Hydrogen Generation through Water Radiolysis

Hydrogen generation via water radiolysis exploits the capacity of ionising radiation to cleave H–O bonds, producing reactive species that recombine to form H₂. In the primary stage, high-energy photons or particles ionise water molecules, yielding hydroxyl radicals (•OH), hydrated electrons (e⁻_aq) and hydrogen atoms (H•). Secondary reactions between these intermediates give rise to molecular hydrogen and hydrogen peroxide. This approach offers a route to green hydrogen that does not rely on electricity or fossil fuels, instead utilising abundant radiation sources such as sunlight UV, γ-rays from nuclear reactors or radioisotope decay. Recent advances have focused on heterogeneous systems in which nanoparticles mediate radical production and steer reaction pathways, leading to enhanced yields, controllable bubble formation and scalable reactor designs. Applications range from nuclear waste remediation to off-grid hydrogen supply, with challenges centred on maximising radiochemical efficiency, managing by-products and engineering safe, continuous-flow reactors.

Research from Nature Portfolio

One pivotal study reported the first direct observation of radiolytic bubble formation in unstirred nanoparticle sludges composed of magnesium hydroxide and alumina. By measuring hydrogen yields in a genuinely quiescent system, researchers established that electron emission from nanoparticle surfaces drives new radiative pathways in the surrounding water. They developed a predictive model linking nanoscale ionisation events to the threshold conditions for bubble nucleation and growth. This work has provided an unprecedented mechanistic framework for understanding how solid–liquid interfaces modulate hydrogen formation under irradiation and offers guidelines for optimising reactor geometries and particle formulations.

Hydrogen Generation through Water Radiolysis publication trend

The graph below shows the total number of articles in hydrogen generation through water radiolysis across all publications each year (not limited to Nature Index journals).

Technical terms

Radiolysis: The dissociation of water molecules by ionising radiation, producing radicals, molecular hydrogen and hydrogen peroxide.

G-value: A measure of the number of molecules of a given product formed per 100 eV of absorbed energy.

Heterogeneous radiolysis: Processes in which solid–liquid interfaces, often involving nanoparticles, modify the pathways and yields of radiation-induced reactions.

Secondary electron: An electron emitted from a material surface following ionising radiation, capable of initiating further chemical reactions in the surrounding medium.

Bubble nucleation: The formation of gas cavities when dissolved molecular hydrogen reaches supersaturation during radiolytic processes.

References

1. Recent updates in direct radiation water-splitting methods of hydrogen production. Journal of Umm Al-Qura University for Applied Sciences (2023).
2. Seawater Splitting for Hydrogen Generation Using Zirconium and Its Niobium Alloy under Gamma Radiation. Molecules (2022).
3. Molecular hydrogen production by radiolysis of water on the surface of nano-ZrO2 under the influence of gamma rays. Synthesis and Sintering (2022).
4. First observation of radiolytic bubble formation in unstirred nano-powder sludges and a consistent model thereof. Scientific Reports (2021).
5. Mechanism of Hydrogen Production in The Processes of Radiation Heterogeneous Splitting of Water with the Presence of Nano-Metal and Nano-MeO. East European Journal of Physics (2024).