Green synthesis of porous carbon guided by phase diagrams for electrochemical rubidium salt desalination

In capacitive deionization for saline wastewater treatment, the properties of porous carbon electrode materials critically determine desalination performance. Here, we prepared biomass porous carbon from waste aquatic organisms. Using phase diagram analysis, we exploited the eutectic characteristics of mixed flux to achieve uniform molten salt encapsulation and activation of the carbon precursor at relatively low temperatures, while enabling recycling of the waste flux. The resulting biochar electrode exhibited a high specific surface area (1,324 m 2 g −1 ) with a hierarchical micro/mesoporous structure, delivering enhanced specific capacitance. The electrode achieved a high deionization capacity of 24.40 mg g −1 in 500 mg L −1 RbCl solution at 1.2 V with 90.82% capacitance retention after 50 cycles. This work provides an effective approach for saline wastewater treatment through sustainable electrode material design.