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The development of Pt on Ni nanoparticles is critical for the improvement of water splitting reactions. Here, the growth of small, below 2 nm Pt islands on crystalline branched Ni nanoparticles was investigated by tuning the size of the islands using a slow seeded-growth synthesis. Smaller island size results in a greater shift in the hydrogen binding energy on the Pt sites, as characterized by the hydrogen underpotential peak position in the voltammogram. This shift indicates the weakening of the binding to hydrogen, which leads to enhanced alkaline hydrogen evolution reaction activity with smaller Pt island size.

Controlling the coordination environment of the nanocatalyst surface is a major synthetic challenge to producing electrocatalysts with high activity and high stability. This is particularly important for the methanol oxidation reaction (MOR) in which multiple neighboring metal atoms are needed to prevent CO poisoning. Using a combination of tunable Pt-island size and a spreading process, we can vary the Pt loading on branched Ru nanoparticles, which leads to tunable proportions of Pt–Pt and Pt–Ru neighboring atoms at the surface. The controlled coordination environments are shown to be critical to stripping poisoning CO intermediates and can be precisely tuned to achieve highly active and stable MOR catalysts. These results show a new concept in synthetically controlling the coordination environment around a catalytic site for improved activity and stability that can be applied to other multimetal nanocatalysts.

Growing Pt on Ag nanoparticles is a promising approach to forming catalysts that present active sites with both Pt and Ag available to improve the activity for the hydrogen evolution reaction (HER). By carefully controlling the concentration of a Pt precursor, the amount of Pt-decorated particles onto the Ag nanoparticles could be controlled to grow Pt islands between 0.6 and 1.5 nm. As a result, the relative amounts of the Ag–Pt active sites could be tuned. The smallest, 0.6 nm Pt islands on the Ag nanoparticle, with the highest ratio of Ag–Pt to Pt–Pt sites was found to have the highest activity and an accelerated Volmer step. DFT modeling showed that the improved performance was due to increased electron density on Pt from electron donation from neighboring Ag that leads to weaker Pt–H binding and the presence of more oxophilic Ag that can bind −OH on the active site that accelerates the water splitting.

Branched metal nanoparticles have unique catalytic properties because of their high surface area with multiple branches arranged in an open 3D structure that can interact with reacting species and tailorable branch surfaces that can maximize the exposure of desired catalytically active crystal facets. These exceptional properties have led to the exploration of the roles of branch structural features ranging from the number and dimensions of branches at the larger scales to the atomic-scale arrangement of atoms on precise crystal facets. The fundamental significance of how larger-scale branch structural features and atomic-scale surface faceting influence and control the catalytic properties has been at the forefront of the design of branched nanoparticles for catalysis. Current synthetic advances have enabled the formation of branched nanoparticles with an unprecedented degree of control over structural features down to the atomic scale, which have unlocked opportunities to make improved nanoparticle catalysts. These catalysts have high surface areas with controlled size and surface facets for achieving exceedingly high activity and stability. The synthetic advancement has recently led to the use of branched nanoparticles as ideal substrates that can be decorated with a second active metal in the form of islands and single atoms. These decorated branched nanoparticles have new and highly effective catalytic active sites where both branch metal and decorating metal play essential roles during catalysis.

Magnetic particle imaging (MPI) is a promising diagnostic imaging technique that enables direct and precise tracking of magnetic tracers. The optimization of iron oxide-based nanoparticle tracers is of utmost importance in MPI for attaining high sensitivity and good spatial resolution. Currently, the state-of-the-art MPI tracers utilize undoped, magnetite iron oxide nanoparticles (NPs). In this study, we present the first comprehensive analysis of how doping with cobalt influences the MPI performance of iron oxide-based NPs. We observed a 1.4–1.7-fold and 1.2–1.3-fold enhancement in the saturation magnetization (Msat) value by doping Co into 9 and 20 nm magnetite NPs, respectively. The amplification in the maximum point spread function (PSF) signal showed a significant increase, ranging from 1.6 to 1.8 times higher for both 9 and 20 nm NPs when subjected to doping with 12 at. % Co. Importantly, in NPs with a higher degree of doping of 22 at. % Co, the augmentation in maximum PSF signal was even more remarkable, achieving a 2-fold increase when compared to undoped magnetite NPs. By introducing Co doping, we show that tracers can be created that have excellent MPI performance while achieving a smaller size, making them highly suitable for a wide range of in vivo applications.

The direct growth of Pt islands on lattice mismatched Ni nanoparticles is a major synthetic challenge and a promising strategy to create highly strained Pt atoms for electrocatalysis. By using very mild reaction conditions, Pt islands with tunable strain were formed directly on Ni branched particles. The highly strained 1.9 nm Pt-island on branched Ni nanoparticles exhibited high specific activity and the highest mass activity for hydrogen evolution (HER) in a pH 13 electrolyte. These results show the ability to synthetically tune the size of the Pt islands to control the strain to give higher HER activity.

A major synthetic challenge is to make metal nanoparticles with nanosized branches and well-defined facets for high-performance catalysts. Herein, we introduce a mechanism that uses the growth of hexagonal crystal structured branches off cubic crystal structured core nanoparticles. We control the growth to form Pd-core Ru-branch nanoparticles that have nanosized branches with low index Ru facets. We demonstrate that the branched and faceted structural features of the Pd–Ru nanoparticles retain high catalytic activity while also achieving high stability for the oxygen evolution reaction.

Bimetallic nanostructures show exciting potential as materials for effective photothermal hyperthermia therapy. We report the seed-mediated synthesis of palladium–gold (Pd–Au) nanostructures containing multiple gold nanocrystals on highly branched palladium seeds. The nanostructures were synthesized viathe addition of a gold precursor to a palladium seed solution in the presence of oleylamine, which acts as both a reducing and a stabilizing agent. The interaction and the electronic coupling between gold nanocrystals and between palladium and gold broadened and red-shifted the localized surface plasmon resonance absorption maximum of the gold nanocrystals into the near-infrared region, to give enhanced suitability for photothermal hyperthermia therapy. Pd–Au heterostructures irradiated with an 808 nm laser light caused destruction of HeLa cancer cells in vitro, as well as complete destruction of tumor xenographs in mouse models in vivofor effective photothermal hyperthermia.

Creating high surface area nanocatalysts that contain stacking faults is a promising strategy to improve catalytic activity. Stacking faults can tune the reactivity of the active sites, leading to improved catalytic performance. The formation of branched metal nanoparticles with control of the stacking fault density is synthetically challenging. In this work, we demonstrate that varying the branch width by altering the size of the seed that the branch grows off is an effective method to precisely tune the stacking fault density in branched Ni nanoparticles. A high density of stacking faults across the Ni branches was found to lower the energy barrier for Ni2+/Ni3+oxidation and result in enhanced activity for electrocatalytic oxidation of 5-hydroxylmethylfurfural. These results show the ability to synthetically control the stacking fault density in branched nanoparticles as a basis for enhanced catalytic activity.