Reducing carbon dioxide to formate is one of the most promising methods to achieve peak carbon dioxide emissions. Nevertheless, the low overpotential in energy conversion remains a major challenge. Herein, a new composite catalyst consisting of cuprous sulfide and graphite-phase carbon nitride with nitrogen defects (Cu₂S/NDg-C₃N₄) is synthesized, which simultaneously achieves a high Faradaic efficiency of 82.3% to formate at a low overpotential of 57 mV. Our studies suggest that electron-rich N defects serve as Lewis basic sites to activate CO₂ and increase the local CO₂ concentration of active sites, which improves the catalytic activity. The catalyst can spontaneously form a heterojunction by in situ Raman spectroscopy detected during the CO₂ reduction process, which improves the electrolysis durability. The *OCHO* species detected by in situ ATR-IR spectroscopy verified the O-end adsorption pathway of CO₂ reduction to formate on Cu₂S/NDg-C₃N₄. DFT calculations show that sulfur promotes the activation of interface water, forming hydrogen species that can promote intermediate hydrogenation to *OCHO*, which reduces the overpotential. This work shows lower overpotentials than other reported copper-based catalysts and provides a new strategy for designing a simple and energy-saving CO₂ reduction catalyst.

将二氧化碳还原为甲酸盐是实现二氧化碳排放峰值的最有希望的方法之一。然而，能量转换的低过电位仍然是一个重大挑战。在此，合成了一种由硫化亚铜和具有氮缺陷的石墨相氮化碳组成的新型复合催化剂（Cu ₂ S/NDg-C ₃ N ₄），同时在低过电位下实现了 82.3% 的高法拉第效率甲酸化。 57毫伏。我们的研究表明，富含电子的 N 缺陷可作为 Lewis 碱性位点激活 CO ₂并增加局部 CO ₂活性位点集中，提高催化活性。_{该催化剂在CO 2}还原过程中通过原位拉曼光谱检测可自发形成异质结，提高了电解耐久性。原位ATR-IR光谱检测到的*OCHO*物种验证了CO ₂还原为Cu ₂ S/NDg-C ₃ N _{4上的O端吸附途径}. DFT 计算表明，硫促进界面水的活化，形成可促进中间氢化成 *OCHO* 的氢物种，从而降低过电位。这项工作显示出比其他报道的铜基催化剂更低的过电位，并为设计简单且节能的 CO ₂还原催化剂提供了新策略。