Oscillatory instabilities during formic acid oxidation on Pt(100), Pt(110) and Pt(111) under potentiostatic control. I. Experimental

Strasser, Peter; Lübke, M.; Raspel, Frank; Eiswirth, M.; Ertl, G.

doi:10.1063/1.474450

Cited by 135 publications

(132 citation statements)

References 37 publications

(55 reference statements)

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“…In contrast to previous statements, [55][56][57][58] Behm and co-workers [59][60][61] found that an adsorbed bridge-bonded formate species does not take part as a reaction intermediate in the direct pathway, but rather it acts as a spectator that blocks the catalyst surface in the, dominant, direct pathway. The authors propose a triple pathway mechanism which includes the direct pathway, 61 HCOOH Oscillatory kinetics during the electrooxidation of formic acid on platinum has been observed many times [62][63][64][65][66][67][68][69][70][71] and is known to result from the presence of a negative differential resistance in an N-shaped current potential curve. 72 The phenomenon has been explained in terms of the interaction between positive and negative feedback loops acting on the electrode potential and can be rationalized in terms of the interaction of 73 (a) surface poisoning along the indirect pathway, (b) cleaning of the surface by the reaction between adsorbed carbon monoxide and oxygenated species, and (c) feedback between the total surface coverage and the electrode potential.…”

Section: Resultsmentioning

confidence: 99%

Temperature (Over)Compensation in an Oscillatory Surface Reaction

et al. 2008

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Biological rhythms are regulated by homeostatic mechanisms that assure that physiological clocks function reliably independent of temperature changes in the environment. Temperature compensation, the independence of the oscillatory period on temperature, is known to play a central role in many biological rhythms, but it is rather rare in chemical oscillators. We study the influence of temperature on the oscillatory dynamics during the catalytic oxidation of formic acid on a polycrystalline platinum electrode. The experiments are performed at five temperatures from 5 to 25°C, and the oscillations are studied under galvanostatic control. Under oscillatory conditions, only non-Arrhenius behavior is observed. Overcompensation with temperature coefficient (q 10 , defined as the ratio between the rate constants at temperature T + 10°C and at T) < 1 is found in most cases, except that temperature compensation with q 10 ≈ 1 predominates at high applied currents. The behavior of the period and the amplitude result from a complex interplay between temperature and applied current or, equivalently, the distance from thermodynamic equilibrium. High, positive apparent activation energies were obtained under voltammetric, nonoscillatory conditions, which implies that the non-Arrhenius behavior observed under oscillatory conditions results from the interplay among reaction steps rather than from a weak temperature dependence of the individual steps.

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Section: Resultsmentioning

confidence: 99%

Temperature (Over)Compensation in an Oscillatory Surface Reaction

et al. 2008

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“…Those features are rather astonishing if one considers the plethora of oscillatory patterns observed for instance in the electrooxidation of formic acid. [28][29][30][31][32][33][34] In the present work we report the investigation of the oscillatory instabilities in the methanol electrooxidation reaction on a polycrystalline platinum electrode and in aqueous sulfuric acid media. Besides conventional electrochemical experiments under potentiostatic and galvanostatic control, in situ FTIR spectroscopy was also employed to quantify the mean carbon monoxide coverage during the oscillations.…”

Section: Introductionmentioning

confidence: 99%

Oscillatory instabilities during the electrocatalytic oxidation of methanol on platinum

Martins¹,

Batista²,

Sitta³

et al. 2008

J. Braz. Chem. Soc.

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Descreve-se neste artigo a observação experimental de dinâmica oscilatória durante a oxidação eletrocatalítica de metanol sobre platina. Além das, previamente relatadas, oscilações de potencial, oscilações de corrente obtidas sob controle potenciostático também são apresentadas. A região de existência de oscilações de corrente é mapeada no plano de bifurcação voltagem aplicada x resistência. Conjuntamente com investigações eletroquímicas, espectroscopia FTIR in situ também foi aplicada nestes estudos. Apesar de não ter sido possível acompanhar eventuais variações de intermediários reacionais durante as oscilações, tais experimentos revelaram que a cobertura média de monóxido de carbono permanece consideravelmente alta durante as oscilações. Os resultados são discutidos e comparados com as oscilações observadas na eletrooxidação de ácido fórmico, um sistema cujo comportamento é mais entendido e amplamente fundamentado por dados espectroscópicos obtidos in situ.It is described in this paper the experimental observation of oscillatory dynamics during the electrocatalytic oxidation of methanol on platinum. Besides the previously reported potential oscillations, current oscillations obtained under potentiostatic control are also presented. The existence region of current oscillations is mapped in an applied voltage x resistance bifurcation diagram. Conjointly with electrochemical investigations, in situ FTIR spectroscopy was also employed in the present studies. Although we were not able to follow eventual intermediate coverage changes during the oscillations, those experiments revealled that the mean coverage of adsorbed carbon monoxide remains appreciably high along the oscillations. Results are discussed and compared with the oscillations observed in the electrooxidation of formic acid, a system whose behavior is more understood and widely supported by in situ spectroscopic data. Keywords: current and potential oscillations, methanol, electrocatalysis, in situ FTIR IntroductionMethanol has been pointed as one of the most promising organic molecules to be used in large scale energy conversion systems, as in the so-called direct methanol fuel cells (DMFC). [1][2][3] Limitations associated to the high overpotential and the existence of parallel reaction pathways makes its understanding a rather challenging task. Studies have been carried out mainly on platinum surfaces, both polycrystalline and single crystals, by means of different electrochemical approaches sometimes coupled to other in situ and on line techniques. [4][5][6][7][8][9][10][11][12][13][14][15][16] In most of these reports, the focus stands on the electrocatalytic aspects of the methanol oxidation and encompasses questions such as the relationship between reaction rate and applied potential, the impact of the interfacial structure on reaction rate and selectivity, and the nature and geometry of adsorbates, to list a few. By far less studied however are the issues related to the complex kinetic aspects associated to the electrooxidation of methanol.In o...

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“…At a current density higher than 8 A/dm², the whole sample surface is bright. This effect of pattern formation is a frequently discussed phenomenon in the electroplating technology [3][4][5][6][7][8][9][10][11][12][13][14]. Several studies have been done for better understanding of pattern formation of inhomogeneous interfacial potential in electrodissolution reactions [15], electrocatalytic oxidation reactions and electrocatalysis [16].…”

Section: I-e-investigationsmentioning

confidence: 99%

Recent developments in the preparation of nano-gold composite coatings

Freudenberger¹,

Zielonka²,

Funk³

et al. 2010

Gold Bull

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New possibilities in the design of gold-containing electrochemical coating systems for electronic applications are given by the incorporation of gold-nanoparticles in metal-matrix-systems. The major problem for the application of nanoparticles is the strong agglomeration of the particles in the electrolyte solutions, preventing the incorporation of nanoscaled dispersants.A complete new concept for the deposition of nano dispersion layers, overcoming this agglomeration challenge, is the application of core shell systems. Using these systems, it becomes possible for the first time to incorporate metal nanoparticles into electrodeposited metal layers to form metal nanoparticle metal matrix systems (MNP-MMS). The advantage of such layers is to form nanocomposite materials far away from the thermodynamic equilibrium. Especially for the combination of gold nanoparticles with a nickel matrix, a way is shown for the manufacturing of temperature-stable nanocomposite structures, because at least in the temperature range of electronic applications no loss of the dispersive character by diffusion processes is expected. By incorporating the precious metal material into the nickel matrix as the main electrodeposit, and reducing the top gold layer thickness, a possible way of reducing the gold consumption and an economic use of gold resources is shown.

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Oscillatory instabilities during formic acid oxidation on Pt(100), Pt(110) and Pt(111) under potentiostatic control. I. Experimental

Cited by 135 publications

References 37 publications

Temperature (Over)Compensation in an Oscillatory Surface Reaction

Temperature (Over)Compensation in an Oscillatory Surface Reaction

Oscillatory instabilities during the electrocatalytic oxidation of methanol on platinum

Recent developments in the preparation of nano-gold composite coatings

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