Optimizing Optical Absorption, Exciton Dissociation, and Charge Transfer of a Polymeric Carbon Nitride with Ultrahigh Solar Hydrogen Production Activity

Abstract

Polymeric or organic semiconductors are promising candidates for photocatalysis but mostly only show moderate activity owing to strongly bound excitons and insufficient optical absorption. Herein, we report a facile bottom-up strategy to improve the activity of a carbon nitride to a level in which a majority of photons are really used to drive photoredox chemistry. Co-condensation of urea and oxamide followed by post-calcination in molten salt is shown to result in highly crystalline species with a maximum π-π layer stacking distance of heptazine units of 0.292 nm, which improves lateral charge transport and interlayer exciton dissociation. The addition of oxamide decreases the optical band gap from 2.74 to 2.56 eV, which enables efficient photochemistry also with green light. The apparent quantum yield (AQY) for H evolution of optimal samples reaches 57 % and 10 % at 420 nm and 525 nm, respectively, which is significantly higher than in most previous experiments.

Bandgap Engineering of Organic Semiconductors for Highly Efficient Photocatalytic Water Splitting

“…[1] As the photocatalytic Taking graphitic carbon nitride (g-C 3 N 4 or GCN), the most widely reported heptazine-based polymers, as an instance, the conduction band (CB) is considered to consist of conjugated C and N 2p orbitals in the heptazine while the VB is mostly composed of the 2p orbitals of edge N atoms, resulting in a π-π* excitation bandgap of over 2.7 eV. [25,26] Very recently, we have theoretically and experimentally proved that the oxygen and nitrogen linker-controlled heptazine-based chains strongly influence the polymer's electronic structure. [25,26] Very recently, we have theoretically and experimentally proved that the oxygen and nitrogen linker-controlled heptazine-based chains strongly influence the polymer's electronic structure.…”

Crystalline Carbon Nitride Semiconductors for Photocatalytic Water Splitting

“…[39] TheX RD patterns of the asobtained CN-OA-m showed an enlarged in-planar period and ad ecreased interlayer distance compared with bulk CN (Figure 14 a). [39] TheX RD patterns of the asobtained CN-OA-m showed an enlarged in-planar period and ad ecreased interlayer distance compared with bulk CN (Figure 14 a).…”

Kohlenstoffnitridmaterialien für photochemische Zellen zur Wasserspaltung

“…Wirs tellen uns den Einbau von CN-Photoanoden als Absorber mit breiter Bandlücke zusammen mit einer Photokathode mit kleiner Bandlücke (bestehend aus reichlich vorhandenen Materialien wie etwa Si, [7,98,148] Cu-(In,Ga)Se 2 , [149] CuSbS 2 [150] und Sb 2 Se 3 [151] )f ürd ie gesamte Wasserspaltung vor. [156][157][158][159] Dies kann durch Umkristallisation auf einem Substrat [92] sowie durch das sorgfältige Design des Syntheseverfahrens bei erhçhten Drücken (z. [156][157][158][159] Dies kann durch Umkristallisation auf einem Substrat [92] sowie durch das sorgfältige Design des Syntheseverfahrens bei erhçhten Drücken (z.…”