Effect of Applied Voltage on the Formation of Self-Organized Iron Oxide Nanoporous Film in Organic Electrolyte via Anodic Oxidation Process and their Photocurrent Performance

Abstract

Anodisation of iron foil was done to produce anodic film with nanoporous structure. The effect of anodic voltage on the morphology of the anodic oxide formed was investigated. Anodic film formed on iron foil anodised at 10 V is rather compact no obvious pores. Pores can be detected on oxide anodised at 30 V despite not very uniform. For foil anodised at 50 V, 1.8 µm thick anodic layer which consisted of uniform circular pores is observed. This film was then annealed at 450°C for 3 h in air as to induce crystallinity. The annealed nanoporous film exhibits a light illuminated photocurrent of 0.45 mA in 1 M NaOH + H2O2 solution.

Annealing temperature-dependent crystallinity and photocurrent response of anodic nanoporous iron oxide film

“…Our result is higher than a photocurrent of ;0.26 mA/cm 2 at 0.6 V versus Ag/AgCl, reported by previous authors (for anodic nanoporous iron oxide annealed at 400°C for 30 min) 10 or a photocurrent of ;0.45 mA/cm 2 at 0.6 V versus Ag/AgCl for air-annealed sample. 13 This anodic nanoporous iron oxide was predominantly a-Fe 2 O 3 with a small amount of Fe 3 O 4 , and had a barrier layer thickness of ;800 nm. 10 The higher photocurrent for our sample may be attributed to the small thickness of the barrier layer for the nitrogen-annealed sample which is ;200 nm, as shown in Fig.…”

“…For instance, Lee et al reported on photocurrent of 0.25 mA/cm 2 at 0.39 V versus Ag/AgCl in 1 M KOH (100 mW/cm 2 , AM 1.5) for air-annealed nanoporous film with a thickness of ;0.2 lm. 15 Similarly in our previous report, a photocurrent of 0.33 mA/cm 2 at 0.39 V versus Ag/AgCl was reported utilizing an anodic nanoporous photoanode with a thickness of ;1.8 lm annealed in air at 450°C for 3 h. 13 The relatively low photocurrent values may be attributed to the above mentioned problems: oxidation of iron during annealing, thickening of barrier layer and Fe 3 O 4 and/or FeO formation. In this present work, we investigated on the formation of the nanoporous iron oxide and on the effect of nitrogen annealing to the properties of the nanoporous oxide and on the photocurrent response when the oxide film was illuminated.…”

“…10,12,13 These undesirable phases can be removed by annealing the as-anodized iron at high temperature. However with annealing comes another issue which is thermal oxidation of the underlying iron foil.…”