1 research outputs found
Understanding and Controlling Nanoporosity Formation for Improving the Stability of Bimetallic Fuel Cell Catalysts
Nanoporosity is a frequently reported phenomenon in bimetallic
particle ensembles used as electrocatalysts for the oxygen reduction
reaction (ORR) in fuel cells. It is generally considered a favorable
characteristic, because it increases the catalytically active surface
area. However, the effect of nanoporosity on the intrinsic activity
and stability of a nanoparticle electrocatalyst has remained unclear.
Here, we present a facile atmosphere-controlled acid leaching technique
to control the formation of nanoporosity in Pt–Ni bimetallic
nanoparticles. By statistical analysis of particle size, composition,
nanoporosity, and atomic-scale core–shell fine structures before
and after electrochemical stability test, we uncover that nanoporosity
formation in particles larger than ca. 10 nm is intrinsically tied
to a drastic dissolution of Ni and, as a result of this, a rapid drop
in intrinsic catalytic activity during ORR testing, translating into
severe catalyst performance degradation. In contrast, O<sub>2</sub>-free acid leaching enabled the suppression of nanoporosity resulting
in more solid core–shell particle architectures with thin Pt-enriched
shells; surprisingly, such particles maintained high intrinsic activity
and improved catalytic durability under otherwise identical ORR tests.
On the basis of these findings, we suggest that catalytic stability
could further improve by controlling the particle size below ca. 10
nm to avoid nanoporosity. Our findings provide an explanation for
the degradation of bimetallic particle ensembles and show an easy
to implement pathway toward more durable fuel cell cathode catalysts