KOH Activated Walnut Shell Biochar Electrode of Capacitive Deionization and Its Desalination Performance

The flake biochar electrode materials with fast ion transport function were prepared by KOH activation walnut shell used as raw material. The effects of carbonization temperature and KOH-to-biochar ratio were systematically evaluated using physicochemical characterization and electrochemical performance testing. The optimized walnut shell biochar (WSC800–2), produced at 800 °C with a KOH-to-biochar ration of 2:1, exhibited an exceptional specific surface area (2,287 m 2 g −1 ), the highest porosity (0.824 cm 3 g −1 ), and an excellent specific capacitance (369.51 F g −1 , 10 mV s −1 ). Furthermore, in desalination experiments, WSC800–2 achieved a high salt adsorption capacity of 15.70 mg g −1 at 1.2 V, 500 mg l −1 NaCl solution. The electrode also exhibited outstanding cycling stability, retaining 97.0% of its performance after 10 adsorption/desorption cycles. These findings highlight the potential of walnut shell-derived biochar as an effective material for capacitive deionization and future desalination technologies.