Direct Ice Splitting into H₂ and O₂ Enabled by High Ionic Conductivity

The molecular splitting of H₂O is fundamentally significant in energy conversion and storage. While liquid water splitting has achieved scientific and engineering success, the decomposition of solid-state ice has yet to be realized. Here we demonstrate that ice can be directly split at temperatures as low as -40 °C. We show that ice can serve as a high-performance solid electrolyte for proton and hydroxide conduction, with proton mobility estimated to be 1-2 orders of magnitude higher than in liquid water. As a result, ice splitting is achieved at a voltage of 2.18 V at 10 mA cm^-2, with an energy efficiency of approximately 70% at -10 °C. By using ice as a solid electrolyte, ice splitting circumvents the issue of hydrogen crossover, which is inherent in water splitting. These findings introduce new pathways for energy conversion and storage through ice at sub-0 °C temperatures and further provide new insights for the understanding of the electrochemical process in ice.