Oxygen voltammetric wave

A problem that has been prominent for many years has been the catalysis of oxygen electro-reduction. The objective and problem with oxygen are illustrated by the cyclic voltammetric i-E waves shown in Fig. 9. Curve a is the computer simulated i-E wave for a reversible, four electron reduction of oxygen to water (E° = +1.23 V vs NHE). The i c value is 8 times the peak height that... 

The procedure involves adding APDC to a final concentration of 25 pmoVL, and a pH buffer (pH values between 7 and 8.5) to a final concentration of 0.01 mol/L, to seawater in the voltammetric cell. If the seawater had been acidified then its pH should be adjusted to a more neutral pH using ammonia prior to the reagent addition. Oxygen is removed by 7 min purging with water saturated nitrogen. A deposition potential of -1.3 V is used for a period of 3 min, followed by a 10 s equilibration time the scan is initiated from -0.8 V and stopped at -1.3 V. The reaction is electrochemically reversible which means that a wave modulation can be used like the differential-pulse (10 Hz) or the square-wave (50 Hz or faster) modulation. 

The reduction of oxygen in aqueous solutions is irreversible in nature in terms of both the chemical and electrochemical processes involved, and hence it is not reoxidised on the reverse pulse, such that the voltammetric wave as measured is not enhanced. Thus in a solution containing a reversible species of interest and oxygen (where both react electrochemicaUy at similar potentials), the use of SWV may allow analytically useftil voltammetric data to be obtained without degassing of the solution. As a caveat, it should be noted that although it is possible to measure an analytically useftil voltammetric response in the presence of oxygen, the chemistry occurring within the solution may be altered by its presence. 

The voltammetric response arises as the amount of C is increased which is attributed to the oxygenated species of the GO in this case [106]. Bear in mind that this response is unique to hexaammine-ruthenium(III) chloride and also occurs to a lesser extent for potassium hexachloroiridate(III) [106]. Crucially, the observed voltammetric reduction waves evident in Fig. 3.28 coupled with the voltammetry observed in Fig. 3.29 can be used as a measure to determine whether GO has been efficiently (electrochemically) reduced prior to its application in a plethora of areas [105, 106]. 

---