A photocatalyst is a material able to utilize photons to drive a chemical reaction. One example of a photocatalyst is tantalum nitride (Ta3N5 ). The material is used as a photoanode in photoelectrochemical (PEC) cells and catalyzes the oxygen evolution reaction (OER). Together with its high theoretical solar-to-hydrogen (STH) efficiency and non-toxicity, Ta3N5 is regarded as an ideal photocatalyst for water photo-electrolysis and beyond. It is important to emphasize that in order to achieve high hydrogen production from PEC water electrolysis, the OER must be significantly improved, as it is currently the major bottleneck for scaled-up applications. The reason is simple: the hydrogen evolution reaction (HER) is a two-electron process with well-defined intermediate products, while the OER is a much more complicated process of four electrons with many more intermediate steps. Moreover, the operating conditions during the OER are highly oxidizing and this brings extra challenges to the OER catalyst materials that are related to durability and robustness. In the case of Ta3N5, it of course oxidizes during the photo-assisted OER, forming TaON and Ta2O3 species.
On the other hand, Ta3N5 has a band gap of 2.1 eV and a theoretical STH efficiency of 12.9%, which in principle exceeds the benchmark efficiency set by the US Department of Energy (DOE) of 10% STH. In this project, we address a fundamental issue in Ta3N5, which is the unavoidable oxygen defects and the introduction of electron donor species (ON) in the lattice of the material.
Main research questions:
- By changing the thin film composition,
- How can we improve the photocurrent onset potential?
- How can we improve the stability of the material for long-term operation under harsh, oxidizing OER conditions?
- Can we introduce an additional protection layer without sacrificing the performance?
The study is conducted using a plethora of different synthesis and characterization techniques, including pulsed-laser deposition (PLD), sputtering, ammonolysis, PEC measurements, (AP)-XPS, XRD, SEM, TEM, and many more to investigate the effect of dopants, protection layers. We also strive to utilize a combinatorial approach to accelerate the scientific study