Visualizing formation of high entropy alloy nanoparticles with liquid phase transmission electron microscopy

Abstract

High entropy alloy (HEA) nanoparticles hold promise as active and durable (electro)catalysts. Understanding their formation mechanism will enable rational control over composition and atomic arrangement of multimetallic catalytic surface sites...

Unraveling chemical processes during nanoparticle synthesis with liquid phase electron microscopy and correlative techniques

“…59 Sun et al used systematic solution chemistry to synthesize HEA nanoparticles from a mixture of metal salts and PEG-SH, together with LPTEM to understand the formation mechanism. 7 Interestingly, the HEA nanoparticles formed by solution chemistry here were found to co-exist with stable sub-nanometer clusters and free metal atoms as shown in Fig. 5a.…”

“…Recent work by the Jones lab demonstrating the importance of atomically precise metal nanoclusters in seeded nanoparticle synthesis emphasizes the need to consider the molecular structure of intermediate species when developing growth mechanisms for nanoparticles. 130 While studies of bimetallic and HEA nanoparticle revealed sub-nanometer metal clusters in the reaction solution following synthesis, 7,59 these species were below the LPTEM spatial resolution so it could not be verified these clusters were indeed intermediates to the final crystalline nanoparticles. Future research should focus on detecting and characterizing metal cluster reaction intermediates during LPTEM experiments and drawing concrete connections between these intermediates and the nanoparticle formation dynamics.…”

“…5e). 7 Here, the rate limiting step during nanoparticle formation is diffusion limited aggregation of clusters in solution, as opposed to nucleation of nanoparticle seeds. Importantly, aggregation of metal cluster intermediates mitigates the problem of preferential reduction of certain metals by promoting mixing of disparate metal species.…”

“…For instance, there remain gaps in understanding the mechanisms for symmetry breaking, 4 nanoparticle nucleation and growth, 4 molecular scale reaction intermediates, 5,6 and formation mechanisms of multimetallic nanoparticles. 7,8 There remains debate about the rate limiting step involved in initial nanoparticle seed formation with potential limiting factors including nucleation, reaction kinetics, or other mechanisms. 9,10 For instance, Polte et al proposed that metal nanoparticles do not form by nucleation but instead by aggregation of metal atoms into clusters and subsequently into nanoparticles, which is supported by X-ray scattering experiments.…”