Anisotropic photocatalytic properties of hematite

Abstract

Hematite is a semiconducting mineral with a role in natural photoelectrochemical processes, and has been studied from the viewpoint of solar energy utilization. Hematite is an anisotropic conductor, with faster conduction parallel to (001) planes. Flatband potentials and photocurrent onset potentials for natural hematite single crystals and synthetic nanocrystalline hematite films are similar, and show Nernstian behavior within error. At pH 7, the flatband potential of single crystals is -0.25AE0.1 V vs. Ag/AgCl. Photocurrent onset potential is 0.02 to 0.03 V more negative for crystal faces than for crystal edges. Photocurrent density is a factor of 5 to 10 higher for crystal edges than for crystal (001) faces, presumably because of more rapid charge separation for the edges. Falling photocurrent transients decay more slowly for edges than for faces, consistent with more rapid removal of conduction band electrons into the bulk and therefore reduced availability of such electrons for back reaction. Rising photocurrent transients occur at higher potential, and have the same rise time for both faces and edges. This suggests that the rising transients are due to slow conduction through bulk hematite. The transition from falling to rising transients occurs at a more positive potential for edges than for faces, which is also consistent with more rapid charge transport away from edge surfaces and with Fermi level pinning at edges.

Solar Water Splitting: Progress Using Hematite (α‐Fe2O3) Photoelectrodes

“…In comparison to the extensive work done on TiO 2 , [138] relatively little is known about the surface chemistry of hematite. Only recently have some important and interesting reactivity differences on hematite surfaces have been observed, [139][140] and further work on this topic is necessary.…”

Inner-Helmholtz potential development at the hematite (α-Fe2O3) (001) surface

“…doi:10. 1016/j.gca.2011.05.013 potential measurements using photocurrent onset methods (Eggleston et al, 2009), by surface X-ray reflectivity measurements (Catalano et al, 2010), by Mö ssbauer measurements , as well as being implicated in Fe(II)-catalyzed atom exchange reactions with goethite (Handler et al, 2009). Given the potential links between interfacial redox processes such as these and scavenging, occlusion, or transformation of metal ions and contaminants of environmental importance, a better understanding of the influence of surface specific charging on interfacial electron transfer is needed.…”

The Oxygen Evolution Reaction: Water Oxidation Photocatalysis—Photocatalytic Water Oxidation with Suspended alpha-Fe2O3 Particles—Effects of Nanoscaling

“…3.2c, d) show the 0.2 nm characteristic lattice spacing of Ag (011). Interestingly, we observe preferential deposition onto one facet, most likely the (001) facet, which can be explained by a higher anisotropic conductivity in this direction [14]. Notably, the material retained crystallinity after 24 h full spectrum irradiation (Fig.…”

“…Bulk-Fe 2 and CO 2 + [8][9][10][11][12][13] to decrease defects. Other attempts involve selective film growth on the most active crystal face (001) for more efficient electron and hole transport [14], or enhancing purity via chemical vapor deposition and enhancing electron transport with Si-doping [15]. Many of the issues (fleeting electron/hole transport properties), however, can be addressed on the nanoscale size regime.…”