A water-soluble copolymer for storage and electron conversion in photocatalytic ondemand hydrogen evolution

Cost- and energy-efficient long-term storage of excess solar energy remains amajor bottleneck in the transition to a sustainable society. Here, we present awater-soluble redox-active copolymer containing viologen moieties that canbe chargedwith electrons upon visible light irradiation using a tris[4,4’-bis(tertbutyl)−2,2’-bipyridine]ruthenium(II) complex as chromophore. In the presenceof a sacrificial donor, the system achieves charging efficiencies above80% and fully maintains this state for several days. Subsequent acidificationand the addition of various catalysts enable on-demand usage of the storedelectrons for proton reduction to hydrogen with up to 72% efficiency. Thesystem further demonstrates reversibility via a simple pH switch, allowingmultiple charging, storage, and catalysis cycles without time-consumingpolymer isolation. The present study presents a direct on-demand hydrogenevolution method through discharging of a water-soluble polymer that functionsas a temporary energy and electron storage material.