Chelation-enabled efficient CO2 electroreduction to methane in natural seawater using low-coordinated Cu catalyst

Electrochemical CO 2 reduction (CO 2 RR) to CH 4 in seawater is attractive because CH 4 is a high energy-density fuel compatible with existing gas infrastructure, and seawater’s abundant ions confer high conductivity. However, performance is limited by sluggish eight-electron proton-coupled kinetics and deactivation by Mg 2+ /Ca 2+ in seawater. Herein, a Cu/Cu 2 O mixed-phase catalyst, which undergoes in-situ reconstruction in seawater into low-coordinated Cu nanoparticles, enabling efficient CO 2 -to-CH 4 conversion. In NaCl-based electrolyte, the reconstructed catalyst achieves 74.7% CH 4 faradaic efficiency (FE) in H-cell system. Theoretical calculations show a reduced barrier for CO hydrogenation on low-coordinated Cu, favoring CH 4 over C-C coupling. To mitigate divalent-cation induced deactivation and salt precipitation, we introduce ethylenediaminetetraacetic acid (EDTA) as a selective chelate agent. EDTA forms stable Mg 2+ /Ca 2+ complexes, suppresses deactivation, and enhances CH 4 selectivity by restructuring the electric double layer and weakening the interfacial hydration network. Consequently, in natural seawater with EDTA, the system achieves CH 4 FE exceeding 65% with stable operation for 24 h in a flow cell. These experiments and calculations together outline a practical route to selective CO 2 RR to CH 4 in seawater by coupling in-situ catalyst reconstruction with chelation-enabled electrolyte engineering.