Stanford researchers have discovered that, in the complex world of nanotechnology, five heads — or rather, five metals — are better than one.
Along with Korea Advanced Institute of Science and Technology (KAIST), the team synthesized a uniform nanocrystal composed of five different metals: ruthenium, iron, cobalt, nickel, and copper.
This breakthrough in nanomaterial engineering has use in sustainable energy, as these multimetallic catalysts could improve the efficiency of hydrogen production and use.
The crystal formation
Nanocrystals possess a high surface-area-to-volume ratio and are efficient catalysts to accelerate chemical reactions in applications ranging from vehicle exhaust systems to medical diagnostic tests.
Plus, these particles are essential components of modern electronics, powering transistors and high-definition displays in smartphones and computers.
In this new work, Professor Matteo Cargnello’s team, in partnership with KAIST and BASF, has challenged conventional chemistry by synthesizing highly uniform nanocrystals composed of five distinct metals.
The research reveals a “self-organizing” phenomenon: increasing the complexity of the metallic mixture results in more consistent, stable particles rather than chaotic ones.
The creation began with ruthenium, a high-activity precious metal, as the foundation of their study.
Researchers attempted to blend it with four cheaper, more abundant metals: iron, cobalt, nickel, and copper.
Initially, it was expected that this complex mixture would result in a chaotic “jumble” of inconsistent particles due to each metal’s unique reaction speed. Surprisingly, this complexity actually drove consistency.
While mixtures of two or three metals were messy and unstable, the five-metal combination paradoxically self-organized into a single, uniform product, streamlining 31 possible chemical outcomes into a single, precise nanocrystal.
“The surprising discovery is that when you start adding more elements, all the way up to five, it’s the opposite of what we expected,” Cargnello said. “All five elements together in a single nanocrystal ended up looking like a single product.”
Role of copper
The secret to this order was, surprisingly, a refusal to cooperate.
Through time-lapse analysis, researchers identified copper as the essential architect of the self-organizing process.
Copper, the most eager metal in the mix, refuses to blend with ruthenium. Like oil and water, they stay separate but joined. This creates a physical scaffold — a chemical invitation — for the other metals to arrive in a specific sequence.
Cobalt and nickel move in next, followed finally by iron, which wraps the entire structure in a protective shell, in an onion-like arrangement.
“The result is an onion-like structure with ruthenium at the core, copper nestled beside it, cobalt and nickel forming intermediate shells, and an outer iron-rich layer,” the press release noted.
Use in hydrogen transportation
The five-metal nanocrystals have proven effective in accelerating ammonia decomposition, a process vital for the hydrogen energy economy. As hydrogen is difficult to transport as a gas, it is often converted into liquid ammonia for shipping and then “cracked” back into fuel at its destination.
While this chemical reversal typically requires extreme temperatures, these new multimetallic catalysts provide a feasible solution for driving the reaction under such demanding industrial conditions.
In performance tests, the five-metal nanocrystal catalyst achieved a reaction rate 4 times faster than that of standard ruthenium and demonstrated exceptional thermal stability.
Compared with standard catalysts that degrade or clump together through sintering at high temperatures, these multimetallic particles remained effective even after 12 hours at 900°C.
BASF is currently putting these crystals through the wringer in industrial settings.
If the results hold, the messy science of mixing five metals might just be the clean solution the world’s energy grid has been waiting for.
The study was published in the journal Science on May 7.