Potential-Mediated Recycling of Copper From Brackish Water by an Electrochemical Copper Pump

Copper ions (Cu²⁺) disposed to the environment at massive scale pose severe threat to human health and waste of resource. Electrochemical deionization (EDI) which captures ions by electrical field is a promising technique for water purification. However, the removal capacity and selectivity toward Cu²⁺ are unsatisfying, yet the recycling of the captured copper in EDI systems is yet to be explored. Herein, an efficient electrochemical copper pump (ECP) that can deliver Cu²⁺ from dilute brackish water into much more concentrated solutions is constructed using carbon nanosheets for the first time, which works based on reversible electrosorption and electrodeposition. The trade-off between the removal capacity and reversibility is mediated by the operation voltage. The ECP exhibits a removal capacity of 702.5 mg g⁻¹ toward Cu²⁺ and a high selectivity coefficient of 64 for Cu²⁺/Na⁺ in the presence of multiple cations; both are the highest reported to date. The energy consumption of 1.79 Wh g^–1 is among the lowest for EDI of copper. More importantly, the Cu species captured can be released into a 20-fold higher concentrated solution. Such a high performance is attributed to the optimal potential distribution between the two electrodes that allows reversible electrodeposition and efficient electrosorption.