Hydrogen Fuel Cells

Hydrogen Fuel Cells

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Description: Hydrogen fuel cells (HFCs) are a type of electrochemical cell. HFCs generate electricity by reduction and oxidation reactions within the cell. They use three main components, a fuel, an oxidant and an electrolyte.

HFCs operate like batteries, although they require external fuel. HFCs are a thermodynamically open system. HFCs use hydrogen as a fuel, oxygen as an oxidant, a proton exchange membrane as an electrolyte, and emit only water as waste.

 
Author: David Lorse (Senior) | Visits: 514 | Page Views: 598
Domain:  Green Tech Category: Battery & Fuel Cell 
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Contents:
Hydrogen Fuel Cells

David Lorse
ESS 315

What is a hydrogen fuel cell?
•Hydrogen fuel cells (HFCs) are a type of
electrochemical cell.
•HFCs generate electricity by reduction
and oxidation reactions within the cell.
•They use three main components, a
fuel, an oxidant and an electrolyte.
•HFCs operate like batteries, although
they require external fuel.
•HFCs are a thermodynamically open
system.
•HFCs use hydrogen as a fuel, oxygen as
an oxidant, a proton exchange
membrane as an electrolyte, and emit
only water as waste.

How do they work?
•Fuel (H2) is first transported to
the anode of the cell

•Fuel undergoes the anode
reaction
•Anode reaction splits the fuel
into H+ (a proton) and e•Protons pass through the
electrolyte to the cathode

•Electrons can not pass through
the electrolyte, and must travel
through an external circuit which
creates a usable electric current
•Protons and electrons reach the
cathode, and undergo the
cathode reaction

Chemistry behind the technology
Oxidation

Reduction

At the anode of the cell, a
catalyst (platinum powder)
is used to separate the
proton from the electron in
the hydrogen fuel.
Anode half-reaction:
2H2  4H+ + 4eEo = 0.00V

At the cathode of the cell, a
second catalyst (nickel) is used to
recombine the protons,
electrons, and oxygen atoms to
form water.
Cathode half- reaction:
4H+ + O2 + 4e-  2H2O
Eo = 0.68V

In electrochemistry, the Eocell value (energy) of a fuel cell is equal to the Eo of
the cathode half-reaction minus the Eo of the anode half-reaction. For a
hydrogen fuel cell, the two half reactions are shown above. So to calculate the
energy of one fuel cell, we need to subtract the anode energy from the
cathode energy. For a HFC, the Eocell = 0.68V – 0.00V which equals 0.68V

Uses of hydrogen fuel cells
There are many different uses of fuel cells being utilized right now. Some of these
uses are…
•Power sources for vehicles such as cars, trucks, buses and even boats and submarines

•Power sources for spacecraft, remote weather stations and military technology

•Batteries for electronics such as laptops and smart phones

•Sources for uninterruptable power supplies.

Problems regarding hydrogen fuel cells
•Lack of hydrogen infrastructure
•Need for refueling stations
•Lack of consumer distribution system
•Cost of hydrogen fuel cells
•2009 Department of Energy estimated $61/kw
•Honda FCX Clarity costs about half a million dollars to make
•Carbon cost of producing hydrogen
•Problems with HFC cars

•Short range (~260 miles)
•Warm up time (~5 minutes)

References
•http://www.fueleconomy.gov/feg/fuelcell.shtml

•http://www.howstuffworks.com/fuel-efficiency/alternative-fuels/fuel-cell.htm
•http://www.energy.gov

•Chemical Principles, Sixth Edition, Zumdahl