Ta3N5 Photoelectrodes for Solar Hydrogen Production: Overcoming the Kinetic Bottleneck at the Solid–Liquid Interface

by Pietro Mani (Uni Trento)

Tuesday 24 Jun 2025, 09:30 → 10:30 Europe/Zurich

OHSA/B17

Ta₃N₅ represents a novel and interesting material in the photoelectrochemical field. Its small band-gap energy of about 2 eV allows for the harvesting of a large portion of the solar spectrum, and the position of the energy bands’ edges is suitable for driving both cathodic hydrogen generation and anodic water oxidation. Despite these promising features, the performance is limited by low charge-transfer kinetics, strong charge recombination rate, and poor stability, which highly reduces its efficiency when applied in a photoelectrochemical cell. In this seminar, I present experimental strategies to overcome both bulk and interfacial limitations. Ti-doped Ta₃N₅ photoanodes were synthesized via RF sputtering of a Ta target in an oxygen reactive plasma, followed by nitridation in ammonia. Electrochemical measures, such as Impedance Spectroscopy, revealed that the real bottleneck is its low charge-transfer kinetics at the film-solution interface, which prevents photogenerated holes from being easily transferred to the redox couple. This, in turn, caused an undesired oxidation of the interface, which dramatically reduced the performance within a few minutes. The photo-generated current was increased by around ten times by the addition of a hole scavenger, K₄Fe(CN)₆, which also inhibited surface oxidation, confirming the hypothesis regarding the formation of this detrimental layer. The Ti doping led to a further increase in photocurrent, and the reason for this behaviour remains to be investigated. To overcome the kinetic bottleneck at the solid-liquid interface, NiFeO_x co-catalyst was deposited on the surface using Pulsed Laser Deposition. Preliminary results show improved interfacial hole transfer. These findings underline the importance of integrated bulk and surface engineering to exploit the full potential of Ta₃N₅-based photoelectrodes for solar hydrogen generation.