Hollow Metal Nanocrystals with Ultrathin, Porous Walls and Well-Controlled Surface Structures.

Recent developments of a novel class of catalytic materials built on hollow nanocrystals having ultrathin, porous walls, and well-controlled surface structures are discussed, with a focus on platinum and the oxygen reduction reaction (ORR). An introduction is given to the critical role of platinum in the proton exchange membrane fuel cells, and the pressing need to develop a strategy for achieving cost-effective and sustainable use of this precious metal. How to maximize the mass activity of ORR catalysts based on platinum by rationally engineering the surface structure while increasing the utilization efficiency of atoms is then discussed. After reporting on the synthetic methods involving galvanic replacement and seed-mediated growth followed by etching, respectively, a number of examples to demonstrate the enhancement in activity and durability for this new class of catalytic materials are showcased. The feasibility to have the methodology extended from platinum to other precious metals such as gold and ruthenium is highlighted. In conclusion, some of the remaining issues and emerging solutions are examined.