General Fuel Cells

Question 1

What is the anode reaction in fuel cells?

Answer 1

1. The direct oxidation of hydrogen.
2. The oxidation of methanol.
3. The indirect oxidation (via reforming step).

Question 2

What is the overall reaction in a hydrogen / oxygen fuel cell?

Answer 2

H2 + 1/2 O2 => H2O
ΔG = -237 kJ / mol

Question 3

What is the formula for voltage in a fuel cell (ΔU)?

Answer 3

ΔU = - ΔG / nF

Question 4

What are fuel cells?

Answer 4

Galvanic cells, where the free energy of a chemical reaction is converted into electrical energy (via electrical current).

Question 5

What is the Gibbs Free Energy change relating to the cell voltage?

Answer 5

ΔG = - n x F x ΔUo
n: number of e-
F: Faraday constant
ΔUo: voltage of cell

Question 6

What are the three types of fuel cells, and explain.

Answer 6

1. Classification by fuel
   - direct conversion (H/air, Me/air) = take fuel and convert it
   - indirect conversion = change fuel before conversion
2. Classification by charge carrier in electrolyte
   - H+
   - O2-
3. Classification by electrolyte
   - solid oxides
   - carbonates
   - H3PO4
   - Proton exchange membrane (PEM)

Question 7

At what temperatures do PEM fuel cells operate?

Answer 7

80 dC

Question 8

What are PEM cells suitable for and give an example of the proton exchange membrane?

Answer 8

For applications like:
1. Domestic installations
2. Automotive applications

E.g. Nafion

Question 9

What are the two properties of Nafion and two requirements?

Answer 9

Properties:
1. Acts as electrolyte for charge transport.
2. Acts as separator between fuel and oxidant.

Requirements:
1. Must be kept wet during operation to enable ionic transport.
2. Amount of water must be controlled to avoid flooding of electrodes.

Question 10

Operation of Hydrogen PEM fuel cell

Answer 10

page 14

Question 11

What is the preparation for a standard catalyst in a PEM fuel cell?

Answer 11

Combination of Pt/C supported catalyst and Nafion dispersion.
1. magnetic stirring
2. Ball-milling
3. Ultrasound
4. Solvent

Question 12

What is the preparation of Pt/C?

Answer 12

1. HSA Carbon support combined with Pt(0) undergoing sono(Electro)chemical reduction
2. Addition of that product with Nafion dispersion
3. Solvent

Question 13

What are the fuel cell constituents?

Answer 13

1. Flow Field Plate (FFP)
2. Gas diffusion Layer (GDL)
3. Catalyst Layer (CL)

Question 14

Of what components do the fuel cells stacks consist of (in order)?

Answer 14

1. Endplate
2. Membrane Electrode Assembly
3. Bipolar Plate
4. Gass Flow channels
   (Repeat units)

Question 15

What is the voltage range of fuel cells?

Answer 15

0.6 - 0.8 V

Question 16

What do Bipolar Plates consist of?

Answer 16

1. Non-metal
   - non-porous graphite plates
2. Metal
   - metal plates (coated / non-coated)
3. Composites
   - metal based
   - carbon based