Highly Polymerized Wine-Red Carbon Nitride to Enhance Photoelectrochemical Water Splitting Performance of Hematite

Polymeric carbon nitride photocatalyst has attracted much attention due to its visible light response and high chemical stability. However, bulk carbon nitride has a wide band gap and low polymerization, limiting its photocatalytic performance for water splitting. Synthesizing highly polymerized carbon nitride with a narrow band gap still remains challenging. Herein, we propose an ionothermal protocol using supramolecular precursors to fabricate highly polymerized wine-red carbon nitride (WRCN) nanosheets. Both theoretical and experimental investigations revealed that the supramolecular precursor with a high C:N ratio leads to an upward shift of the valence band edge, while the ionothermal synthesis promotes a high polymerization degree, leading to a narrow band gap of 1.82 eV for WRCN. Benefiting from enhanced light absorption and charge separation efficiency, WRCN-loaded hematite photoanode exhibits a much higher photocurrent density than both pristine hematite and bulk carbon nitride decorated hematite. This work may provide a novel strategy to manipulate the electronic structures of carbon nitrides for enhanced photoelectrochemical performances.