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.