Limiting current observed under activation

The nanostructured Au and AuPt catalysts were found to exhibit electrocatalytic activity for ORR reaction. The cyclic voltammetric (CV) curves at Au/C catalyst reveal an oxidation-reduction wave of gold oxide at +200 mV in the alkaline (0.5 M KOH) electrolyte but little redox current in the acidic (0.5 M H2SO4) electrolyte. Under saturated with O2, the appearance of the cathodic wave is observed at -190 mV in the alkaline electrolyte and at +50 mV in the acidic electrolyte. This finding indicates that the Au catalyst is active toward O2 reduction in both electrolytes. From the Levich plots of the limiting current vs. rotating speed data, one can derive the electron transfer number (w). We obtained n = 3.1 for ORR in 0.5 M KOH electrolyte, and 2.9 for ORR in 0.5 M H2SO4 electrolyte. The intermittent n-value between 2 and 4 indicates that the electrocatalytic ORR at the Au/Ccatalyst likely involved mixed 2e and 4e reduction processes. 

These are fundamental considerations and are of interest not just to electrochemists and sonochemists, but care must be taken in correctly attributing an apparent shift in an experimentally observed potential under ultrasound. As already mentioned, system parameters and other factors may influence an observation beyond the effect under investigation. Thus there have been reports on the use of the titanium tip of the sonic horn itself, suitably electrically insulated, as the electrode material [50]. Dubbed the sonotrode , this is a clever idea to combine the two active components of a sonoelectrochemical system the authors noted the expected enhancements in limiting currents and an alteration in the morphology of copper electrodeposited from aqueous solution on to the titanium tip, which was the reaction under test. However, although titanium is widely used in sonochemistry because of its low-loss characteristics under vibration, it is not a common electrode material for electroanalysis because of its inferior electron transfer characteristics... 

The last set of overcharge tests on the 4P bank was with 4 A and a 12 V limit. This test also activated the CIDs without any catastrophic failures. Figure 17.14 gives a plot of the current, voltage, and temperature for this test. Although the current was constantly being shared as one would observe for an unbalanced cell configuration, the CIDs activated as expected with no catastrophic failures. The test was repeated under the same conditions and the same results were observed. 

Purified receptor together with ATPase was reconstituted in BLM by Thompson et al. (25) for electrochemical experiments as outlined above. Figure 7.9 shows the electrochemical response of a BLM to fractions of receptor protein, ATP and naphthalene-1-acetic acid in various time sequences under an applied dc voltage of 15 mV. Only when all three components are present (in any order) is a substantial increase in current observed. Adjustment of hydronium ion concentration in solution resulted in a correlation of current at various pH values with the known receptor biochemical activity at the same values. This behaviour indicates that previous suggestions that an ATPase pump acts to translocate protons are indeed correct. From the sensor point of view, it is interesting to note that the signals exhibited a limit of detection of about 10 M NAA and were quite selective for the hormone. 

---