Hydrogen produced by splitting water using solar energy is also called “solar hydrogen” and represents a possible future clean and cheap fuel. In particular, photoelectrocatalysis allows the direct production of very high purity hydrogen and represents an alternative method of using solar energy for electricity generation and subsequent storage of the surplus. An efficient application of photoelectrocatalysis requires the development and fabrication of active, stable and economical photoelectrodes in the form of thin films obtained by suitable deposition techniques. Efficient production systems under visible light irradiation have not yet been achieved, making the development of stable and efficient photocatalytic materials a key to the future of solar hydrogen.

In order to produce electrodes for the production of hydrogen through the photocatalytic water splitting reaction, the research activity of this report was dedicated to the identification and characterization of photo-active materials and their deposition in the form of thin films.

Among the anode materials identified through the study of the literature, BiVO ₄ was selected and was synthesized through a combustion synthesis procedure, found in the literature and optimized to allow its deposition in the form of a crystalline film on a suitable conductive glass support. For the cathode material, attention was instead focused on C₃N ₄, investigating the possibility of improving its performance as a photocatalyst through the formation of heterojunctions with other semiconductor materials. The material was synthesized through pyrolysis in a nitrogen flow, both in the form of powders and thin films.

Both the cathode and anode materials were characterized in film form both electrochemically by cyclic voltammetry and morphologically by scanning electron microscopy (SEM).

As cathode co-catalysts, perovskite phases were investigated whose optical and electronic properties are highly tunable to adapt to the process under consideration. A wide range of perovskites, hybrids and inorganics containing different metal cations were studied:

PEA₂PbBr₄, PEA₂PbCl_4, PEA₂SnBr_4, Cs₃Bi₂I₉, MA₃Bi₂I₉, Cs₃Bi₂Br_9, PhBZA₂GeBr₄, biPEA₂GeBr₄.

Perovskites were synthesized by precipitation and showed a good stability in an aqueous environment. The most stable materials in this sense were PEA₂SnBr₄ and the two germanium perovskites.

The stable phases in water were then characterized in terms of their ability to produce hydrogen. The best was found to be Cs₃Bi₂Br₉, with hydrogen production one order of magnitude higher than all other perovskites.

Some perovskites were selected for the formulation of composite systems with C₃ N₄, which showed a synergistic effect resulting in significantly better performance than pure materials. In all cases, the best performing composite materials were those with a low perovskite content composition.

The most efficient system was found to be C₃N₄ – PEA₂SnBr₄, however for the initial study of fine-tuning the deposition of thin films by sputtering, Cs₃Bi₂Br₉ was selected, as it is more thermally stable and therefore more suitable for coupling with C₃N₄. For the deposition, precursor powders were used as targets, pressed onto the cathode, in an Ar atmosphere.