For years, high-entropy alloys have tantalized scientists with their promise as next-generation catalysts — materials made from five or more elements blended in nearly equal amounts, their complex surfaces theoretically capable of accelerating chemical reactions at remarkable rates. The catch? No one could control what those surfaces actually looked like at the nanoscale. "High-entropy alloys have been a black box for catalysis because you could never control the surface," said Chad A. Mirkin, a professor of chemistry at Northwestern University. "We fixed that."
Mirkin, alongside colleague Christopher M. Wolverton, has developed a three-step synthesis strategy that finally unlocks precise control over both the composition and surface structure of high-entropy alloy nanoparticles. Their research, published in the Journal of the American Chemical Society, represents a breakthrough that the field has pursued for over a decade.
The solution works in three stages. First, target metals are combined with liquid gallium, which acts as a nanoscale solvent to form a stable, well-mixed alloy. Second, a volatile metal — tellurium, antimony, or bismuth — is introduced to alloy with the particle. Third, most of that volatile metal is evaporated at high temperature, leaving only trace amounts on the surface that shift the surface energy and lock the particle into a tetrahexahedral shape characterized by stepped, kinked atomic arrangements.
These high-index facets, as they're called, provide a greater density of active sites for chemical reactions than the flatter, smoother surfaces previously achieved. They are more reactive and better suited for catalysis — but also less stable and far harder to engineer. By solving this puzzle, Mirkin and Wolverton's team has opened a new chapter in catalyst discovery.
What makes this work especially powerful is scale. Mirkin's team applied the synthesis method to megalibraries — a nanomaterials discovery platform he invented — producing approximately 36 million nanoparticles across 90,000 unique compositions on a single chip. "The megalibrary lets you search for materials at a scale nobody else can match," said Wolverton, who led the computational studies validating the approach. "What this study adds is the ability to control not just what the particles are made of but how their surfaces are structured. For catalysis, that is the whole game."
The implications stretch from the lab bench to the clean energy transition. High-entropy alloy catalysts could eventually replace scarce, expensive materials like iridium — used in the oxygen evolution reaction critical for clean hydrogen production. In fact, previous work with megalibraries already identified a commercially viable replacement for iridium-based catalysts, a discovery made in a single afternoon rather than the years such a breakthrough would require using older methods. Now, with surface structure also under precise control, researchers can finally study these materials the way they deserve to be studied — and accelerate the search for sustainable energy solutions at a scale never before possible.