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Physics 470Lecture

Hydrogen Fuel CellsMay 9, 2012

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The hydrogen fuel cell

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The PEM fuel cell

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Features of a fuel cell Sir William Grove invented the fuel cell in

1839 Hydrogen gas is fed to the negative terminal

(the anode) A catalyst helps the hydrogen to split,

sending its electrons through an external circuit and the protons through an electrolyte

22H 4H 4e

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Features of a fuel cell Oxygen combines with the electrons at

the positive terminal (the cathode) and protons to form water

The overall reaction combines hydrogen

and oxygen to produce electricity and water.

2 2O 4 4H 2H Oe

2 2 22H O 2H O

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The proton exchange membrane fuel cell Has a high power density and low operating

temperature The electrolyte is a specially treated polymer

(chemically related to Teflon) that conducts only positive ions

The membrane must be hydrated (7 water molecules for every proton conducted!)

The membrane is “poisoned” by carbon monoxide

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The proton exchange membrane fuel cell The anode-membrane-cathode

assemblies are stacked for higher voltage

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The PEM fuel cell

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PEM Fuel Cell Stack

10 kW Fuel Cell Power SupplyGENEPAC by PSA Puegot Citroën, France

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Other types of fuel cells Phosphoric Acid Molten Carbonate Solid Oxide Alkali See comparison chart from the

Department of Energy

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Compare Fuel Cell Types

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Fuel cell problems PEM cells: Hydration of the membrane

requires careful water control and/or pressurization (adds weight, complexity). New membranes such as PBI may require less water.

For all fuel cells, drawing large currents reduces performance

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Fuel cell losses

Ohm’s Law Applet

0V I R E

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Which of the following statements is FALSE?

A. Catalysts help fuel cells increase the gas transport rate to the electrodes.

B. Fuel cells operate on the chemical reaction that combines hydrogen and oxygen.

C. Fuel cells are like a battery with a continuous supply of chemical reactants.

D. The only outputs of a fuel cell are water and electrical energy.

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Which of the following statements is FALSE?

A. Catalysts help fuel cells increase the gas transport rate to the electrodes.

B. Fuel cells operate on the chemical reaction that combines hydrogen and oxygen.

C. Fuel cells are like a battery with a continuous supply of chemical reactants.

D. The only outputs of a fuel cell are water and electrical energy.

16Suppose a fuel cell has an internal resis-tance of 0.025 . What is the output voltage when the ideal voltage is 12.0 V and the current is 30 A ?

A. 0.30 VB. 0.75 VC. 9.00 VD. 11.25 V

17Suppose a fuel cell has an internal resis-tance of 0.025 . What is the output voltage when the ideal voltage is 12.0 V and the current is 30 A ?

A. 0.30 VB. 0.75 VC. 9.00 VD. 11.25 V

30A 0.025

12V 0.75V

11.25 V

12VV

V

IR

18Suppose a fuel cell has an internal resis-tance of 0.025 . What fraction of the power is lost when the ideal voltage is 12.0 V and the current is 30 A ?

A. 2.5%B. 3.6%C. 6.25%D. 12.0%

19Suppose a fuel cell has an internal resis-tance of 0.025 . What fraction of the power is lost when the ideal voltage is 12.0 V and the current is 30 A ?

A. 2.5%B. 3.6%C. 6.25%D. 12.0%

2loss

2

loss

30A 0.025

22.5 W22.5 W% loss

12V 30A

22.5 W 100 6.25%360 W

P I R

P

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Stationary Power Fuel Cells

Fuel Cell power plant, Santa Rita Jail, Dublin, CA

Biogas-powered fuel cell power plant, Sierra Nevada Brewing Co, Chico, CA

200 kW fuel cell, Central Park, NY police station

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Fuel Cell-Powered Zero Emission Vehicles

Ford Focus FC5 Fuel Cell Car

Hyundai FC Tucson

Honda FCX Clarity

Thor UTC Bus

Several other fuel cell cars in this 2008 article. More links at fueleconomy.gov.

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Fuel cell airplane

Boeing fuel cell aircraft first flight: April 3, 2008. It used a battery to assist the takeoff.

DLR Antares, the world’s first fuel-cell-only aircraft, takes off July 7, 2009 in Hamburg, Germany.