Circumventing Metal Dissolution Induced Degradation of Pt-Alloy Catalysts in Proton Exchange Membrane Fuel Cells: Revealing the Asymmetric Volcano Nature of Redox Catalysis

One of the major obstacles to the commercialization of proton exchange membrane fuel cells (PEMFCs) is the usage of scarce platinum in the cathode for the oxygen reduction reaction (ORR). Although progress has been made in reducing Pt usage by alloying with transition metals M (M = Co, Ni, Cu, etc.), practical applications of Pt-M/C catalysts are impeded by their insufficient durability under the highly corrosive conditions at a PEMFC cathode. Herein, we reconcile the durability difficulty by demonstrating that the high mass activity of the dealloyed PtNi3/C catalyst with low nanoporosity further increases after 30k voltage cycles in PEMFCs. A novel method has been developed to implement an in situ X-ray absorption spectroscopy study of these PEMFC-cycled catalysts under operating conditions to understand the unusual activity trend. We reveal that the ORR activity of PtNi3/C catalysts with varied nanoporosities exhibits a Sabatier volcano curve as a function of the strain governed by Ni content, and the volcano is skewed toward the Pt–O weak binding leg owing to the asymmetric site-blocking effect. The Ni dissolution during PEMFC operation, which was previously believed to be detrimental, becomes beneficial for the solid PtNi3/C catalysts located on the Pt–O weak binding leg because it leads to the activity ascending toward the apex, and meanwhile the activity remains high throughout the long-term operation owing to the minimal site-blocking effect. More generally, the fundamental insights into the universal asymmetric volcano curve of redox catalysis will potentially guide the rational design of a broad variety of catalytic materials.