The Photoelectrochemical Behavior of Ferric Oxide in the Presence of Redox Reagents

Abstract

The influence of dissolved sulfide ion and the ferri/ferrocyanide redox system on the photoelectrochemical behavior of iron oxide has been investigated. Particular attention was given to transient behavior and to clark current phenomena. An interpretation of the results is given in terms of a back-reaction of photogenerated species with conduction band electrons via surface s~ates.

Controlling Photoactivity in Ultrathin Hematite Films for Solar Water‐Splitting

“…The studies of iron oxide transient behavior already published have explained that light causes accumulation of charges at interfaces, especially holes at the SCLJ due to the slow reaction kinetics of the oxygen evolution reaction (OER). [3][4]11] During the accumulation process, an anodic current spike is measured which decreases rapidly as the accumulated holes perturb the charge distribution in the spacecharge layer. Eventually, a steady state between water oxidation and carrier recombination is attained which depends on the light intensity and applied potential.…”

“…In addition to accumulating at the SCLJ due to slow water oxidation kinetics, photogenerated holes can oxidize trap states in the bulk [5] and on the surface [4] to result in similar transient current spikes. It has been suggested that the transient behavior depends strongly on the density and energy of these trapping states which are a result of reduced crystalline quality of the surface, [3][4] and the presence of other iron oxide phases (e.g., Fe 3 O 4 or g-Fe 2 O 3 ). [3] Therefore, the lower potential disappearance of the transients in Sample C implies a smaller density of trapping states as compared to the control case.…”

“…It has been suggested that the transient behavior depends strongly on the density and energy of these trapping states which are a result of reduced crystalline quality of the surface, [3][4] and the presence of other iron oxide phases (e.g., Fe 3 O 4 or g-Fe 2 O 3 ). [3] Therefore, the lower potential disappearance of the transients in Sample C implies a smaller density of trapping states as compared to the control case. In light of the XRD results, this reasonably comes from increased crystalline order.…”

“…The seminal efforts to study hematite as an oxygen-evolving photoanode for water decomposition detailed its promising aspects and limitations. [1, [2][3][4][5] As a drawback, hematite possesses a conduction band edge at an energy level below the reversible hydrogen potential. Thus, an external electrical bias is required to provide hydrogen evolution at the cathode.…”

Immobilization of a molecular cobalt electrocatalyst by hydrophobic interaction with a hematite photoanode for highly stable oxygen evolution

“…Illumination on hematite induces the accumulation of photogenerated charges at the interfaces, in particular, hole congregation at the semiconductorelectrolyte junction due to the low mobilities for the charge carriers and the slow kinetics of the oxygen generation reaction. 21,22 Small transient response with our bare hematite may be due to dense nature of film with low surface area. For the Co-Pi/hematite sample (Figure 3), an anodic current spike is also observed during this charge accumulation phase, which decreases rapidly with time and forward potential sweep because the accumulated holes disorder the charge dissemination in the space charge layer.…”