High-Entropy-Alloy Nanocrystal Based Macro- and Mesoporous Materials

Abstract

High-entropy-alloy (HEA) nanoparticles are attractive for several applications in catalysis and energy. Great efforts are currently devoted to establish composition–property relationships to improve catalytic activity or selectivity. Equally importantly, developing practical fabrication methods for shaping HEA-based materials into complex architectures is a key requirement for their utilization in catalysis. However, shaping nano-HEAs into hierarchical structures avoiding demixing or collapse remains a great challenge. Herein, we overcome this issue by introducing a simple soft-chemistry route to fabricate ordered macro- and mesoporous materials based on HEA nanoparticles, with high surface area, thermal stability, and catalytic activity toward CO oxidation. The process is based on spray-drying from an aqueous solution containing five different noble metal precursors and polymer latex beads. Upon annealing, the polymer plays a double role: templating and reducing agent enabling formation of HEA nanoparticle-based porous networks at only 350 °C. The formation mechanism and the stability of the macro- and mesoporous materials were investigated by a set of in situ characterization techniques; notably, in situ transmission electron microscopy unveiled that the porous structure is stable up to 800 °C. Importantly, this process is green, scalable, and versatile and could be potentially extended to other classes of HEA materials.

Self-Regulating VO2 Photonic Pigments

“…This suggests that here the PMMA latex is not simply a sacrificial template for inducing structuration, but plays a key chemical role for ensuring phase selectivity. Previous works from our group have shown that under an inert atmosphere, PMMA acts both as a templating and as a reducing agent, 48,49 which explains why a pure V 2 O 3 phase is obtained only for templated particles. In summary, pure monoclinic VO 2 (P2 1 /c) could be obtained only by pseudomorphic transformation with a controlled re-oxidation of the porous V 2 O 3 particles, due to the important role played by PMMA in this process.…”

Multifunctional, Hybrid Materials Design via Spray‐Drying: Much more than Just Drying

“…On the plus side, as obvious from the previous section, stands out the possibility to enable the design of diverse materials, hybrids, and exotic combinations. A few examples are macro and mesoporous high‐entropy‐alloy (HEA) particles ( Figure a), [ 53 ] silica‐enzyme particles (Figure 6b), [ 81 ] silicon–carbon–graphene combinations (Figure 6c), [ 79 ] iron oxide‐polymer (e.g., polylactic acid) composites (Figure 6d), [ 6 ] lipid–silica structures containing living cells (Figure 6e), [ 80 ] zeolite–enzyme–polyelectrolyte hybrids (Figure 6f), [ 60 ] LiMnO 2 –carbon black materials, [ 82 ] or iron oxide–MOF hybrids. [ 37 ]…”

“…One representative example concerns the fabrication of high entropy alloys, multi-principal element alloys, composed of five or more homogeneously mixed metals in nearly equimolar ratios. [53,95] The second advantage of fast kinetics concerns the structuration and the possibility to achieve controlled matter phase separation. Indeed the evaporation of the droplets taking place at the liquid/air interface leads to thermal and chemical gradients (solutes concentrations, surface tension, and polarity) from this interface towards the heart of the volume.…”

“…a) Porous high-entropy-alloy particles; b) silica-enzyme (hexose oxidase) particles: c) silicon-carbon-graphene combinations; d) iron oxide-polymer composites; e) lipid-silica structures containing living cells; and f) zeolite-enzymepolyelectrolyte hybrids. a) Adapted with permission [53]. Copyright 2022, American Chemical Society.…”

Status and Prospects of High-Entropy Materials for Lithium–Sulfur Batteries

“…Aerosol droplets are formed under spray, and the oxide is converted to phosphate phase in situ during high temperature and rapid heating. Jennifer et al [82] analyzed the formation mechanism of HEA nanocrystalline-based macro-and mesoporous materials and the role of templating agents by using different templating agents to synthesize HEA by spray pyrolysis. The level of chemical and structural complexity achievable by spray pyrolysis was significantly improved by fabricating HEAs-based particles with controlled porosity.…”