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Tantalate perovskites are considered as potential candidates for photocatalytic hydrogen production because their electronic band structure satisfies the requirements for water splitting. However, these oxides have large bandgaps which results in their low photocatalytic activity. In this study, to enhance the photocatalytic activity of tantalate perovskites, CsTaO3 as a new photocatalyst is mechanically subjected to severe plastic strain of ε ≥ 13 using the high-pressure torsion (HPT) method and its performance is compared with LiTaO3. Both super-strained tantalates exhibit bandgap narrowing together with decreasing the conduction band energy with similar enhancement of the photocatalytic hydrogen production (by a factor of ~2.5 without cocatalyst addition). Such bandgap narrowing is mainly due to the formation of oxygen vacancies and lattice straining, although the formation of nanocrystals and partial amorphization also occur. These findings not only introduce CsTaO3 as a photocatalyst but also confirm that the production of strain-induced vacancies is an effective approach to improve the photocatalytic activity of perovskites.

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