Molecular solar battery stores energy for days, yields hydrogen on demand

A research team from Ulm University and Friedrich Schiller University Jena has developed a molecular solar battery that stores photovoltaic energy and releases it as hydrogen on demand – including in the dark, without any solar input. The results were published in Nature Communications.

The system’s core is a water-soluble copolymer with high redox activity, designed to act simultaneously as an electron storage medium and a photocatalytic platform. The material captures electrons generated by solar irradiation and holds them stably for several days at a charging efficiency of more than 80%.

The approach decouples solar generation from hydrogen production – a departure from conventional systems that require electrolysis and renewable generation to run simultaneously. Once energy is stored in the copolymer, adding an acid and a hydrogen evolution catalyst combines the stored electrons with protons, generating hydrogen at 72% conversion efficiency. The process works in darkness, giving operators flexibility over when and how hydrogen is produced.

The system is also chemically reversible. Multiple charge, storage, and discharge cycles are possible without isolating the active material. Regeneration requires only a pH adjustment – neutralization – which reactivates the photocatalytic process under irradiation. The researchers said the cyclical behavior, grounded in reversible copolymer redox reactions, positions the material as a candidate for chemical energy storage applications.

The work brings together macromolecular chemistry and photocatalysis – two fields with limited prior overlap – in a single molecular architecture that handles capture, storage, and conversion. The researchers said the approach could support low-cost, scalable hydrogen storage, with potential applications in energy-intensive industrial processes such as steelmaking and synthetic fuel production, where on-demand hydrogen generation could ease the integration of variable renewables.

The research is part of the CataLight consortium, which focuses on converting solar energy into chemical energy using molecular catalysts.

From pv magazine España