Toward Broad-Spectrum Overall Water Splitting: An Iodide-Mediated Z-Scheme Pairing Spectrally Complementary WO3 and Single-Walled Carbon Nanotube Photocatalysts

Extending particulate overall water splitting beyond ultraviolet (UV) and short-wavelength visible light is important for more fully utilizing the solar spectrum. Here, we report a particulate Z-scheme system comprising a single-walled carbon nanotube (SWCNT)/fullerodendron nanohybrid (CNT photocatalyst) for H2 evolution, commercially available WO3 for O2 evolution, and an iodide-derived redox mediator. Under air mass (AM) 1.5G simulated sunlight (1000 W m−2) and without sacrificial reagents or external bias, the optimized system evolved H2 and O2 at 15.2 and 7.6 µmol h−1, respectively—a stoichiometric 2:1 ratio—corresponding to a solar-to-hydrogen conversion efficiency of 0.08%. Near-stoichiometric gas evolution was sustained over three 6 h cycles, with 91% of the initial activity retained in the third cycle; X-ray diffraction revealed no detectable bulk structural change in WO3. The two photocatalysts play complementary roles: WO3 oxidizes water under near-UV and short-wavelength visible light, whereas the CNT photocatalyst exhibits chirality-dependent absorption spanning the visible to near-infrared region and evolves H2 at selected wavelengths in sacrificial half-reactions. Coupling these functions through an iodide-based redox shuttle extends CNT photocatalysis beyond sacrificial H2 evolution and offers a materials-design strategy for extending the usable spectral range of particulate overall water splitting.