Breaking the 50% Efficiency Ceiling: A Tandem Electrochemical Cycle for Efficient Singlet Oxygen Electrosynthesis.

Singlet oxygen (1O2) electrosynthesis from dioxygen (O2) offers a sustainable route to value-added oxygenation reactions in pharmaceutical manufacturing. Conventional electrochemical generation, however, relies on the one-electron reduction of O2 to superoxide (O2•-) followed by disproportionation of two O2•- producing only one molecule of 1O2, which limited to a maximum electron-to-1O2 efficiency at 50%. Here, we overcome this constraint using an electrochemical tandem strategy implemented in a compact flow-through reactor, wherein O2•- is selectively generated at a modified porous titanium foam cathode and rapidly transported to a titanium-supported platinum single-atom anode for oxidation to 1O2. This design suppresses unproductive pathways, enabling an electron-to-1O2 efficiency exceeding 93%. The system achieves a high 1O2 production rate of 510 μmol L-1 min-1, facilitating phosphine oxygenation with 96.2% selectivity and the electrochemical semisynthesis of artemisinin in 44.5% yield. This work establishes a general platform for efficient, continuous 1O2 electrosynthesis, opening avenues for sustainable oxidative manufacturing.