Electrodeposition of Nanometer-Sized Ferric Oxide Materials in Colloidal Templates for Conversion of Light to Chemical Energy

Abstract

Colloidal crystal templates were prepared by gravitational sedimentation of 0.5 micron polystyrene particles onto fluorine-doped tin oxide (FTO) electrodes. Scanning electron microscopy (SEM) shows that the particles were close packed and examination of successive layers indicated a predominantly face-centered-cubic (fcc) crystal structure where the direction normal to the substrate surface corresponds to the (111) direction. Oxidation of aqueous ferrous solutions resulted in the electrodeposition of ferric oxide into the templates. Removal of the colloidal templates yielded ordered macroporous electrodes (OMEs) that were the inverse structure of the colloidal templates. Current integration during electrodeposition and cross-sectional SEM images revealed that the OMEs were about 2 μm thick. Comparative X-ray diffraction and infrared studies of the OMEs did not match a known phase of ferric oxide but suggested a mixture of goethite and hematite. The spectroscopic properties of the OMEs were insensitive to heat treatments at 300• C. The OMEs were utilized for photoassisted electrochemical oxidation. A sustained photocurrent was observed from visible light in aqueous photoelectrochemical cells. Analysis of photocurrent action spectra revealed an indirect band gap of 1.85 eV. Addition of formate to the aqueous electrolytes resulted in an approximate doubling of the photocurrent.

Combining Mesoporosity and Ti-Doping in Hematite Films for Water Splitting

“…[4][5][11][12][13][14][15][16][17][18] Nanostructuration of the photoanode is used as a strategy to address the short diffusion length of holes in hematite by reducing the distance that photogenerated holes have to travel to reach the electrolyte. [4][5] 4 Nanostructuration of the hematite photoanode can be achieved by various methods, such as colloidal solution deposition [19][20][21][22] , electrochemical deposition [23][24][25][26] , spray pyrolysis 11, 27-28 , hydrothermal synthesis 13,[29][30] , atmospheric pressure chemical vapor deposition 5,31 or copolymerbased soft templating. 16,[32][33] In this latter technique, copolymer micelles act as a template for the condensation of a sol-gel precursor of hematite.…”

“…Nanostructuration of the hematite photoanode can be achieved by various methods, such as colloidal solution deposition, − electrochemical deposition, − spray pyrolysis, ,, hydrothermal synthesis, ,, atmospheric pressure chemical vapor deposition, , or copolymer-based soft templating. ,, In this last technique, copolymer micelles act as a template for the condensation of a sol–gel precursor of hematite. The removal of the templating agent, usually by heat treatment, produces a mesoporous film with a continuous inorganic network and interconnected porosity.…”

Size-Dependent Bandgap of Nanogoethite

“…To investigate this apparent inconsistency, we systematically explored the particle size dependence of the bandgap of goethite. The size-dependence of the goethite bandgap predicts the size-dependence of its reactivity in the environment , and is also relevant for technical applications (e.g., lithium battery electrodes and solar energy devices , ).…”

Crafting a Next-Generation Device Using Iron Oxide Thin Film: A Review

“…Various chemical nonvacuum deposition methods such as spray pyrolysis, chemical bath deposition, dip coating, , etc. as shown in Table were reported to successfully fabricate the iron oxide thin film, especially the stable iron oxides phase such as Fe 3 O 4 , , γ-Fe 2 O 3 , and α-Fe 2 O 3 . − To the best our knowledge, the nonvacuum methods are insufficient for the synthesis of metastable iron oxides. Therefore, this is a challenge to obtain and develop the nonvacuum method to synthesize the metastable polymorph Fe 2 O 3 .…”