Annealing-temperature-dependent relation between alloying degree, particle size, and fuel cell performance of PtCo catalysts

Pt-M (M is typically 3d transition metal) alloy nanoparticles as the state-of-the-art electrocatalysts exhibit supe-rior activity for the sluggish cathodic oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells (PEMFCs). The specific activity (SA) of Pt-M alloy catalysts is strongly correlative to their surface compressive strains that are majorly dependent on the M type and content. In order to promote the alloying of Pt with M to improve the SA, a high-temperature annealing is normally inevitable, which however accelerates the metal sin-tering resulting in larger particles and lowers electrochemical surface areas (ECSAs) as well as the high-current-density PEMFCs performance. Herein, we systematically studied the ORR/PEMFCs performance of a family of PtCo catalysts with varied alloying degree and particle size, which were prepared at different anneal-ing temperatures ranging from 400 to 1000 degrees C. We found the annealing-temperature-dependent trade-off rela-tion between the alloying-degree-dependent SA and particle-size-dependent ECSA. The optimal PtCo catalyst was thus achieved at a medium annealing temperature of 600 degrees C, showing a high mass activity (MA) of 1.04 A mg(-1) and a large rated power density of 1.07 W cm(-2) with a low Pt loading of 0.1 mg(Pt) cm(-2).