Nanobubble Chemistry Enables Catalyst Free Ammonia Synthesis Under Mild Conditions

Ammonia is a cornerstone of global agriculture and a promising carrier for renewable energy storage. Yet nearly all of it is still produced via the Haber‑Bosch process, which operates above 400 °C and 200 atm, consumes about two percent of global energy, and emits large amounts of carbon dioxide. That is why finding a greener route under mild conditions has become a major challenge in chemistry and energy.

Now, a research team led by Profs. CHEN Lan and GE Guanglu from the National Center for Nanoscience and Technology (NCNST) of the Chinese Academy of Sciences (CAS) has developed a catalyst‑free nanobubble chemistry strategy for ammonia synthesis at room temperature and low pressure.

Their work, which proposes an entirely new reaction paradigm that harnesses the high transient energy released by nanobubble collapse in water to drive reactions that are normally difficult to achieve under conventional conditions, was published in the Journal of the American Chemical Society.

By harnessing free radicals generated from the collapse of N₂/H₂ bulk nanobubbles, the team achieved nitrogen fixation with about 60% selectivity toward ammonia. EPR capture and DFT calculations showed that the chemical potential of H· radicals generated in situ during nanobubble collapse reaches about 2.3 eV, sufficient to directly supply the energy required for N≡N bond activation (energy barrier: 1.59 eV), thereby bypassing the high energy input and catalytic conditions required by traditional pyrolysis.

Nanobubble chemistry deals with reactions driven by gas bubbles at the nanoscale, typically less than one μm in diameter. According to the Young‑Laplace equation, a 100‑nm bubble can contain internal pressure of several dozen atmospheres.

What is more, nanobubbles possess a unique boundary layer and release abundant reactive free radicals when they collapse, making them natural "microreactors" that can drive reactions normally requiring extreme conditions. This approach offers value not only in providing transient localized high temperature and pressure, but also in supplying radical chemical potential with precision—opening up a completely new activation pathway for high‑energy‑barrier reactions.