B-site substitution-induced band edge shifts in perovskite-type Cu(Nb,Ta)O<sub>3</sub> solid solutions for visible-light-driven hydrogen evolution

Haocong Wang; Chihiro Takahashi; Xuemeng Guo; Shunya Okada; Hajime Suzuki; Daiming Tang; Wei Yi; Ikuya Yamada; Xiaojuan Liu; Ryu Abe; Koji Fujita

doi:10.1039/d5tc02066b

Journal article B-site substitution-induced band edge shifts in perovskite-type Cu(Nb,Ta)O₃ solid solutions for visible-light-driven hydrogen evolution

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Haocong Wang, Chihiro Takahashi, Xuemeng Guo, Shunya Okada, Hajime Suzuki, Daiming Tang, Wei Yi, Ikuya Yamada, Xiaojuan Liu, Ryu Abe, Koji Fujita. B-site substitution-induced band edge shifts in perovskite-type Cu(Nb,Ta)O₃ solid solutions for visible-light-driven hydrogen evolution. Journal of Materials Chemistry C. 2025, 13 (39), 20146-20155. https://doi.org/10.1039/d5tc02066b

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The rational design of photocatalysts with precise bandgap and band-edge control is crucial for achieving the visible-light-driven conversion of solar to hydrogen. This study demonstrates a novel strategy for band-edge engineering through B-site cation substitution and symmetry evolution in Cu (3d10)-based perovskites. Substitution of Ta5+ (5d0) for Nb5+ (4d0) in CuNbO3 induces sequential phase transitions (Pc–R3c–R[3 with combining macron]c), accompanied by systematic bandgap modulation from 1.57 to 2.23 eV. The R[3 with combining macron]c CuTaO3 phase exhibits a much higher conduction band (−0.90 V vs. standard hydrogen electrode) than the H+/H2 potential and a slightly lower valence band than the O2/H2O potential. Visible-light-driven hydrogen evolution occurs efficiently on CuTaO3 with Ru cocatalyst, in the presence of S2−/SO32− sacrificial agents. Our experiments and first-principles calculations reveal that the Ta-for-Nb-substitution widens the bandgap by lowering the valence band maximum via weakened Cu–O hybridization, while simultaneously elevating the conduction band minimum via Ta 5d orbital contributions. The inherent bandgap-narrowing tendency of structural evolution from polar Pc to centrosymmetric R[3 with combining macron]c symmetry is attenuated by Ta substitution-induced elongation of Cu–O bonds. The interplay between B-site cation engineering and symmetry-induced electronic degeneration establishes a materials design paradigm for visible-light-driven photocatalysis, demonstrating how to enable targeted bandgap optimization by coupling orbital-level modifications and phase transition.

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