CO-tolerance of low-loaded Pt/Ru anodes for PEM fuel cells
Zhigang Qi
*
, Arthur Kaufman
H Power Corporation, 60 Montgomery Street, Belleville, New Jersey, NJ 07109, USA
Abstract
Anodes with various Pt/Ru loadings were prepared using three different anode catalysts: E-TEK 40% Pt-Ru/Vulcan XC-72 and Engelhard
40 and 50% Pt-Ru/C. These anodes were tested for their CO-tolerance at a cell temperature of 70 8C in the presence of 10 and 50 ppm CO,
respectively. The performance declined with CO concentration for all the anodes. However, Engelhard catalysts showed better performance
than E-TEK catalyst under our experimental conditions. A minimum Pt/Ru loading of 0.43, 0.22 and 0.30 mg/cm
2
was needed to achieve the
maximum performance for E-TEK 40% Pt-Ru/C, Engelhard 40 and 50% Pt-Ru/C, respectively, when 10 ppm CO/70% H
2
/30% CO
2
was used
at a cell current density of 0.20 A/cm
2
. Using 50 ppm CO/70% H
2
/30% CO
2
and at a cell current density of 0.20 A/cm
2
, a minimum Pt/Ru
loading of 0.60, 0.32 and 0.36 mg/cm
2
was needed to achieve the highest performance for E-TEK 40% Pt-Ru/C, Engelhard 40 and 50% Pt-Ru/
C, respectively.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: PEM fuel cells; CO-tolerance; E-TEK; Engelhard
1. Introduction
Anode poisoning by CO substantially lowers the perfor-
mance of a proton exchange membrane (PEM) fuel cell.
Mitigating such a poisoning effect has been an ongoing task
challenging scientists and engineers in this ®eld. One solu-
tion to mitigating the poisoning is to use alloyed catalysts
such as Pt/Ru, Pt/Mo, Pt/Ru/Mo, Pt/Sn, Pt/Ru/WO
3
and Pd/
Au, which exhibit improved CO-tolerance [1±12]. The
improvement is due to either a lowered CO oxidation
potential or a weakened adsorption of CO on these catalysts.
This is the most convenient approach because it does not
introduce any additional steps or hardware. It is quite
effective to handle a reformate containing less than
10 ppm CO, but it is not adequate when the CO concentra-
tion is higher. In the presence of higher CO concentration, an
additional step involving bleeding an oxidant into the anode
compartment has been explored [13±17]. The bleeding
oxidant, which can be air, oxygen, or hydrogen peroxide,
chemically oxidizes CO to CO
2
and thus lowers its con-
centration. Caution must be taken in exercising this proce-
dure to assure safe fuel cell operation. Furthermore, only
about 1 out of 400 oxygen molecules participates in the
oxidation of CO [17], and the remaining oxygen chemically
combusts with hydrogen. The combustion reaction not only
lowers the fuel ef®ciency, but might also accelerate the
sintering of catalyst particles to lead to a performance
decline with time. In addition, the chemical combustion
might also create pinholes in the electrolyte membrane,
which could result in cell failure.
Currently, Pt-Ru/C is the most popular CO-tolerant cat-
alyst used in anodes for PEM fuel cells. The Pt/Ru loading in
the catalyst layer determines the degree of CO-tolerance,
and the optimal loading is also dependent on the fuel cell
operation conditions such as current density, cell tempera-
ture, and CO concentration. Normally, higher current den-
sity, lower cell temperature, and higher CO concentration
require a higher Pt/Ru loading. Recently, we found that even
when all these conditions were the same, catalysts made by
different manufacturers had different CO-tolerance. This
article reports the relative CO-tolerance of E-TEK 40%
Pt-Ru/Vulcan XC-72, and Engelhard 40 and 50% Pt-Ru/C.
2. Experimental
Catalyst mixtures were prepared by directly mixing a Pt-
Ru/C catalyst with Na®on at a mass ratio of cat-
alyst:Nafion 70:30. All the carbon-supported Pt-Ru cat-
alysts reported here had a Pt:Ru atomic ratio of 1:1. The
carbon black in E-TEK 40% Pt-Ru/C was Vulcan XC-72,
Journal of Power Sources 113 (2003) 115±123
*
Corresponding author. Tel.: 1-973-450-4400x5560;
fax: 1-973-450-9850.
E-mail address: zqi@hpower.com (Z. Qi).
0378-7753/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0378-7753(02)00489-5