Instrumentation bipotentiostat

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. 

The scanning electrochemical microscope (SECM) consisted of a positioning system from Marzhauser (Wetzlar, Germany), a bipotentiostat CH701 (CH Instruments, Austin, TX, USA) and a homemade control software. 

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. 

Figure 1 shows a schematic diagram of the basic SECM instrument employing an amperometric microprobe. An UME tip is attached to a three-dimensional (3D) piezo positioner controlled by a computer, which is also used for data acquisition. A bipotentiostat (i.e., a four-electrode potentiostat) controls the potentials of the tip and/or the substrate versus the reference electrode and... 

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. 

The model 900 SECM (CH Instruments) is the first commercial instrument specifically designed for SECM. Although STM instruments equipped with electrochemical accessories can be adapted for some SECM experiments, they cannot replace a general purpose SECM instrument. This section will describe the features of the model 900. The model 900 includes the cell and probe positioner illustrated in Figure 5 as well as a computer, motor controller, and bipotentiostat (35). 

Instrumentation. In order to operate a STM under in situ conditions, i.e. in the presence of an electrolyte solution, some conditions have to be fulfilled. The design of the STM must allow investigation of a horizontal surface at the bottom of the microscope. The tip has to be coated as completely as possible in order to minimize the Faradaic current. Since the potential of the electrode surface under investigation has to be maintained at a fixed, controlled potential with respect to a reference electrode, a four-electrode arrangement requiring a corresponding bipotentiostat is necessary. The schematic drawing of the electrochemical cell as depicted in Fig. 7.3 shows the major components. 

Instrumentation. A suitable microelectrode [119] or nanoelectrode [127] is attached to a piezo-driven micropositioner. It is connected as the working electrode with a potentiostat. A counter electrode and a reference electrode are wired in a three-electrode arrangement. Investigations with conducting substrates require the use of a bipotentiostat. The surface to be investigated is immersed into the electrochemical cell together with the other electrodes. The position of the microelectrode and the flowing current are controlled and monitored by a computer equipped with... 

The relative simplicity and low cost of STM instrumentation has contributed significantly to the rapid increase in the number of in situ electrochemical studies. An excellent discussion of the general aspects of STM design and construction is available in a recent textbook [2, 3]. In the last decade, several reliable instruments have also become available from commercial vendors. The instruments incorporate bipotentiostatic operation, for independent control of the tip and substrate relative to some reference electrode, and, more recently, some degree of atmospheric control is usually implemented. Nevertheless,... 

SECM instruments suitable for imaging require a PC equipped with an interface board to synchronize acquisition of the electrochemical data with the movement of the tip. Building an SECM for kinetic experiments at fixed tip position or approach curve measurements is relatively easy, but fairly sophisticated software and some electronic work is necessary to construct a computer-controlled apparatus for imaging applications. Details on the construction of SECM instruments can be found elsewhere [6, 13-18, 53, 55]. An SECM is now available commercially from CH Instruments, Inc. (Austin, TX, USA). The instrument employs piezoelectric actuators, a three-axis stage, and a bipotentiostat controlled by an external PC under a 32-bit Windows environment. Various standard electrochemical techniques are incorporated along with SECM imaging, approach curves, and the modes described in Sect. 3.3.I.I. 

In situ conductimetry is a convenient tool for studying the influence of different conditions on the preparation of conductive polymers. Conductivity is perhaps the best single parameter that describes the quality of a CP. In addition, the dopingundoping processes can be studied by monitoring conductance as potential is being scanned. Unfortunately, no commercial instrument directly applicable for in situ conductimetry is yet available, although it is possible to construct one from a commercial bipotentiostat and appropriate microelectrodes. The double-band platinum electrode can be constructed relatively easily without any special tools [7] (Fig. 12).. 

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... 

The electrochemical measurements were carried out in a conventional 3-electrode electrochemical cell. A Model 400 bipotentiostat from EG G Princeton Applied Research was used for the amperometric measurements, and a KIPP ZONEN BDlOl strip chart recorder was used to record the data. The rotator used was from Pine Instruments. All steady-state currents were measured at 0.4 V vs SCE. 

What sort of instrumentation would be needed for electrochemical experiments A potentiometry experiment requires little more than a pH meter. A potentiostat or galvanostat can be used for the controlling potential or current in an experiment. In a coulometric procedure, a device to integrate the current (i.e., a coulometer) would also be needed. A hydrodynamic voltammetry [e.g., a rotating disk electrode (RDE)] experiment would require an electrode rotor (to spin the electrode at a precisely known rotation speed), and the rotating ring-disk or RRDE refinement (see below) would necessitate the use of a bipotentiostat so that the disk and ring potentials can be independently controlled. An ac impedance measurement involves the use of a sine-wave oscillator and... 

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