153
© Springer Nature Switzerland AG 2020
R. Adzic, N. Marinkovic, Platinum Monolayer Electrocatalysts,
https://doi.org/10.1007/978-3-030-49566-4_9
Chapter 9
Performance Stability and Scale-Up
Syntheses of Pt Monolayer Electrocatalysts
Stability is one of the main requirements for commercializing fuel cell electrocatalysts for automotive applications. Platinum is the best-known catalyst for oxygen
reduction in cathodes, but it undergoes dissolution during potential changes while
driving electric vehicles. As mentioned in previous sections, platinum monolayers
on palladium–gold alloy nanoparticles are an active, stabile electrocatalyst that can
be used in automotive application. In fuel cell tests, this electrocatalyst with its
ultra-low platinum content showed minimal degradation in activity over
100,000 cycles between potentials 0.6 and 1.0 V. Under more severe conditions with
a potential range of 0.6–1.4 V, no marked losses in platinum and gold are registered
despite the dissolution of palladium. Potential cycling in certain range provides
accelerated test of catalyst stability. These data coupled with theoretical analyses
demonstrated that adding a small amount of gold to palladium and forming highly
uniform nanoparticle cores make the platinum monolayer electrocatalyst significantly tolerant to degradation.
Activity and stability of Pt ML electrocatalysts in fuel cell tests in Fig. 9.1 displays
the TEM image of the cross-section of MEA after 100,000 potential cycles from 0.6
to 1.0 V, and the corresponding distribution of Pt, Au, and Pd in the catalytic
nanoparticles after the stability test is displayed in Fig. 9.1b [1]. A Pd band forms in
the middle due to Pd dissolution and redeposition in reduction by small amount of
H 2 diffusing from the anode. This is very promising for the automotive application
of fuel cells because Pd, i.e., reduced Pd
2+
, does not affect conductivity of the
membrane.
Pd
2+
is reduced by H 2 diffusing from the anode; Pt and Au remain in the cathode.
Pd is a slightly more reactive metal than Pt and so dissolves at slightly lower potentials (0.92 (Pd) vs. 1.19 (Pt) V). The small dissolution limits the excursions of potential in an operating fuel cell or at least minimizes it. Such partial dissolution of Pd
entails a small contraction of the Pt ML shell, giving rise to a more stable structure
with increased dissolution resistance and specific activity. This is the self-healing
effect observed with this core–shell system as depicted in the model insert in
Fig. 9.1b: the slow dissolution of Pd causes the decrease in the particle’s size,
© Springer Nature Switzerland AG 2020
R. Adzic, N. Marinkovic, Platinum Monolayer Electrocatalysts,
https://doi.org/10.1007/978-3-030-49566-4_9
Chapter 9
Performance Stability and Scale-Up
Syntheses of Pt Monolayer Electrocatalysts
Stability is one of the main requirements for commercializing fuel cell electrocatalysts for automotive applications. Platinum is the best-known catalyst for oxygen
reduction in cathodes, but it undergoes dissolution during potential changes while
driving electric vehicles. As mentioned in previous sections, platinum monolayers
on palladium–gold alloy nanoparticles are an active, stabile electrocatalyst that can
be used in automotive application. In fuel cell tests, this electrocatalyst with its
ultra-low platinum content showed minimal degradation in activity over
100,000 cycles between potentials 0.6 and 1.0 V. Under more severe conditions with
a potential range of 0.6–1.4 V, no marked losses in platinum and gold are registered
despite the dissolution of palladium. Potential cycling in certain range provides
accelerated test of catalyst stability. These data coupled with theoretical analyses
demonstrated that adding a small amount of gold to palladium and forming highly
uniform nanoparticle cores make the platinum monolayer electrocatalyst significantly tolerant to degradation.
Activity and stability of Pt ML electrocatalysts in fuel cell tests in Fig. 9.1 displays
the TEM image of the cross-section of MEA after 100,000 potential cycles from 0.6
to 1.0 V, and the corresponding distribution of Pt, Au, and Pd in the catalytic
nanoparticles after the stability test is displayed in Fig. 9.1b [1]. A Pd band forms in
the middle due to Pd dissolution and redeposition in reduction by small amount of
H 2 diffusing from the anode. This is very promising for the automotive application
of fuel cells because Pd, i.e., reduced Pd
2+
, does not affect conductivity of the
membrane.
Pd
2+
is reduced by H 2 diffusing from the anode; Pt and Au remain in the cathode.
Pd is a slightly more reactive metal than Pt and so dissolves at slightly lower potentials (0.92 (Pd) vs. 1.19 (Pt) V). The small dissolution limits the excursions of potential in an operating fuel cell or at least minimizes it. Such partial dissolution of Pd
entails a small contraction of the Pt ML shell, giving rise to a more stable structure
with increased dissolution resistance and specific activity. This is the self-healing
effect observed with this core–shell system as depicted in the model insert in
Fig. 9.1b: the slow dissolution of Pd causes the decrease in the particle’s size,