Electrochemical Atomic-level Controlled Syntheses of Electrocatalysts for the Oxygen Reduction Reaction - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 156

the ORR has been proposed in a patent assigned to Wang and Adzic. 30 The
method includes contacting hydrogen adsorbed palladium or palladium
alloy (PdNi, PdCo, PdFe, PdAu) particles with one or more metal salts, par-
ticularly Pt, to produce a sub-monolayer or mono-atomic metal or metal-
alloy coating on the surface of the hydrogen-absorbed Pd or Pd alloy par-
ticles. The method does not require electro-deposition and does not generate
waste. Hydrogen absorbed Pd or Pd alloy particles are produced by exposing
the particles to hydrogen gas for a period of time su cient to bring stoi-
chiometric coecient x in PdH x to value of 0.6. After that the hydrogen
absorbed Pd or Pd alloy particles are exposed to a solution containing Pt salt
(or mixture of Pt salt with other metal salts) and an atomic monolayer of Pt
or mixed Pt alloy monolayer-shell is deposited on the Pd or Pd alloy-core.

d n 9 r 4 n g | 4

6.3 Platinum Monolayer on Electro-deposited
Mono- and Bi-metallic (Pd, PdAu, PdIr, NiW)
Nanostructures: Highly Ecient Electrocatalysts
for the ORR
Among all strategies for Pt ML core-shell electrocatalyst processing, the
SLRR of Cu UPD ML by Pt ML is the most viable for fuel cell catalysts syn-
thesis. The catalysts obtained by this strategy use as a core Pd or Pd alloys
nanoparticles supported on carbon, which are synthesized by conventional
chemical methods, and then are cleaned from the surfactants that are
commonly used during the synthesis. This type of Pt ML catalysts is well
studied in the literature and several reviews have been published. 5,6,24,28,31
In addition, the method for the Pt ML shell deposition on Pd and PdAu
nanoparticles cores has been scaled up. Furthermore, these electrocatalysts
are considered as the most promising candidate for the second generation of
the PEMFCs for the electric vehicles.
In this chapter we report on the next generation fuel cell electrocatalysts
where the cores of mono-, bimetallic- or multi-component Pd alloys (in-
cluding refractory alloys) nanostructures are electro-deposited on functio-
nalized carbon (C ox ) or directly on the gas diffusion layer (GDL), which serve
also as a current collector, and then Pt ML is deposited on their surface by
SLRR of Cu UPD monolayer. The advantages of the electro-deposition over
the conventional chemical methods for synthesis of electrocatalysts are as
follows: (i) ultra-precise quantitative control of the deposited nano-
structures; (ii) fine tuning of the microstructure and the morphology of the
deposits without the need for the presence of any surfactants in the elec-
trolyte; (iii) versatility in metals or alloys deposition; (iv) high utilization rate
of the row materials and low materials waste; (v) low energy consumption;
(vi) little capital investment; and (vii) ease of development of large-scale
manufacturing processes.
In the Pt ML shell catalyst on electro-deposited nanostructures cores the
total precious metal loading could be reduced to 50 mgcm 2 , which is a half

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