Pt Alloy Nanocrystal Catalysts: Diminishing Sizes and Improving Stability

Polymer electrolyte membrane fuel cells (PEMFCs) are one of the most promising energy conversion devices with the advantages of clean and efficient, low-temperature operation, abundant fuel sources, and portability. Due to limited availability and high cost, the use of noble metal Pt catalysts in oxygen reduction reaction (ORR) must be reduced in order to achieve large-scale commercial application of PEMFCs. Alloying with transition metals to reduce the Pt usage and increase the utilization of Pt is by far the main way to develop ORR catalysts with high activity and superior stability. Particularly, diminishing the sizes can increase the Pt atom utilization as well as the Pt mass activity, but the smaller nanocrystals with higher surface energy are typically thermodynamically and electrochemically unstable. How to acquire smaller and even ultrafine Pt alloy nanocrystals with high stability is thus especially important. Herein, we review the research progress in this field in the very recent years. A fundamental understanding of the size–activity and the size–durability relationship is first introduced. Then the discussions focused on the synthetic strategies and design concepts for reducing nanocrystal size and simultaneously enhancing their stability. Finally, the challenges and future perspectives on the research directions of Pt-based alloy nanocrystal catalysts are briefly summarized.