Preparation
Procedure
Ion-Exchange
Polymer Metal Composites (IPMC) Membranes
Osaka National Research Institute, AIST, Japan
This homepage is part of the Worldwide Electroactive
Polymer (EAP) Webhub and it is maintained by the JPL's NDEAA
Technologies Group
Supply
·
Base polymer:
Nafion 117 (duPont)
·
Aqueous
solution of platinum ammine complex ([Pt(NH3)4]Cl2
or [Pt(NH3)6]Cl4) [Can be purchased from: Aldrich Chemical Co., Milwackee, WI phone 800-558-9160,
Catalog #275905]
·
Sodium
borohydride (NaBH4, reducing agent for primary reduction)
·
Hydrazine
hydrate (NH2NH2- ~1.5H2O, reducing agent for
secondary reduction)
·
Hydroxylamine
hydrochloride (NH2OH-HCl, reducing agent for secondary reduction)
·
Dilute ammonium
hydroxide solution (NH4OH 5% solution)
·
Dilute
hydrochloric acid (HCl aq, 2 N solution and 0.1 N solution)
·
Deionized water
1. Surface
Roughening of the Membrane
a.
Mild Sandblast: Sandblasting the surface of the membrane in
order to increase the surface area. Use fine glass beads (GP 105A, Toshiba Co.
Ltd.) that are blown onto the dry membrane by compressed air. The speed of sandblasting is ~1 sec/cm2
membrane area. It is also possible to use emery paper to sand the material.
b.
Ultrasonic Washing: Remove the glass beads and residues by
washing the membrane with water preferably using ultrasonic cleaner.
c.
Treatment with HCl: Boil the membrane in dilute hydrochloric
acid (HCl aq, 2 N solution) for 30 minutes to remove impurities and ions
in the membrane. Rinse it with deionized water.
d.
Treatment with Water: Boil the membrane in deionized water for 30
minutes to remove acid and to swell the membrane. The roughened membrane can
store in deionized water.
Prepare a platinum
complex ([Pt(NH3)4]Cl2 or [Pt(NH3)6]Cl4)
solution of 2 mg Pt/ml. Although the
adsorbing amount depends on charge of the complex, either complex gives good
electrodes. Immerse the membrane in the solution containing more than 3 mg of
Pt per cm2 membrane area. For instance, more than 45 ml of the Pt
solution is required for a membrane of 30 cm2. Excess amount of the Pt solution is
preferable. After immersing the membrane, add 1 ml of ammonium hydroxide
solution (5 %) to neutralize. Keep the membrane in the solution at room
temperature for more than 3 hours (one night usually).
Prepare a 5 wt%
aqueous solution of sodium borohydride. After rinsing the membrane with water,
place the membrane of 30 cm2 in stirring water of 180 ml in a water
bath at 40oC. Then, add 2 ml of the sodium borohydride solution (5
wt% NaBH4 aq) every 30 min for 7 times. The amount of the reagent
should be proportional to the area of the membrane. In the sequence of
addition, raise the temperature up to 60oC gradually. Then, add 20
ml of the reducing agent and stir for 1.5 hr at 60oC. Black layer of
fine Pt particles deposits only on the surface of the membrane. Rinse the
membrane with water and immerse it in dilute hydrochloric acid (0.1 N)
for an hour.
The amount of
platinum deposited by the 1st plating (reduction process) is only less than 0.9
mg/cm2, which depends on the ion exchange capacity, thickness of the
membrane and the structure of the Pt complex. Additional amount of platinum is plated by developing process on
the deposited Pt layer. When you add 2 mg/cm2 of Pt on the area of
60 cm2 (both sides of 30 cm2 of membrane), you need Pt
complex solution containing 120 mg of Pt. Prepare a 240 ml aqueous solution of
the complex ([Pt(NH3)4]Cl2 or [Pt(NH3)6]Cl4)
containing 120 mg of Pt and add 5 ml of the 5% ammonium hydroxide solution. Plating
amount is determined by the content of Pt in the solution. Prepare a 5% aqueous
solution of hydroxylamine hydrochloride (NH2OH-HCl) and a 20%
solution of hydrazine (NH2NH2). Place the membrane in the
stirring Pt solution at 40oC. Add 6 ml of the hydroxylamine
hydrochloride solution and 3 ml of the hydrazine solution every 30 minutes. In
the sequence of addition, raise the temperature up to 60oC gradually
for 4 hours, and gray metallic layers will form. At the end of this process,
sample a small amount of the solution and boil it with the strong reducing
agent (NaBH4) to check the end point. It is dangerous to add NaBH4
powder in a hot solution, because of the gas explosion. So add NaBH4
solution to a cold solution, then, warm the solution on a water bath. If any Pt
ion remains in the plating solution, the color of the solution turns to black.
In such cases, continue to develop Pt with addition of the NH2OH-HCl
and NH2NH2 solutions. If you check that there is none of
Pt ion in the chemical plating solution, rinse the membrane with water, and
boil in dilute hydrochloric acid (0.1 N) to remove the ammonium cation
in the membrane. After washing with water, H+ in the composite can
be exchanged for any cation by immersing in a solution of the chloride salt of
the cation.
ACKNOWLEDGMENT
The
Editor of the WW-EAP Webhub would like to express his sincere appreciation to
Dr. Keisuke Oguro for contributing his fabrication recipe. Dr. Oguro is one of
the pioneers of the IPMC and leading EAP scientist. His contribution is a very important milestone for the field of
EAP particularly since there is no recommended commercial source of such
materials. The Editor would like to express his hope to seeing more scientists
who are developing new EAP materials to share their recipe by allowing it to be
published on the WW-EAP Webhub to promote progress in this emerging field of
EAP.
To return to:
NDEAA Webhub
or to theWorldWide Electroactive Polymers (WW-EAP) Webhub