Constructing a visible-light-excited Z-scheme heterojunction by engineering the directional N–C/Cu insertion layer: overcoming work function mismatches

The construction of S-scheme heterojunctions is constrained by stringent work function (<i>Φ</i>) matching between oxidation and reduction photocatalysts, which limits material selection. Here, we present an innovative interfacial engineering strategy to overcome <i>Φ</i>-mismatched barriers by introducing a nitrogen-doped carbon (N-C) mediator and Cu nanoparticles at the WO₃/Cu₂O interface. Through a "post-deposition and pyrolysis" approach, we fabricated a tightly integrated Z-scheme WO₃/N-C/Cu/Cu₂O heterojunction, where the N-C layer and metallic Cu synergistically redirect photogenerated carrier recombination, preserving the high redox potentials of WO₃ (VB: +2.62 V) and Cu₂O (CB: -1.41 V). Femtosecond transient absorption spectroscopy and electron paramagnetic resonance data revealed that interfacial electrons from WO₃ transferred to N-C and recombined with holes originating from Cu₂O on Cu <i>via</i> the directional N-C/Cu insertion layer. The optimized heterojunction exhibits exceptional photocatalytic performance under blue light (450 nm), achieving a 99% yield in homo-coupling of terminal alkynes to 1,3-conjugated diynes and a hydrogen evolution rate 300-fold higher than that of conventional WO₃/Cu₂O. This work provides a universal paradigm for designing Z-scheme systems with mismatched components, unlocking new possibilities for solar energy conversion and organic synthesis.