Interplay of thickness and photoelectrochemical properties in nanostructured α-Fe₂ O₃ thin films

Abstract

Nanostructured Fe 2 O 3 thin films were grown by plasma enhanced-chemical vapor deposition (PE-CVD) from Ar/O 2 plasmas for photoelectrochemical (PEC) water splitting applications. Iron oxide coatings were deposited on fluorinedoped tin oxide (FTO) substrates at 300 8C under optimized conditions, and subsequently annealed ex situ in air at 650 8C. Structural and compositional analyses confirmed the formation of pure a-Fe 2 O 3 (hematite), free from other crystalline iron oxide phases. Controlled variations of the deposition time enabled tuning of the thickness and nano-aggregate sizes in the resulting deposits and, correspondingly, their current-voltage characteristics. A maximum photocurrent density close to 1 mA cm À2 was achieved at 1.23 V versus the reversible hydrogen electrode (RHE), without the need of any oxygen evolution catalyst or over/underlayer. The present findings revealed the key role played by the engineering of Fe 2 O 3 -based nanomaterials, resulting ultimately in a lowered carrier diffusion length, and in an optimal diffusion of tin from FTO into thinner layers. These features offer an amenable opportunity for harvesting radiant energy to trigger water photoelectrolysis and produce clean hydrogen in a carbonneutral fashion.

Construction of Heterostructured Fe2O3‐TiO2 Microdumbbells for Photoelectrochemical Water Oxidation

“…Since the seminal work by Fujishima and Honda, semiconducting TiO 2 has been widely studied as an important photocatalyst for PEC water splitting, which shows relatively high activity and stability under ultraviolet‐light (UV‐light) . Fe 2 O 3 is also an attractive photocatalyst with a band gap of 1.9–2.2 eV and good performance under visible‐light (Vis‐light) . These two earth‐abundant, non‐toxic and robust semiconductor materials are good candidates for the construction of heterojunction photocatalysts with high charge separation efficiency and good light absorption ability, leading to enhanced performance for PEC water oxidation .…”

Plasma‐assisted deposition of iron oxide thin films for photoelectrochemical water splitting

“…To verify if there was a migration of tin from the FTO substrate into the FeO x film, as often reported in the literature, [28][29][30] sputtering depth profiling was performed on selected samples. Tin migration, indeed, is considered beneficial for water splitting application, as it improves the electrical conductivity by increasing the carrier density.…”

WO3-decorated ZnO nanostructures for light-activated applications

“…This effect could be traced back to an efficient in-depth dispersion of WO 3 into the porous ZnO deposit, further favored by the inherent infiltration power characterizing RF-Sputtering. 45,48 The efficient intermixing of the two oxides, resulting in an intimate ZnO/WO 3 contact, is likely to beneficially affect the system functional behavior, since it involves the formation of a high density of heterojunctions.…”

“…The reported binding energies (BEs) were corrected for charging by assigning a BE of 284.8 eV to the C1s line of adventitious carbon. 44 After a Shirleytype background subtraction, atomic percentages (at.%) were calculatedby integration of photoelectron signals using sensitivity factors provided by Φ V5.4A software.Calculation of the surface tungsten molar fraction (X W ) was performed according to the following relation: 24,45 X W = (W at.%)×100/[(W at.%) + (Zn at.%)]…”