Question

A direct methanol fuel cell generates 1000 A and 0.3 V at STP. Methanol and air are supplied to the fuel cell at 0.003 mol/s and 0.03 mol/s, respectively. Calculate(a) the output mass flux (mol/s) of methanol, air, water, and carbon dioxide, (b) the stoichiometric factors for methanol and air, (c) the heat generation rate (J/s)for this fuel cell assuming delta h of reaction is -719.19 kJ/mol for methanol at STP.

Answer 1

Stoichiometric equation: At Anode: CH_3 0K + 60K rightarrow 5 k_2 0 + 6 e^- + CO_2 At Cathode: 3/2 0_2 + 3k_1 0 + 6e^- rightarrow 60k^- Overall Redox Reaction: CK_3 0k + 3/2 0_2 rightarrow 2H_2 0 + Co_2 (a) Now, let as calculate the output mass flux. CK_3 + 3/2 rightarrow 2x_2 0 + Co_2 t = 0 0.003 0.03 0 0 t = t 0 0.03 -3/2 times 0.003 2 times 0.003 0.003 Therefore V_Me OH, out = 0 V_0_2, out = 0.02 - 3/2 times 0.03 implies V_02, out = 0.0255 V_H_20, out = 2 times 0.003 implies V_H_2 0, out = 0.006 V_c_02, out = 0.003 (b) Stoichiometric factor lambda is given as lambda = V_fuel /i /nF = nF V_fuel /i Hence, n = 6 [We can see 6 electrons in anode and cathode equations] lambda_Me OH = 6 times 96485 times 0.003 /1000 = 1.7367 lambda_air = 6 times 96485 times 4.5 times 10^-3/1000 times 0.21