High-Entropy Perovskite Oxide Enables Visible-Light-Driven Overall Water Splitting via "inner-Z-Scheme" Pathway

The high degree of chemical complexity and expanded compositional space enabled by high-entropy engineering offers opportunities for rationally designing new type semiconductor photocatalysts with tailored electronic structure favorable for full-spectrum solar energy utilization. Here, we construct a high-entropy photocatalyst featuring an "inner-Z-scheme" stepwise photoexcitation that enables efficient visible-light-driven overall water splitting. This inner-Z-scheme is realized through the formation of a delocalized intermediate band within the wide bandgap of a perovskite NaNbO₃ host, achieved by selectively incorporating closed-shell d⁰ and open-shell dⁿ transition-metal cations into a single-phase solid solution. Electron microscopy confirms that the resulting high-entropy perovskite oxide (termed Na(HE)O₃) retains a highly crystalline structure while exhibiting the short-range lattice distortions characteristic of high-entropy materials. Complementary spectroscopic analyses identify a pronounced intermediate-band feature that enables sequential sub-bandgap electronic excitation and extends the photoresponse into the visible region. The compositional diversity further creates varied local coordination environments with the formation of intrinsic catalytic centers to enable overall water splitting without additional cocatalysts. Under AM 1.5G solar illumination, Na(HE)O₃ achieves stable overall water splitting with a solar-to-hydrogen efficiency of 1.34%. This work establishes high-entropy-stabilized intermediate-band semiconductors as a viable platform for band-structure engineering in photocatalyst design.