DNA‑inspired molecular fuel achieves 1.65 MJ/kg for seasonal solar heat storage

A lab team created a rechargeable, liquid organic fuel that stores sunlight chemically at 1.65 MJ/kg and keeps that charge for months, with some derivatives showing a calculated half‑life of up to 481 days. The material switches into a high‑energy Dewar isomer when hit by UV light and releases heat on demand when triggered, enabling the concept of roof‑mounted collectors, a storage tank, and an on‑demand heat release stage.

The molecule is based on a 2‑pyrimidone scaffold engineered to form fused four‑membered rings, creating compounded strain that raises stored energy per kilogram well above previous MOST candidates. In side‑by‑side terms, this system outperforms norbornadiene (0.97 MJ/kg) and azaborinine (0.65 MJ/kg), and it exceeds typical Li‑ion battery gravimetric heat equivalents, while remaining a pumpable liquid compatible with aqueous leaks.

The researchers demonstrated operational resilience through at least 20 charge‑discharge cycles with negligible loss, and they showed the released heat can boil water in a reaction test. However, efficient charging is constrained because the molecule absorbs primarily in the 300–310 nm band, which represents roughly 5% of surface solar irradiance, and measured photo‑conversion occurs with a single‑digit quantum yield.

A second practical issue is the current heat‑release trigger: the lab used an acid catalyst mixed into the fluid, which would need neutralization or removal in a closed‑loop home system and thereby reduce net energy density. The team proposes a workaround that passes the fuel over an acid‑functionalized solid surface to trigger discharge, avoiding bulk neutralization and simplifying recycling.

From an engineering viewpoint, the chemistry converts brief UV exposure into a long‑lived chemical state, decoupling collection from consumption and enabling true seasonal storage if optical and quantum limits are addressed. Scaling requires molecules that harvest a wider portion of the solar spectrum and route a larger fraction of absorbed photons into the storage isomer rather than losing energy through non‑radiative decay. Improvements in chromophore design and photophysics are the most direct levers to raise practical efficiency.

If those bottlenecks are solved, the approach could complement or replace some heat‑focused solutions by storing daytime solar energy chemically for months and releasing it through conventional heat exchangers. Near‑term development will center on shifting absorption toward visible wavelengths, increasing quantum yield, integrating catalyst surfaces for clean discharge, and validating longevity across hundreds of cycles. The work establishes a new performance benchmark for the MOST field but stops short of a turnkey technology for household heating.