Redox-enhanced photocatalysis: Boosting hydrogen peroxide production in conjugated triazine frameworks with dihydrophenazine cycling

Abstract

Solar-driven hydrogen peroxide (H₂O₂) synthesis is crucial for sustainable solar fuel production. Covalent triazine frameworks (CTFs) are promising photocatalysts for solar-driven H₂O₂ generation due to their tunable structures. However, the catalytic mechanism is not fully understood, and efficiency remains limited, making it a significant challenge to extend their application to practical H₂O₂ production. To address this, inspired by the role of dihydrophenazine (DHPZ) as an electron transfer carrier in biochemical reactions, we introduce a dihydrophenazine (DHPZ)-functionalized CTF (TA–DHPZ) designed to facilitate effective electron transfer, leveraging DHPZ’s redox cycling to promote the reduction of O₂ to H₂O₂. The DHPZ unit in TA–DHPZ sequentially oxidizes to phenazyl radical (PZ^•+) and phenazinium salt (PZ²⁺) during H₂O₂ synthesis, then photoreduces back to DHPZ, maintaining continuous electron flow and lowering the energy barrier. As a result, TA–DHPZ achieves a remarkable H₂O₂ production rate of 7787 μmol g⁻¹h⁻¹, outperforming its molecular counterpart TA–AN (anthracene-functionalized CTF), by capitalizing on DHPZ’s redox efficiency. This investigation not only introduces a valuable functional moiety for the design of CTFs but also lays the groundwork for innovative approaches in molecular-level design of photocatalysts for efficient solar-to-chemical energy conversion.