(111)-layered Ba5Ta4O15 photocatalysts were synthesised by a solid state reaction route and a citrate synthesis route, and their structural and electronic properties were investigated. After citrate route preparation, the presence of a second phase, namely Ba3Ta5O15, was determined by X-ray powder diffraction and absorption spectroscopy. The existence of this phase had a profound effect on the photocatalytic activity of this Ba5Ta4O15/Ba3Ta5O15 composite in comparison to the pure Ba5Ta4O15 materials. The photocatalytic performance of the barium tantalates was evaluated by investigating the capability in ˙OH radical formation and hydrogen generation. Strongly increased hydrogen evolution rates for the Ba5Ta4O15/Ba3Ta5O15 composite, up to 160% higher than for the pure Ba5Ta4O15, were determined, and only very small amounts of Rh co-catalyst, deposited on the photocatalysts by stepwise reductive photo-deposition, were needed to achieve these results.

The combination of effective charge carrier separation and improved electron transfer in highly crystalline barium tantalate composites modified with Rh-Cr 2 O 3 core-shell co-catalyst systems induces enhanced activity for overall water splitting (OWS) with stoichiometric amounts of H 2 and O 2 (2 : 1). A sol-gel route employing complexing reagents was investigated to prepare selectively defined mixed oxide materials with improved surface areas and smaller particle sizes compared to the conventional solid state reaction (SSR). The catalytic activities of the materials are investigated in photocatalytic test reactions for hydrogen production and overall water splitting. The formation of Rh-Cr 2 O 3 core-shell co-catalyst systems for water splitting is evidenced by transmission electron microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). Moreover, we developed new and highly active barium tantalate composites for hydrogen generation from aqueous methanol solutions under UV-light, which show the highest hydrogen evolution rate for a three-component composite consisting of Ba 5 Ta 4 O 15 /Ba 3 Ta 5 O 15 / BaTa 2 O 6 . Hydrogen rates of more than 6 mmol h À1 can be achieved without any co-catalyst. Using Rh-Cr 2 O 3 core-shell co-catalysts on these three-component composites simultaneous generation of H 2 and O 2 from pure water splitting reaches rates up to 70% higher than for the pure Ba 5 Ta 4 O 15 .

The (111)-layered perovskite materials Ba5 Ta4 O15 , Ba5 Ta2 Nb2 O15 and Ba5 Nb4 O15 are prepared with nanofiber morphology via electrospinning for the first time. The nanofibers are built up from small single crystals, with up to several micrometers length even after calcination. The formation mechanism is investigated in detail, revealing an intermediate formation of amorphous barium carbonate strengthening the nanofiber morphology for high temperature treatment. All nanofiber compounds are able to generate hydrogen without any co-catalyst in photocatalytic reformation of methanol. After photodeposition of Rh-Cr2 O3 co-catalysts, the nanofibers show better activity in overall water splitting compared to sol-gel-derived powders.

The (1 1 1)‐layered perovskite material Ba5Ta4O15 represents a suitable photoabsorber with remarkable photocatalytic activity in overall water splitting. We are the first to demonstrate overall water splitting without the presence of a noble‐metal‐based co‐catalyst over this catalyst. The photocatalytic activity of Ba5Ta4O15 was investigated by overall water splitting after reductive photodeposition of amorphous Cr2O3. The formation of Cr2O3 nanoparticles for water splitting was evidenced by X‐ray photoelectron spectroscopy and transmission electron microscopy. The reductive photodeposition of very low amounts of Cr2O3 on Ba5Ta4O15 induces stable rates in overall water splitting up to 465 μmol h−1 H2 and 228 μmol h−1 O2.