The Effect of Doping with Ti(IV) and Sn(IV) on Oxygen Reduction at Hematite Electrodes

Abstract

We examined the reduction of oxygen at doped hematite (␣-Fe 2 O 3 ) electrodes to determine how the identity of the dopant affected the reaction and how changes in reactivity compared with changes in dopant concentration. Our results indicated that Sn͑IV͒ and Ti͑IV͒ dopants have a similar effect on the open-circuit potential, cathodic transfer coefficient, and exchange current density, suggesting that any bandgap states associated with the introduction of dopants and directly involved in the reduction of oxygen have similar energies. The greatest difference between the electrodes doped with Sn͑IV͒ and Ti͑IV͒ was in the apparent cathodic transfer coefficient. The cathodic transfer coefficients for the Sn-doped electrodes were slightly smaller than those for the Ti-doped, suggesting that the density of interface states is greater in the Sn-doped electrodes. In comparing electrodes with two different dopant concentrations, we found that the relative increase in reactivity was significantly less than the increase in dopant concentration. This may be due to the electrochemical creation of surface Fe͑II͒ sites that catalyze the reduction of O 2 . Other factors that may also contribute include bandgap states associated with the dopants and the fact that not all the dopants lead to creation of Fe͑II͒ sites.

Enhancing the Water Splitting Efficiency of Sn‐Doped Hematite Nanoflakes by Flame Annealing

“…Particularly, Sn IV -doped hematite, for example, in the form of pressed pellets, was reported to lead to a strong increase in the hematite specific conductivity. [12,13] In 2010, Sivula et al [6] reported that thermal treatment of solution-processed Fe 2 O 3 films at a sufficiently high temperature (800 8C) induced the diffusion of tin atoms from a transparent fluorine-doped tin oxide (FTO) substrate. This resulted in a large increase of PEC performance (from ca.…”

Morin transition suppression in Polycrystalline 57Hematite (α-Fe2O3) exposed to 56Fe(II)

“…Respiration of Fe(III) minerals by dissimilatory iron reducing bacteria (DIRB) produces a flux of aqueous Fe(II) ions at the mineral surface that may influence both mineral formation in ancient rocks [10], as well as more recent concerns regarding water quality (e.g. [11]) and iron corrosion [12].…”

Redox behavior of magnetite in the environment

“…followed by electron transfer, (ii) electrochemical reduction of the Fe 3+ oxide, and (iii) the introduction of dopant elements with higher valence charges (e.g., Ti 4+ ) (38). Several previous studies have doped Fe oxides with elements commonly found in the environment, such as Al 3+ and Mn 2+ , focusing primarily on the observed structural changes (1 and refs.…”

“…therein). Blako and Clarkson (38) showed that when hematite was doped with Sn 4+ or Ti 4+ , Fe 2+ was present structurally to neutralize the charge balance within the crystal lattice. The doped hematite was capable of oxygen reduction, indicating that the reduction potential had increased with the addition of the dopant.…”