Nanotechnologies / Materials
Development of energy resource conversion, Fuel cells, Optical functional materials, etc.

Next-generation alloy nanoparticle catalyst with high activity,
high temperature resistance, and high durability
Division of Materials and Manufacturing Science, Graduate School of Engineering
Associate Professor Kohsuke Mori
https://researchmap.jp/7000018582

Nanotechnologies / Materials

Abstract
High-entropy alloys (HEAs) represent a new class of metallic
materials in which more than five near-equimolar components are
mixed to form single-phase solid solutions with high mixing entropy
values, rather than intermetallic phases. Various unique synergistic effects result from such mixtures, including high configuration
entropy, lattice distortion, sluggish diffusion and cocktail effects,
which endow HEAs with high mechanical strength, good thermal
stability, and superior corrosion resistance. However, a simple
nanoparticle synthesis method has not been established, and it iscompletely unexplored as a catalyst material. We have establisheda method for making high-entropy alloys into nanoparticles withthe aim of exhibiting catalytic functions, and have found that they
exhibit unique catalytic activity and high durability in the CO2 hydrogenation reaction.

▍ Background & Results
Metal nanoparticles are used in various catalytic reactions, but
due to their high surface energy, they are deactivated and changes
in the surface structure under harsh environments. In order to overcome this problem, we focused on high entropy alloy (HEA), which
exhibits high specific strength, high-temperature strength, and corrosion resistance. However, the development of HEA nanoparticles(NPs) with a mean diameter of less than 10 nm lags significantly
behind, despite the potential practical applications of these NPs incatalysis.
We have previously demonstrated that TiO2 is a promising platform for the synthesis of non-equilibrium binary alloy NPs, such as
RuNi and RhCu, which are essentially immiscible at equilibrium
due to the positive enthalpies of formation of their solid solution alloys. This process is driven by the pronounced hydrogen spillover
effect on TiO2 in conjunction with coupled proton/electron transfer.
In the present work, we developed and demonstrated that this facile strategy can be applied to the synthesis of TiO2-supported HEA
NPs. Specifically, CoNiCuRuPd HEA NPs on TiO2 displayed highactivity and outstanding stability during the CO2 hydrogenation reaction.

▍ Significance of the research and Future perspective
The high-entropy alloy nanoparticle-supported catalysts are in
powder form, which is highly stable even in harsh environments
and easy to separate and recover. Furthermore, theoretical calculations have been used to prove that unique catalytic activity andthe structural stability of the nanoparticles are caused by the cocktail effect and sluggish diffusion effect, which is of extremely highacademic significance. The results of this research are expected
to have a significant ripple effect not only in the field of catalysis,
which aims at the effective use of energy resources, but also in thefield of advanced material science based on nanotechnology.

P a t e n tMori, Kohsuke; Hashimoto, Naoki; Yamashita, Hiromi et al. Hydrogen Spillover-driven Synthesis of High Entropy Alloy Nanoparticles as a Robust Catalyst
T r e a t i s e for CO2 Hydrogenation, Nature Communications, 2021, 12, p.3884–3893, doi: 10.1038/s41467-021-24228-z
URL https://www.eng.osaka-u.ac.jp/wp-content/uploads/2021/06/PR20210623_2.pdf
K e y w o r d nanostructured catalysts, metal alloy nanoparticle, CO2 transformation