Self-assembled growth of Pd-Ni sub-microcages as a highly active and durable electrocatalyst

Metal nanoparticles (NPs) are prone toOstwald ripening, which usually leads to a quick loss of the catalytic activity. Herein, we report a bottom-up synthesis of Pd35Ni1 sub-microcages (MCs) as a selfsupported catalyst for the methanol oxidation reaction (MOR), showing excellent activity and durability. The key is to use a phosphine oxide as a weak capping agent to allow the aggregation of Pd-Ni NPs. The subsequent thermal ripening of the assembled NPs leads to the formation of the Pd-Ni MCs. Due to the high porosity, electrical conductivity, and atomically stepped surfaces, these MCs afford a current density of 3.2 mA cmPd 2 in the MOR in an alkaline medium, which is superior to those of Pd-Ni NPs and Pd NPs. Thanks to the well-defined bicontinuous self-supported structure, more than 91.4% of the current remained after 2000 cyclic voltammetry cycles. The excellent catalytic durability makes the MCs superior to the carbonsupported NP catalysts. This work provides a facile and environmentally benign approach to fabricate porous precious metallic nanomaterials as a highly active and durable electrocatalyst with enhanced utilization of the precious metals.