Cathodic reduction, continued kinetics

If a process gas is supplied to the cathode with an H,S level of 2000 ppm, a CO, level of 1%, and an H,0 level of 12% (a saturated natural gas composition), it is assumed that 99% of the H,S is removed by reaction (5), and if the process and sweep gas flowrates are equal, then there exist an activity ratio of a oJa of 665 in the anolyte before significant (e.g. 1%) of the carbonate is oxidized. This assiunes equivalent electrode kinetics for the cathodic and anodic reactions. When compared to the activity ratio of Ocos a of 26.9, this shows the thermodynamic preference for the oxidation of to elemental sulfur by equation (8) when there is an absence of reductant at the anode. This mode of operation is preferable for commercial application, with direct production of elemental sulfur vapor, eliminating this need for a Claus reactor for sulfur production. The net effect, under these conditions, is continuous removal of H,S from the process gas accompanied by enrichment of the process gas with H, and direct generation of elemental sulfrur. ITie only reagent required is electric power at a potentially attractive rate, which will be shown. 

For such systems, initial CV reduction of the Cr(III) complex shows a broad cathodic wave whose position shifts from about -1.4 to -1.6 V as the sweep rate is increased. This is typical of an irreversible reduction with sluggish electrode kinetics and is assigned to the process. If the voltage sweep is reversed after the irreversible reduction and the CV continued, then anodic (-1.18 V) and cathodic (-1.25 V) peaks appear, typical of a reversible process. These were assigned to Jk,, 2, the oxidation/reduction of the ring-opened species. Values of and were determined by comparison of voltamograms at various sweep rates to the digital... 

The oxygen reduction reaction (ORR) has been, and continues to be, the focus of widespread R D efforts, in part due to the importance on this reaction in fuel cells. Fuel cells typically operate with the ORR as the cathode half reaction, but slow ORR kinetics and the use of expensive ORR catalysts have hindered efforts to... 

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