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

Abstract

Hematite is a low band gap, earth abundant semiconductor and it is considered to be a promising choice for photoelectrochemical water splitting. However, as a bulk material its efficiency is low because of excessive bulk, surface, and interface recombination. In the present work, we propose a strategy to prepare a hematite (α-Fe2O3) photoanode consisting of hematite nanorods grown onto an iron oxide blocking layer. This blocking layer is formed from a sputter deposited thin metallic iron film on fluorine doped tin oxide (FTO) by using cyclic voltammetry to fully convert the film into an anodic oxide. In a second step, hematite nanorods (NR) are grown onto the layer using a hydrothermal approach. In this geometry, the hematite sub-layer works as a barrier for electron back diffusion (a blocking layer). This suppresses recombination, and the maximum of the incident photon to current efficiency is increased from 12% to 17%. Under AM 1.5 conditions, the photocurrent density reaches approximately 1.2 mA/cm2 at 1.5 V vs. RHE and the onset potential changes to 0.8 V vs. RHE (using a Zn-Co co-catalyst).

The behavior of hydrothermally synthesized hematite nanorods prepared on spin coated seed layers

“…The photocurrent densities of all samples noticeably yielded lower onset potentials compared to those of the dark currents. This is attributed to the enhanced suppressed leakage of dark currents from the electron back-injection, associated with the use of seed layers [48]. This observation compares well with the dark current onset potential range presented by seeded hematite NRs in comparison with those directly grown on FTO by Sun et al [18].…”

Scalable Route toward Superior Photoresponse of UV-Laser-Treated TiO2 Nanotubes

“…The presence of such rapid current changes results from the electron recombination with the surface-trapped holes and the back-reaction of electrons from the conduction band with accumulated holes. On the other hand, Poornajar et al 52 pointed out that such spikes are related to electron−hole recombination rate at low external bias. By increasing the applied potential, recombination rate is inhibited by an electric field forced charge separation (electrons are collected on the counter electrode faster along with an increasing potential, reducing the probability of their recombination with holes).…”

One-step synthesis of carbon nanospheres with an encapsulated iron-nickel nanoalloy and its potential use as an electrocatalyst

“…To analyze if the composite can work under these circumstances without suffering corrosion, 500 series of cyclic voltammograms were performed from −0.48 V vs. RHE to 1.5 V vs. RHE. In figure 6, it is observed changes at current density in the first 200 cycles, caused by the recrystallization of nickel [34][35][36] and the thickening of the iron layer [32,33]. After these 200 cycles, no significant variations are observed (around 9 mA), proving that the material is stable in these conditions.…”

“…Also, from figure 5, when ammonia is in the solution, a well-defined reduction peak with higher current density is observed at the Fe redox process. This result can be related to the chemical and electrochemical formation of iron oxides at the interphase when the anodic process is occurring [32,33].…”