Solar-floating Co–N4 single-atom catalyst platform for neutral-pH H2O2 generation and algal bloom mitigation

Harmful algal blooms present severe ecological and public health challenges, creating an urgent need for sustainable remediation strategies. Here, we present a solar-powered electrochemical platform that generates hydrogen peroxide (H 2 O 2 ) in - situ via the two-electron oxygen reduction reaction (2e – ORR), using a cobalt single-atom catalyst with Co–N 4 sites anchored on crystalline carbon nanohorns (Co–N 4 Cl/CNH). Synchrotron X-ray absorption spectroscopy and electron microscopy confirm isolated Co–N 4 active sites on the carbon support. The axial Cl coordination is known to modulate the oxidation state of Co-N 4 , suppressing O–O cleavage and promoting selective H 2 O 2 generation. The Co–N 4 Cl/CNH catalyst achieves ~80% Faradaic efficiency for H 2 O 2 production in a flow-cell under both alkaline and neutral conditions, enabling effective oxidation of cyanobacteria under environmentally relevant conditions. Compared to conventional chemical dosing of H 2 O 2 , this in situ electrochemical approach achieves faster and more complete cyanobacterial cell lysis within 6 hours. To demonstrate real-world applicability, the Co–N 4 Cl/CNH cathode was integrated into an autonomous solar-powered floating platform that continuously generates H 2 O 2 using only sunlight and ambient air, sustaining 24-hour operation with ~9 hours of daily solar charging and requiring no external power or chemical additives. Overall, this work showcases a unique integration of advanced single-atom catalysis with renewable energy and autonomous operation, bridging fundamental catalysis with practical environmental applications for sustainable harmful algal bloom remediation. A solar-powered floating electrochemical platform employing atomically dispersed Co–N 4 single-atom catalysts on crystalline carbon nanohorns enables efficient in-situ hydrogen peroxide generation via the two-electron oxygen reduction reaction under both neutral and alkaline conditions. The system autonomously converts dissolved oxygen into H 2 O 2 using only sunlight, achieving rapid and effective degradation of harmful algal blooms without external energy or chemical dosing. This work bridges advanced single-atom catalysis with practical, sustainable water treatment for environmental remediation. • Atomically dispersed Co–N 4 single-atom catalysts on crystalline carbon nanohorns were synthesized. • The catalyst achieves ~80% Faradaic efficiency for H 2 O 2 production in neutral and alkaline media. • A solar-powered floating electrochemical system enables autonomous in - situ H 2 O 2 generation. • Rapid algal bloom removal is realized within 6 h without external energy or chemical dosing. • The study bridges advanced single-atom catalysis with sustainable water treatment applications.