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 (3.1 D), 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.