SILAR-Deposited Hematite Films for Photoelectrochemical Water Splitting: Effects of Sn, Ti, Thickness, and Nanostructuring

Abstract

Hematite (α-Fe 2 O 3 ) has been widely investigated for photoelectrochemical (PEC) water splitting, but questions remain regarding the nature of improvements induced by different dopants. We report on facile annealing treatments to dope hematite with Ti and Sn, and we provide insight into the effects of the dopant concentration profiles on two key steps of PEC water oxidation: charge separation and interfacial hole transfer. Hematite thin films were deposited by successive ionic layer adsorption and reaction (SILAR), with and without the presence of a TiO 2 underlayer on the F:SnO 2 substrate, and annealed to drive diffusion of Ti and Sn from the underlying layers into the hematite. PEC measurements showed that Ti and Sn at the hematite surface increase hole injection efficiency from nearly zero to above 80%. Ti and Sn also slightly improve charge separation efficiency, although separation efficiency remains below 20% due to low hole mobility and high recombination rate. To overcome the small hole transport length, extremely thin hematite coatings were deposited on Sb:SnO 2 monolayer inverse opal scaffolds. Photocurrent increased proportionately to the surface area of the scaffold. This study provides insight into the use of dopants and nanostructured architectures to improve PEC performance of hematite photoanodes.

Fe2O3 Blocking Layer Produced by Cyclic Voltammetry Leads to Improved Photoelectrochemical Performance of Hematite Nanorods

“…As an example, Hisatomi et al reported a 2 nm Nb 2 O 5 buffer layer between hematite and the FTO substrate to reduce recombination at the interface of the semiconductor and the substrate [40]. Abel et al [41] successfully investigated thin films (10-20 nm) of TiO 2 on FTO. They investigated hematite thin films made by a successive ionic layer adsorption and reaction (SILAR) method, with and without TiO 2 underlayer on the FTO.…”

Enhanced photocatalytic water splitting of a SILAR deposited α-Fe2O3 film on TiO2 nanoparticles

“…In this method, 0.05 M FeCl 3 and 0.1 M NaOH, were used as iron and hydroxide precursors. 42 The synthesis process is shown in Fig. 2, in which each immersion stage lasted 10 seconds.…”

“…8, the tangent lines indicates that the Fe 2 O 3 has an indirect band gap of about 2.04 eV and direct band gap of TiO 2 is about 3.35 eV for our sample; which is agreed with other observations. 42,45 Photoelectrochemical characterization Fig. 9 shows the results of PEC measurements for the a-Fe 2 O 3 / TiO 2 samples.…”

“…[30][31][32] Accordingly, the combination of these two semiconductors has attracted many attentions recently. [33][34][35][36][37][38][39][40][41][42][43] In this work, a composite electrode of a-Fe 2 O 3 /TiO 2 was introduced as a photoanode for PEC cells. The SILAR method was used for the deposition of a-Fe 2 O 3 on the TiO 2 substrate.…”

Sn-doped 3D ATO inverse opal/hematite hierarchical structures: facile fabrication and efficient photoelectrochemical performance

“…Among these, element doping, such as doping with Ti, Sn, or Si, can improve the electron conductivity of hematite and hence improve the charge transfer of hematite electrodes. [12][13][14] In particular, Sn ions can be readily incorporated into hematite due to their similar ionic radius and Pauling electronegativity to Fe ions. 15 It was found that Sn-doping is effective to improve the electronic conductivity of hematite.…”