Quinary, Senary, and Septenary High Entropy Alloy Nanoparticle Catalysts from Core@Shell Nanoparticles and the Significance of Intraparticle Heterogeneity

Abstract

Colloidally prepared core@shell nanoparticles (NPs) were converted to monodisperse high entropy alloy (HEA) NPs by annealing, including quinary, senary, and septenary phases comprised of PdCuPtNi with Co, Ir, Rh, Fe, and/or Ru. Intraparticle heterogeneity, i.e., subdomains within individual NPs with different metal distributions, was observed for NPs containing Ir and Ru, with the phase stabilities of the HEAs studied by atomistic simulations. The quinary HEA NPs were found to be durable catalysts for the oxygen reduction reaction, with all but the PdCuPtNiIr NPs presenting better activities than commercial Pt. Density functional theory (DFT) calculations for PdCuPtNiCo and PdCuPtNiIr surfaces (the two extremes in performance) found agreement with experiment by weighting the adsorption energy contributions by the probabilities of each active site based on their DFT energies. This finding highlights how intraparticle heterogeneity, which we show is likely overlooked in many systems due to analytical limitations, can be leveraged toward efficient catalysis.

Chemical Insights into the Formation of Colloidal High Entropy Alloy Nanoparticles

“…Solution-based colloidal syntheses are among the most powerful for nanoparticles, as they can facilitate the controlled nucleation and growth of solids through chemical or thermal triggers and can allow for exquisite control over size and shape while offering liquid dispersibility and processing, as well as the potential for scalability. , Significant advances over the past two decades have provided detailed chemical insights into the reactions that produce metal and simple alloy nanoparticles and especially noble metal systems. − As a result, it is now possible to synthesize hundreds of different types of metal and alloy nanoparticles in solution with a high degree of control over size and shape. In contrast, methods to synthesize colloidal HEA nanoparticles are only beginning to emerge. − Additionally, little is known about the reaction chemistry that leads to their formation, given the large number of elemental reagents and their range of chemical reactivities, both individually and together. − Methods that sidestep the complex reaction chemistry by predesigning heterostructured nanoparticle precursors and annealing them to form HEAs provide promising alternatives but still require the particles to be anchored on refractory supports and annealed at high temperatures. , …”

Designing strategies and enhancing mechanism for multicomponent high-entropy catalysts

“…In another work, Sandra et al 113 adopted DFT methods to disclose the O and OH adsorption energies of PdCuPtNiCo and PdCuPtNiIr surfaces, which were adopted as computational descriptors for oxygen reduction activity (Fig. 7d).…”

“…Meanwhile the inclusion of the bridge pathway reveals a mixture of Ru, Ir and possibly a small amount of Rh as the optimum. In another study, Sandra et al 113 adopted DFT methods to disclose the O and OH adsorption energies of PdCuPtNiCo and PdCuPtNiIr surfaces, which were adopted as computational descriptors for oxygen reduction activity ( Fig. 7d ).…”

Facet-Controlled Synthesis of Platinum-Group-Metal Quaternary Alloys: The Case of Nanocubes and {100} Facets

“…Recently, a number of solution-phase methods have also been explored for the synthesis of MMNPs, ,− with notable examples including those built on polyol reduction, laser ablation toward water, ultrasonication-assisted wet chemistry, droplet-mediated electrodeposition, and solvothermal conditions . A combination of solution-phase colloidal synthesis and thermal annealing has also been explored . Despite remarkable progress, it remains an unmet challenge for the robust synthesis of MMNPs featuring all merits key to the establishment of the structure–property relationship and thus theory-guided design of catalytic materials.…”

“…17 A combination of solution-phase colloidal synthesis and thermal annealing has also been explored. 18 Despite remarkable progress, it remains an unmet challenge for the robust synthesis of MMNPs featuring all merits key to the establishment of the structure−property relationship and thus theory-guided design of catalytic materials. In general, the MMNPs reported in the literature are often plagued by the following issues: (i) relatively large (>10 nm) and/or broadly distributed sizes; (ii) a poorly defined surface in terms of both composition and atomic structure; (iii) a polycrystalline structure with multiple domains in the same particle; and (iv) multiple phases rather than a single phase.…”