Molecularly engineered water oxidation sites in D-A conjugated polymers for efficient H₂O₂ photosynthesis in pure...

Photocatalytic generation of H₂O₂ from air and water has been regarded as a promising strategy to produce this vital chemical. Currently, H₂O₂ production primarily occurs via the two-electron oxygen reduction reaction (ORR), coupled with the four-electron water oxidation reaction (WOR). However, the overall efficiency is severely hampered by the sluggish kinetics of the multi-electron/proton-coupled WOR. To address this limitation, three donor-acceptor (D-A) conjugated polymers (BP, TP, and PD) were designed by integrating biphenyl, bithiophene, and bipyridine units as distinct water-oxidation sites, respectively, with benzodithiazole as the electron-accepting moiety to enable efficient H₂O₂ conversion. Impressively, PD exhibited a high H₂O₂ evolution rate of 6687 μmol g^-1 h^-1 in pure water under ambient conditions, significantly exceeding BP (3200 μmol g^-1 h^-1) and TP (4650 μmol g^-1 h^-1). It was revealed that the striking performance of PD stems from enhanced charge separation and accelerated WOR kinetics, which promote proton-coupled electron transfer for the 2e^- ORR, thereby enhancing H₂O₂ formation. Moreover, the superoxide radical (•O₂^-) can be stabilized over PD via cycloaddition with singlet oxygen (¹O₂), thus facilitating the H₂O₂ evolution. These mechanisms were systematically validated using techniques such as Kelvin probe force microscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy. This tailored molecular design not only promotes spatial charge separation but also accelerates WOR kinetics, offering a robust strategy for high-performance H₂O₂ photosynthesis.