Design of Core@Shell Nanoparticles Based on Gold and Magnetic NiFe Prussian-Blue Analogues Featuring Shape-Dependent Magnetic and Electrochemical Activity

Au@Prussian-Blue analogue (PBA) core@shell nanoparticles (NPs) are highly versatile nanostructures with complementary and shape-dependent properties of interest in the current technologies. However, due to the high reactivity of cyanides toward Au, scarce PBAs have been successfully synthesized in direct contact with Au NPs, leaving the formation of anisotropic Au@PBA NPs as a significant synthetic challenge. Here, we have developed a robust protocol for synthesizing core@shell NPs, composed of a magnetic CsNi[Fe(CN)6] PBA shell grown on individual Au NPs, regardless of the core morphology (spheres, rods, or stars). Specifically, the uniqueness of our protocol lies in the prior Au core functionalization with anchoring molecules that facilitate PBA growth while preventing Au etching and preserving the initial oxidation states of the metals. This has afforded direct growth of ferromagnetic NiIIFeIII PBAs on Au NPs. Moreover, by exploiting the structural mismatch at the Au/PBA interface and the curvature of anisotropic Au templates, we manage to induce a substantial structural strain within the PBA shell. When star-shaped Au nanoparticles are used, a maximum strain of 2.0% is reached. This strain combined with an increased polycrystallinity lead to modifications in the PBA catalytic properties, resulting in a 10-fold improvement in the intrinsic electrocatalytic activity.