• A novel GDY/Co(OH)2 heterointerface catalyst achieves an overpotential of only 83 mV at 10 mA cm−2 for chlorine evolution, outperforming conventional Ru/Ir-based anodes.
• The catalyst exhibits a high Faradaic efficiency of 91.54% and a chlorine yield of 157.11 mg h−1 cm−2 in acidic simulated seawater, demonstrating excellent selectivity.
• In-situ growth of graphdiyne on Co(OH)2 creates strong electron transfer at the heterointerface, enhancing conductivity, active surface area, and active sites.
• This work provides a cost-effective, Ru/Ir-free strategy for efficient chlorine production, addressing key limitations of the chlor-alkali process.