Design aspects of all atomic layer deposited TiO 2 –Fe 2 O 3 scaffold-absorber photoanodes for water splitting

• Published in: Sustainable energy & fuels 2018, Vol.2 (9), p.2124-2130
• Main Authors: Hiltunen, Arto, Ruoko, Tero-Petri, Iivonen, Tomi, Lahtonen, Kimmo, Ali-Löytty, Harri, Sarlin, Essi, Valden, Mika, Leskelä, Markku, Tkachenko, Nikolai
• Format: Article
• Language: English
• ISSN: 2398-4902; 2398-4902
• DOI: 10.1039/C8SE00252E

Iron and titanium oxides have attracted substantial attention in photoelectrochemical water splitting applications. However, both materials suffer from intrinsic limitations that constrain the final device performance. In order to overcome the limitations of the two materials alone, their combination has been proposed as a solution to the problems. Here we report on the fabrication of an atomic layer deposited (ALD) Fe 2 O 3 coating on porous ALD-TiO 2 . Our results show that successful implementation requires complete mixing of the TiO 2 and Fe 2 O 3 layers via annealing resulting in the formation of a photoactive iron titanium oxide on the surface. Moreover, we found that incomplete mixing leads to crystallization of Fe 2 O 3 to hematite that is detrimental to the photoelectrochemical performance. IPCE and transient photocurrent measurements performed using UV and visible light excitation confirmed that the iron titanium oxide extends the photocurrent generation to the visible range. These measurements were complemented by transient absorption spectroscopy (TAS), which revealed a new band absent in pristine hematite or anatase TiO 2 that we assign to charge transfer within the structure. Taken together, these results provide design guidelines to be considered when aiming to combine TiO 2 and Fe 2 O 3 for photoelectrochemical applications.