Method to manufacture composite polymer electrolyte membranes coated with inorganic thin films for fuel cells

Abstract

The present invention relates to a method for manufacturing composite polymer electrolyte membranes coated with inorganic thin films for fuel cells using a plasma enhanced chemical vapor deposition (PECVD) method or a reactive sputtering method, so as to reduce the crossover of methanol through polymer electrolyte membranes for fuel cells and enhance the performance of the fuel cells. The manufacturing method of composite polymer electrolyte membranes coated with inorganic thin films for fuel cells according to the present invention is characterized to obtain composite membranes by coating the surface of commercial composite polymer electrolyte membranes for fuel cells with inorganic thin films using a PECVD method or a reactive sputtering method. The inorganic materials to form the inorganic thin films are chosen one or more from the group comprising silicon oxide (SiO2), titanium oxide (TiO2), zirconium oxide (ZrO2), zirconium phosphate (Zr(HPO4)2), zeolite, silicalite, and aluminum oxide (Al2O3). The present invention, by coating the polymer electrolyte membranes for fuel cells with inorganic thin films via a PECVD method or a reactive sputtering method, reduces the methanol crossover sizably without seriously reducing the ionic conductivity of polymer electrolyte membranes, thereby, when applied to fuel cells, realizes a high performance of fuel cells.

Description

[0001] This application is a division of U.S. application Ser. No. 10 / 751,138 filed on Dec. 30, 2003, which claims priority to Korean Application 10-2003-0035127 filed on May 31, 2003 which applications are incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a method to manufacture composite polymer electrolyte membranes coated with inorganic thin films for fuel cells and applications of these membranes; more particularly to a method of coating the surface of commercial polymer electrolyte membranes with inorganic thin films using a plasma enhanced chemical vapor deposition (PECVD) method or a reactive sputtering method, thus reducing the methanol permeability without a sizable decrease of ionic conductivity, thereby realizing a lower methanol permeability than that of conventional Nafion® membranes or other composite polymer electrolyte membranes and, therefore, enhancing the performance of methanol f...

AI Technical Summary

Benefits of technology

[0019] An object of the invention is to provide a method to manufacture composite polymer electrolyte membranes coated with inorganic thin films for fuel cells and the membranes made by the same method, in which the surface of composite polymer electrolyte membranes are coated with inorganic thin films using a PECVD method or a reactive sputtering method, thus reducing the methanol permeability without a sizable decrease of ionic conductivity, thereby realizing a more reduced methanol permeability than that of conventional Nafion® membranes or other composite polymer electrolyte membranes and, therefore, enhancing the performance of methanol fuel cells.

[0027] In the method to manufacture composite polymer electrolyte membranes coated with inorganic thin films for fuel cells according to the present invention, said reactive sputtering method is characterized to vapor-depositing an in organic film on the target surface after cleaning by sputtering the surface in a 99.9% or higher argon gas atmosphere so as to prevent oxidation of the target surface during the sputtering.

[0038] A method of manufacturing an MEA according to the present invention includes a process of coating catalyst compounds for electrodes directly on the composite polymer electrolyte membranes coated with inorganic thin films for fuel cells manufactured via the aforementioned method. Said direct coating of the electrode catalyst, in which the electrode comprises catalysts and ionic conductive materials, is to reduce the contact resistance between the electrolyte membrane and the electrodes.

Problems solved by technology

However, the DMFC has drawbacks that its electrode performance is low due to the methanol oxidation at the cathode side, the platinum catalyst is poisoned by carbon monoxide which is one of reaction products, and the power density is lower than that of PEMFCs.

Also, the DMFC has other drawbacks of excessive consumption of expensive platinum catalyst and gradual performance degradation.

Yet, the most serious problem of the DMFC is the degradation of its cell performance due to methanol crossover from the anode to the cathode.

However, although Nafion® membranes of Du Pont in general use or other commercially available membranes have a superior ionic conductivity, they have the problem that methanol is permeated from the anode to the cathode.

This permeated methanol is oxidized on the cathode, poisoning the platinum catalyst thereby causing mixed potentials and, therefore, degrading the whole performance of the cell.

However, this method is short of reducing the methanol crossover.

Yet, it has drawbacks that the mechanical property of the composite membrane is inferior and the manufacturing process is complicated.

However, this method has drawbacks that the ionic conductivity is decreased compared with Nafion® membranes and the performance is decreased with increasing silicon oxide content more than 12%.

However, this modified membrane does not reduce the methanol crossover as compared with Nafion® membrane, and shows a drawback that sulfonic groups on the surface are eliminated to a sizable degree.

Images