Calcium-tolerant electrode strategy for efficient hydrogen peroxide electrosynthesis in natural water

Calcium scaling is traditionally regarded as a major impediment to the practical application of decentralized H₂O₂ electrosynthesis via two-electron oxygen reduction reaction (2e^- ORR). Herein, we demonstrate that the calcium scale unexpectedly enhances H₂O₂ electroproduction. Dissolved Ca²⁺, rather than precipitated scale, is the dominant factor suppressing H₂O₂ electrosynthesis. Interfacial enrichment of Ca²⁺ facilitates water dissociation and proton accessibility, shifting the pathway toward 4e^- ORR. To address this challenge, a quaternary ammonium cationic surfactant-modified cathode is developed, demonstrating a 2.3-fold enhancement in H₂O₂ yield. Theoretical calculations suggest that surfactant modification weakens Ca²⁺ adsorption and reduces its interfacial accumulation through enhanced electrostatic repulsion. Simultaneously, hydrophobic side-chain grafting decreases proton accessibility by disrupting the interfacial hydrogen-bond network, thereby improving 2e^- ORR selectivity. Furthermore, a 3D polyurethane sponge-fenced cathode architecture establishes an alkaline microenvironment via pore confinement, mitigating the Ca²⁺-enhanced proton accessibility and increasing H₂O₂ electroproduction by 293.3%. These strategies of interfacial field manipulation and 3D alkaline confinement provide a promising paradigm for designing Ca²⁺-tolerant cathode for efficient H₂O₂ electrosynthesis.