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Precise regulation of the active site structure is an important means to enhance the activity and selectivity of catalysts in CO 2 electroreduction. Here, we creatively introduce anionic groups, which can not only stabilize metal sites with strong coordination ability but also have rich interactions with protons at active sites to modify the electronic structure and proton transfer process of catalysts. This strategy helps to convert CO 2 into fuel chemicals at low overpotentials. As a typical example, a composite catalyst, CuO/Cu-NSO 4 /CN, with highly dispersed Cu(II)-SO 4 sites has been reported, in which CO 2 electroreduction to formate occurs at a low overpotential with a high Faradaic efficiency (-0.5 V vs. RHE, FE formate =87.4 %). Pure HCOOH is produced with an energy conversion efficiency of 44.3 % at a cell voltage of 2.8 V. Theoretical modeling demonstrates that sulfate promotes CO 2 transformation into a carboxyl intermediate followed by HCOOH generation, whose mechanism is significantly different from that of the traditional process via a formate intermediate for HCOOH production., (© 2024 Wiley-VCH GmbH.)