The recent discovery that metal-free polyterthiophene (PTTh) prepared by iodine-vapor-assisted polymerization (IVP) can catalyze the hydrogen evolution reaction (HER) when illuminated, and this light-enhanced electrolysis expresses a non-Nernstian relation with pH, provides the foundation for further improvement of the photovoltage of the reaction by engineering the band structure of the light-absorbing polymer. Deviating from an all-thiophene backbone, using poly(1,4-di(2-thienyl))benzene (PDTB) lowers the highest occupied molecular orbital level by ≈0.3 eV compared with polythiophene, and PDTB simultaneously maintains the photoelectrocatalytic properties without an all-thiophene backbone, resulting in very high conversion rate of 600 mmol(H2) h−1 g−1 at 0 V versus the reversible hydrogen electrode (RHE) at pH 11. PDTB shows the same non-Nernstian behavior as PTTh with increasing onset potential (versus RHE) at higher pH, and the open circuit potential on PDTB under visible light reaches 1.4 V versus RHE at pH 12. The PDTB photocathode thus produces a photovoltage above the theoretical potential for the complete water-splitting (1.229 V) and is indeed able to produce hydrogen in a one-photon-per-electron light-driven water splitting setup with MnOx as the anode at a rate of 6.4 mmol h−1 gPDTB −1.
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