A Value‐Added Solar‐Mediated Rechargeable Battery Integrating Efficient Photoelectrochemical Energy Storage with Sunlight‐Boosted Self‐Powered H ₂ O ₂ Production from Natural Seawater

Abstract Developing sustainable functional batteries capable of generating valuable chemicals during electricity storage/release represents challenging frontiers. Here, we present a new battery chemistry that enables the first value‐added solar‐mediated rechargeable seawater battery integrating photoelectrochemical energy storage with sunlight‐boosted self‐powered H 2 O 2 production from seawater without external power/O 2 supply. This system is enabled by rationally‐designed bifunctional S‐scheme heterojunction photocathodes (MP‐COP@TiO 2 ) comprising A3‐(D‐core) polymer (MP‐COP) encapsulated TiO 2 . A3‐(D‐core) topology induces favorable electronic modulation that optimizes oxygen specie adsorption and steering oxygen reduction reaction (ORR) toward one‐step 2e – pathway—while facilitating electronic coupling with oxygen evolution reaction (OER)‐active TiO 2 to establish S‐scheme charge transfer mechanism alongside strengthened built‐in electric field. These endow MP‐COP@TiO 2 with sunlight‐boosted 4e – OER for in situ O 2 ‐generation during photo‐charge and 2e – ORR for on‐site H 2 O 2 synthesis during photo‐discharge, establishing solar‐mediated self‐sustaining value‐added reaction cycles. Integrating MP‐COP@TiO 2 with sodium anodes and seawater creates previously‐unexplored functional battery, yielding remarkable H 2 O 2 yield of 5.47 mmol g −1 h −1 during photo‐discharge—9.4 times those in dark and exceeding most reported seawater systems while delivering near‐zero charge/discharge voltage gap under illumination. Mechanistic studies reveal promoting effect of A3‐(D‐core) modulation and its synergistic role with S‐scheme charge transfer that promotes Yeager‐type O 2 adsorption and facilitates one‐step 2e – ORR toward H 2 O 2 .