Synthesis of intermetallic PtCo fuel cell catalysts from bimetallic core@shell structured nanoparticles

Abstract

The high activity and stability of intermetallic PtCo nanocatalysts toward oxygen reduction reaction make them a top candidate as low-Pt cathode catalysts in proton exchange membrane fuel cells (PEMFCs). However, forming intermetallic structures typically requires high-temperature annealing, posing a challenge for achieving well-size control and highly ordered structures. Here we report the design and synthesis of bimetallic core@shell structured precursors for affording high-performance intermetallic PtCo catalysts. The fabrication of the core@shell precursor involves using a molecular ligand containing both sulfur and oxygen donors to selectively bind with Pt colloidal nanoparticles as the core and chelate Co ions as the shell. During high-temperature annealing, the ligand transforms into carbon coatings around alloy nanoparticles, preventing particle sintering; meanwhile, Co ions in the shell can easily diffuse into the Pt core, which helps to increase the thermodynamic driving force for forming intermetallic structures. These benefits enable us to obtain the catalyst with finely dispersed nanoparticles (∼3.5 nm) and a high ordering degree of 72%. With 0.1 mg_Pt/cm² cathode loading, the catalyst delivers superior performance and durability in PEMFCs, showing an initial mass activity of 0.56 A/mg_Pt, an initial power density of 1.05 W/cm² at 0.67 V (H₂-air), and a voltage loss of 26 mV at 0.8 A/cm² after the accelerated durability test.