Study of Electrode Reactions and Interfacial Properties

It is well known that the maximum efficiency of electrochemical devices depends upon electrochemical thermodynamics, whereas real efficiency depends upon the electrode kinetics. To understand and control electrode reactions and the related parameters at an electrode and solution interface, a systematic study of the kinetics of electrode reactions is required. When ILs are used as solvents and electrolytes, many oftheelectrochemical processes will be differentandsomenewelectrochemical processes may also occur. For example, the properties of the electrode/electrolyte interface often dictate the sensitivity, specificity, stability, and response time, and thus the success or failure of the electrochemical detection technologies. The IL/electrode interface properties will determine many analytical parameters for sensor applications. Thus, the fundamentals of electrochemical processes in ILs need to be studied in order to have sensor developments as well as many other applications such as electrocatalysis, energy storage, and so on. Based on these insights, this chapter has been arranged into three parts (1) Fundamentals of electrode/electrolyte interfacial processes in ILs (2) Experimental techniques for the characterization of dynamic processes at the interface of electrodes and IL electrolytes and (3) Sensors based on these unique electrode/IL interface properties. And in the end, we wiU summarize the future directions in fundamental and applied study of IL-electrode interface properties for sensor applications. 

Empirical kinetics are useful if they allow us to develop chemical models of interfacial reactions from which we can design experimental conditions of synthesis to obtain thick films of conducting polymers having properties tailored for specific applications. Even when those properties are electrochemical, the coated electrode has to be extracted from the solution of synthesis, rinsed, and then immersed in a new solution in which the electrochemical properties are studied. So only the polymer attached to the electrode after it is rinsed is useful for applications. Only this polymer has to be considered as the final product of the electrochemical reaction of synthesis from the point of view of polymeric applications. 

In contrast to metal electrodes, for a semiconductor-electrolyte interface most of the potential drop is located in the semiconductor making it difficult to study interfacial processes using potential perturbation techniques [11,20,55,58,60-65,75-78]. H. Gerischer [76] proposed a model in which electrons and holes are considered as individual interfacial reactants. Distinct and preferential electron transfer reactions involve either the conduction band or valence band as dependent on the nature of the redox reactants of the electrolyte, with specific properties dependent upon the energy state location. 

EIS is an efficient electrochemical technique for studying a variety of chemical, electrochemical, and surface reactions. This technique is used due to the ability of the method to give information on both the bulk and the interfacial properties of polymer-coated electrodes. EIS is the technique which is measuring impedance (complex... 

Research in low temperature fuel cell reactions has mainly focused on the study of platinum, and/or platinum based materials. " These studies have also been aimed at understanding the fundamentals of the electrode/electrolyte interfacial behavior, in order to optimize the catalytic properties of such materials.The reason why most of these studies have been devoted to platinum is evident this material is the best catalyst, especially for processes occurring at the anode and cathode of low temperature fuel cells... 

In conclusion, the study of the overall process of electrochemical formation of polypyrrole must include not only the simple oxidation of monomer and the coupling of the charged species to produce the polymer chains, but also the nature, kinetics and effects on polymer structure and properties of all the parallel electrochemical and chemical processes which accompany it. Models of interfacial reactions, including the different processes taking place at the electrode/ electrolyte interface, must be developed showing the possibilities for the use of electrochemical methods of synthesis to obtain specific polymer films for each technological application. 

Impedance spectroscopy has been extensively used to follow changes of the interfacial properties of electrodes upon immobilization of enzymes and to characterize biocatalytic processes at enzyme-modified electrodes. Faradaic impedance spectroscopy can be used to study the kinetics of the electron transfer originating from bioelectrocatalytic reactions. It should be noted, that for characterizing redox-active biomolecules by impedance spectroscopy no additional redox probe is added to the electrolyte solution, and the measured electron-transfer process corresponds to the entire bioelectrocatalytic reaction provided by the biocatalyst. Under the condition that the enzyme is not saturated by the substrate, the electron-transfer resistance of the electrode is also controlled by the substrate concentration. Thus, the substrate concentration can be analyzed by the impedance spectroscopy following values [9]. 

The interfacial properties of IL/electrode interfaces are different from other media (i.e., aqueous or traditional nonaqueous media) because of the unique properties of ILs, especially the electrochanical properties. To understand the electrode/electrolyte interface chanistry for sensor research, the mechanisms of the electrochemical reactions, and the essential performance-limiting factors, both in the bulk and at the surface of the electrode materials need to be investigated, preferably in situ. In situ analysis is much desired due to the fact that ex situ measurements are usually not able to follow the fast kinetics at electrode interfaces. The past decades have been characterized by a spectacular development of in sim techniques for studying interfacial processes at metal electrodes. Radioactive tracer [31, 32], pulse potentiody-namic [33, 34], and galvanostatic methods [35] have been applied quantitatively to study the adsorption of organic compounds at solid metals. In the study of complex... 

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