Galvanostatic anode polarization

Figure 13. Typical polarization and relaxation transients of catalyst potential, (Fwr-// ), and ethylene combustion reaction rate, r, on Ir02/YSZ catalyst. Galvanostatic anodic polarization with / = 10 pA during 100 min. (a), (b), (c) and (d) designate the subsequent transient steps. Catalyst loading 77 pg IrCh. Feed composition at pm = 100 kPa PC2H4 = 12.5 Pa, - 1.25 kPa, balance helium. Flow rate 200 mL min" STP 7 =375°C. Reprinted from J. Electroanal. Chem., Q. F6ti, V. Stankovii, I. BolzoneUa, and Ch. Comninel-lis. Transient Behavior of Electrochemical Promotion of Gas-Phase Catalytic Reactions, (2002), in press, with permission from Elsevier Science,...

Figure 6.2. Galvanostatic anodic polarization curve for iron in 1A/ H2SO4.

Anodes for boilers can be tested by such methods. Good-quality magnesium anodes have a mass loss rate per unit area < 30 g m d", corresponding to a current yield of >18% under galvanostatic anode loading of 50 /xA cm" in 10 M NaCl at 60°C. In 10 M NaCl at 60°C, the potential should not be more positive than t/jj = -0.9 V for the same polarization conditions [27],... 

FIGURE 16.4 Galvanostatic vs. i curve for the anodic polarization of lead in 5 M H2SO4... 

The SEM micrograph of Figure 12.7(a) shows the surface morphology of a deposited aluminum layer obtained galvanostatically at a current density of—5 mAcrn-2 for 2h in the upper phase of the biphasic mixture [EMIM] TFSA/6M AICI3 at room temperature. Prior to Al electrodeposition, the electrode was anodically polarized at a potential of 1V (vs. Al) for 2 min. As seen, the deposited Al layer is dense and contains crystallites in the micrometer regime. 

The effect of ultrasound on the process of tellurium anodic dissolution in alkaline solutions was studied by the method of plotting polarization and galvanostatic curves [148]. Tests were made in NaOH solutions (concentrations of 0—20 g/L), subjected to the action of ultrasound at a frequency 17.5 kHz and using Te electrodeposited under ultrasound. The anodic polarization curves plotted without ultrasound and in its presence shifted with increased NaOH concentration towards negative values as a result of the increasing rate of Te anodic dissolution. The presence of ultrasound inhibited the process of Te anodic dissolution, probably due to the desorption of OFT anions from the anode surface. This sonoelectrodeposited Te thus showed greater corrosion resistance in alkaline solution than that deposited... 

Figure 6.39 Galvanostatic polarization of Ni in the transpassive potential region in sodium nitrate solution (a) anodic polarization curve in the transpassive potential region (b) the current efficiency for metal dissolution and (c) the apparent thickness of the film as measured by coulometry [36].

In electrochemical experiments for the determination of the pitting potential one either controls the potential (potentiodynamic method) or, more rarely, the current (galvanostatic method). The composition and temperature of the electrolyte are selected such as to represent the real environment to which the metal will be exposed, but without the oxidant present, whose effect is simulated by the anodic polarization. 

Instrumentation. The electrochemical instrumentation included (a) EG G Model 273 potentiostat-galvanostat, (b) 80486 computer, and (c) EG G M270 Electrochemical Software and programs developed in this Laboratory. All potentials quoted in the paper were measured with respect to the reversible hydrogen electrode, RHE upon anodic polarization the potentials were held constant to within 1 mV and were monitored on a Fluke 45 digital multimeter. 

The cell employed for the electrolytic production of NF3 was a cylindrical nickel cell of 1.5 dm in volume. A BDD with boron concentrations of 2500, 5000, 7500, 8000,10 000, and 12 500 ppm was used as the anode for the electrolytic production of NF3. For galvanostatic measurement of the anode polarization curve, a carbon anode (FE-5 Toyo Tanso Co., Ltd.) was also used in addition to the BDD anode. The BDD thin film (Permelec Electrode Ltd.) was prepared by the hot filament chemical vapor deposition (HFCVD) method on a carbon substrate using a gas mixture composed of CH4-H2-B(CH30)3-Ar. The anode was located at the center of the cell and the cell wall was utilized as the cathode. A nickel rod of 0.1 cm surface area pre-treated with anodic oxidation in a dehydrated NH4F-2HF melt was used as the reference electrode. The nickel rod functions as NiF Oy/Ni (0.073 V versus RHE) [4]. A PTFE skirt was provided between the anode and the cathode compartments, and the anode gas was separated from hydrogen evolved at the cathode to prevent an explosion. The cell bottom was covered with a PTFE sheet to avoid hydrogen evolution. 

Why is a galvanostatic anode pulse technique preferred over a linear polarization technique ... 

Two characteristic times, with kinetic significance, have been observed on the anodic galvanostatic transients the peak time, Tpeak. that is, the time elapsed from the moment of switching on the rectangular current pulse until the peak value is reached and the transition time, r s, that is, the time necessary for the relaxation processes between the nonsteady state and the steady state. Because the measurement of the transition time is uncertain, due to the asymptotic character of the decay curve, it is preferable to use the time constant, a term borrowed from electrodynamics, which refers to the time necessary to reach 37% of the steady-state value. The following main features characterize the anodic polarization transients ... 

Figure 5.37 reveals some additional interesting, although well expected, features and provides additional proof for the oxygen ion backspillover mechanism Upon anodic galvanostatic polarization, the Zr 3ds/2 electron... 

The opposite conclusion was reported by Lin et al., who used a three-electrode configuration to study the electrode polarization of the MCMB anode and LiCo02 cathode under galvanostatic conditions. They found that in all cases the polarization at the MCMB anode surface far outweighs that at the cathode to such an extent that the potential profile... 

A cell with a capacity of 1 L was made of mild steel. An amorphous carbon rod (diameter 25 mm length 15 cm) was used as anode, the inside wall of the cell as cathode and a platinum wire was used as reference electrode. The anode compartment of the cell was separated from the cathode compartment by a skirt of steel welded to the cell cover. The anode gas was passed through a tube filled with tablets of NaF to absorb anhyd HF gas and then led to a gas sampler. Fluorine was detected with K.I soln. After the starting material was added into the molten KIIF2/HF salt, the electrolyte was pre-electrolyzed at a low current density until NF2 was detected, and then current efficiency of each product and polarization curves by galvanostatic or potential sweep method were determined (Table 1). At optimum conditions the current efficiency of NF3 was 55%. 

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