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

Abstract

Photoelectrochemical (PEC) cells offer the ability to convert electromagnetic energy from our largest renewable source, the Sun, to stored chemical energy through the splitting of water into molecular oxygen and hydrogen. Hematite (α-Fe(2)O(3)) has emerged as a promising photo-electrode material due to its significant light absorption, chemical stability in aqueous environments, and ample abundance. However, its performance as a water-oxidizing photoanode has been crucially limited by poor optoelectronic properties that lead to both low light harvesting efficiencies and a large requisite overpotential for photoassisted water oxidation. Recently, the application of nanostructuring techniques and advanced interfacial engineering has afforded landmark improvements in the performance of hematite photoanodes. In this review, new insights into the basic material properties, the attractive aspects, and the challenges in using hematite for photoelectrochemical (PEC) water splitting are first examined. Next, recent progress enhancing the photocurrent by precise morphology control and reducing the overpotential with surface treatments are critically detailed and compared. The latest efforts using advanced characterization techniques, particularly electrochemical impedance spectroscopy, are finally presented. These methods help to define the obstacles that remain to be surmounted in order to fully exploit the potential of this promising material for solar energy conversion.

Formation of nitrogen-doped graphene nanoscrolls by adsorption of magnetic γ-Fe2O3 nanoparticles

“…Both hematite and maghemite have technologically interesting properties: hematite is used as catalyst for water oxidation 19,20 or as paint pigment, whereas maghemite is used as a contrast media in magnetic resonance or as magnetic recording media 21 . Despite many similarities, the two materials also display significant differences.…”

How Should Iron and Titanium be Combined in Oxides to Improve Photoelectrochemical Properties?

“…[10][11][12] TiO 2 has been the first material tested for water oxidation. 13,14 The TiO 2 absorption edge is 3.2 eV, allowing only 4% of the incident solar energy to be absorbed at best.…”

Cobalt Phosphate Group Modified Hematite Nanorod Array as Photoanode for Efficient Solar Water Splitting

“…Hematite (␣-Fe 2 O 3 ) has been extensively investigated as a promising semiconductor due to its favourable band gap (E g = 2.2 eV), excellent chemical and physical stabilities, abundant natural reserves, and low cost [4][5][6]. However the reported efficiencies of hematite are relatively lower than theoretically predicted value of 12.4%, mainly because of the extremely short photogenerated charge carriers' lifetime and diffusion length, chemically inert oxygen evolution reaction, and low flat band potential [7][8][9].…”