Maximum current density during

Fig. 4 shows the current density over the supported catalysts measured in 1 M methanol containing 0.5 M sulfuric acid. During forward sweep, the methanol electro-oxidation started to occur at 0.35 V for all catalysts, which is typical feature for monometallic Pt catalyst in methanol electro-oxidation [8]. The maximum current density was decreased in the order of Pt/CMK-1 > Pt/CMK-3 > Pt/Vulcan. It should be noted that the trend of maximum current density was identical to that of metal dispersion (Fig. 2 and Fig. 3). Therefore, it is concluded that the metal dispersion is a critical factor determining the catalytic performance in the methanol electro-oxidation.

As it is shown in figure 1, the maximum current density of the oxidation peak, observed at 0.69 V/RHE during the positive potential sweep, is very low (imax=0.13 mA cm ). The modification of the so called "hydrogen region"... 

This is particularly shown in figure 2. The under-potential deposition of lead adatoms occurs during the negative sweep of the potential. During the positive sweep, the first oxidation wave is shifted towards more negative potential and starts from 0.4 V/RHE. The maximum current densities are obtained in presence of 10 5 M Pb2+ at 0.75 V/RHE. 

Otherwise, during the negative potential sweep an oxidation process is observed with a maximum current density at 0.62 V/ HE. 

In most cases, additional metal ions are present, mainly those with a positive standard potential, which are deposited preferentially at the cathode and have a low overpotential for hydrogen evolution. On the other hand, zinc sponge is deposited even at relatively low current densities during electrolysis of ZnSO solutions in the presence of Cu, As or Sb ions these are nobler than zinc and are deposited at the maximum rate (i.e. at their limiting current) in a powdery form, and the zinc deposited on them "copies" their powdery structure. Powdered metals (Fe, Cu, Mi) are usually deposited at the cathode at current densities higher than the limiting one with simultaneous evolution of hydrogen. 

As mentioned above, the total treatment time required varies from a few weeks to a few months. If the maximum current density is respected, the removal efficiency and the required final result (in terms of the acceptable level of remaining chloride) determine the duration. As the steel is repassivated quickly during the treatment, the main consideration should be the durability, that is the period after the end of the treatment in which corrosion wiU most likely be absent... 

Figure 8.4 shows a typical pattern of the cell voltages as a function of the current density in an RFC. The plots are calculated and not measured, but the values are in accordance with measurements. U FC is the polarization curve during FC operation and U Ely is the polarization curve in electrolyzer mode. The square (U LHV) indicates the lower heating value voltage. A difference in the maximum current density achievable in FC or electrolyzer operation is typical of real systems and can be affected by the use of different electrolytes in RFCs or in URFCs by different diffusion behaviors of the operating media. 

With currently built and tested devices, the most widely used material for the electrolyte is YSZ. Therefore this material has been chosen to study bio-fuel fueled SOFC. Achievable levels of fuel utilization factor in cells used commercially reach 80%. Other cell parameters were fixed as follows electrolyte thickness of 15 pm, maximum current density (/max) of 2.6 A/cm, cell working temperature of 800°C, and cell pressure at atmospheric pressure. During the analysis of the oxidant, flow was kept at a constant excess air factor (2) of 3. 

As mustbc the case, the maximum and minimum sweeprates (2—20 mV s ) depend on assumptions (e.g., the minimum current density to be measured or the fraction of the time during a sweep in which the limiting current is reached). Depending on these variables, then, one can only conclude that the rate may vary according to the reaction characteristics and for likely current densities between about 1 and lOOmV s-1. 

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