Implementing Structural Disorder as a Promising Direction for Improving the Stability of PtNi/C Nanoparticles

Abstract

Because of their enhanced oxygen reduction reaction (ORR) kinetics (9 and 6-fold) enhancement of specific activity and mass activity for the ORR relative to those of a commercial Pt/C catalyst, respectively), hollow PtNi/C nanoparticles are attracting a growing level of interest. This catalytic enhancement arises from the synergetic combination of strain and ligand effects, the presence of structural defects, and their hollow morphology producing a convex and concave catalytic sites. However, preventing a loss of catalytic activity under practical proton exchange membrane fuel cell (PEMFC) cathode operating conditions on alloys of platinum with other transition metals (PtM alloys, M being a transition metal) or M-rich core@Pt-rich shell nanoparticles remains highly challenging. A loss of performance is usually observed because of the dissolution of Pt and M under the harsh operating conditions of a PEMFC cathode, but the question remains unanswered for nanomaterials in which catalytic activity is not solely due to alloying effects. Herein, we have carefully investigated the changes in the ORR activity of solid and hollow PtNi/C nanoparticles with identical chemical compositions but different nanostructures during an accelerated stress test simulating PEMFC cathode operation. By combining chemical, physical, and electrochemical techniques, we show that the dissolution of Ni atoms constitutes the primary reason for the loss of ORR catalytic activity but that the initial catalytic advantage of hollow over solid PtNi/C nanoparticles is maintained in the long term. Hence, implementing structural disorder in PEMFC cathode electrocatalysts represents a promising direction for sustainably improving ORR kinetics.