Facile Tuning of the Iridium Valence State Augments Visible Light-Induced Photoelectrochemical Water Splitting in Iridium-Doped BaTiO₃

To further enhance the solar hydrogen generation efficiency of titanate-based perovskites, inducing visible light absorption via doping and promoting charge transfer through tailored cocatalysts are indispensable. Significant advancement in this direction is hampered due to a lack of rational insights into doping-induced changes in the optoelectronic properties. In this work, we develop a one-step facile approach to realize both hydrogen and oxygen evolution reactions via photoelectrochemical water splitting under visible light in Ir-doped BaTiO₃. Complementary spectroscopy, optoelectronics, and high-resolution microscopy tools revealed efficient, selective, and simultaneous conversion of the Ir valence state from +4 to +3 and Ir⁰. Obtaining such precise control over a favorable valence state enhanced the photocathodic current by ≈5.7 times at a lower onset potential under visible light up to 610 nm. The origin of such enhancement is attributed to the generation of free electrons in the conduction band by virtue of Ir³⁺-occupied donor levels and their efficient transfer facilitated by metallic Ir⁰ on the surface. Similarly, a photoinduced enhancement in the anodic current was also noticed, thus imparting bifunctional photoelectrochemical activity. Results offer insights into the rational design of bifunctional perovskite-based photocatalysts for various oxidation and/or reduction reactions beyond water splitting activity and how to efficiently harness a wider part of the solar spectrum.