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.