Electrochemical CO₂ reduction reaction (CO₂RR) into high-value chemicals and fuels is recognized as a promising strategy for mitigating energy and environmental challenges. However, this process frequently faces limitations due to inadequate selectivity towards specific products and insufficient electrochemical stability. Main group indium (In) catalysts have emerged as promising materials for CO₂RR to highly valued formate. In this study, we constructed an indium cluster material with charge-asymmetric atomic structure anchored on nitrogen-free carbon nanoframeworks (designated as In Clu/C), which exhibits exceptional efficiency as a CO₂RR catalyst for formate production. Notably, the In Clu/C achieves a remarkable formate Faradaic efficiency of 98.7% at −0.70 V. Furthermore, in-situ X-ray absorption spectroscopy (XAS) measurements reveal that the superior catalytic performance can be attributed to partially positively charged In^δ+ (0 < δ < 3) active sites. This discovery may provide new insights into the precise synthesis of metal cluster catalysts for environmental and energy applications.

Designing catalysts with highly active, selectivity, and stability for electrocatalytic CO₂ to formate is currently a severe challenge. Herein, we developed an electronic structure engineering on carbon nano frameworks embedded with nitrogen and sulfur asymmetrically dual-coordinated indium active sites toward the efficient electrocatalytic CO₂ reduction reaction. As expected, atomically dispersed In-based catalysts with In-S₁N₃ atomic interface with asymmetrically coordinated exhibited high efficiency for CO₂ reduction reaction (CO₂RR) to formate. It achieved a maximum Faradaic efficiency (FE) of 94.3% towards formate generation at −0.8 V vs. reversible hydrogen electrode (RHE), outperforming that of catalysts with In-S₂N₂ and In-N₄ atomic interface. And at a potential of −1.10 V vs. RHE, In-S₁N₃ achieves an impressive Faradaic efficiency of 93.7% in flow cell. The catalytic performance of In-S₁N₃ sites was confirmed to be enhanced through in-situ X-ray absorption near-edge structure (XANES) measurements under electrochemical conditions. Our discovery provides the guidance for performance regulation of main group metal catalysts toward CO₂RR at atomic scale.