Surface electronic modulation of CN via Pd-N bonds for pH universal photocatalytic H2 evolution

Precise atomic-scale interface engineering across the entire pH range remains a formidable challenge for photocatalytic H 2 evolution. Herein, hexamethylenetetramine (HMT) is introduced as a bifunctional surface modifier that spontaneously constructs Pd-N coordination bridges on g-C 3 N 4 . The interfacial Pd-N bonds collectively down-shift the N-p-band center away from the Fermi level, break intrinsic surface charge symmetry of C/N atoms, and fully expose the originally buried N active sites, thereby steering the hydrogen adsorption free energy (|ΔG H* |) toward thermoneutral. Simultaneously, the Pd-N bond confines Pd cluster growth to ∼5 nm, doubling specific surface area and enriching edge active sites that serve as primary proton reduction centers. Transient photoelectric voltage results reveal that the Pd-N electron transfer channel shortens the carrier transfer path and prolongs photoelectron lifetime, enabling quantitative electron delivery under acidic, neutral, and alkaline environments. As a result, the Pd-CN-HMT sample presents an efficient H 2 evolution rate across the entire pH window. This work advances the field by providing a versatile ligand-based strategy to precisely tailor the interfacial electronic structure via strong chemical bonding, offering a distinct and scalable solution for constructing high-performance pH-universal photocatalysts.