MIT10_626S11_lec02

MIT10_626S11_lec02 - I. Equivalent Circuit Models Lecture...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
I. Equivalent Circuit Models Lecture 2: Electrochemical Energy Conversion MIT Student Galvanic cells convert different forms of energy (chemical fuel, sunlight, mechanical pressure, etc.) into electrical energy and heat. In this lecture, we are interested in some examples of galvanic cells. Galvanic Cell Energy in Electrical Energy e - e - Anode Cathode Electrical Current Resistor Chemical fuel Sunlight Mechanical pressure …… 1. Voltage Sources 1.1 Polymer Electrolyte Membrane (PEM) Fuel Cell PEM fuel cells employ a polymer membrane to move ions from anode to cathode. Figure 2 shows the structure of Hydrogen-oxygen PEM fuel cell. Hydrogen molecules are oxidized to protons at the anode. Electrons travel through an external load resistance. Protons diffuse through the PEM under an electrochemical gradient to the cathode. Oxygen molecules adsorb at the cathode, are reduced and react with the protons to produce water. The product water is absorbed into the PEM, or evaporates into the gas streams at the anode and cathode. The detailed reactions are 1 Figure 1: Energy Conversion of Galvanic Cell
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
H 2 O 2 gas gas H + PEM Porous anode Porous cathode Pt catalyst e - H 2 O Resistor Anode (oxidation reaction, produces electrons): Cathode (reduction reaction, consumes electrons): Net reaction: Lecture 2: Electrochemical energy conversion 10.626 (2011) Bazant The equivalent circuit of PEM fuel cell is shown in Figure 3. The resistors and capacitors are related to different effects: R a D : gas diffusion at anode R c D : gas diffusion at cathode R a i : interfacial charge transfer at anode R c i : interfacial charge transfer at cathode R M : ion transfer in membrane C a i : interfacial charge storage at anode C c i : interfacial charge storage at cathode 2 Figure 2: Hydrogen-oxygen PEM fuel cell
Background image of page 2
V a 0 R i a R M R i c V c 0 R D c R D a C i a C i c - e R ext Lecture 2: Electrochemical energy conversion 10.626 (2011) Bazant 1.2 Solid Oxide Fuel Cell (SOFC) Solid oxide fuel cells are a class of fuel cell characterized by the use of a solid oxide material as the electrolyte. In contrast to PEM fuel cells, which conduct positive hydrogen ions (protons) through a polymer electrolyte from the anode to the cathode, the SOFCs use a solid oxide electrolyte to conduct anions, e.g. negative oxygen ions, from the cathode to the anode, as shown in Figure 2. The electrochemical oxidation of the oxygen ions thus occurs on the anode side. The detailed reactions are Anode (oxidation reaction, produces electrons): Cathode (reduction reaction, consumes electrons): Net reaction: 3 Figure 3: Equivalent circuit of PEM fuel cell
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Lecture 2: Electrochemical energy conversion 10.626 (2011) Bazant H 2 O 2 gas gas O 2- Solid Oxide Electrolyte Porous anode Porous cathode e - H 2 O Resistor
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/27/2011 for the course CHEMICAL E 20.410j taught by Professor Rogerd.kamm during the Spring '03 term at MIT.

Page1 / 10

MIT10_626S11_lec02 - I. Equivalent Circuit Models Lecture...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online