In a carbon (graphite)/oxygen fuel cell the cathodic reaction is O2(g) + 4 e- = 2 O2- and the anodic one is CO2(g) + 4 e- = C(s) + 2 O2-. If one uses data from Chapter 10: Data Section, the standard electrode potential difference of the fuel cell at 1000 K and 1 bar is ?

Solution

Having the two half cell equations

O2(g) + 4 e- ———>2O2-

CO2(g) + 4 e- ——->C(s) + 2O2- (reverse one equation the add)

———————————————–

overall equation C + O2 ——————-> CO2

O2 (g) + 4e + 4 H+ <————–>H2O———————– E0/V =1.229

CO2 (g) + 4e + 4H+ <————>C(S) + 2H2O ————- E0/V = -0.203

C(S) + 2H2O<———————–>CO2 (g) + 4e + 4H+ —– E0/V = +0.203

Now we have

E0 cell = E0 cathode – E0 anode

= E0 reduction – E0 oxidation

= 1.229 – 0.203

= 1.026 V

Thus the standard electrode potential difference of the fuel cell is 1.026V

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