Ultrasmall (<5 nm diameter) noble metal nanoparticles
with a
high fraction of {111} surface domains are of fundamental and practical
interest as electrocatalysts, especially in fuel cells; the nanomaterial
surface structure dictates its catalytic properties, including kinetics
and stability. However, the synthesis of size-controlled, pure Pt-shaped
nanocatalysts has remained a formidable chemical challenge. There
is an urgent need for an industrially scalable method for their production.
Here, a one-step approach is presented for the preparation of single-crystal
pyramidal nanocatalysts with a high fraction of {111} surface domains
and a diameter below 4 nm. This is achieved by harnessing the shape-directing
effect of citrate molecules, together with the strict control of oxidative
etching while avoiding polymers, surfactants, and organic solvents.
These catalysts exhibit significantly enhanced durability while, providing
equivalent current and power densities to highly optimized commercial
Pt/C catalysts at the beginning of life (BOL). This is even the case
when they are tested in full polymer electrolyte membrane fuel cells
(PEMFCs), as opposed to rotating disk experiments that artificially
enhance electrode kinetics and minimize degradation. This demonstrates
that the {111} surface domains in pyramidal Pt nanoparticles (as opposed
to spherical Pt nanoparticles) can improve aggregation/corrosion resistance
in realistic fuel cell conditions, leading to a significant improvement
in membrane electrode assembly (MEA) stability and lifetime.