Improving Activity and Stability of ORR Electrocatalysts with Pt-Rich Hollow Nanostructures

The ever-growing energy demand worldwide and the announced end of the so-called “fossil fuel era” are currently boosting the development of electrochemical energy technologies, such as fuel cells, batteries and supercapacitors. In proton-exchange membrane fuel cells (PEMFC), special effort has been paid to improve the catalytic activity for the oxygen reduction reaction (ORR) of the cathodic material, its stability and to decrease its precious metal content.  

This study describes the advantages of hollow nanostructures composed of a Pt-rich outer-layer surrounding a central void. Pt-rich hollow nanoparticles with different Pt-shell thicknesses were synthesized via a method involving the galvanic replacement of Ni atoms by Pt atoms, and the nanoscale Kirkendall effect [1]. Increasing the Pt:Ni stoichiometry from 1:1 to 1:5 in the initial metal precursor solution resulted into a thinner Pt-rich shell and an increased Pt lattice contraction. The specific activity and the mass activity for the ORR at E = 0.95 V vs. RHE of the most active hollow electrocatalyst were 9-fold and 3.6-fold that of a reference solid carbon-supported Pt nanocrystallites with a comparable crystallite size (Figure 1). Their structural stability was investigated at different temperatures ranging from T= 293 to 353 K by identical-location and conventional transmission electron microscopy.

Acknowledgements

This work was performed within the framework of the Centre of Excellence of Multifunctional Architectured Materials "CEMAM" n° AN-10-LABX-44-01 funded by the "Investments for the Future" program. The authors acknowledge financial support from University of Grenoble-Alpes through the AGIR program (grant # LL1492017G), and from the French national Research Agency through the HOLLOW project (grant # ANR-14-CE05-0003-01).

References

[1] L. Dubau, M. Lopez-Haro, J. Durst, L. Guétaz, P. Bayle-Guillemaud, M. Chatenet, F. Maillard, “Beyond conventional electrocatalysts: Hollow nanoparticles for improved and sustainable oxygen reduction reaction activity”, J. Mater. Chem. A. 2 (2014) 18497-18507.