Have you ever wondered where Earth’s missing elements went? It’s a mystery that’s baffled scientists for nearly a century. Compared to the Sun and some meteorites, our planet is shockingly low on lighter elements like hydrogen, carbon, nitrogen, sulfur, and noble gases—in some cases, by over 99 percent! While some of this disparity is explained by losses during Earth’s formation, researchers have long suspected there’s more to the story. But here’s where it gets fascinating: a recent study suggests these elements might be hiding in plain sight—deep within Earth’s solid inner core. Under mind-boggling pressure (360 gigapascals, or 3.6 million times atmospheric pressure), iron behaves strangely, transforming into an electride—a rare form of metal that can absorb lighter elements like a sponge. And this is the part most people miss: electrides aren’t just solving planetary puzzles; they’re revolutionizing chemistry, too.
Electrides are having a moment—and not just because they might explain Earth’s missing elements. These materials, once thought to exist only under extreme conditions, can now be created at room temperature and pressure from a variety of elements. What makes them truly special? They contain reactive electrons that are easily donated to other molecules, making them ideal catalysts for challenging chemical reactions. One electride is already being used to produce ammonia—a key fertilizer component—with 20 percent less energy than traditional methods. And chemists are discovering new electrides that could lead to greener, cheaper ways to produce pharmaceuticals. The challenge now? Finding more of these materials and understanding the rules that govern their formation.
But here’s where it gets controversial: While electrides are hailed as game-changers, their behavior and formation are still shrouded in mystery. For instance, the idea that Earth’s inner core contains an electride is based on simulations, and not everyone agrees. Iron’s strong pull on its outer electrons makes it less likely to form electrides compared to metals like sodium or calcium, which have looser electrons. So, is the inner core really hiding these elements? The debate is far from over.
Most solids are made of ordered atomic lattices, but electrides break the mold. Their lattices contain tiny pockets where electrons sit alone, trapped in what are called non-nuclear attractor sites. These trapped electrons give electrides their unique properties. In Earth’s core, for example, these negatively charged electrons could stabilize lighter elements under extreme pressure, explaining where they’ve disappeared to. The first electride discovered under high pressure was sodium, which transforms from a shiny metal into a transparent, insulating material at 200 gigapascals. This finding was so unexpected that Stefano Racioppi, a chemist at the University of Cambridge, called it ‘very weird.’ Early theories predicted sodium’s electrons would move more freely under pressure, not get trapped.
The breakthrough came from computational simulations in the late 1990s, which showed that as sodium atoms are squeezed closer together, their electrons experience increasing repulsive forces. This reorganizes their positions, forcing them into non-nuclear attractor sites. Since these electrons are stuck, the material loses its metallic properties. Racioppi and his team later confirmed this experimentally by squeezing sodium crystals between diamonds and using X-ray diffraction to map electron density—proving the electrons were indeed trapped.
Electrides are a catalyst’s dream. Their isolated electrons can donate themselves to break and form chemical bonds, but they need to work under normal conditions to be useful. One standout example is mayenite, a calcium aluminate oxide discovered in 2003. When treated with metal vapor, mayenite’s tiny pores trap electrons, turning it into an electride. Unlike high-pressure electrides, mayenite starts as an insulator but becomes a conductor as its trapped electrons jump between sites. This makes it an excellent catalyst, already being used to produce ammonia more efficiently than the energy-intensive Haber-Bosch process.
By 2017, the company Tsubame BHB began commercializing mayenite-based catalysts, opening a pilot plant in 2019. Their larger facility in Japan and a 20,000-ton green ammonia plant in Brazil are expected to avoid 11,000 tons of CO2 emissions annually—equivalent to the emissions of 2,400 cars. But ammonia is just the start. Mayenite could also convert CO2 into useful chemicals or even immobilize radioactive waste in nuclear power stations. It’s even been studied as a propulsion system for satellites!
The electride family keeps growing. In 2024, chemist Fabrizio Ortu accidentally discovered a room-temperature-stable electride made from calcium ions and organic molecules. Unlike mayenite, this electride doesn’t conduct electricity, but its trapped electrons can activate unreactive bonds—a job typically done by expensive palladium catalysts. Ortu’s team used it to join pyridine rings, a reaction common in pharmaceutical synthesis. The catch? This electride is too sensitive to air and water for industrial use. Ortu is now hunting for a more stable alternative.
Despite their promise, electrides remain enigmatic. There’s no theory to predict when a material will become one, and their chemical behavior defies intuition. Lee Burton, a computational materials scientist, is using AI to screen 40,000 known materials for potential electrides. ‘The potential is enormous,’ he says, but reliable data is scarce. With only a handful of experimentally confirmed electrides, Burton’s team is creating high-resolution simulations to train AI models. The goal? Uncover more of these materials and unlock their full potential.
So, what do you think? Are electrides the key to solving Earth’s mysteries and revolutionizing chemistry, or is their potential overhyped? Let’s debate in the comments!
