Defective CeO₂/Copper Phthalocyanine S-Scheme Heterojunctions With Molecular Copper Centers for Selective CO₂-To-CO Photoconversion

Abstract

Simultaneously regulating charge carrier dynamics and catalytic selectivity remains a critical challenge in photocatalytic CO₂ reduction. Here, we report a copper (II) phthalocyanine/oxygen-vacancy-rich (CuPc/CeO₂) S-scheme heterojunction featuring atomically dispersed Cu–N₄ sites. Ultraviolet photoelectron spectroscopy establishes a 0.24 eV work function difference between CeO₂ and CuPc, generating a built-in electric field that drives S-scheme charge transfer. X-ray photoelectron spectroscopy confirms oxygen vacancies in CeO₂ (evidenced by Ce³⁺ states), enabling the energetic alignment that spatially separates reductive electrons (−1.05 V vs. NHE) at molecular Cu sites from oxidative holes (+2.44 V) in CeO₂. Time-resolved photoluminescence spectroscopy confirmed that the reduction in carrier lifetime (from 7.42 to 6.57 ns) corroborates an efficient charge separation process. In situ diffuse reflectance infrared Fourier-transform spectroscopy demonstrates that the Cu–N₄ centers preferentially stabilize the *COOH intermediate while facilitating rapid CO desorption from Cu(I) sites, thereby directing selective two-electron reduction and suppressing over-reduction to CH₄. The optimized 20CuPc/CeO₂ catalyst achieves a CO generation rate of 90.23 μmol g⁻¹ h⁻¹—representing a 16.96-fold enhancement over pristine CeO₂—with 92.2% selectivity for CO versus CH₄, and maintains robust stability over five consecutive photocatalytic cycles. This work establishes a unified design strategy integrating defect-engineered S-scheme charge separation with single-atom molecular catalysis to achieve selective solar-driven CO₂-to-CO conversion.

Keywords

copper phthalocyanine / oxygen vacancies / photocatalytic CO₂ reduction / S-scheme heterojunction / selective CO evolution

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