Interrogation of the Interfacial Energetics at a Tantalum Nitride/Electrolyte Heterojunction during Photoelectrochemical Water Splitting by <i>Operando</i> Ambient Pressure X-ray Photoelectron Spectroscopy
Øystein Dahl, Martin F. Sunding, Veronica A.-L. K. Killi, Ingeborg-Helene Svenum, Mathieu Grandcolas, Magnus Andreassen, Ola Nilsen, Annett Thøgersen, Ingvild Julie Thue Jensen, Athanasios Chatzitakis
Abstract
High Resolution Image Download MS PowerPoint Slide Photoelectrochemical (PEC) water electrolysis is an important energy conversion (power-to-chemical) method, providing a solution to the intermittent nature of solar energy. However, as PEC systems usually suffer from low operational stability, they are seriously lagging in up-scaled demonstrations and viability. PEC systems are based on semiconductor/liquid interfaces, which have been extensively studied by experiments and theory, but there is a significant knowledge gap in the energetics of such interfaces during operation. In this work, operando ambient pressure X-ray photoelectron spectroscopy (AP-XPS) has been used to characterize the electrical and spectroscopic properties of a pristine Ta 3 N 5 photoelectrode and a Ta 3 N 5 /NiO x protection/passivation layer system, which stabilizes an otherwise quickly corroding pristine photoelectrode. We directly observed Fermi-level pinning of Ta 3 N 5 within the applied potential window under both dark and illumination conditions, detrimental to the performance and stability of the photoelectrode. Interestingly, in the Ta 3 N 5 /NiO x protection/passivation layer system, the Fermi level gets unpinned under illumination, allowing quasi-Fermi-level splitting and sustaining a significant PEC performance as well as high stability.