properties of the oxades FexTii_ xO v.

Advances in Electrochemical Sciences and Engineering, 2015

Surface Science Tools for Nanomaterials Characterization, 2015

Scanning electrochemical potential microscopy (SECPM) and electrochemical scanning tunnelling mic... more Scanning electrochemical potential microscopy (SECPM) and electrochemical scanning tunnelling microscopy (EC-STM) allow for imaging the solid-liquid interface under in situ electrochemical conditions. In this chapter we take a look at two important aspects of SECPM and EC-STM studies: First, investigations on model electrode systems relevant for electrocatalysis are presented. Second, studies on the behavior of biomolecules immobilized on electrodes are shown. In both cases the use of EC-STM or SECPM allows for insights into the electrochemistry at a molecular level which cannot be achieved by other, rather integrating, methods.

Electrochimica Acta, 2014

ChemPhysChem, 2014

Polyoxovanadate Na6V10O28 is investigated for the first time as electrode material for supercapac... more Polyoxovanadate Na6V10O28 is investigated for the first time as electrode material for supercapacitors (SCs). The electrochemical properties of Na6V10O28 electrodes are studied in Li+‐containing organic electrolyte (1 M LiClO4 in propylene carbonate) by galvanostatic charge/discharge and cyclic voltammetry in a three‐electrode configuration. Na6V10O28 electrodes exhibit high specific capacitances of up to 354 F g−1. An asymmetric SC with activated carbon as positive electrode and Na6V10O28 as negative electrode is fabricated and exhibits a high energy density of 73 Wh kg−1 with a power density of 312 W kg−1, which successfully demonstrates that Na6V10O28 is a promising electrode material for high‐energy SC applications.

Fresenius Journal of Analytical Chemistry, 1997

Model electrodes with defined mesoscopic structure were either generated by adsorption of surfact... more Model electrodes with defined mesoscopic structure were either generated by adsorption of surfactant stabilized metal clusters from colloidal solution on a support of gold or by electrochemical deposition of platinum on gold substrates. Both types of model electrodes were characterized by STM (scanning tunnelling microscopy), cyclic voltammetry and electrooxidation of adsorbed CO. The supported colloidal Pt as well as the electrochemically deposited Pt revealed different reactivities regarding the CO monolayer electrooxidation as compared to a polycrystalline Pt bulk electrode. In addition, in-situ FTIR (Fourier transformed infrared) spectroscopy was applied to characterize CO adsorbed on electrochemically deposited Pt on gold. Combined with the structural information from STM it seems likely that the differences regarding the catalytic properties of the model electrodes are due to different coverages of the substrate with catalyst particles.

Solid State Ionics, 1997

The interface HgHClO4 · 5.5H2O was investigated by cyclic voltammetry and electrochemical impedan... more The interface HgHClO4 · 5.5H2O was investigated by cyclic voltammetry and electrochemical impedance spectroscopy between 170 and 300 K. In this temperature range, phase transitions occur for electrode and electrolyte, such that within 6 K the electrode-electrolyte interface changes from solid-solid over solid-liquid to liquid-liquid or vice versa. The double layer capacity was investigated as a function of potential for

Solid State Ionics, 2004

The electrochemical behaviour of Ni-Ce0.9Gd0.1O2−δ (Ni-CGO) with a NiO content of 2.5 and 70 wt.%... more The electrochemical behaviour of Ni-Ce0.9Gd0.1O2−δ (Ni-CGO) with a NiO content of 2.5 and 70 wt.% was investigated by impedance spectroscopy. Symmetrical cells with yttrium-stabilized zirconia as electrolyte were prepared with screen printing and then sintered at 1250 °C for 5 h. The microstructure of the anode material after sintering was analysed by SEM. Impedance spectroscopy measurements were carried out in atmospheres containing H2, CH4 and N2 at various compositions humidified with 3% H2O in the temperature range 700–850 °C. No visible carbon deposition on both electrodes was found after measurements in variable atmospheres of H2 and CH4 (Balance N2) despite the high content of Ni. However, carbon deposition occurred on the anode with 70 wt.% NiO during continuous exposure in stability testing for 90 h in 97% CH4/3% H2O.

Small, 2008

The nonadiabatic limit of weak electronic coupling between the redox center and the enclosing ele... more The nonadiabatic limit of weak electronic coupling between the redox center and the enclosing electrode was applied for the present case. 1-6 At finite bias voltages, the two step tunneling current (I t) dependence on the effective overpotential (eξη) and the bias voltage (eV bias) is represented by two step ET rate constants in the following combination:

Materialwissenschaft und Werkstofftechnik, 2002

In order to compare the electrochemical performance of Ce 0.9 Gd 0.1 O 2Àd (CGO) in various fuels... more In order to compare the electrochemical performance of Ce 0.9 Gd 0.1 O 2Àd (CGO) in various fuels, impedance spectroscopy measurements were carried out in the atmospheres containing H 2 , CO, CO 2 , CH 4 , N 2 at various compositions, in the temperature range 650 8C to 850 8C. Ohmic loss and polarization resistance were derived from impedance spectroscopy measurements. The stability at different temperatures of the anode was also investigated in 9%H 2 /91%N 2 humidified with 3% H 2 O. The microstructure of the anode before and after degradation test was analysed by SEM. These investigations indicated similarities in the impedance and the activation enthalpies in hydrogen/water, methane/water and CO/CO 2 atmospheres. No indications of methane cracking leading to carbon formation were found. Durch impedanzspektroskopische Messungen wurde ein Vergleich des elektrochemischen Verhaltens von Ce 0.9 Gd 0.1 O 2Àd (CGO) in verschiedenen Brenngasatmospha Èren bei Temperaturen zwischen 650 8C und 850 8C durchgefu Èhrt. Die untersuchten Brenngase enthielten unterschiedliche Anteile an H 2 , CO, CO 2 , CH 4 und N 2. Der Ohmsche Verlust und der Polarisations-Widerstand wurden aus den Impedanzmessungen bestimmt. Die elektrochemische Stabilita Èt der Anode wurde bei verschiedenen Temperaturen in 9%H 2 / 91%N 2 (befeuchtet mit 3% H 2 O) untersucht. Die Mikrostruktur der Anodenschicht wurde vor und nach den Messungen mittels REM analysiert. Die Untersuchungen zeigen A È hnlichkeiten auf sowohl bezu Èglich des Impedanzverhaltens als auch der Aktivierungsenergien bei Wasserstoff/Wasser, Methan/Wasser und CO/CO 2 Atmospha Èren. Es wurden keine Anzeichen von zu Kohlenstoffbildung fu Èhrendem Methan-Cracking gefunden.

Journal of The Electrochemical Society, 1992

This study reports electrochemical phenomena observed during reduction of H 2 O 2 at n- and p-CuI... more This study reports electrochemical phenomena observed during reduction of H 2 O 2 at n- and p-CuInSe 2 (photo)cathodes in alkine medium (pH 9 to 10). After cycling the electrode potential in a given potential rfange, pronouced hysteresis is observed between the two half-cycles of the voltammetry. At both n- and p-materials, during the positive sweep a pronouced increase of the cathodic current is observed at potentials positive of aoubt - 0.8 V. In the potential region corresponding to the i/U banch with negative slope, the n- and p-type materials show inverted photocurrents

Journal of Electroanalytical Chemistry, 2007

This paper provides further insights into the particle size effects in CO monolayer oxidation. St... more This paper provides further insights into the particle size effects in CO monolayer oxidation. Strong particle size effects are confirmed in the size range from 1.8 to 5 nm. The discrepancies in the literature concerned with the particle size effects in CO monolayer oxidation are reconciled by exploring the influence of the experimental conditions on the stripping voltammograms and chronoamperograms. Evidence supporting the contribution of slow non-electrochemical step to the overall mechanism of CO oxidation is presented. The particle size effects in CO monolayer oxidation are attributed to the size-dependent CO ads + OH ads interaction as well as to the size-dependent CO ads surface diffusion coefficient.

Journal of Electroanalytical Chemistry, 1996

Journal of Applied Electrochemistry, 2007

ABSTRACT The oxygen reduction reaction in sulphuric acid on commercial carbon supported platinum ... more ABSTRACT The oxygen reduction reaction in sulphuric acid on commercial carbon supported platinum and ruthenium catalysts as well as on a home-made carbon supported ruthenium selenide catalysts (RuSe x /C) was investigated. The RuSe x /C catalysts were synthesised using similar procedures to those found in the literature. A dependency of H2O2 formation on the selenium content was found using the thin-film rotating ring disc electrode technique, namely that the H2O2 formation in the typical operation range of a Direct Methanol Fuel Cell (0.7–0.4V) on Pt/C is below 1% and 1–4% on Ru/C and RuSe x /C catalysts. Finally for comparing the intrinsic activities of the catalysts the electrochemically active surface areas were determined in-situ by means of copper underpotential deposition. Our results indicate a comparable activity of the present RuSe x /C catalyst to commercial Pt/C if the activities are related to the electrochemical active areas.

Electrochimica Acta, 1995

A comparative investigation of the formation, stability, and dissolution of copper and silver clu... more A comparative investigation of the formation, stability, and dissolution of copper and silver clusters on polycrystalline gold electrodes with in-situ STM was conducted in order to access three closely related problems in parallel. The first topic is the dynamic behaviour of metal clusters in electrochemical environments. The second is the relation between macroscopic kinetic parameters and the structural dynamics on the nm-scale. These two topics are directly connected to the question, whether and how the STM tip affects the local electrochemical kinetics.