Question

(2) (24 pts) A fuel cell produces electricity via a combustion reaction. A DMFC is a proton-exchange fuel cell that uses methanol CH3OH) as the fuel, which reacts with molecular oxygen to produce carbon dioxide and water. (a) (4 pts) Write the balanced combustion reaction for this methanol fuel cell. (b) (4 pts) Write the balanced half-reactions occurring at the cathode and anode of this fuel cell (assume standard acidic conditions) (e) (4 pts) Evaluate AGº (kJ) and AE° (V) for the reaction in part (a) at 298 K. (d) (4 pts) Another possible product in the methanol fuel cell could be carbon monoxide. Write the balanced reaction between methanol and oxygen gas to give only carbon monoxide and water. (e) (4 pts) Write the balanced half-reactions occurring at the cathode and anode of this fuel cell (assume standard acidic conditions) (1) (4 pts) Evaluate AGⓇ (kJ) and AE (V) for the reaction in part (d) at 298 K.

Answer 1

DMFC - Direct methand fuel cell The fuel cell is based on combustion of methand i Combustion of methanol • Overall combustion of methanced should gjeld only CO2 & H2O as its products, Reaction in : - CH3OH + 302 - CO2 + 2H2O 2 a) · - Balanced combustion lieaction: CH₂OHut 3 02 CO₂ + 2H20 (2) At Cathode, the reduction meaction takes place where O₂ gets reduced, - 3 0₂ t 6 Htt bé 3 H2Ow 2 419) The bé aue mereived are ferom anode, where onidation of CH₃OH takes place. - CH₂OH + H2O 647 thet CO2 SHA CH2OH =*238.6 lIlmal 126.8 co = ~393.5 IcJ/mol 213.6 HOU)= -285.8 kJ/mol 69.9 O₂ = 0 kJ/mol 205.o 1

Stivation (E n; ohledna (neos x 26 con troba (3 n; Sej) se cements teine ) - ( nemout 614 nou + no2 x DHjor) IX(+238.6) + 3x0 (1X (-393.5+ 2x (-285-8) 3-393.5-57):6 +238-65-72615 kJ/molo, CH3 OH. Ass (m; ši ) pasice - (nj si Jucasus - ( 1 X 213.6 + 2X699) - ( 1 X 12618+ 3 x 205) Z - 353.4 - 434.3 = -80.9 J/mol K. =-0,08 kJ/malk AG° = AH-TAS = - 726.5-298 =-702.66 kJ Imol. AGO=-702.66 kJ/moli 762.66 x 10 =-702.66 X 10² J/mol Also, AG"=-ne na nog é transferred = 6 moles F = 96500 Clma é ; -702166x10°. - 6%96.500 X AE oc°. 1.213 V i SEO = 1.213 V

When only as products, obtained Carbon mononide & water are Onenall reaction: CH₃OHAnt 02 CO + 2H20 (1) e) At Cathoolea O2 at HHt the 2H20 (1) At anode , CH₂OH, o cott Ht thé

CH3OH co H2Old) AH - 238.6 -110.5 - 28.5.8 126.8 197-9 69.9 ДН ес (нер (бо хди со + родно ) - (hелдон анд ньон - thog o H oz) = 1X (-110.5) + 2x (~2858) - ( 1*~238.6) = -110-5 - 571-6 +238.6 -443.5 kJ/mol of CH₃OM AS = (Scox hot Shox no- (SCHGOH * Nengont Soxno2) (197-9x! + 69,9 x 2) - ( 126,8x1 + 205 = 337.7 - 126.8-205 = 5.9 Ilma. K . = 0.005 l I l mol K. .. AGO - AH-TAS° -443-5-298x(0.005) = -442.01 kJ lmal suo = - NFE -H42.61x102 4496500 x SEO iDE² -1.145 V na 4 é transferred F = 96500 Clnde (moles) i SEO=-1.145V