Crystalline Oxygen-Modified Carbon Nitride Photocatalyst with Enhanced Internal Electric Field and Strong Resistance to Ionic Interference for Robust Seawater Splitting

Photocatalytic seawater splitting to produce clean hydrogen from nonpotable water using sunlight is a crucial endeavor. However, the scarcity of high-performance photocatalysts in the promising yet fledgling field presents a formidable challenge. Herein, we successfully synthesized a crystalline oxygen-modified carbon nitride (CCNO) polymeric semiconductor that served as an effective photocatalyst for seawater splitting. Comprehensive characterizations and theoretical calculations revealed that nitrogen vacancies and bridging oxygen in the CCNO lattice acted as potent Lewis acid–base pairs, creating an enhanced built-in electric field. This advancement significantly accelerated charge dynamics and bolstered resistance to ionic interference in seawater. Consequently, CCNO exhibited a robust photocatalytic H2 evolution activity of 29.51 mmol g–1 h–1 in natural seawater, with an impressive apparent quantum efficiency of 66.86% under 420 nm monochromatic light. Seawater splitting for H2 production reached 16.83 mmol g–1 under natural light irradiation for 3 h (9–12 o’clock), showcasing its great potential for practical applications. This work presents strategies for developing a metal-free photocatalyst and elucidates its reaction mechanism in the seawater splitting process, laying the foundation for scalable production of clean hydrogen.