Kelvin probe technique

The work function, , of a metal surface can be measured relatively easily and when using the Kelvin probe technique, in situ, i.e., during catalyst operation.54,55 Three techniques are the most commonly used54-58 ... 

All three techniques are quite straightforward to use. The Kelvin probe technique has the advantage that it does not require vacuum conditions, thus a catalyst can be studied under atmospheric or higher pressure. 

As also already shown in Figures 5.8 to 5.16 the validity of Eqs. (5.18) and (5.19) has been confirmed by several laboratories using the Kelvin probe technique, as well as UPS (via electron cutoff energy) and in a semiquanti-tative manner via the PEEM technique. Experiment has also clearly shown that the validity of these equations, which include only thermodynamic properties, does not depend on which, if any, electrode is grounded.31 The same is clearly tme for electrochemical promotion in general, as should be obvious to every electrochemist reader. 

The technique of photoemission electron spectroscopy (PEEM) is a particularly attractive and important one for spatially resolved work function measurements, as both the Kelvin probe technique and UPS are integral methods with very poor ( mm) spatial resolution. The PEEM technique, pioneered in the area of catalysis by Ertl,72-74 Block75 76 and Imbihl,28 has been used successfully to study catalytic oscillatory phenomena on noble metal surfaces.74,75... 

Equation (7.12) has been reported since 199031 by several groups31 39,40,42 45 and has been confirmed using both the Kelvin probe technique and UPS, as already discussed in Chapter 5. Only one group46 has reported significant deviations from it, but the SEMs in that work show massive blocking nonporous electrodes which apparently do not allow for ion spillover. 

By comparing Figure 11.9 and the characteristic Po2(Uwr) rate breaks of the inset of Fig. 11.9 one can assign to each support an equivalent potential Uwr value (Fig. 11.10). These values are plotted in Figure 11.11 vs the actual work function G>° measured via the Kelvin probe technique for the supports at po2-l atm and T=400°C. The measuring principle utilizing a Kelvin probe and the pinning of the Fermi levels of the support and of metal electrodes in contact with it has been discussed already in Chapter 7 in conjunction with the absolute potential scale of solid state electrochemistry.37... 

Figure 11.11. Correlation between the equivalent potentials of the supports defined in Figure 11.10 and of the work function or absolute potential of the supports measured via the Kelvin probe technique in po2 =1 atm at 400°C.22...

Kelvin probe technique and work function measurement, 138, 205, 340 experimental details, 340 two-probe arrangement, 340 Kinetics... 

The Kelvin Probe technique allows measurement of the Work Function of a given surface, not only in stationary conditions but also during absorption - desorption processes. 

The catalyst work function is a directly measurable quantity, by using either the Kelvin probe technique or the electron cut-off energy technique. It was found experimentally that, for steady-state... 

The difference in the inner potentials of the two phases at an electrochemical interface, the inner potential difference or Galvani potential difference, cannot be measured directly. The difference between the outer potentials of the two phases is called the Volta potential difference, and is measured by the Kelvin Probe technique, as described in Sect. 7.8 in this volume. 

The origin of NEMCA effects is also studied, and it is reported that the surface modification of reactant by ion back spillover of an effective double layer at the metal-gas interface is strongly related with unique improvement in reaction rate and selectivity [5, 7], In situ work function measurements are performed by the Kelvin probe technique [7] or UPS [8] for explanation of NEMCA effects. These measurements show that over a wide range of temperatures, work function of metal catalyst linearly changes with increasing potential and the supplied ion species like oxide ion, proton, or Na" spiU over [9] on the metal catalyst to form electric double layer. Schematic image of electrochemical modification is shown in Fig. 3 for the case of oxide ion conductor, in which 8 value is not still determined yet [5]. 

D Amico A, Di Natale C, Paolesse R, Mantini A, Goletti C, Davide F, FUosofi G (2(XX)b) Chemictil sensing materials characterization by Kelvin probe technique. Sens Actuators B 70 254-262 Di Natale C, Paolesse R, Mantini A, Macagnano A, Boschi T, D Amico A (1998) Kelvin probe investigation of self-assembled-monolayers of thiol derivatized porphyrins interacting with volatile compounds. Sens Actuators B 48 368-372... 

The Kelvin Probe Technique as Reference Electrode for Application on Thin and Ultrathin Electrolyte Films... 

The Kelvin probe technique is a unique reference electrode that allows non-contact measurement of electrode potentials. It can be used for measuring electrode potentials through insulating dielectric media such as air or polymeric films. It is mainly used where standard electrochemical techniques, which require a finite ionic resistance between working and reference electrodes, will fail. 

Other than for electrodes immersed in bulk electrolyte, on electrodes covered by ultrathin layers the electrode potential may differ significantly across the electrode surface. Hence, localised measurements are of interest, being performed by scanning the tip across the sample. This was first applied for organic coated metals where the coating was electrochemically delaminating, driven by corrosion [12-14, 29], Even on the submicron scale the Kelvin probe technique can be applied for such studies, and then based on a modified atomic force microscope, see [34, 35]. Recent developments are the combination of Kelvin probe and SECM [36] and the use of Kelvin probe for hydrogen detection [37]. 

G. Williams, H. N. McMuiray, and D. A. Worsley, Cerium(III) inhibition of corrosion-driven organic coating delamination studied using a scanning Kelvin probe technique , J. Electrochem. Soc., 149, B154 (2002). 

H. N. McMurray, D. Wilhams, G. Williams and D. Worsley, Inhibitor pietreatment synergies demonstrated using a scanning Kelvin probe technique . Corrosion Engineering, Science and Technology, 38,112 (2003). 

In a more recent work, Michalik and Rohwerder (2005) stndied the self-healing effect in defected PPy conducting coatings deposited on gold, using the scarming Kelvin probe technique. They concluded that, in thick (1 pm) PPy films doped with tosylate anions, the transport of small cations is fast and responsible for polymer reduction and delamination. According to this study, the cationic transport... 

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