Copolymer of Phenylene and Thiophene toward a Visible‐Light‐Driven Photocatalytic Oxygen Reduction to Hydrogen Peroxide

π ‐Conjugated polymers including polythiophenes are emerging as promising electrode materials for (photo)electrochemical reactions, such as water reduction to H 2 production and oxygen (O 2 ) reduction to hydrogen peroxide (H 2 O 2 ) production. In the current work, a copolymer of phenylene and thiophene is designed, where the phenylene ring lowers the highest occupied molecular orbital level of the polymer of visible‐light‐harvesting thiophene entities and works as a robust catalytic site for the O 2 reduction to H 2 O 2 production. The very high onset potential of the copolymer for O 2 reduction (+1.53 V vs RHE, pH 12) allows a H 2 O 2 production setup with a traditional water‐oxidation catalyst, manganese oxide (MnO x ), as the anode. MnO x is deposited on one face of a conducting plate, and visible‐light illumination of the copolymer layer formed on the other face aids steady O 2 reduction to H 2 O 2 with no bias assistance and a complete photocatalytic conversion rate of 14 000 mg (H 2 O 2 ) g photocat −1 h −1 or ≈0.2 mg (H 2 O 2 ) cm −2 h −1 .