Enhanced Photocatalytic Water Splitting by Plasmonic TiO₂–Fe₂O₃ Cocatalyst under Visible Light Irradiation

Abstract

In this study, we introduce a plasmonic TiO2–Fe2O3 cocatalyst photoelectrode to improve the water-splitting process. The absorption of incident photons and the separation rate of photogenerated electron–hole pairs are enhanced due to the broadband absorption and strong electric field of the composite formed from these two metal oxide semiconductors and plasmonic silver nanoparticles (Ag NPs). Plasmonic TiO2–Fe2O3 cocatalyst photoelectrodes were fabricated using a precipitation and solution processing method. Under visible light irradiation, a photocurrent that is 20 times higher than that of pure Fe2O3 was observed using an optimized ratio of the plasmonic TiO2–Fe2O3/Ag cocatalyst. The mechanism for this enhancement in the plasmonic cocatalyst system was investigated using different structural configurations of the photoelectrode. Both the crystallinity and absorption band edge of the TiO2–Fe2O3 cocatalyst were characterized using X-ray diffraction (XRD) and ultraviolet–visible absorption spectroscopy (UV–vis). Furthermore, the spatial distribution of the photocurrent was investigated using this plasmonic cocatalyst system.

Sol–gel synthesis of TiO 2 -Fe 2 O 3 systems: Effects of Fe 2 O 3 content and their photocatalytic properties

“…Thus, structural deformations and presence of defects in the TiO 2 crystals might have formed by the substitution of Ti 4+ by Fe 3+ , which marginally reduces the crystallinity of TiO 2 [8]. As noted earlier, in composites with above 25% content of Fe 2 O 3 in TiO 2 , anatase TiO 2 peaks start diminishing while peaks for rutile phase start appearing.…”

“…It is found that chemical synthetic route and parameters involved in the entire synthesis of TiO 2 -Fe 2 O 3 materials have a significant effect on the morphology, porous structure and phase structure. Some research works have delicately reported the synthesis of TiO 2 -Fe 2 O 3 using solgel process from chloride precursor [7][8][9][10], but no available work reports the presented water based sol-gel method and with the physicochemical properties for both oxides revealed in the present study. The photocatalytic activity of prepared fine powders was tested in the reaction for degradation of methylene blue dye.…”

“…Better catalytic activity for TiFe5 and TiFe8 is convincing as TEM and nitrogen gas physisorption analysis had suggested the superiority of TiFe5 and TiFe8 composites in terms of morphology and porosity. However, photocatalytic process not only requires effective absorption of light for generating electron-hole pairs but avoiding electron hole recombination is equally important for photocatalytic reaction to proceed [8,43]. Addition of Fe 2 O 3 (E g = 1.9 eV) to TiO 2 not only facilitates the promotion of electron to the conduction band but also because of lower conduction band position acts as an electron/hole trap and inhibits electron-hole recombination process [12].…”

“…Iron (III) oxide (Fe 2 O 3 ) with lower band gap energy of 2.3 eV has emerged as an encouraging candidate to form TiO 2 composites with improved optical and morphological properties [7]. Several research studies have recognized the unique potential of Fe 2 O 3 doped TiO 2 materials for catalytic applications [8][9][10]. Addition of appropriate amounts of Fe 2 O 3 to TiO 2 shifts the optical and physicochemical features of TiO 2 toward a more favorable state [7,11].…”

Interfacial insight in multi-junction metal oxide photoanodes for water-splitting applications

“…Former studies on Fe 2 O 3 /TiO 2 heterostructures have also observed a more efficient separation of electron-hole pairs. [45,46] On the other hand, the band alignment also leads to a barrier for hole transport towards the surface and is therefore detrimental to high photocurrents. For this reason we propose that the efficiency of a coated hematite photoelectrode could be improved by employing a material for the over layer where the band alignment not only favors fast electron depletion at the surface but also fast hole transport towards the surface.…”