Effects of Catalyst Processing on the Activity and Stability of Pt–Ni Nanoframe Electrocatalysts

Pt-based alloys have shown great promise as cathodic catalysts for cost-effective proton-exchange membrane fuel cells. Post-synthesis treatment has been recognized as a critical step to improve the catalytic performance of Pt-based alloys. Here, we present the effects of catalyst processing on the catalytic behavior of Pt–Ni nanoframe electrocatalysts in oxygen reduction reaction. The Pt–Ni nanoframes were made by corroding the Ni-rich phase from solid rhombic dodecahedral particles. A total of three different corrosion procedures were compared. Among them, electrochemical corrosion led to the highest initial specific activity (1.35 mA cm–2 at 0.95 V versus reversible hydrogen electrode) by retaining more Ni in the nanoframes. However, the high activity gradually went down in a subsequent stability test due to continuous Ni loss and concomitant surface reconstruction. On the other hand, the best stability was achieved by a more-aggressive corrosion using oxidative nitric acid. Although the initial activity was compromised, this procedure imparted a less-defective surface, and thus, the specific activity dropped by only 7% over 30？000 potential cycles. These results indicate a delicate trade-off between the activity and stability of Pt–Ni nanoframe electrocatalysts. The obtained understanding of how to balance the activity–stability trade-off via catalyst processing can be generalized to other Pt-based alloys