PCT
WORLD INTELLECTUAL PROPERTY ORGANIZATION
International Bureau
INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
(51) International Patent Classification4 :
(11) International Publication Number:
WO 861 01642
4
HOlM 4/90,4/96
A1 (43) International Publication Date:
13 March 1986 (13.03.86)
so, 3000 Coimbra (PT). JAMIESON, Keith, Roderick
[GB/GB]; St. Catherines College, Oxford OX1 3UJ
(22) International Filing Date: 6 September 1985 (06.09.85)
(GB). HAMNETT, Andrew [GB/GB]; 66 Margaret
Road, Headington, Oxford OX3 8NQ (GB). MANO8422546
(31) Priority Application Numbers:
HAFUN,
Ramasamy [IN/GB]; 52 William Street,
8507185
New Marston, Oxford OX3 OER (GB).
(32) Priority Dates:
6 September 1984 (06.09.84) (74) Agent- NEVILLE, Peter, Warwick; Patent Department, National Research Development Corporation,
20 March 1985 (20.03.85)
101 Newington Causeway, London SE1 6BU (GB).
(21) International Application Number:
(33) Priority Country:
PCT/GB85/00400
GB
(81) Designated States: DE (European patent), FR (Euro(71) Applicant f o r all designated States except US): NApean patent), GB (European patent), JP, SE (Euroi
pean patent), US.
TIONAL RESEARCH DEVELOPMENT CORPORATION [GB/GB]; 101 Newington Causeway, London
Published
SE1 6BU (GB).
With international search report.
Before the expiration of the time limit for amending the
(72) Inventors; and
claims and to be republished in the event of the receipt
(75) Inventors/Applicants @or US onryl :GOODENOUGH,
of amendments.
John, Bannister TUS/GBl; 31 Linton Road, Oxford
OX2.6UL (GB). SHUKLA, Ashok, Kumar -[IN/IN];
Solid State & Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012 (IN). SILVA PALITEIRO, Carlos, Antonio da [c/PT
Rua
J;Cidade de
St Clara da California No. 77-3DT0, Monte Formo. .
(54) Title: ELECTRODE FOR REDUCING OXYGEN
(57) Abstract
An electrode for reducing oxygen has a substrate of low-ash carbon, such as coconut shells converted to charcoal.
The substrate is loaded with a catalyst such as (i) platinum phtalocyanine or (ii) lead-ruthenium oxide. In case (ii), to make
the electrode, lead ions are adsorbed onto the substrate, which is then treated with a solution of ruthenium (VI) oxide, to
precipitate the catalyst on the substrate.
FOR THE PURPOSES OFnVFOMATION ONLY
Codes used to identify Statesparty to the PCT on the front pages ofpamphletspublishing international applications under the PCT.
AT Austria
AU Australia
BB Barbados
BE Belgium
BG Bulgaria
BR Brazil
CF
CG
CH
CM
DE
DK
FI
FR
Central African Republic
Congo
Switzerland
Cameroon
Germany, Federal Republic of
Denmark
Finland
France
GA Gabon
GB United Kingdom
HU Hungary
IT
Italy
Japan
Democratic People's Republic
of Korea
KR Republic of Korea
LI Liechtenstein
LK SriLanka
LU Luxembourg
M C Monaco
M G Madagascar
M L Mali
JP
KE'
MR Mauritania
MW Malawi
Netherlands
Norway
.
Romania
Sudan
Sweden
Senegal
Soviet Union
TD Chad
TG Togo
US United States of America
NL
NO
RO
SD
SE
SN
SU
WO 86/01642
-
1 -
ELECTRODE FOR REDUCING OXYGEN
T h i s i n v e n t i o n relates t o a n e l e c t r o d e f o r reducing oxygen,
t o a f u e l c e l l i n c l u d i n g such an e l e c t r o d e , t o a method of reducing
oxygen a t such a n e l e c t r o d e , and t o a method of making c e r t a i n
such e l e c t r o d e s .
05
According t o t h e p r e s e n t i n v e n t i o n , a n e l e c t r o d e f o r reducing
oxygen comprises a s u b s t r a t e which is an e l e c t r o n i c conductor
c a p a b l e of reducing elemental oxygen t o water y i e l d i n g n o t more
t h a n 5% ( p r e f e r a b l y n o t more t h a n I%, more p r e f e r a b l y n o t more
t h a n 0.1%) hydrogen peroxide, t o which s u b s t r a t e i s a t t a c h e d a
10
c a t a l y s t which can reduce e l e m e n t a l oxygen t o water y i e l d i n g n o t
more t h a n 5%, ( p r e f e r a b l y n o t more t h a n I%, more p r e f e r a b l y n o t
more t h a n 0.1%) hydrogen peroxide when used a t c a t h o d i c p o t e n t i a l s
of -300 mV a g a i n s t t h e Hg/HgO e l e c t r o d e i n a l k a l i n e o r non-alkaline
s o ht i o n .
15
A preferred. s u i t a b l e s u b s t r a t e is carbon of an ash c o n t e n t
less t h a n 0.1%, p r e f e r a b l y less t h a n 0.05%, p r e f e r a b l y n o t more
t h a n 0.01%.
An example of suchaa carbon i s 'coconut carbon',
which is d e r i v e d from coconut s h e l l s by c o n v e r t i n g t h e s e t o
charcoal., washing and comminuting t h e c h a r c o a l , and exposing t h e
20
comminuted charcoal. t o gas, p r e f e r a b l y f i r s t carbon d i o x i d e and,
Another example is carbon which
2
i s of amorphous t y p e and h a s a s u r f a c e area of a t least 200 m / g ,
p r e f e r a b l y , a f t e r w a r d s , ammonia.
a mean p a r t i c l e s i z e i n t h e range 5 nm t o 50 nm, and an a p p a r e n t
3
d e n s i t y of 80 t o 110 kg/m , which may be t r e a t e d b y comminuting i t
25
and exposing i t t o gas a t e l e v a t e d temperature.
Preferably t h e
carbon b e f o r e t h e treatment h a s a s u r f a c e area of n o t more
2
t h a n 300 m /g.
P r e f e r a b l y t h e carbon b e f o r e t h e t r e a t m e n t h a s
a pH below 7,
The carbon may b e exposed t o only carbon d i o x i d e ,
f o r example a t 800C t o lOOOC, p r e f e r a b l y f o r 40 t o 90 minutes,
30
such as 9OOC f o r 1 hour.
P r e f e r r e d s u i t a b l e c a t a l y s t s are:
(i)
macrocyclic d e r i v a t i v e s of t r a n s i t i o n metals o r of
B-metals (i.e.
Cu, Ag, Au, Zn, Cd, Hg, In, T1, Sn, Pb, Sb o r B i )
f o r example platinum phthalocyanine, and
-
WO 84101642
- 2 (ii)
oxides containing ruthenium, f o r example Pb2+yRu206+x
where 0 6 x
4
1 o r Pb2,xBixRu206+y where x i s from 0 t o 2 and y is-
from 0 t o 1.
L
C a t a l y s t loadings in case ( i ) are 1 t o 15%by weight of t h e
05
s u b s t r a t e , p r e f e r a b l y 2 t o 12%.
*
H i t h e r t o , e f f o r t s i n t h e a r t of reducing oxygen a t an
e l e c t r o d e have been d i r e c t e d mainly towards minimising o r circumv e n t i n g t h e harmful e f f e c t s of hydrogen peroxide which is evolved
a t the e l e c t r o d e .
10
It has n o t h i t h e r t o been attempted t o select
e l e c t r o d e materials on t h e b a s i s of t h e i r l o w production of
hydrogen peroxide, except f o r a t t e m p t s t o i n h i b i t hydrogen
peroxide e v o l u t i o n by gold- plating carbon.
The i n v e n t i o n extends t o a f u e l c e l l i n c l u d i n g an e l e c t r o d e
as set f o r t h above.
15
The i n v e n t i o n a l s o provides a method of
reducing oxygen, comprising c o n t a c t i n g elemental oxygen w i t h a
s o u r c e of hydrogen (such a s a hydroxide s o l u t i o n ) a t an e l e c t r o d e
as set f o r t h above and applying t o t h e e l e c t r o d e a p o t e n t i a l of
from 0.1 t o -0.2 v o l t s w i t h r e s p e c t t o t h e Hg/HgO e l e c t r o d e . For
example, where t h e c a t a l y s t i s platinum phthalocyanine with an
20
e l e c t r o l y t e of 6M KOH, t h e p o t e n t i a l is p r e f e r a b l y from 0.1
t o -0.2 V, and where t h e c a t a l y s t is l e a d -r u t h e n a t e (nominally
Ru 0
) w i t h an e l e c t r o l y t e of 1M KOH, t h e p o t e n t i a l i s
Pb2+y 2 6+x
p r e f e r a b l y 0.2 t o -0.2 V; a t more p o s i t i v e p o t e n t i a l s , no
a p p r e c i a b l e r e d u c t i o n c u r r e n t flows;
25
c u r r e n t s become excessive.
a t more n e g a t i v e p o t e n t i a l s ,
A l t e r n a t i v e l y , t h e source of hydrogen
may be an a c i d o r n e u t r a l aqueous s o l u t i o n .
According t o a n o t h e r a s p e c t , t h e i n v e n t i o n provides a method
of making an e l e c t r o d e as s e t f o r t h above, wherein t h e c a t a l y s t i s
an oxide c o n t a i n i n g ruthenium and a n o t h e r metal, comprising adsorb-
30
i n g i o n s of t h e o t h e r m e t a l o n t o t h e s u b s t r a t e and t r e a t i n g t h e
s u b s t r a t e w i t h a s o l u t i o n of ruthenium 0x0-anion complex (nominally
ruthenium ( V I ) o x i d e ) , whereby t h e d e s i r e d c a t a l y t i c oxide is
p r e c i p i t a t e d on, and is a t t a c h e d t o , t h e s u b s t r a t e .
The i n v e n t i o n
extends t o t h e e l e c t r o d e so made, and t o f u e l cells, methods of
.
35
reducing oxygen etc. using it.
For u s e in a l k a l i n e media, t h e
WO 86101642
- 3 'coconut' carbon i s p r e f e r r e d , p r e f e r a b l y w i t h c a t a l y s t s of case ( i i )
above.
For u s e in a c i d media, t h e amorphous carbon i s p r e f e r r e d ,
p r e f e r a b l y w i t h c a t a l y s t s of case ( i ) above o r e.g.
.
05
thiocyanate.
The i n v e n t i o n w i l l now be d e s c r i b e d by way of example.
In
t h e accompanying drawings, F i g u r e s 1 and 2 show t h e performance of
e l e c t r o d e s according t o Examples 1 and 2 of t h e i n v e n t i o n respect i v e l y , compared w i t h o t h e r e l e c t r o d e s , under v a r i o u s c o n d i t i o n s .
SUBSTRATE PREPARATION EXAMPLE
A porous carbon e l e c t r o d e i s made u t i l i s i n g coconut s h e l l
10
charcoal.
Active coconut s h e l l c h a r c o a l o b t a i n e d from T a l a u l i c a r
carbons (P) Ltd.,
Londa, I n d i a , w a s Subjected t o r e p e a t e d g r a v i t y
s e p a r a t i o n w i t h s a t u r a t e d calcium c h l o r i d e s o l u t i o n t o remove any
d e n s e r i n g r e d i e n t s and t h e n s u b j e c t e d t o r e p e a t e d 'Soxhlet'
15
treat-
ment w i t h a z e o t r o p i c h y d r o c h l o r i c a c i d and t h e n r e p e a t e d l y washed
i n t h e 'Soxhlet' i t s e l f w i t h d i s t i l l e d water.
After drying in a
vacuum oven a t 15OoC, t h e a s h c o n t e n t of t h i s carbon was found t o
be about 0.03%.
This c h a r c o a l w a s s u b j e c t e d t o mechanical g r i n d i n g
and s i e v i n g through a 400 mesh s i e v e .
20
T h i s carbon w a s g a s - a c t i v a t e d
by h e a t i n g i n a carbon- dioxide atmosphere a t 900°C f o r 4 h o u r s and
then i n an ammonia atmosphere a l s o a t 9OO*C f o r 4 hours. Gasa c t i v a t i o n w a s chosen i n s t e a d of f u r t h e r g r i n d i n g , t o minimise
agglomeration.
25
S u b s t r a t e s f o r e l e c t r o d e s were prepared by h o t (1 40°C)
-2
p r e s s i n g , under 0.05 tonne cm , t h i s gas- activated carbon mixed
w i t h 20% by weight p o l y e t h y l e n e powder ( 5 micron average p a r t i c l e
s i z e ) onto an expanded platinum mesh (0.06 mm diameter w i r e ,
a t 0.3 mm c e n t r e s ) .
2
The BET s u r f a c e area of such a s u b s t r a t e was about 600 m / g
30
and t h e r e s i s t i v i t y a b o u t 0.4 ohm cm.
An e l e c t r o c h e m i c a l c e l l f o r measuring e l e c t r o c h e m i c a l p e r f o r mance parameters w a s set up c o n t a i n i n g t h i s s u b s t r a t e as a working
e l e c t r o d e , a Hg/HgO, OH- r e f e r e n c e e l e c t r o d e , a high s u r f a c e area
f l a t b e d c o u n t e r e l e c t r o d e , and a n e l e c t r o l y t e , which was a 27% KOH
35
s o l u t i o n i n d i s t i l l e d water.
The c e l l w a s o p e r a t e d w i t h a c u r r e n t
WO 86/01642
- 4 d e n s i t y of 100 mA/cm
2
on t h e working e l e c t r o d e a t a p o t e n t i a l
of -0.125 V a g a i n s t t h e r e f e r e n c e e l e c t r o d e a t 3OoC, and oxygen
w a s reduced t o water w i t h minimal (under 1%) by- production of
hydrogen peroxide.
05
ELECTRODE EXAMPLE 1
Porous carbon f o r an e l e c t r o d e s u b s t r a t e was made as
d e s c r i b e d i n t h e S u b s t r a t e P r e p a r a t i o n Example, up t o and
including t h e gas- activation b u t excluding t h e h o t pressing.
Platinum phthalocyanine w a s d i s s o l v e d i n t h e least p o s s i b l e
10
q u a n t i t y of c o n c e n t r a t e d s u l p h u r i c a c i d , and t h e n t h e carbon w a s
d i s p e r s e d i n t o the s o l u t i o n .
The s o l u t i o n w a s t h e n d i l u t e d slowly
w i t h t h e least q u a n t i t y of d i s t i l l e d water t o o b t a i n a s l u r r y .
The s l u r r y i s s t i r r e d w i t h t h e carbon f o r one hour, washed u n t i l
15
t h e s u p e r n a t a n t l i q u o r h a s a pH of 5 t o 7, and t h e n c e n t r i f u g e d .
-2
with
The carbon i s d r i e d and hot- pressed a t 0.05 tonne c m
p o l y e t h y l e n e b i n d e r as i n t h e S u b s t r a t e P r e p a r a t i o n Example.
In F i g u r e 1, t h e performance oxygen r e d u c t i o n of v a r i o u s
e l e c t r o d e s is compared. In all cases, t h e e l e c t r o l y t e w a s 6M
0
aqueous KOH under a p r e s s u r e of gaseous oxygen o f 130 mB, at 35 C.
20
The performance of t h e e l e c t r o d e j u s t d e s c r i b e d is curve 1A (5%
platinum phthalocyanine) and c u r v e ll3 (10%platinum phthalocyanine)
The o t h e r curves r e p r e s e n t o t h e r e l e c t r o d e s :
a = u n t r e a t e d carbon (= a of F i g u r e 2)
b = a + 7% platinum (= b of F i g u r e 2)
25
c = carbon according t o S u b s t r a t e P r e p a r a t i o n Example (= c of
F i g u r e 2)
d = c + 7% platinum
Curve 1A l i e s above t h e o t h e r s a t a l l c u r r e n t d e n s i t i e s
2
2
over 150 mA/cm , and 1B above t h e o t h e r s o v e r 400 mA/cm
Life-
.
30
time tests on 1A and 1B showed h i g h s t a b i l i t y a t c u r r e n t d e n s i t i e s
2
of up t o 400 mA/cm
.
ELECTRODE EXAMPLE 2
In t h i s Example, a novel method i s f e a t u r e d f o r a t t a c h i n g a
catalyst t o a substrate.
.
PCT/G B85/00400
WO 86/01642
-
5 -
A porous carbon s u b s t r a t e w a s made as d e s c r i b e d i n t h e S u b s t r a t e
w a s p r e c i p i t a t e d on
Ru 0
2+y 2 6+x
2+
t h e s u b s t r a t e by a s u r f a c e chemical r e a c t i o n between Pb
pre-
P r e p a r a t i o n Example.
The c a t a l y s t Pb
adsorbed on t h e s u b s t r a t e and a ruthenium complex in s o l u t i o n .
05
T h i s w a s achieved as follows:
The s u b s t r a t e was dipped f o r 30 minutes i n a 0.001M aqueous
s o l u t i o n of l e a d n i t r a t e Pb(N03)2.
In t h i s way, lead i o n s Pb
were adsorbed on t h e s u r f a c e of t h e s u b s t r a t e .
2+
.
Meanwhile, a
ruthenium s o l u t i o n w a s made by f u s i n g 0.1 g Ru02, 0.5 g NaOH
10
and 5 g KN03 f o r 5 minutes and d i l u t i n g t h e m e l t w i t h d i s t i l l e d
water t o 250 m l .
The dipped s u b s t r a t e was t h e n dipped for 30
minutes i n t h i s ruthenium s o l u t i o n , whereby t h e c a t a l y s t Pb2+yRu206+x
was p r e c i p i t a t e d on, and bound t o , t h e s u r f a c e of t h e s u b s t r a t e .
T h i s r e a c t i o n i s r a t h e r s e n s i t i v e t o pH;
15
t h e above q u a n t i t i e s
e n s u r e a s u i t a b l e pH.
After dipping and r i n s i n g i n d i s t i l l e d water, t h e r e s u l t i n g
0
e l e c t r o d e i s d r i e d a t 70 C.
I n F i g u r e 2, t h e performance of v a r i o u s e l e c t r o d e s a t reducing
oxygen is compared.
20
I n each case except c u r v e 2 t h e e l e c t r o l y t e
w a s 6M aqueous KOH under p r e s s u r e of gaseous oxygen of 160 mB,
a t 35OC.
T h a performance of t h e e l e c t r o d e j u s t d e s c r i b e d is
curve 2, i n which t h e e l e c t r o l y t e w a s 1M aqueous KOH under a
0
p r e s s u r e of gaseous oxygen o f 160 mB, a t 35 C.
The o t h e r curves r e p r e s e n t o t h e r e l e c t r o d e s :
2s
a = u n t r e a t e d carbon (= a of F i g u r e 1)
b = a + 7% platinum (= b of F i g u r e 1)
c = carbon according t o S u b s t r a t e P r e p a r a t i o n Example (= c of
Figure 1)
d = p r o p r i e t a r y t r e a t e d carbon +I 5% platinum.
30
e = t e f l o n (40%)-bonded u n t r e a t e d carbon.
Although showing
h i g h a c t i v i t y , t h i s sample i s s h o r t - l i v e d because it evolves
hydrogen peroxide, which degrades i t ;
e l e c t r o d e s c and d do n o t
e x h i b i t such e v o l u t i o n .
f = p y r o c h l o r e on u n t r e a t e d carbon s u b s t r a t e .
'
WO 86/01642
- 6 SECOND SUBSTRATE PREPARATION EXAMPLE
.
High- surface- area Vulcan XC-72 carbon w a s o b t a i n e d from t*h e
Cabot Corp., Billerica, MA.
The a s h c o n t e n t of t h i s carbon w a s
found t o b e about 0.05%. The o t h e r p h y s i c a l and chemical
05
parameters of t h i s carbon are as follows:
257 m2/g
S u r f a c e area
Mean p a r t i c l e s i z e
30 nm
Approximate d e n s i t y
3
96 kg/m
5
PH
T h i s carbon was s u b j e c t e d t o mechanical g r i n d i n g and t h e n
10
g a s - a c t i v a t e d by h e a t i n g i n a C 0 2 atmosphere a t 900°C f o r 1 hour.
G a s a c t i v a t i o n r a t h e r t h a n continued g r i n d i n g w a s chosen t o
minimise p a r t i c l e agglomeration;
i t produced a 27%weight loss o f
t h e carbon, i n c r e a s e d t h e e f f e c t i v e s u r f a c e area, and modified t h e
15
s u r f ace.
The d e s i r e d q u a n t i t y of p l a t i n u m w a s d i s p e r s e d i n t o t h e
gas- activated carbon by reducing c h l o r o p l a t i n i c a c i d w i t h sodium
formate s o l u t i o n as d e s c r i b e d elsewhere.
This p r o c e d u r e y i e l d s
f i n e platinum p a r t i c l e s of uniform s i z e (about 63g diameter) on a
20
carbon s u b s t r a t e .
C h l o r o p l a t i n i c acid s o l u t i o n c o n t a i n i n g t h e
r e q u i r e d p r o p o r t i o n of platinum w a s t a k e n from a 2 weight -% s t o c k
s o l u t i o n , mixed w i t h h a l f of i t s volume of isopropanol, and
n e u t a l i s e d with a d i l u t e s o l u t i o n of sodium carbonate.
An
a p p r o p r i a t e q u a n t i t y of g a s - a c t i v a t e d Vulcan XC-72 carbon w a s
25
added, and t h e entire mixture w a s d r i e d i n an a i r oven b e f o r e i t
w a s added, w i t h vigorous s t i r r i n g , t o a n excess of b o i l i n g 5
weight % sodium formate s o l u t i o n t o reduce t h e c h l o r o p l a t i n i c a c i d
t o platinum metal.
The r e s u l t i n g mass w a s f i l t e r e d and washed
r e p e a t e d l y with h o t , d i s t i l l e d water b e f o r e b e i n g d r i e d i n a n a i r
30
oven.
Teflon-bonded e l e c t r o d e s were prepared f o r e l e c t r o c h e m i c a l
measurements under gas- fed c o n d i t i o n s .
The Teflon b i n d e r p r o v i d e s
t h e necessary mechanical s t r e n g t h t o p r e v e n t e l e c t r o d e c o l l a p s e
. . .
PCT/GBS5/00400
WO 86/01642
- 7 under t h e g a s p r e s s u r e r e q u i r e d f o r g a s - e l e c t r o l y t e i n t e r f a c e
c o n t r o l i n a g a s - d i f f u s i o n e l e c t r o d e , and i t does s o w h i l e
r e t a i n i n g t h e necessary e l e c t r o d e p o r o s i t y .
e l e c t r o d e s were made as follows:
05
The Teflon-bonded
Tetrahydrofuran (THF) w a s added
t o a measured q u a n t i t y of c a t a l y s e d s u b s t r a t e powder i n a beaker,
and t h e mixture w a s a g i t a t e d i n a n u l t r a s o n i c b a t h f o r a b o u t 30
minutes b e f o r e a few m l of d i l u t e suspension of Teflon emulsion
(ICI GP2 Fluon d i s p e r s i o n , particle s i z e 0,1-0,2
microns) w a s
added t o t h e m i x t u r e without i n t e r r u p t i o n of t h e a g i t a t i o n .
10
The
product material w a s c e n t r i f u g e d r e p e a t e d l y w i t h THF and f i n a l l y
s p r e a d on a platinum expanded-metal (Exmet) s c r e e n (0.076 mm
-2
diameter w i r e , 1024 mesh cm
). The coated s c r e e n w a s a i r - d r i e d
-2
f o r about 15 minutes b e f o r e i t w a s cold- pressed a t 125 kg cm
f o r 5 minutes.
15
The pressed mass was d r i e d f o r 2 hours a t 11OC and
t h e n cured i n a i r a t 360C f o r 30 minutes.
The T e f l o n c o n t e n t of
t h e e l e c t r o d e s w a s optimal a t 25 t o 35%by volume.
Short- term p o l a r i s a t i o n c u r v e s were obtained f o r dioxygen
r e d u c t i o n i n 5M H2S04 s o l u t i o n on v a r i o u s Vulcan XC-72 carbon
electrodes.
20
P o l a r i s a t i o n curves were o b t a i n e d a t 2OoC f o r u n p l a n t i n i s e d
carbon e l e c t r o d e s t h a t were n o t gas- activated.
Although t h e
e l e c t r o d e s f u n c t i o n a t c u r r e n t d e n s i t i e s of 400 t o 600 mA cm-2,
t h e i r p o l a r i s a t i o n v a l u e s are high.
F u r t h e r curves were o b t a i n e d on gas- activated Vulcan XC-72
25
s u b s t r a t e s impregnated w i t h 7 weight % d i s p e r s e d metal and loaded
w i t h 30%T e f l o n and c l e a r l y show a s u f f i c i e n t l y reduced masst r a n s f e r p o l a r i s a t i o n f o r l o a d i n g of t h e e l e c t r o d e s t o h i g h
These e l e c t r o d e s could be loaded i n t e r m i t -2
t e n t l y a t c u r r e n t d e n s i t i e s of 1 . 1 A c m
f o r p e r i o d s of several
current densities.
30
minutes.
This enhanced performance i n d i c a t e s t h a t t h e high-
temperature CO
t r e a t m e n t h a s n o t o n l y i n c r e a s e d t h e s u r f a c e area,
2
b u t h a s a l s o peroduced a w e l l d e f i n e d p o r e s t r u c t u r e t h a t o p t i m i s e s
a uniform gas d i f f u s i o n i n t o t h e e l e c t r o d e .
It a l s o i n d i c a t e s a
good platinum d i s p e r s i o n on t h e s u r f a c e , and any s u r f a c e modifica35
t i o n by t h e C 0 2 t r e a t m e n t would a p p e a r t o be b e n e f i c i a l .
No
PCT/GBS5/00400
WO 86101642
-
8 -
d e t e c t a b l e H 0 w a s evolved, whereby t h e carbon w a s n o t d e s t r o y e d
2 2
from t h i s cause (improving t h e l i f e t i m e of t h e e l e c t r o d e ) and
whereby e f f i c i e n c y w a s improved (none of t h e reduced oxygen b e i n g
if
w a s t e f u l l y converted t o r e a p p e a r as H202).
05
To p u t t h e f o r e g o i n g i n t o c o n t e x t , t h e long- range g o a l of
3
f u e l - c e l l r e s e a r c h is t h e development of f u e l - c e l l b a t t e r i e s t h a t
o p e r a t e on inexpensive f u e l s and have a i r as t h e oxidant.
These
b a t t e r i e s must c o n v e r t chemical energy t o electric power w i t h h i g h
e f f i c i e n c y a t practical c u r r e n t d e n s i t i e s ;
10
long o p e r a t i o n a l l i f e
they must a l s o have
- o r a low- cost replacement of
ageing p a r t s
-
i f they are t o compete w i t h p r e s e n t forms of power g e n e r a t i o n from
t h e same i n e x p e n s i v e f u e l s .
A primary impediment t o t h e commercial r e a l i s a t i o n of f u e l -
c e l l technology is f a i l u r e t o i d e n t i f y s u i t a b l y c a t a l y t i c e l e c t r o d e s
15
having a long o p e r a t i o n a l l i f e i n a c i d i c e l e c t r o l y t e s .
Alkaline
e l e c t r o l y t e s react w i t h carbon d i o x i d e t o form c a r b o n a t e s t h a t
from t h e a i r can b e
2
slowed t o n e a r l y t o l e r a b l e rates f o r low- cost, exchangeable a l k a l i n e
f o u l the electrodes.
Although f o u l i n g by CO
a i r e l e c t r o d e s in a p u r e hydrogen- air f u e l c e l l , a n a c i d i c e l e c t r o l y t e
20
h a s g r e a t advantages.
High performance r e q u i r e s f a b r i c a t i o n of a porous e l e c t r o d e
s u b s t r a t e of h i g h s u r f a c e area on which-a s u i t a b l e c a t a l y s t i s
e f f e c t i v e l y disposed;
moreover, t h e e f f e c t i v e s u r f a c e area must
n o t be degraded by normal o p e r a t i o n a l c o n d i t i o n s .
25
Degradation may
b e caused by:
(1)
chemical a t t a c k from the product of a n unwanted s i d e
reaction,
30
(2)
porosity,
(3)
mechanical c o l l a p s e , o r
( 4 ) s i n t e r i n g due t o h e a t from i n t e r n a l l o s s e s .
T h e r e f o r e a t t e n t i o n must be d i r e c t e d t o the c h o i c e of s u b s t r a t e
-
c
material and c a t a l y s t as w e l l as t o t h e method of e l e c t r o d e f a b r i c
c a t i o n and c a t a l y s t d i s p e r s i o n .
S e l e c t i o n of a s u i t a b l e s u b s t r a t e material is d i c t a t e d by a t
35
least six f a c t o r s :
c o s t , i n e r t n e s s i n o p e r a t i n g medium, ease of
WO 86101642
- 9 f a b r i c a t i o n i n c o l l o i d a l - s i z e p a r t i c l e s , high electrical conduct i v i t y , e f f e c t i v e n e s s as s u b s t a t e f o r a h i g h l y d i s p e r s e d c a t a l y s t ,
and i n e r t n e s s t o unwanted s i d e r e a c t i o n s .
Various t y p e s of a c t i v e
(high- surface- area) carbon have been examined as s u p p o r t s f o r
05
platinum- metal c a t a l y s t s i n e l e c t r o d e s used f o r both oxygen
r e d u c t i o n and methanol o x i d a t i o n i n a c i d s o l u t i o n .
a s h c o n t e n t prove t o be s u p e r i o r ;
Carbons of low
t h e s e appear t o be f r e e of t h e
i m p u r i t i e s r e s p o n s i b l e f o r hydrogen- peroxide g e n e r a t i o n , a s i d e
r e a c t i o n r e s p o n s i b l e f o r chemical a t t a c k of t h e s u b s t r a t e s .
I0
Vulcan XC-72 carbon, made by Cabot Corp., which h a s a low a s h
c o n t e n t , functions as a n excellent a i r - e l e c t r o d e s u b s t r a t e i n a c i d
i f i t s s u r f a c e i s s u i t a b l y p r e - t r e a t e d and platinum is uniformly
d i s p e r s e d onto it.
Such a Teflon-bonded e l e c t r o d e as set f o r t h
above a p p e a r s t o reduce dioxygen t o water i n 5M H SO
w i t h no
4'
d e t e c t a b l e formation of hydrogen peroxide and t o be a b l e t o
2
15
s u s t a i n l o a d c u r r e n t s of a b o u t 900 mA cm-2
w i t h o u t s e r i o u s degradation.
43u
f o r long p e r i o d s
W O 86101642
- 10 CLAIMS
1.
An e l e c t r o d e f o r reducing oxygep, comprising a s u b s t r a t e
which i s an e l e c t r o n i c conductor c a p a b l e of reducing elemental
oxygen t o water y i e l d i n g n o t more t h a n 5%hydrogen peroxide, t o
which s u b s t r a t e i s a t t a c h e d a c a t a l y s t which can reduce elemental
05
oxygen t o water y i e l d i n g n o t more t h a n 5%hydrogen p e r o x i d e when
used a t c a t h o d i c p o t e n t i a l s of -300 mV a g a i n s t t h e Hg/HgO e l e c t r o d e
i n a l k a l i n e o r non- alkaline s o l u t i o n .
2.
An e l e c t r o d e according t o Claim 1, wherein t h e e l e c t r o n i c
conductor i s capable of reducing elemental oxygen t o water y i e l d i n g
10
n o t more t h a n 1%hydrogen peroxide.
An e l e c t r o d e a c c o r d i n g t o C l a i m 2, wherein the c a t a l y s t can
reduce elemental oxygen t o water y i e l d i n g n o t more t h a n 1%hydrogen
3.
peroxide
4.
15
An e l e c t r o d e according t o C l a i m 3 , wherein t h e e l e c t r o n , i c
conductor is capable of reducing elemental oxygen t o water y i e l d i n g
n o t more t h a n 0.1% hydrogen peroxide.
An e l e c t r o d e a c c o r d i n g t o C l a i m 4 , wherein the c a t a l y s t can
reduce elemental oxygen t o w a t e r y i e l d i n g not more t h a n 0.1%
5.
hydrogen peroxide.
20
6.
An e l e c t r o d e a c c o r d i n g t o any preceding claim, wherein t h e
s u b s t r a t e is carbon of a n ash e o n t e n t less- t h a n 0.1%.
7.
An e l e c t r o d e according t o C l a i m 6 , wherein t h e s a i d a s h
c o n t e n t i s less t h a n 0.05%.
8.
25
A n e l e c t r o d e according t o C l a i m 7 , wherein t h e s a i d a s h
c o n t e n t i s less t h a n 0.01%.
9.
An e l e c t r o d e according t o any preceding claim, wherein t h e
carbon i s 'coconut carbon'.
10.
An e l e c t r o d e according t o C l a i m 9, wherein t h e carbon is
d e r i v e d from coconut s h e l l s by c o n v e r t i n g t h e s e t o c h a r c o a l ,
30
washing and comminuting t h e c h a r c o a l , and exposing t h e comminuted
c h a r c o a l t o gas.
11.
An e l e c t r o d e according t o C l a i m 10, wherein t h e gas is f i r s t
carbon d i o x i d e and a f t e r w a r d s ammonia.
PCT/GB85/00400
WO 86/01642
- 11 . 12.
An e l e c t r o d e according t o any of Claims 1 t o 8, wherein t h e
s u b s t r a t e is made by t r e a t i n g t h e carbon, which is of amorphous
2
t y p e and h a s a s u r f a c e area of a t least 200 m /g, a mean p a r t i c l e
s i z e i n t h e range 5 nm t o 50 nm, and an a p p a r e n t d e n s i t y of 80
05
t o 110 kg/m
3
, by
comminuting it and exposing i t t o gas a t e l e v a t e d
temperature.
13.
An e l e c t r o d e according t o C l a i m 12, wherein t h e carbon b e f o r e
2
the treatment h a s a s u r f a c e area of n o t more t h a n 300 m /g.
14.
10
An e l e c t r o d e according t o C l a i m 1 2 o r 13, wherein- t h e carbon
b e f o r e t h e t r e a t m e n t h a s a pH below 7.
15.
r
An e l e c t r o d e according t o C l a i m 12, 1 3 o r 14, wherein t h e g a s
t o which the carbon i s exposed i s carbon d i o x i d e .
16.
An e l e c t r o d e according t o C l a i m 15, wherein t h e s a i d e l e v a t e d
temperature i s from 800 C t o 1000 C.
15
17.
An e l e c t r o d e according t o C l a i m 16, wherein t h e d u r a t i o n of
t h e exposure a t s a i d e l e v a t e d t e m p e r a t u r e is from 40 t o 90 minutes.
18.
An
e l e c t r o d e according t o any of Claims 12 t o 17, when i n
u s e t o reduce oxygen t o water i n an a c i d medium.
19.
20
An
e l e c t r o d e according t o any of Claims 9 t o 11, when i n
u s e t o reduce oxygen t o water i n a n a l k a l i n e medium.
20.
An e l e c t r o d e according t o any preceding claim, wherein t h e
c a t a l y s t i s a macrocyclic d e r i v a t i v e of t r a n s i t i o n metals o r of
B- metals (i.e.
21.
25
Cu, Ag, Au, Zn, Cd, Hg, In, T1, Sn, Pb, Sb o r Bi).'
An e l e c t r o d e according t o C l a i m 20, wherein t h e c a t a l y s t
l o a d i n g i s 1 t o 15%by weight of t h e s u b s t r a t e .
22.
An e l e c t r o d e according t o C l a i m 21, wherein s a i d c a t a l y s t
l o a d i n g is 2 t o 12%.
23.
An e l e c t r o d e according t o any of Claims 1 t o 19, wherein t h e
c a t a l y s t is an oxide c o n t a i n i n g ruthenium.
30
24.
An e l e c t r o d e according t o C l a i m 23, wherein t h e c a t a l y s t i s
a n oxide c o n t a i n i n g ruthenium and one o r more o t h e r metals.
r
25.
An e l e c t r o d e according t o C l a i m 24, wherein t h e c a t a l y s t
B i Ru 0
where x i s from 0 t o 2 and y is from 0 t o 1.
is Pb2-x x 2 6+y
26. Amethod of making an e l e c t r o d e according t o Claim 24 o r 25,
35
comprising adsorbing i o n s of t h e o t h e r m e t a l ( s ) o n t o t h e s u b s t r a t e
WO 86/01642
PCT/GB85/00400
- 12 and t r e a t i n g t h e s u b s t r a t e w i t h a s o l u t i o n of ruthenium 0x0-anion
complex, whereby t h e d e s i r e d c a t a l y t i c oxide i s p r e c i p i t a t e d on,
and i s a t t a c h e d t o , t h e s u b s t r a t e .
05
27.
An e l e c t r o d e made by a method according t o C l a i m 2 6 .
28.
A f u e l c e l l i n c l u d i n g an e l e c t r o d e according t o any of Claims 1
t o 25 o r 27.
29.
A method of reducing oxygen, comprising c o n t a c t i n g elemental
oxygen w i t h a s o u r c e of hydrogen a t a n e l e c t r o d e according t o any
of Claims 1 t o 25 or 27, and a p p l y i n g t o t h e e l e c t r o d e a p o t e n t i a l
10
of from 0.1 t o -0.2 v o l t s w i t h r e s p e c t t o t h e Hg/HgO e l e c t r o d e .
30.
Amethod according t o C l a i m 2 9 , wherein the c u r r e n t d e n s i t y
exceeds 8000 A/m
43u
2
.
$
%
WO 86101642
c
PCT/GB85/00400
WO 86/01642
*
PCl"/GB85/004OO
INTERNATIONAL SEARCH REPORT.
Internatlonal ADDiicatlon NO
PCT/GB 8 5 / 0 0 4 0 0
I. CLASSlFlCATlON OF SUBJECT MATTER (if several classificition symbols apply. indicate all)
'
According to International Patent Classification (IPC) or to both Natlonat Clrrsification and IPC
*
IPC :
H 0 1 *M 4 / 9 0 ;
H 01 M 4/96
11. FIELDS SEARCHED
Mlnlmum Documentation Searched
Classification System
4
IPC
I
1I
7
Classlficatlon Symbols
H 0 1 M
Oocumentation Searched other than Minlmum Documentation
to the Extent that such Document8 are Included In the Flrldr Searched 8
111. D O C U M E N T S CONSIDERED TO BE RELEVANT'
Citation of Document. with lndlcatlon. where appropilate. of the relevant passages
:ategory
11
X
Y
(2
?elevant to Claim No. 13
P a t e n t s A b s t r a c t s of J a p a n , vol. 8 , no. 1 9 0 ,
31 August 1 9 8 4 ; ( E - 2 6 3 ) ( 1 6 2 7 )
& J P , A , 5 9 7 9 9 7 7 (PENTEL K . K . )
9 May
1 9 8 4 , see t h e whole a b s t r a c t
1,9,10,19,2(
21
6,7,8,11 ,l5,
16,23,25,28
--
X
P a t e n t s A b s t r a c t s of Japan, v o l . 4 , no. 56,
25 A p r i l 1 9 8 0 : (E-8) (538)
& J P , A , 5 5 2 5 9 1 6 (TOSHIBA RAY-0-VAC KK)
2 5 February 1 9 8 0 , see t h e w h o l e >.a b s t r a c t 1 , 9 , 1 0 , 1 9 , 2 c
--
Y
J o u r n a l of P o w e r Sources, v o l . 1 0 , no. 4 ,
November 1 9 8 3 ( A m s t e r d a m , N L )
R. Manoharan e t a l . : "Oxygen r e d u c i n g
porous carbon electrode for electrochemical p o w e r sources w i t h a l k a l i n e
e l e c t r o l y t e " , pages 3 3 3 - 3 4 1 , see page
334, line 7
page 335, l i n e 1 2 ;
f i g u r e s 7 , 8 ; page 3 3 9 , l i n e 1 1
page
3 4 0 , l i n e 5; page 3 4 0 , l i n e s 13- 21
-
.
*
-
--
*
oat0 Of the Actual Completlon of th8 International Search
1 9 t h December 1 9 8 5
international Searching Authority
E U K P E A N PATENT OFFICE
Signature of Authorlred Omcar
28
International Application
ill. DOCUMENTS CONSIDERED TO BE RELEVANT
No-PCT/GB 8 5 / 0 0 4 0 0 -2-
(CONTINUED FROM THE SECOND SHEET)
Cttrtton of Document. witn indiutmn. where amrowrate. of ma rebvant mssams
:ategor
US, A, 4292197 (R.D. CHAMBERLIN) 2 9
September 1981
see c l a i m s 1 , 2 ; column 3 , l i n e 57
column 4 , l i n e 18; column 6 , l i n e s
4- 12; column 7, l i n e s 34-44, 57-61
A
-
Relevant to Claim No
1,9,19,27
--
Extended A b s t r a c t s , ~0.1.
8 7 , no. 2 , 1981
(Pennington , N e w .Jerssv,US)
a b s t r a c t no. 1 1 4 : J . G i n e r e t a l . :
"Gasdiffusion e l e c t r o d e f o r m e t a l
a i r - b a t t e r i e s " , pages 289-291, see
page 2 9 0 , p a r a g r a p h 3
Y
23-25
--
J o u r n a l of t h e E l e c t r o c h e m i c a l S o c i e t y ,
v o l . 130, no. 9 , September 1983
(Manchester, New Hampshire, U S )
H . S . Horowitz: "Oxygen e l e c t r o c a t a l y s i s
on some o x i d e p y r o c h l o r e s " , pages
1853-1859, see a b s t r a c t ; f i g u r e 3;
page 1858; l e f t - h a n d column; p a r a g r a p h s
4-5
Y
1,23-25
--
EP, A , 0068664 (AJINOMOTO CO.) 5 J a n u a r y
1983
see claims 1 , 2 , 6 , 7 ; example 1 ; page 2 ,
l i n e s 5-19; page 3 , l i n e s 26- 30
A
1-5 ,2 0 ,28
--
Extended A b s t r a c t s , v o l , 8 3 , no. 2 , 1983
(Washington DC, U S ) a b s t r a c t no.' 391:
S.L. Eupta e t a l . : "The r o l e of
t r a n s i t i o n metal i n t h e p y r o l y z e d
m a c r o c y c l i c s t o w a r d s oxygen r e d u c t i o n
i n concentrated photophoric acid" ,
pages 624-625, see page 6 2 4 , l e f t - h a n d
column, p a r a g r a p h s 1-2; r i g h t - h a n d
column, p a r a g r a p h 1 ; f i g u r e 1
A
1-5 ,18 ,28
4
--
Chemical A b s t r a c t s , v o l . 9 7 , no. 18,
November 1982 (Columbus, Ohio, U S )
see page 570, column 1 , a b s t r a c t no.
153063a; & J P , A , 82107244 ( P e n t e l Co.)
3 J u l y 1 9 8 2 , see t h e whole a b s t r a c t
A
1,9,29
--
J o u r n a l of Applied E l e c t r o c h e m i s t r y , v o l .
15, no. 5 , September 1985; Chapman and
Hall;
A.K. Shukia e t a l . : "High e f f i c i e n c y
cathodes f o r a l k o l i n e a i r e l e c t r o d e s " ,
pages 7 7 4 - 7 7 6 , see page 774,- l e f t - h a n d
r i g h t - h a n d column,.
column, l i n e 1
l i n e 15; page 775, f i g u r e 1
-
I
Form PCT ISA!210 (extra 8hee~t)(January 1985)
--
1,6,7,8,9,
10,11,15,16
19,20,21 ,22
2 7 ,28
=I*
intrrnationii Application No.
111. D O C U M E N T S CONSIDERED TO BE R E L E V A N T
(CONTINUED
PCT/GB 8 5/ 0 0 4 0 0
FROM T H E SECOND SHEET)
Cititm of Doarment. wdh indication. vhrr aporopnite. of
r a b m t prasagen
Relevant t o Claim No
E l ec t r o c h i m i c a A c t a , v o l . 30, no. 2 ,
February 1985, Pergamon Press ( G B )
R. Elanoharan e t a l . : "Oxides s u p p o r t e d
carbon a i r e l e c t r o d e s f o r a l k o l i n e
power d e v i c e s " , pages 205-209, see
a b s t r a c t ; page 2 0 5 , r i g h t - h a n d colu.m,
p a r a g r a p h s 1-3; f i g u r e 1
--
J o u r n a l of Power S o u r c e s , vol. 1 3 , no. 4,
December 1984 (Lausanne, CH)
R. Manoharan e t a l . : "High performance
p l a t i n i z e d carbon e l e c t r o d e s f o r oxygen
r e d u c t i o n i n power s o u r c e s w i t h a.lkalinc
e l e c t r o l y t e s " , pages 273-285, see
page 2 7 4 , l i n e s 26- 30; f i g u r e 3
GB, A , 2 0 0 9 1 3 0
(EXXON RESEARCH)
1 3 June 1971
FR, A , 2445031 (ETAT FRANCAIS REPRESENTE
PAR LE DELEGUE GENERAL POUR L'ARMEMENT)
18 J u l y 1980
see c l a i m s 1 , 3
m PCT ISA:210 (extra rhea0 (January lS85)
1
- 3-
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see Official Journal of the European Patent Office, No. 12/82