Question

1. (a) Write the two electrochemical half reactions for ethanol (C2H5OH) direct electrochemical conversion in a fuel cell with an oxygen ion (O=) conducting electrolyte. (b) Is the direct oxidation of this fuel likely to occur in a solid oxide fuel cell, or are there other sets of chemical and electrochemical reactions that may dominate the conversion of this fuel? Write down the set of reactions that you expect. (c) What electrochemical half reactions could convert ethanol directly in a fuel cell that conducts hydrogen ions (H+)? (d) What half reactions would be required to operate an hydroxyl ion (OH–) conducting fuel cell on this same fuel?

Answer 1

(a) Two electrochemical half reactions for ethanol
`(C_(2)H_(5)OH)` is written below

`C_(2)H_(5) + 60` ⇒
`2CO_(2) + 3H_(2)O + 12e^(-) (anode)`

`3O_(2) + 12e^(-)` ⇒
`60^(=)`
`(Cathode)`

(b) The direct oxidation of the fuel will occur in a solid oxide fuel cell but we have to compete with other sets of chemical electrochemical reaction such as water-gas-shift reaction

`CO + H_(2)O` ⇆
`CO_(2) + H_(2)(WGSR)`

(c) The electrochemical half reaction that could convert ethanol directly into a fuel cell that conducts hydrogen ions is shown below

`C_(2)H_(5)OH + 3H_(2)O` ⇒
`2CO_(2) + 12H^(+) + 12e^(-) (anode)`

`3O_(2) + 12H^(+) + 12e^(-) - 6H_(2)O (Cathode)`

`C_(2) H_(5) OH + 3O_(2)` ⇒
`3H_(2)O + 2CO_(2)`

(d) The half reactions that would be required are shown below

`C_(2)H_(5) OH + 12OH^(-)` ⇒
`CO_(2) + 9H_(2)O + 12e^(-) (anode)`

`3O_(2) + 6H_(2)O + 12e^(-)` ⇒
`12OH^(-) (Cathode)`

`C_(2)H_(5)OH + 3O_(2)` ⇒
`3H_(2)O + 2CO_(2)`