Realizing C-C Coupling via Accumulation of C1 Intermediates within Dual-Vacancy-Induced Dipole-Limited Domain Field to Propel Photoreduction of CO₂-to-C2 Fuel

Photocatalytic conversion of CO₂ and H₂O into high-value-added C2 fuels remains a tough challenge, mainly due to the insufficient concentration of photogenerated electrons for the instability of C1 intermediates, which often tend to desorb easily and disable to form C─C bonds. In this work, photoreduction of CO₂-to-C₂H₆ is successfully achieved by introducing adjacent C, N dual-vacancy sites within the heptazine rings of ultrathin g-C₃N₄, which results in the opening of two neighboring heptazine rings and forms a distinctive dipole-limited domain field (DLDF) structure. In situ X-ray photoelectron spectra and in situ fourier transform infrared spectra provide direct evidence of the rapid accumulation and transformation of C1 intermediates, especially CO^* and CHO^*, within the DLDF. Ab initio molecular dynamics further substantiates the role of DLDF in promoting C-C coupling between CO^* and CHO^*, through the analysis of interaction trajectories and energy changes of their central atoms, ultimately achieving a high yield of C₂H₆ up to 57.86 µmol g^-1 h^-1. It is for the first time to propose the concept of DLDF for significant advancement in photoreduction of CO₂-to-C2 fuel with the evident breakthrough to address the challenge of coupling carbon-containing intermediates between active sites, offering new insights for the design of C-C coupling sites in single-component photocatalysts.