NL8003387A - Activation or iridium complex catalysts for fuel cells - by heating in inert gas atmos - Google Patents

Abstract

Catalysts for fuel cell electrodes, comprising an Ir complex (I) in which the Ir is coordinated to an aromatic macrocyclic ligand via 4 N atoms, are activated by heating to a temp. of at least 300 deg.C. in an inert gas atmos. Pref. (I) is a porphyrin, phthalocyanine or tetraazaannulene complex. Activation is pref. effected at 300-1000 deg.C. for at least 20 min. The activated catalysts have an activity which is an order of magnitude higher than that of analogous Co and Fe catalysts, while having comparable stability. Unlike known catalysts, (I) can be used in cells employing Co as fuel.

Description

• $

1K 5529 NET

WEEKLY FOR ACTIVATING A CATALYST FOR FUEL CELL ELECTRODES

The present invention relates to a method of activating a catalyst for fuel cell electrodes, to a catalyst so activated, to a fuel cell electrode containing this catalyst and to a fuel cell containing this electrode.

The possibility of being able to use fuel cells on a large scale depends on the condition that highly active catalysts must be available, both for oxidation at the anode of commercially interesting fuels (methanol, formaldehyde, carbon monoxide and the like) and for conversion of oxygen at the cathode.

The search for a suitable catalyst for the electrochemical reduction of oxygen in an acidic environment, especially important for the development of low temperature dissolved fuel fuel cells, which catalyst does not contain metallic particles of a noble metal such as platinum, is in addition to other developments have also gone toward cobalt or iron as a metal element. Particularly known are metal chelates on carbon, namely cobalt and iron complexes of tetra-azaannulene (TAA), tetra (para-substituted) phenylporphyrin (T (pX) PP), phthalocyanine (Pc) and anthraquinocyanine ( ACC).

In themselves, these chelates on carbon have insufficient activity and stability; a method to improve both by heating in an inert gas to H00 ° C-1000 ° C has been successfully applied to some cobalt complexes, namely to complexes of TAA, Pc and of TPP, and to T (pX) PP complexes of iron. With regard to the latter, reference is made to the applicant's Netherlands Patent Application 711-575 filed for public inspection.

The applicant has now continued the research in a broader sense, mainly focusing on complexes of metals other than cobalt and iron.

800 33 87 Γ 'u 2

Surprisingly, it has now been found that the activity of an aromatic, macrocyclic complex of iridium, where the iridium is coordinated by four nitrogen atoms, increased upon heating so that it exceeded the activity of the cobalt by so much that the activity the order of magnitude is higher, while the stability is comparable.

According to the invention, the method of activating a catalyst suitable for fuel cell electrodes is characterized in that a catalyst consisting of an aromatic macrocyclic complex of iridium, the iridium being coordinated by four nitrogen atoms, in an inert gas is heated to a temperature of at least 300 ° C. Iridium complexes of a porphyrin, of a phthalocyanine, or of a tetra-aza-annulene are preferably used.

The heating time should preferably be at least 20 minutes, while the heating is below 1000 ° C; can stay.

It has further been found that the catalyst obtained by the above process is surprisingly also particularly suitable for the electrochemical oxidation of the fuel carbon monoxide. This catalyst differs from the previously known catalysts in that the oxidation takes place at hitherto unattainably low potentials (less than 0.25 V vs RHE (reversible hydrogen electrode; standard for comparison measurement) at room temperature) and a CO / gas mixture only the CO component is converted.

The following Examples illustrate the favorable results that can be achieved with the method according to the invention.

EXAMPLE I

IrT (p-isopropyl)? P Cl was precipitated on activated carbon (Norit BRX) by diluting a DMF (dimethylformamide) solution slowly with water (0.2 mg metal porphyrin per mg coal) . The oxygen reduction catalyst activity was 0.10 mA / mg at 850 mV vs EHE; the potential loss at galvanic static load with 1 mA was 80 mV for the first 5 16 hours.

After heat treatment in Ng at 700 ° C for 1 hour, the activity was 2 mA / mg cat. at 850 mV vs EHE; the potential loss at 1 mA galvanostatic load was 10 mV for the first 16 hours.

The same method applied to the analog iron compound resulted in an activity of only 0.1 mA / mg cat. at 850 mV vs EHE.

EXAMPLE II

Ir (octaethylporphyrin) (C0) C1 was precipitated on activated carbon (Norit BRX) by slowly diluting a DMF solution with water (0.2 mg metal porphyrin per mg carbon). The activity of the oxygen reduction catalyst was 0.10 mA / mg cat. at 850 mV vs EHE; the potential loss at 1 mA galvanostatic load was 100 mV during the first 16 hours.

After a heat treatment in Ng at 700¾ for 1 hour, the activity was 0.1+ mA / mg cat. at 850 mV vs EHE, the potential loss under galvanostatic load with 1 mA was l + O mV during the first 16 hours.

Using the same method applied to the analog iron-25 compound, only an activity of 0.07 mA / mg cat was achieved. obtained at 85Ο mV vs EHE.

EXAMPLE III

The catalyst was prepared as in Example 1. The activity for CO oxidation was nil at potentials below 0.2 V 30 vs EHE. After heat treatment (in Ng, at J00 ° C3 time 1 hour), the activity was 0.15 mA / mg cat. at 0.06 V vs EHE. The activity is proportional to the CO partial voltage regardless of whether CO / H 2 or CO / N 2 gas mixtures are used.

300 33 87 4

Finally, it should be noted that the upper limit of the heat treatment duration is not critical. Times from 20 minutes to 1 hour give essentially the same result.

«80 0 3 3 87

Claims (8)

Method for activating a catalyst suitable for fuel cell electrodes, characterized in that a catalyst containing an aromatic macrocyclic complex of iridium, wherein the iridium is coordinated by four nitrogen atoms, is heated in an inert gas to a temperature at least 300 ° C, A method according to claim 1, characterized in that the iridium complex is a porphyrin complex. 3. A method according to claim 1, characterized in that the iridium complex is a phthalocyanine complex. k. Process according to claim 1, characterized in that the iridium complex is a tetra-aza-annulene complex. 5. Process according to claims 1-1, characterized in that the catalyst is heated to a temperature of at most 1000 ° C. 6. Process according to claims 1-5, characterized in that the heating time of the catalyst is at least 20 minutes. 7. Catalyst prepared by the process of any one of claims 1-6. Fuel cell electrode containing a catalyst according to claim 7. Fuel cell containing an electrode according to claim 8. 800 3 3 87