Laser-generated high entropy metallic glass nanoparticles as bifunctional electrocatalysts

Abstract

High entropy metallic glass nanoparticles (HEMG NPs) are very promising materials for energy conversion due to the wide tuning possibilities of electrochemical potentials offered by their multimetallic character combined with an amorphous structure. Up until now, the generation of these HEMG NPs involved tedious synthesis procedures where the generated particles were only available on highly specialized supports, which limited their widespread use. Hence, more flexible synthetic approaches to obtain colloidal HEMG NPs for applications in energy conversion and storage are highly desirable. We utilized pulsed laser ablation of bulk high entropy alloy targets in acetonitrile to generate colloidal carbon-coated CrCoFeNiMn and CrCoFeNiMnMo HEMG NPs. An in-depth analysis of the structure and elemental distribution of the obtained nanoparticles down to single-particle levels using advanced transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) methods revealed amorphous quinary and senary alloy phases with slight manganese oxide/hydroxide surface segregation, which were stabilized within graphitic shells. Studies on the catalytic activity of the corresponding carbon-HEMG NPs during oxygen evolution and oxygen reduction reactions revealed an elevated activity upon the incorporation of moderate amounts of Mo into the amorphous alloy, probably due to the defect generation by atomic size mismatch. Furthermore, we demonstrate the superiority of these carbon-HEMG NPs over their crystalline analogies and highlight the suitability of these amorphous multi-elemental NPs in electrocatalytic energy conversion.

Identification of the main mixing process in the synthesis of alloy nanoparticles by laser ablation of compacted micropowder mixtures

“…Selective oxidation of Fe was not surprising due to its higher oxygen affinity. Similar element-specific surface oxidation has recently been reported for laser-generated Mn-rich high entropy alloy metallic glass nanoparticles, where the slight manganese oxide/hydroxide surface segregation has been observed, which increased with Mn content in the alloy [41].…”

“…They found that independent of the solvent, a combination of both solvent purification methods leads to oxidationminimized Fe-Rh nanoparticles, proven even by atom probe tomography, and no impact of the bound oxygen in the molecule of the organic solvent could be found. But Johny et al recently discovered that acetonitrile as dispersant leads to amorphous (metallic glass) nanoparticles if a quinary or senary alloy is ablated and discussed the role of solventdelivered carbon as glass morphology stabilizer [41]. This amorphization phenomenon was not observed for quinary alloy nanoparticles produced by lases ablation in ethanol [46].…”

High‐entropy alloy catalysts: From bulk to nano toward highly efficient carbon and nitrogen catalysis

“…15,[72][73][74][75] When the synthesis duration and quenching time are even faster than those of HEAs or using easily glass-forming elements, metallic glass nanoparticles with a disordered atomic structure (lattice) can be formed. [76][77][78] For example, Glasscott et al 76 reported high-entropy metallic glass nanoparticles up to eight elements CoCrCuGdInMnNiV fabricated with precisely tunable stoichiometric ratios by the nanodroplet-mediated electrodeposition, which is an electroshock process with a feature time scale of ∼100 ms but at a much lower temperature (∼room temperature; Figure 2D,E). 76 The energy-dispersive X-ray mapping showed that these elements were distributed uniformly over the nanoparticles, which had calculated mixing entropy ΔS > 1.61 R, qualifying as high entropy mixing (Figure 2E).…”

“…Similarly, other shock methods are also used to prepare HEA nanoparticles with different characteristics, such as microwave, 42,82 ultrasonication, 46 radiative shock heating, 41,83,84 and laser methods (Figure 3A). 16,43,77,85 For example, Qiao et al 42 fabricated the PtPdFeCoNi HEA nanoparticles uniformly distributed on reduced graphene oxide film via microwave energy (at 1800 K for several seconds) to realize high temperature for rapid synthesis of HEAs. Using highenergy acoustic cavitation in the ultrasonication process, NM precursors could be coreduced and transformed into alloy structures to synthesize multicomponent alloy nanoparticles by ultrasonication-assisted wet chemistry at room conditions.…”

“…When the synthesis duration and quenching time are even faster than those of HEAs or using easily glass‐forming elements, metallic glass nanoparticles with a disordered atomic structure (lattice) can be formed 76–78 . For example, Glasscott et al 76 .…”