Abstract
Toward sustainable hydrogen peroxide (H(2)O(2)) production, photo(electro)catalytic oxygen (O(2)) reduction/H(2)O(2) production has attracted increasing attention. Recently, we have found that a thin film of the π-conjugated polymer, poly(1,4-bis(2-thienyl)benzene) (PBTB), exhibits exceptionally high (photo)electrocatalytic activity for O(2) reduction/H(2)O(2) production. To achieve higher photoelectrocatalytic activity and efficient visible-light-driven photoelectrocatalytic H(2)O(2) production, we investigated the molecular design related to the highest occupied molecular orbital (HOMO) energy level (E(HOMO)) of these polymers. We designed and synthesized poly(1,4-bis(2-thienyl)naphthalene) (PBTN), in which replacing the phenyl unit of PBTB with a naphthalene unit-a stronger electron-withdrawing group-and increasing the polymer chain twist angle selectively deepened E(HOMO) relative to PBTB. The degree of E(HOMO) deepening quantitatively affected the onset potential of PBTN. Under visible-light irradiation and 0 V vs. Ag/AgCl, the PBTN thin film achieved a high O(2) reduction/H(2)O(2) production rate (1.11 × 10(3) mmolH2O2 /g(photoelectrocatalyst)), 1.47 times higher than that of PBTB, with excellent Coulombic efficiency (99%) and selectivity (99%). The onset potential of PBTN for visible-light-assisted O(2) reduction enabled a photocatalytic H(2)O(2) production setup. Upon visible-light irradiation, this setup achieved a high photocatalytic O(2) reduction/H(2)O(2) production rate of 128 mmolH2O2 /g(photocathode). These results clearly demonstrate the tunability of the photoelectrocatalytic activity of π-conjugated polymers through E(HOMO)-related molecular design.