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).