Two-step production of 30 wt% aqueous H2O2 from air and water by solar photocatalysis and downstream concentration

Hydrogen peroxide (H 2 O 2 ) is widely needed for chemical synthesis, environmental remediation, and emerging energy technologies, 1-3 yet over 95% of its production relies on the energy-intensive anthraquinone process. 2,4 Photocatalytic H 2 O 2 synthesis from water and oxygen (or air) offers a green alternative, 5-7 but achieving commercially concentrations (30 wt%, ~9.8 M) remains a grand challenge. 8 Herein, a two-step strategy of continuous-flow photocatalytic H 2 O 2 generation from water and air coupled with subsequent concentration is developed. In the first step, a family of composition-tuned covalent organic framework (COF) photocatalysts is screened, and the component-optimized catalyst COF-4 delivers the highest activity of 6.16 mmol g -1 h -1 in batch reactor and enables stable production of dilute H 2 O 2 (~1.1 mM) for over 50 hours in a lab-made flow reactor, with a solar-to-chemical conversion (SCC) efficiency of 0.13%, exceeding that of natural photosynthesis (0.1%). The system is further extended to a scaled-up panel reactor (0.25 m 2 ) under natural sunlight, delivering very high H 2 O 2 rate (0.24 mmol h –1 ). The resulting dilute stream is subsequently converted into a crystalline H 2 O 2 -containing solid intermediate using a proprietary solidification protocol, and redissolution affords an aqueous H 2 O 2 solution up to 30 wt%. This work demonstrates that continuous solar H 2 O 2 generation and downstream concentration can be decoupled to produce concentrated H 2 O 2 from water, air and sunlight.