Rough Electrode Surfaces

FIGURE 13.8 Real periodic electrocatalyst smooth or rough electrode surfaces. A smooth catalyst exhibits no preferential growth along a single axis, while the rough periodic surface shows a (x, y) plane preferential crystallization. 

Instrumentation. The experimental setup is similar to the one used in SPR. An additional photomultiplier mounted at fixed angle with respect to the base of the prism at the solution side of the electrode films is used to detect light scattered from the rough electrode surface and/or the polymer film deposited on the metal film (see Fig. 5.153). 

This may be considered an inhomogeneous homogeneous model inasmuch as the properties of the first layer differ from those of the bulk film. The CPE elements have been used to describe both the double-layer capacitance and the low-frequency pseudocapacitance, their frequency-dependent nature being attributed to the nonuni-formity of the electric field at rough electrode surfaces [24,96,137,140],... 

Fig. 3.1 Schematic representation of a rough electrode surface area...

Many techniques have been developed to characterize the properties of the SEI layer on the anodes, such as X-ray photoelectron spectroscopy (XPS), EELS and selected area electron diffraction (SAED) " as well as FTIR and HRTEM. Most of these techniques provide ex situ information on both the elechonic and crystalline stmctural variations of the electrode. Electrochemical impedance spectroscopy (EIS) and electrochemical quartz crystal microbalance (ECQCM) can provide in situ information of macro-scale properties of the SEI layers. Reflectance FTIR techniques and atomic force microscopy (AFM) have been used in situ to study the surface of metal lithium and electrochemically nonactive electrodes, such as Pt, Au and Ni as well. Nevertheless, it is still difficult to study rough electrode surfaces of composite materials in lithium ion batteries with these techniques. In addition, none of the above techniques, except for FTIR spectroscopy, can provide structural information at the molecular levels. 

DFT-D2 calculations in comparison to AFM measurements have been employed to study the interplay between the so far described Au-N binding and vdW interactions between pyridine terminated structures (4,4-bipyridine and the l,2-bis(4-pyridyl)ethylene) and gold electrodes. For the low-conductance case, modelled by a gold dicomplex, the dispersion contribution is minimal to the bond rupture force. The high conductance of a rough electrode surface is modelled by a Au(lll) surface in addition with a ridge of two layers (Fig. 23). The chemical Au-N... 

Figure Bl.22.6. Raman spectra in the C-H stretching region from 2-butanol (left frame) and 2-butanethiol (right), each either as bulk liquid (top traces) or adsorbed on a rough silver electrode surface (bottom). An analysis of the relative intensities of the different vibrational modes led to tire proposed adsorption structures depicted in the corresponding panels [53], This example illustrates the usefiilness of Raman spectroscopy for the detennination of adsorption geometries, but also points to its main limitation, namely the need to use rough silver surfaces to achieve adequate signal-to-noise levels.

The dependence of the C,E curves for a solid metal on the method of electrode surface preparation was reported long ago.10 20 67 70 219-225 in addition to the influence of impurities and faradaic processes, variation in the surface roughness was pointed out as a possible reason for the effect.10 67,70 74 219 For the determination of R it was first proposed to compare the values of C of the solid metal (M) with that of Hg, i.e., R = C-M/c-Hg 10,74.219-221 data at ff=0 for the most dilute solution (usually... 

Leikis et al,223 used the Parsons-Zobel method to obtain the roughness factor fpz for pc/Ag electrodes. It was found that /pz 1.2, which was explained by the geometric inhomogeneity of the pc-Ag electrode surface. A more detailed analysis is given in Section II.2. Thus it should be noted that in the case of pc electrodes with appreciable differences of EamQvalues for the various planes (AEff o > 100 mV), it is impossible to obtain the true roughness coefficient, the actual Ea=0, and the inner-layer capacity. 

Electroreflectance data for pc-Cu579 confirm that the capacity minimum at E- -0.2 to -0.3 V (SCE) is due to the oxidation of the electrode surface. According to impedance data,564,565 as for pc-Ag and pc-Au,63 67 74 roughness factor for a pc-Cu electrode is approximately 2, which has been explained by the high surface inhomogeneity of the electrode surface. 

Electrochemically polished and chemically treated Cd(0001), Cd(10T0)t Cd(l 120), Cd(lOTl), and Cd(ll2l) electrodes have been studied by impedance and cychc voltammetry by Lust et al.152 153 249 664 665 a slight variation of capacitance (3 to 6%) has been observed with v. In the case of chemically treated electrodes, a somewhat higher (5 to 10%) dependence of C on v has been explained by the geometric roughness of the electrode surface. 

Daikhin, double layer capacitance of solid at rough electrodes, 52 Debye screening and diffuse layer near the surface, 50... 

Equations (5.18) and (5.19), particularly the latter, have only recently been reported and are quite important for solid state electrochemistry. Some of then-consequences are not so obvious. For example consider a solid electrolyte cell Pt/YSZ/Ag with both electrodes exposed to the same P02, so that Uwr = 0. Equation (5.19) implies that, although the work functions of a clean Pt and a clean Ag surface are quite different (roughly 5.3 eV vs 4.7 eV respectively) ion backspillover from the solid electrolyte onto the gas exposed electrode surfaces will take place in such a way as to equalize the work functions on the two surfaces. This was already shown in Figs. 5.14 and 5.15. 

A Specular X-ray reflection While the specular X-ray reflection (SXR) approach is again a means of probing solid coatings at the atomic level, it does have the advantage that the model obtained at the surface can include information on the atomic-scale roughness of the buried , i.c. usually inaccessible, electrode/surface layer interface. 

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