Highly Efficient Singlet Oxygen Production in a Cascade Photoelectrocatalytic System for Water Decontamination

Singlet oxygen (¹O₂) demonstrates great potential for selective wastewater detoxification, which raises the appeal to achieve a controllable, mild, and efficient generation of this reactive species for water decontamination. Herein, we present a novel cascade photoelectrocatalytic (PEC) system operated via the interaction between the photoanodic and cathodic reactions without the addition of chemical precursors, realizing highly efficient ¹O₂ production (79.7 µmol L^-1 min^-1) and low energy consumption (0.052 kWh m^-3 -log) for antibiotic degradation. The enhanced ¹O₂ production is proven to benefit from the synergistic effect of multiple activation pathways under PEC excitation. With the combined action of both the built-in electric field and external electric field, the holes in the Z-scheme heterojunction photoanode are maximally retained, and electrons are transferred to cathode to undergo the oxygen reduction reaction (ORR), leading to the production of the crucial reactive oxygen species as intermediates. The occurrence of a cascade reaction is initiated by electrocatalytic 2e^- ORR on the cathode and terminated by superoxide species oxidation by holes on the photoanode. The hole-involved ¹O₂ generation pathway circumvents the thermodynamically unfavorable process of traditional ¹O₂ generation. This work highlights a new PEC route for highly efficient ¹O₂ generation, making it a potential application in more effective environmental remediation.