The renewable energy-powered methane (CH4) conversion at ambient conditions is an attractive but highly challenging field. Due to the highly inert feature of CH4, the selective cleavage of its first C-H bond without over-oxidation is essential for upgrading CH4 toward value-added products. In this work, we developed an efficient and selective CH4 conversion approach at room temperatures by intermediate chlorine species (*Cl), which were electrochemically generated and stabilized on cobalt-nickel mixed spinels with different Co/Ni ratios. The lower overpotentials for *Cl formation enabled effective activation and conversion of CH4 to CH3Cl without over-oxidation to CO2 , and Ni3+ at the octahedral sites in cobalt-nickel mixed spinels allowed to stabilize surface-bound *Cl species. The CoNi2Ox electrocatalyst exhibited an outstanding yield of CH3Cl (364 mmol·g-1·h-1 ) and a high CH3Cl-versus-CO2 selectivity of over 400 at room temperatures, with demonstrated capability of direct CH4 conversion under seawater working conditions.