Selective Solar CO ₂ Conversion into Ethanol Using Atomic‐Scale Copper Clusters Anchored π‐extended Poly(heptazine imide)

ABSTRACT Although photocatalytic CO ₂ reduction to C ₁ products has been demonstrated, achieving selective photoconversion to C ₂ products remains a formidable challenge, as it requires sequential proton‐coupled electron transfer and kinetic and thermodynamic control to promote C─C coupling over competing pathways. We address this challenge through the atomic‐scale copper (Cu) clusters anchored on carbon‐doped potassium poly(heptazine imide) (Cu/C‐K‐PHI). Carbon doping extends the π‐conjugation within poly(heptazine imide) framework, narrowing optical bandgap to 1.89 eV, suppressing photogenerated charge‐carrier recombination and enhancing interfacial charge transfer. The anchored Cu clusters lower the kinetic barrier for C─C coupling. Focused on the liquid‐phase C─C coupling pathway, Cu/C‐K‐PHI selectively produces ethanol with ∼100% selectivity among liquid‐phase products, exhibiting production rate of 18.98 µmol g ⁻¹ h ⁻¹ , reaching 77.01 µmol g ⁻¹ after 4 h and retaining ∼98% of its activity over five cycles under 1‐sun illumination without sacrificial agents. The solar‐to‐ethanol conversion efficiency is 0.175% with apparent quantum yield is 0.516%. In situ attenuated total reflectance‐infrared spectra, together with density functional theory calculations, reveal O*C─CO‐mediated *CO dimerization pathway, providing a mechanistic origin for CO ₂ ‐to‐C ₂ H ₅ OH selectivity. These results show that synergistic electronic‐structure modulation and atomic‐scale metal engineering can steer CO ₂ photoreduction selectively toward ethanol under mild conditions without sacrificial agents.