Electrochemical Atomic-level Controlled Syntheses of Electrocatalysts for the Oxygen Reduction Reaction - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 145

eciency in the PEMFCs. In order to compensate this loss a large amount of
Pt is required, which causes their cost raising. Currently, the Pt loading in
the state-of-the-art PEMFCs is 0.4 mg Pt cm 2 . 1 Reduction of the amount of
the Pt contained in the PEMFCs stacks is required for large-scale automotive
applications, both for reasons of cost and Pt supply limitations. In order to
challenge researchers all over the world, and to boost the implementation of
the PEMFCs in the electric vehicles, the United States Department of Energy
(DOE) set challenging technical targets for development of fuel cell elec-
trocatalysts for transportation applications in its Multi-Year Research, De-
velopment and Demonstration Plan. 2 The main goal of this plan is to
develop and demonstrate fuel cell power system technologies for transpor-
tation, stationary and portable power applications. One of the objectives is to
develop a 60% peak-ecient, 5000-h durable, direct hydrogen fuel cell power
system for transportation at a cost of $30/kW by 2017. According to the DOE
targets for 2020, the platinum group metal (PGM) total loading in both
electrodes of the PEMFCs should be as low as 0.125 mg PGM cm 2 . 2 The mass
activity is targeted to be 0.44 A mg Pt 1 at 900 mV (vs. RHE) as determined
from the iR-free polarization curve measured at 80 1CH 2 /O 2 in MEA, fully
humidified with total outlet pressure of 150 kPa, anode and cathode sto-
chiometry 2 and 9.5, respectively. The loss in the initial catalytic activity is
targeted to be less than 40%, after 5000 accelerated stability tests, performed
in a 25-50 cm 2 MEA, during triangle sweep cycles at 50 mV s 1 between 0.6 V
and 1.0 V (vs. RHE) at 80 1C, atmospheric pressure, 100% relative humidity,
H 2 at 200 sccm and N 2 at 75 sccm. 2 There are two methodologies for de-
termining the mass activity and fundamentally more meaningful specific
activity (in units of mAcm 2 Pt ) of the electrocatalysts for the ORR. 1 The first
one is so-called thin-film rotating-disc electrode (RDE) method that is used
for studding high-surface-area catalysts in aqueous electrolyte. In this
method a thin layer (about 1 mm) of catalyst is deposited from catalysts ink
on a glassy carbon RDE electrode and then is dryed. Then the electrode is
immersed in de-aerated or oxygen saturated solution of perchloric acid and
the mass and specific activities are calculated from the polarization and
cyclic voltammetry (CV) curves. 3 The second method requires preparation of
membrane electrode assemblies (MEAs) which consist of an anode, cathode
electrodes and proton-conducting membrane (Nafion s ), and testing them in
aH 2 /O 2 -fed single cell. Both approaches are shown to yield similar
activities. 1,3
Different types of electrocatalysts have been developed in the last several
decades in order to meet the DOE targets. 1,4 The general trend in the
research and development of advanced electrocatalysts for the ORR is to
reduce or even to eliminate the Pt and the other precious metals from the
composition of the catalysts. Generally, the electrocatalysts for the ORR can
be systematized in three main groups: 1,4 (i) Pt-based electrocatalysts,
(ii) non-Pt catalysts, and (iii) non-precious catalysts. Among those, the Pt-
based catalysts are the most promising for real fuel cell applications since, at
the moment, only they satisfy all DOE requirements. This group of catalysts

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