Proton exchange membrane fuel cells

Proton exchange membrane fuel cells

1. T.Y. B.TECH
SCHOOL OF MECHANICAL ENGINEERING
ADVANCED MATERIALS
PROTON EXCHANGE MEMBRANE FUEL CELLS

2. ABOUT FUEL CELL
●A fuel cell is an electrochemical cell that converts the chemical energy of a
fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity
through a pair of redox reactions.
●Fuel cells are different from most batteries in requiring a continuous source of
fuel and oxygen (usually from air) to sustain the chemical reaction, whereas in
a battery the chemical energy usually comes from metals and their ions or
oxides that are commonly already present in the battery, except in flow
batteries.
●Fuel cells can produce electricity continuously for as long as fuel and oxygen
are supplied.

3. INTRODUCTION
●The proton exchange membrane (PEM) fuel cell consists of a cathode, an
anode and an electrolyte membrane. Hydrogen is oxidized at the anode and
the oxygen is reduced at the cathode.
●Protons are transported from the anode to the cathode through the electrolyte
membrane and the electrons are carried over an external circuit load. On the
cathode, oxygen reacts with protons and electrons producing heat and
forming water as a by-product.
●The complete process of a PEMFC is shown in Figure. Depending on the
operating temperature, we can distinguish two different types of PEMFCs.
The first type, Low-Temperature Proton Exchange Membrane Fuel Cell,
operates in a range of 60–80 °C.

4. ...
●The second type operates in a range of 110–180 °C, therefore, it is called
High-Temperature Proton Exchange Membrane Fuel Cell.
●The standard electrolyte material used in Low-Temperature PEM fuel cells is
a fully fluorinated Teflon-based material produced by DuPont for space
applications in the 1960s, which is generally called Nafion.For
High-Temperature PEM fuel cells, it is possible to use Nafion or
Polybenzimidazole (PBI) doped in phosphoric acid.
●Platinum is classically used in the catalyst for Low-Temperature
PEMFCs,while Platinum–Ruthenium is used for High-Temperature PEMFCs
catalyst.The electrical efficiency for Low-Temperature PEM fuel cells is about
40–60%, while for High-Temperature PEM fuel cells it is about 50–60%.

5. WORKING
PEMFCs create electrochemical reactions
using positive hydrogen ions as carrier
ions; the direction of the flow of the ions is
from anode to cathode .
In PEMFCs, the fuel (hydrogen, H2) enters
at the anode. There, a chemical reaction
causes the hydrogen molecules to
separate into positive hydrogen ions (H+ or
protons) and electrons (e−). This reaction
releases heat. The positive hydrogen ions
pass through the electrolyte made of a
polymer membrane and travel to the
cathode.

6. ...
The electrons remain behind and thereby give the anode a negative charge,
creating a voltage difference between the anode and the cathode. Because
electrons travel from negative to positive, the electrons follow an external circuit
from the anode to the cathode. At the same time, oxygen (O2) enters the fuel cell
at the cathode and combines there with the electrons, which have traveled through
the external circuit, and the positive hydrogen ions, which have traveled through
the electrolyte, to produce water (H2O) at the cathode. The chemical reaction is
represented here:
2H2→4H++4e−
O2+4e−+4H+→2H2O

7. APPLICATIONS
PEMFCs are regarded as best suited for fuel cell vehicles (FCVs) and small
stationary applications. They have been the fuel cells most favored by researchers
and developers. In 1994, when Daimler (then Daimler-Benz) demonstrated its first
FCV powered by hydrogen-fueled PEMFCs, global automakers were thrilled by
the commercial potential of PEMFCs as a primary power of vehicles. Major global
automakers joined in the race to develop PEM-based FCVs. PEMFCs’ popularity
is partly based on their easy-to-handle characteristics, including moderate
operating temperatures, use of manageable polymer materials, and absence of
corrosive electrolytes. Over the decade, PEMFCs for FCVs and small stationary
applications received much attention and investments that likely surpassed all the
other types of fuel cells combined. More corporations and research institutions are
involved in R&D of PEMFCs than in any other fuel cell type.