(Ebook) - How To Build A Fuel Cell.pdf - ogniwa paliwowe - j_czaja1

Homebrew

Making

Although the fuel cell described produces a relatively

low voltage, several fuel cells of this kind can be wired

in series to produce higher voltages and do useful

work.

The PEM Material

The PEM (proton exchange membrane) material is a

perfluorosulfonic acid polymer film. Several

manufacturers make PEMs in one form or another. We

used one made by du Pont called Nafion 117. Nafion

117 is a transparent polymer film about 175 microns

(0.007 inches) thick. Dow Chemical Co., Asahi

Chemical Co., and Chloride Engineers Ltd. make

something similar. A patent describing how one PEM

manufacturer’s film is processed is listed in the

references section at the end of this article.

The basic structural unit formula for Nafion 117 is

shown below:

CF 2 = CFOCF 2 CFOCF 2 CF 2 SO 3 H

Electricity

Homebrew

with Hydrogen

Walt Pyle, Alan Spivak, Reynaldo

Cortez, and Jim Healy

recharging! This article

describes a process for building

a fuel cell using tools and techniques

any skilled hobbyist with a well-

equipped shop can duplicate. The fuel

cell that we built can produce direct

current electricity from stored hydrogen

and oxygen. We obtained the hydrogen

for this fuel cell commercially but plan

to produce hydrogen and oxygen from

a renewable energy system based on

solar photovoltaics and water

electrolyzers.

CF 3

Nafion 117 contains fluorine, carbon, oxygen, sulfur,

and hydrogen arranged in repeating polymer

molecules. The hydrogen atom on the SO 3 part of the

molecule can detach from one SO 3 site. The free H+

proton can hop from SO 3 site to SO 3 site through the

material, to emerge on the other side of the membrane.

This is the reason it is called a proton exchange

membrane. It can be thought of as solid sulfuric acid,

an electrolyte.

The PEM is relatively expensive at this point in time.

We paid about $100 for a 30.5 centimeter by 30.5

centimeter (12 inch by 12 inch) piece of Nafion 117

from a chemical supply house. Some manufacturers

want your first born child in exchange for a sample.

However, du Pont really is in the PEM business, and

they will sell it to you with no strings attached from their

pilot plant production. The price comes down to about

$65 for the same size piece when you buy four times

as much PEM direct from du Pont. The piece we

bought was large enough to make about six of our

round fuel cells ($10–$16/cell).

Punching the PEM Disk from a Sheet of Nafion 117

We set the sheet of Nafion 117 on a piece of clean

acrylic plastic using clean cotton gloves to avoid

contaminating the sheet with fingerprints. Then we

punched out some round PEM disks using a 4.76

centimeter (1 7 ⁄ 8 inch) arch punch and a mechanics

hammer filled with lead powder. After one or two tries,

we found that several strikes with the hammer at

different angles was best for cutting the disk free from

the sheet. Striking the punch too hard shattered the

acrylic sheet.

Cookbook Approach to Building a Fuel Cell

In this article we reveal the process we used to make a

proton exchange membrane (PEM) fuel cell.

First, we describe what the PEM material is, and where

to get it. Then we cover the steps necessary for

preparing the membrane to use it in a fuel cell.

Next, we describe the catalyst and binders used on

both sides of the PEM and the method of “hot-

pressing” them all together to form the single fuel cell

catalyst-PEM-catalyst “sandwich”.

Finally, the holder for the catalyzed PEM fuel cell with

its gas supply piping, insulators, and wiring studs is

shown.

Some PEM fuel cell performance data were obtained

using an electrical resistor to provide a variable load.

Two digital multimeters and a shunt resistor were used

to measure the voltage and current, so we could

calculate the power produced.

Home Power #35 • June / July 1993

A gas fed battery that never needs

Homebrew

Above: Solutions in beakers on top of stove.

Photo by Reynaldo Cortez

Above: Punching PEM from sheet with arch punch.

Photo by Reynaldo Cortez

Beaker 4 = 100 milliliters distilled water [rinse

sulfuric acid from surface and hydrate PEM].

Beaker 5 = 100 milliliters distilled water [repeat

rinse].

Beaker 6 = 100 milliliters distilled water [repeat

rinse].

While the PEM disk is in a beaker, there may be a

tendency for the film to curl and lift on the steam

bubbles, rising to the surface. It should be kept

submerged so the top side doesn’t get exposed to air.

Use a clean inert polyethylene plastic or glass probe to

keep it down in the dipping solution.

We used a Taylor candy thermometer for controlling

the beaker bath temperature, and adjusted the gas

stove burner controls as needed. From time to time,

more water had to be added to the bath surrounding

the beakers, due to evaporation.

After the PEM disk was dipped in each of the six hot

solution beakers for an hour, it was then wiped with a

piece of lint-free lens cleaning tissue, and air-dried in a

clean place.

The Catalyst Layer Material

The catalyst layer is the most expensive part of this

fuel cell. It is made from a mixture of platinum, carbon

powder, and PEM powder, bonded to a conductive

carbon fiber cloth. We obtained ours from E-Tek Inc.

The cost for an order of their ELAT catalyst cloth sheet

includes a setup charge. So get together with others

for a larger order if you want to keep costs down. We

paid $360 for a piece of ELAT 15.2 centimeters by

15.2 centimeters [6 inches by 6 inches] including the

$150 setup charge. This piece provides enough for

about twelve disks. Each fuel cell requires two disks of

ELAT and one larger disk of PEM to make the

sandwich, so you can make six cells from this size

Handle the PEM with tweezers or forceps to prevent

contamination. We used a pair of stainless steel

tweezers which were ground flat and polished on the

grasping faces to eliminate burrs and prevent

puncturing or denting the soft PEM. Grasp the PEM

disks only on the outer peripheral edge, never on the

inner active area.

Preparing the PEM for Catalyst Application

We prepared the film for catalyst application by dipping

it in six different heated solutions in glass beakers. The

solutions were all held at 80°C (176°F) by immersing

the beakers in a heated pan of water on top of two gas

stove burners as shown above right.

Each beaker held the PEM film for one hour in

sequence. Use safety glasses and gloves while

working with the solutions. The sequence of beakers

used to dip the PEM was set up as follows:

Beaker 1 = 100 milliliters of distilled water [hydrate

the membrane and dissolve surface contaminants].

Beaker 2 = 100 milliliters of 3% hydrogen peroxide

solution (USP) [remove organic contaminants from

PEM surface].

Beaker 3 = 100 milliliters of sulfuric acid (new

battery electrolyte) [remove metal ion contaminants

from PEM surface, and sulfonate the PEM surface].

Home Power #35 • June / July 1993

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piece of ELAT ($60/cell). The cost may have come

down by now due to increased production at E-Tek.

In the future it may be possible to reduce the cost by

putting the catalyst coating directly on the PEM with a

platinum-carbon ink, as practiced by Los Alamos

National Laboratory.

Preparing the ELAT Catalyst/Binder Layers

Two catalyst layer disks were punched from an E-Tek

ELAT sheet. The sheet was placed on clean acrylic

plastic and the disks were punched with a 3.8

centimeter (1.5 inch) arch punch and the mechanics

hammer.

Next, we coated the heating plates with graphite from a

number two pencil and smoothed it out with a Q-tip to

make a release and contamination shield layer. The

three layers (catalyst-PEM-catalyst) of the sandwich

were then set on top of the lower heating plate. After

carefully aligning the layers, so that the smaller catalyst

disks were centered above and below the larger PEM

disk, the upper heating plate was placed on top of the

sandwich. At this time the heaters were off and the

plates were at room temperature.

Above: Cutting ELAT catalyst disks.

Photo by Reynaldo Cortez

Be careful to keep track of which side is the active side

of the catalyst impregnated carbon cloth. The active

side has more of the carbon-platinum binder powder

and is smoother.

Hot-Pressing the Sandwich Together

A hot press was made using a hydraulic 20 ton shop

press, and two homemade aluminum heating plates.

Each heating plate was drilled to accept an electric

cartridge heater and a thermocouple. A temperature

controller was connected to the heater and

thermocouple on each heating plate.

The bottle jack on the hydraulic press was drilled and

tapped to accept a 1 ⁄ 4 inch NPT pipe to connect to a

pressure gauge.

Procedure for Hot Pressing

First, two ELAT catalyst disks were coated with liquid

Nafion 117. The coating only went on the active side

that was to be bonded to the PEM. We used a

cosmetic brush to put on a single coat (thick enough to

give a wet appearance) then let it air dry at room

temperature in a clean place for one hour. The liquid

Nafion 117 has a strong alcohol odor, so do this

coating process in a well-ventilated area.

Above: Hot press and heating plates.

Photo by Reynaldo Cortez

Next, the two temperature controllers were activated

and the sandwich was taken up to 90°C (194°F) for

one hour to evaporate the solvents from the liquid

Nafion 117 catalyst coating. The temperature was then

raised to 130°C (266°F) over the next 30 minutes. This

is the PEM glass transition temperature.

Once the heating plates and the sandwich reached

130°C, pressure was applied using the hydraulic jack,

up to 2.16 MPa (300 psig). Shortly thereafter, the

pressure fell off as the PEM was squeezed by the

heated plates and the sandwich became thinner.

After two minutes at temperature and pressure, the

temperature controllers were turned off and the plates

and sandwich cooled to room temperature.

Home Power #35 • June / July 1993

Homebrew

Fuel Cell Membrane Test Fixture

Diagram by Alan Spivak

The heater plates were opened, and the finished fuel

cell sandwich was removed using the special tweezers.

We noted that the PEM disk was no longer round, but

instead somewhat elliptical. This may be due to

alignment of the film molecules in one preferential

direction. The fuel cell sandwich did not stick to the

aluminum heater plates, so the graphite release

coating appeared to be effective.

Fuel Cell Test Fixture

Our fuel cell test fixture was made from a commercially

available membrane filter holder. We spot-welded

electrode studs to the two halves of the fixture case, one

for the hydrogen side and one for the oxygen (air) side.

A groove for an “O” ring was machined into each half

of the case, to provide a seal to prevent the gases from

leaking around the edges of the gas distribution plates.

Kapton tape was applied to the inside diameter of one

case to insulate it from the other. Kapton tape was also

applied to the outer diameter of the mating case to

insulate the retaining ring and prevent the two cases

from shorting together. An ohm-meter was used to

assure that the two cases were well-insulated from one

another.

The PEM sandwich was trimmed with a pair of scissors

until it was round again, and placed between the filter

Home Power #35 • June / July 1993

Homebrew

Above: Fuel cell disassembled, showing a gas

distribution plate on the left. Photo by Reynaldo Cortez

Above: Fuel cell assembled.

Photo by Reynaldo Cortez

holder’s two stainless steel gas distribution plates to

make a five layered sandwich. The five-layered

sandwich was then dropped into the Kapton lined case

and the other case (with the Kapton on the outside)

was applied on top and attached by the threaded

retainer ring.

Fuel Cell Load Test System

An electrical testing load system was prepared as

shown below using two variable resistance

potentiometers rated at 0 to 1.0 ohm at 25 watts, a

current measuring shunt, and two digital multimeters.

Above: Electrical test system. The four fixed resistors

were not used. Photo by Reynaldo Cortez

Hydrogen Humidification Bubbler

A hydrogen humidification bubbler was made to

prevent the fuel cell PEM from dehydrating under load.

Moisture management in the PEM is an engineering

challenge, due to ohmic heating when high currents

flow, and osmotic drag of moisture towards the oxygen

side of the sandwich. The osmotic drag is caused by

the migration of protons through the PEM.

Above: H 2 humidification bubbler.

Photo by Walt Pyle

Home Power #35 • June / July 1993

(Ebook) - How To Build A Fuel Cell.pdf

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