Potential step methods electrochemistry

In this chapter the synthetic aspects of the earlier mentioned [M(bipy)2 (PVPjnCl]" polymers (where M = Os,Ru) are discussed. The main part of the chapter is devoted to the effect of electrolyte and polymer loading on the electrochemistry observed at electrodes modified with these materials. Interaction between the polymer layer and the electrolyte is investigated using electrochemical techniques such as cyclic voltammetry, potential step methods, and the electrochemical quartz crystal microbalance. Attention is also paid to mediation reactions using such modified electrodes. Finally, the implications of these observations for analytical applications of these materials are discussed. 

T. R. Mueller and R. N. Adams (see R. N. Adams, Electrochemistry at Solid Electrodes, Marcel Dekker, New York, 1969, p. 128) suggested that by measurement of ip/v for a nemstian linear potential sweep voltammetric curve, and by carrying out a potential step experiment in the same solution at the same electrode to obtain the limiting value of it, the n value of an electrode reaction can be determined without the need to know A, C, or Dq. Demonstrate that this is the case. Why would this method be unsuitable for irreversible reactions ... 

Based on the theoretical electrochemistry method outlined above in combination with DFT calculations, the potential energy of the intermediates can be obtained at a given potential, (Fig. 3.5). Since aU steps involve exactly one proton and electron transfer, the height of the different steps scales directly with the potential. To calculate the potential energy landscape at the equilibrium potential, the levels are moved down hyn X 1.23 eV, where n is the number of the electrons at the given state (the horizontal axis in Fig. 3.5). 

Nanocarbons can also be deposited onto surfaces via electrochemistry, such as electrophoretic deposition described earlier. A method for one-step electrochemical layer-by-layer deposition of GO and PANI has been reported by Chen et al. [199]. A solution of GO and aniline was prepared and deposited onto a working electrode via cyclic voltammetry. GO was reduced on the surface when a potential of approx. -1 V (vs. SCE) was applied compared to the polymerization of aniline which occurred at approx. 0.7 V (vs. SCE). Repeated continuous scans between -1.4 to 9 V (vs. SCE) resulted in layer by layer deposition [199]. A slightly modified method has been reported by Li et al. who demonstrated a general method for electrochemical RGO hybridization by first reducing GO onto glassy carbon, copper, Ni foam, or graphene paper to form a porous RGO coating [223]. The porous RGO coated electrode could then be transferred to another electrolyte solution for electrochemical deposition, PANI hybridization was shown as an example [223]. 

Another view is that electrochemistry is an alternative to chemical redox methods. Indeed, in certain cases the products are similar. This is to be expected if the chemical reagent reacts like an electrode via discrete electron transfer steps - not atom transfers. Even here, however, it is not unusual to observe significant differences between chemical and electrochemical processes. A peculiar advantage of electrochemistry is control of the electrode potential. In particular one can adjust the potential to selectively attack the most easily reduced or oxidized moiety in a complex molecule. This technique can also avoid the over-reductions and oxidations produced by chemicals. 

The next three chapters are concerned with methods in which the electrode potential is forced to adhere to a known program. The potential may be held constant or may be varied with time in a predetermined manner as the current is measured as a function of time or potential. In this chapter, we will consider systems in which the mass transport of electroactive species occurs only by diffusion. Also, we will restrict our view to methods involving only step-functional changes in the working electrode potential. This family of techniques is the largest single group, and it contains some of the most powerful experimental approaches available to electrochemistry. 

The surface electrochemistry of Pt single-crystal electrodes has been exhaustively studied using cyclic voltammetry [5, 8-12, 61-67]. Phenomena of a step reconstruction and step coalescence have been observed [61]. For Pt(lll)-H20 interface, prepared by the flame annealing method, a double-layer charging has been observed only in a very narrow potential region (0.1 < E < 0.35 V (SCE) in 0.05 M H2SO4), which depends on the chemical... 

The AIMD method, based on the Carr and ParrineUo approach [127], has also been applied in the study of electrochemistry [128]. Reactive Force Field approaches are now being used to study the ionomer/water/catalyst interfaces during an electrochemical reaction [129]. Neurock et al. developed a detailed first-principles approach that employs a double-reference method to simulate the influence of the electrochemical potential on the chemistry at the metal/solution interface [130]. hi this method the aqueous solution metal interface and the interfacial potential drop are explicitly treated. However the choice of an appropriate water surface structure is critical for establishing the appropriate electrochemical behavior at the atomistic scale. This method has been applied to smdy some electrochemical steps involved in the ORR and methanol oxidation on Pt (e.g. [131, 132]). 

Potentiodynamic polarization (intrusive). This method is best known for its fundamental role in electrochemistry in the measurement of Evans diagrams. A three-electrode corrosion probe is used to polarize the electrode of interest. The current response is measured as the potential is shifted away from the free corrosion potential. The basic difference from the LPR technique is that the apphed potentials for polarization are normally stepped up to levels of several hundred millivolts. These polarization levels facihtate the determination of kinetic parameters, such as the general corrosion rate and the Tafel constants. The formation of passive films and the onset of pitting corrosion can also be identified at characteristic potentials, which can assist in assessing the overall corrosion risk. 

---