to reduce greenhouse gas and store renewable electricity in the form of chemical bonds. [1,2] During CO 2 RR process, a variety of products (such as carbon monoxide, formic acid, methane, methanol, ethylene, ethanol, n-propanol, etc) can be obtained through different reaction pathways depending on the electrode catalysts used. [3,4] Among these products, CO is a significant C1-building block required for various practical industrial routes, such as methanol synthesis, Fischer-Tropsch reactor and hydroformylation reaction. [4][5][6] More importantly, CO 2 RR to CO is regarded as one of the most promising routes for the chemical industry, owing to its high selectivity and spontaneous separation from electrolyte. Currently, different catalysts, such as metals and their alloys, molecular catalysts, carbon materials and metal atomic site materials, have been developed to promote the conversion of CO 2 to CO. [7][8][9][10][11][12][13][14][15] Among them, the atomic site catalysts (ASCs), especially N-doped carbon supported Ni-based ASCs (Ni-ASCs), are of more interest because of their high selectivity toward CO 2 RR to CO, tunable electronic structure, and low cost. [16][17][18][19][20][21][22] Although great progress has been achieved in making Ni-ASCs, the reported Ni atomic site catalysts usually show the limited current density at the level of Transition-metal atomic site catalysts (ASCs) are a new class of catalytic system for CO 2 electroreduction, however, their practical application is greatly hindered by the challenge that it's still difficult for them to simultaneously achieve industrial-level current density and high selectivity. Herein a new strategy is reported for hundreds of gram-scale and low-cost production of Ni-ASCs on 3D porous nanocarbon with high-loading NiN 3 sites for greatly boosting the electroreduction of CO 2 to CO with both industrial-level current density and high selectivity. It is discovered that although Ni-ASCs with high-loading (Ni-ASCs/4.3 wt.%) and low-loading (Ni-ASCs/0.8 wt.%) both show above 95% Faradic efficiency for CO (FE CO ) under a wide potential range in H-cell, in flow cell, Ni-ASCs/0.8 wt.% can only achieve FE CO of 43.6% at a current density of 343.9 mA cm −2 , significantly lower than those (95.1%, 533.3 mA cm −2 ) of Ni-ASCs/4.3 wt.% under same potential, first revealing the important role of high-loadings of single atom sites in promoting the highselectivity electrolysis at industrial-level current density. Most importantly, it is demonstrated that Ni-ASCs/4.3 wt.%-based membrane electrode assembly (MEA) exhibits outstanding durability at industrial-level current density of 360.0 mA cm −2 , which is one of the best performances for the realistic electroreduction of CO 2 to CO in the reported ASCs-based MEA systems.