An efficient electrocatalytic in-situ hydrogen peroxide generation for ballast water treatment with oxygen groups.

The in-situ electrochemical production of hydrogen peroxide (H₂O₂) offers a promising approach for ballast water treatment. However, further advancements are required to develop electrocatalysts capable of achieving efficient H₂O₂ generation in seawater environments. Herein, we synthesized two-dimensional lamellated porous carbon nanosheets enriched with oxygen functional groups, which exhibited exceptional performance in H₂O₂ electrosynthesis. The carbon nanosheet electrocatalysts demonstrated high selectivity for H₂O₂ production, reaching 90 % at 0.33 V vs. RHE under neutral conditions. Maximum yields were achieved at 2238 mmol g_cat^-1 h^-1 at -0.5 V in an H-type electrolysis cell and 3681 mmol g_cat^-1 h^-1 at a current density of 150 mA cm^-2 in a flow cell, with Faraday efficiencies exceeding 70 %. Notably, a continuous 9-hour electrosynthesis test produced a high cumulative H₂O₂ concentration of 1.2 wt% at a current density of 100 mA cm^-2, highlighting the stability and scalability of carbon nanosheets. The outstanding performance of carbon nanosheets is attributed to the abundant basal plane C-O-C group, which provide optimal *OOH binding energy and minimal overpotential. Additionally, the in-situ generated H₂O₂ from the electrocatalytic system achieved complete sterilization within 60 min against Escherichia coli and several marine bacterial strains isolated from seawater. Furthermore, treatment of real seawater with H₂O₂ significantly altered the bacterial population abundance at both the phylum and genus levels, highlighting its effectiveness in microbial control. This study presents a high-performance electrocatalytic system for ballast water treatment, offering both scalability and environmental sustainability.