High-selectivity CO2-to-methane photoconversion enabled by a donor–acceptor structured polyphosphazene photocatalyst

Abstract

Conventional polyphosphazene catalysts show poor methane selectivity in CO₂ photoreduction owing to weak CO intermediate adsorption. To overcome this challenge, we designed a donor–acceptor (D–A) heterostructured polyphosphazene polymer (CNP) featuring a trichlorophosphine trimer-derived phosphazene ring as an electron donor and a melamine-derived triazine ring as an electron acceptor. The CNP catalyst achieves exceptional methane selectivity (94.4%) with a production rate of 68.9 μmol g⁻¹ h⁻¹, representing a threefold enhancement over the control polymer (CN) synthesized via the same solvothermal method but without the D–A structure. Intramolecular charge transfer within the D–A architecture generates a high dipole moment (3.1D), establishing a robust built-in electric field that enhances charge carrier separation efficiency. DFT calculations further demonstrate that bandgap engineering in CNP optimizes the adsorption energies of critical intermediates (*COOH and *CHO), steering the reaction pathway toward methane generation rather than competing CO evolution. This design strategy establishes a paradigm for directional charge control in CO₂-to-fuel systems, advancing solar-driven carbon-neutral technologies.