Instrumentation electrochemical equipment

Electrochemical Equipment. Electrochemical experiments were performed using either a PAR Model 175 universal programmer and a PAR Model 363 potentiostat/galvanostat, or a Pine Instruments RDE-4 bipotentiostat, coupled with a Kipp and Zonen BD 91 X-y-y recorder. The current-time response for the chronoamperometry experiments was recorded with a Nicolet 4094 digital oscilloscope. All potentials were measured vs. a Ag/10"2 M Ag+ reference electrode. 

There are several types of automated KF titrators available from leading companies that supply electrochemical equipment (Metrohm, for example). It should be noted that the mother solutions of these instruments are highly sensitive to side reactions with components of the nonaqueous solution. Hence, the users have to consult the suppliers of the KF mother solutions to ensure that they are compatible with the composition of the studied solution. 

Bipotentiostat — An instrument that can control the potential of two independent -> working electrodes. A - reference electrode and an -> auxiliary electrode are also needed therefore the cell is of the four-electrode type. Bipotentiostats are most often employed in electrochemical work with rotating ring-disk electrodes and scanning electrochemical microscopes. They are also needed for monitoring the electrode-reaction products with probe electrodes that are independently polarized. All major producers of electrochemical equipment offer this type of potentiostat. The instruments that can control the potential of more than two working electrodes are called multipotentiostats. 

In practice, electrochemistry not only provides a means of elemental and molecular analysis, but also can be used to acquire information about equilibria, kinetics, and reaction mechanisms from research using polarography, amperometry, conductometric analysis, and potentiometry. The analytical calculation is usually based on the determination of current or voltage or on the resistance developed in a cell under conditions such that these are dependent on the concentration of the species under study. Electrochemical measurements are easy to automate because they are electrical signals. The equipment is often far less expensive than spectroscopy instrumentation. Electrochemical techniques are also commonly used as detectors for LC, as discussed in Chapter 13. 

In all experiments, precise control or measurement of potential, charge and/ or current is an essential requirement of the experiment. In addition, modern electrochemical investigation is often supplemented with in situ spectroscopic techniques as an independent probe to monitor changes that occur at the electrode surface this introduces further design criteria. Consequently an electrochemical experiment rapidly becomes complex, and it is the aim of this chapter to examine some of the limitations of electrochemical equipment and to outline the precautions that must necessarily be taken to obtain quantitative data and to avoid erroneous results or incorrect conclusions. Features of cell design will be discussed initially, followed by a section on instrumentation. 

In order for STM to work with electrochemical interfaces, the instrument is equipped with a bipotentiostat for independent potential control of both the tip and surface with respect to a chosen reference electrode in a four-electrode cell, so that both electrodes are under well-defined electrochemical conditions. Furthermore, since Faradaic current could also flow through the tip electrode, this would be superimposed on the tunneling current and interfere severely with the detection of tunneling current, and even destabilize the geometry of the tip apex. It is therefore essential to insulate the side wall of the metallic tip electrode to suppress the Faradaic current while leaving a small tip apex for tunneling [7,8]. 

The positioning system is comprised of micro- to nanoscale precision stepper motors and piezo elements with integrated encoders of a few nm resolution to facilitate precise positioning of the tip at x-, y-grid points at a veiy close distance above the sample surface. SECM instruments are equipped with a potentiostat if an electrochemical signal is to be applied or monitored at only the tip (WEI), or specifically, a bipotentiostat if a second electrochemical signal is to be applied or... 

Finally, the recording of many signals from the output of the analytic and electrochemical instrumentation requires a reliable multi-pen recorder or an equivalent recording system based on a data acquisition card and appropriate software. The recorded signals are normally in the range of a few mV to 10V. The use of reliable temperature controllers and thermocouples is also crucial for the success of the experiments. A lot of suppliers of such equipment can be easily found and will not be reported here. 

Electrochemical On-Line Corrosion Monitoring On-line corrosion monitoring is used to evaluate the status of equipment and piping in chemical process industries (CPI) plants. These monitoring methods are based on electrochemical techniques. To use on-line monitoring effectively, the engineer needs to understand the underlying electrochemical test methods to be employed. This section covers many of these test methods and their applications as well as a review of potential problems encountered with such test instruments and how to overcome or avoid these difficulties. 

While the first STM studies of electrode surfaces were performed with self-built instruments, scanning tunneling microscopes for electrochemical use are nowadays commercially available at a price that hardly justifies the effort of homemade equipment. Nevertheless, new instrumental designs are now and then discussed in the literature, which are still worthwhile to be considered for special applications. There is, however, additional equipment required for the operation of an electrochemical STM, for which homemade designs may be advantageous over commercially available ones and hence is briefly mentioned here in terms of tip preparation and isolation, the electrochemical cell, and vibration damping. 

The wet chemical or classical procedures, including many colorimetric and some electrochemical procedures, can be quite time consuming. They are generally very accurate, however they can be precise, and they do not require special or expensive equipment or facilities. However, these methods are less sensitive than some instrumental methods. 

Recovery of metals such as copper, the operation of batteries (cells) in portable electronic equipment, the reprocessing of fission products in the nuclear power industry and a very wide range of gas-phase processes catalysed by condensed phase materials are applied chemical processes, other than PTC, in which chemical reactions are coupled to mass transport within phases, or across phase boundaries. Their mechanistic investigation requires special techniques, instrumentation and skills covered here in Chapter 5, but not usually encountered in undergraduate chemistry degrees. Electrochemistry generally involves reactions at phase boundaries, so there are connections here between Chapter 5 (Reaction kinetics in multiphase systems) and Chapter 6 (Electrochemical methods of investigating reaction mechanisms). 

In 1999, a Working Group on Instrumentation in Electrochemical Analysis (WG 5) was created by the Technical Committee - Laboratory Equipment of the European Committee for Standardisation (CEN/TC 332). The standard relates to requirements for how to establish traceability between pH measurements performed by the user and the primary reference method using hydrogen electrodes. The revised IUPAC draft for pH is intended to serve as a basis for the new European standard on pH. It has been clearly stated that this standardisation work will not duplicate the work already completed by IUPAC or by the International Electrotechnical Commission (IEC). 

Instrumentation. All electrochemical experiments were carried out in a conventional one-compartment cell. Potentials were applied to the cell with a bipotentiostat (Pine Instruments Inc., USA) model RDE4. Current-time responses were recorded on a XYY recorder model BD 91 (Kipp Zonen, USA) equiped with a time base module. All potentials were measured and quoted against a saturated calomel electrode (SCE). 

Apparatus Cyclic voltammetry and amperometric current-time curves were obtained with a Pine Instrument Inc., Model RDE4 bipotentiostat and Kipp Zonen BD 91 XYY recorder equipped with a time base module. All measurements were performed in a conventional single-compartment cell with a saturated calomel electrode as the reference electrode and a Pt mesh as the auxiliary electrode at room temperature. Chronoamperometry was made with EG G Princeton Applied Research potentiostat/galvanostat Model 273 equipped with Model 270 Electrochemical Analysis Software. 

The electrochemical sensing system was set up in a cylindrical quartz cell equipped with a standard three-electrode configuration and controlled by an electrochemical workstation (CHI 660C, CH Instruments Co., Ltd. USA). Both bare Ti02/Ti and functional GOD-Ti02/Ti nanotube array were used as the working electrodes with an effective reaction area of 2.0 cm2. A standard Hg/Hg2Cl2 saturated calomel electrode (SCE) was used as a reference electrode and Pt foil was used as a counter electrode. Standard calibration curve (responsive current... 

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