Hydrogen Iodide Energy Cycle to Repeat Solar Hydrogen Generation and Battery Power Generation Using Single-Walled Carbon Nanotubes

Herein, a new energy cycle called the hydrogen iodide (HI) cycle is proposed that involves the repeated generation of solar hydrogen and battery power. Solar hydrogen generation using an HI solution allows for the use of a narrow-bandgap photocatalyst. It is demonstrated that the addition of single-walled carbon nanotubes (SWCNTs) effectively enhances solar hydrogen generation from HI solution with methylammonium lead iodide. Electron microscopy observations and spectroscopic experiments reveal that SWCNTs improve hydrogen generation by adsorbing byproduct iodine molecules. Additionally, a zinc-iodine battery, utilizing paper I@SWCNTs recovered from the photocatalyst test cell and zinc metal, operates efficiently with an initial cell voltage of approximately 1.2 V. The battery's capacity, corresponding to the amount of encapsulated iodine molecules, indicates that SWCNTs can effectively adsorb the byproduct iodine molecules within the photocatalyst test cell. It is also discussed that the electrolyte solution after the discharge experiment should include iodide ions, indicating that the solution after battery discharge returns to the starting point of the HI cycle. Raman measurements reveal that I@SWCNTs are transformed back into empty tubes during the discharge experiment. Therefore, SWCNTs can be repeatedly used in the new cyclic energy scheme referred to as the HI cycle. A new energy cycle (hydrogen iodide [HI] cycle), which enables the repetitive generation of solar hydrogen and battery power, is proposed. The HI cycle leverages the capability of single-walled carbon nanotubes to encapsulate iodine.image & COPY; 2023 WILEY-VCH GmbH

Automated summary

A new energy cycle, called the hydrogen iodide (HI) cycle, is proposed for the repetitive generation of solar hydrogen and battery power. The addition of single-walled carbon nanotubes (SWCNTs) enhances solar hydrogen generation from an HI solution by adsorbing byproduct iodine molecules. A zinc-iodine battery, using recovered I@SWCNTs and zinc metal, operates efficiently. The study demonstrates the capability of SWCNTs to effectively adsorb iodine molecules within the photocatalyst test cell.