To investigate a highly active catalyst for CER and explore low concentrations of Cl− electrocatalytic product Cl2, Co3O4/GF catalysts were constructed by a methanesulfonic acid system plating and calcination process. SEM shows Co3O4/GF-0.1 has a uniform distribution of nanoparticles. TEM, XRD, and XPS results confirmed the formation of Co3O4. The catalytic activity in high concentrations of Cl− and low concentrations of Cl− are discussed. LSV suggests Co3O4/GF-0.1 with an initial potential of 1.06 V, The overpotential at a current density of 10 mA cm−2 is 232 m V, Tafel slope 109.26 mV dec−1, the CER reaction order is 0.54 at 1, 2 and 3 M NaCl, and 0.18 at 4, 5 and 6 M NaCl, too high concentration of Cl− slow down control of speed. In low concentration solution, the CER reaction order is 0.99, which can achieve the degradation rate of 90.8% in 50 ppm ammonia nitrogen. The apparent constant and the concentration of Cl− conform to the equation K = 1.44 × 10–3 C00.95. From low concentration to high concentration, energy consumption decreased, and Faraday efficiency increased. Electrode with jECSA = 0.52 mA cm−2, 3D structure GF has a large specific active area that promotes the diffusion of Cl−. This work provides analysis methods and ideas for the preparation of the high activity and stability CER catalyst at low Cl− concentrations in the actual water body.Graphical Abstract: