Asymmetric Cu Valence Engineering in CuInS2 Enables Selective Photocatalytic CO2-to-C2H4 Conversion

Abstract

Achieving efficient C–C coupling in photocatalytic CO₂ reduction is fundamentally limited by the inability of semiconductor surfaces to simultaneously stabilize and differentiate key intermediates (*CO and *CHO). In this work, we establish an asymmetric Cu valence engineering strategy in tetragonal CuInS₂ that enables continuous tuning of the Cu⁺/Cu²⁺ ratio without altering the crystal framework. It is revealed that the Cu valence distribution is closely correlated with C₂H₄ selectivity, while the morphology, surface area, sulfur vacancy, and interfacial environment collectively contribute to the overall photocatalytic activity. Operando spectroscopy and DFT calculations show that such Cu valence-asymmetric sites create a polarized adsorption for key intermediates, where Cu⁺ preferentially stabilizes *CO and Cu²⁺ lowers the barrier for *CHO formation, promoting cooperative C–C coupling via the *OC–CHO intermediate. As a result, the optimized CuInS₂-1.5SC achieves an ethylene production rate of 73.9 ± 6.3 μmol g^–1 h^–1 with 95.4 ± 1.0% product selectivity and 98.0 ± 0.6% electron selectivity, without any cocatalysts or sacrificial agents. This work demonstrates the Cu valence distribution as an important parameter for regulating C₂H₄ selectivity and highlights the cooperative contribution of electronic, structural, and interfacial factors to efficient photocatalytic CO₂-to-C₂H₄ conversion.