Boosting seawater desalination driven by electroreduction of CO2 to formate on bimetallic Sn/Cu polyphthalocyanine frameworks

Electrochemical desalination offers a promising route to address water scarcity, but current methods often face limitations in salt removal rate and capacity. This study introduces an ultrafast electrocatalytic desalination system that leverages the electrochemical reduction of CO 2 to formate (CO 2 RR) to drive efficient salt removal. The optimized bimetallic Sn/Cu-based polyphthalocyanine (Sn 2 Cu 1 PPc) exhibits exceptional CO 2 RR performance, achieving a peak FE formate of 90.3 % at −1.0 V vs. RHE and a j formate of 84.8 mA cm −2 . In-situ spectroscopic analysis and density functional theory (DFT) calculations reveal that the incorporation of Cu-N 4 units into the Sn-based polyphthalocyanine (SnPPc) promotes CO 2 adsorption and facilitates active hydrogen provision, leading to the observed enhancement in CO 2 RR activity. Using the Sn 2 Cu 1 PPc catalyst, our system achieves a salt removal rate of 1701.3 μg cm −2 min −1 and a formate production rate of 0.79 mmol h −1 cm −2 when treating natural seawater, resulting in potable water with 99.06 % salt removal efficiency. This performance is enabled by a high current density (∼70 mA cm −2 ) during CO 2 RR, which significantly enhances ion transport across the membranes, making this one of the most effective desalination approaches reported. This work demonstrates the potential of coupling CO 2 RR with desalination for sustainable water production and CO 2 mitigation, while also advancing the design of efficient Sn-based electrocatalysts for formate production.