Abstract Pt-Ni octahedral nanocrystals with exposed 111 facets are highly active oxygen reduction reaction (ORR) catalysts, yet achieving precise control over their particle size remains challenging. In this work, three Pt-Ni octahedral nanocatalysts with tunable sizes were synthesized using a one-pot colloidal method by adjusting the amount of NiCl 2 ·6H 2 O precursor. Interestingly, both decreasing and increasing the Ni precursor amount relative to the standard value of 0. 05 mmol resulted in smaller octahedra. At low precursor concentrations, limited Ni precursor supply restricts crystal growth, whereas at high concentrations, accelerated nucleation and Cl⁻-induced stabilization of the (111) facets inhibit further growth. Electrochemical measurements show that the catalyst exhibiting the smallest particle size delivers the highest ORR mass activity (1. 98 A/mg Pt), likely due to its large specific surface area. This work highlights the crucial role of precursor concentration in tailoring nanoparticle dimensions and enhancing the electrochemical activity of Pt-Ni catalysts for the ORR. Graphical abstract
Delgado et al. (Fri,) studied this question.