CHEM 3310 Fuel Cell

DG = - nFE DGo = - nFEo Change in Gibbs Free Energy, G G is the free energy that is available to do useful work such as electrochemical work. DG = - nFE DGo = - nFEo An electrochemical cell is able do work if its cell potential, E, is positive. DG < 0 where n is the number of moles of electrons that flow in the cell, F is Faraday’s constant, 96500 coulombs / mole of electrons, Eo is the standard voltage measured of the electrochemical cell. CHEM 3310

DGo = - nFEo Change in Gibbs Free Energy, G G is the free energy that is available to do useful work such as electrochemical work. An electrochemical cell is able do work if its cell potential, Eo, is positive. DGo < 0 DGo = - nFEo where n is the number of moles of electrons that flow in the cell, F is Faraday’s constant, 96500 coulombs / mole of electrons, Eo is the standard voltage measured of the electrochemical cell. CHEM 3310

Example: Hydrogen fuel cell Use solar energy to break apart water to generate H2 and O2 as fuel for the fuel cell. Solar panel Electrolyzer Hydrogen Fuel cell Load box CHEM 3310

Example: Hydrogen fuel cell Electrolyzer Hydrogen Fuel cell Solar panel Load box Eo=1.23 V Anode: 2H2 (g)  4H+ (g) + 4 e- Cathode: O2 (g) + 4 H+ (g) + 4 e-  2 H2O (l) 2 H2 (g) + O2 (g)  2 H2O (l) Eo = 1.23 V CHEM 3310

Theoretical decomposition voltage of water Part A: The Electrolyzer 2 H2O (l)  O2 (g) + 2 H2 (g) E° = - 1.23 V O2 (g) H2 (g) In practice, the external voltage applied to split water always exceeds 1.23 V. The difference between the theoretical decomposition voltage and the actual decomposition voltage is called overpotential or overvoltage. CHEM 3310

Part A: The Electrolyzer 2 H2O (l)  O2 (g) + 2 H2 (g) E° = - 1.23 V Adjust the power supply to obtain, roughly, the following current readings: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45 A CHEM 3310

Part A: The Electrolyzer 2 H2O (l)  O2 (g) + 2 H2 (g) E = - 1.23 V NOTE: Do NOT let the current Exceed 0.5 Amp! Will damage the electrolyzer Overpotential = V – 1.23 CHEM 3310

Measure the Volume of H2 (experimental) produced in Part B: The Faraday Efficiency of the Electrolyzer Measure the Volume of H2 (experimental) produced in approximately 180 s. CHEM 3310

Part B: The Faraday Efficiency, ŋ, of the Electrolyzer 2 moles of electrons per mole of H2O Cathode: 4H+ (g) + 4 e-  2H2 (g) Anode: 2 H2O (l)  O2 (g) + 4 H+ (g) + 4 e- 2 H2O (l)  O2 (g) + 2 H2 (g) E = - 1.23 V . One mole of electrons has a charge equal to 96500 coulombs. At 20oC, the molar volume of H2 (g) is 24000 mL. Determine ŋ for the each of the two currents. In commercial electrolyzers, the Faraday efficiency must be close to 1 (i.e. 100%). CHEM 3310

Part C - The Characteristic Curve of the Hydrogen Fuel Cell 2H2 (g)  4H+ (g) + 4 e- O2 (g) + 4 H+ (g) + 4 e-  2 H2O (l) NafionTM PEM Two platinum coated carbon electrodes bonded to a Proton Exchange Membrane (PEM) CHEM 3310

Part C - The Characteristic Curve of the Hydrogen Fuel Cell 2H2 (g)  4H+ (g) + 4 e- O2 (g) + 4 H+ (g) + 4 e-  2 H2O (l) CHEM 3310

Part C - The Characteristic Curve of the Hydrogen Fuel Cell Record the voltage and current of the cell when the cell is subjected to following loads: 200 , 100 , 50 , 10 , 5 , 3 , and 1 ; Lamp; Motor CHEM 3310

Part C - The Characteristic Curve of the Hydrogen Fuel Cell Record the voltage and current of the cell when the cell is subjected to following loads: 200 , 100 , 50 , 10 , 5 , 3 , and 1 ; Lamp; Motor CHEM 3310

Part C - The Characteristic Curve of the Hydrogen Fuel Cell Power = Voltage  Current CHEM 3310

Other fuel cell: Methanol fuel cell Anode: CH3OH(l) + H2O(l)  CO2(g) + 6 H+ (g) + 6 e- Cathode: O2(g) + 4 H+(g) + 4 e-  2 H2O(l) Overall cell reaction: CH3OH(l) + 1.5 O2(g)  CO2(g) + 2 H2O(l) E° = 1.21 V At the anode methanol is supplied. At the cathode, oxygen from air is fed in. CHEM 3310

What’s in the news? CHEM 3310

What’s in the news? CHEM 3310

What’s in the news? CHEM 3310