Abnormal Cathodic Photocurrent Generated on an n‐Type FeOOH Nanorod‐Array Photoelectrode

Abstract

A simple, wet-chemical method for the synthesis of an FeOOH nanorod-array photoelectrode on fluorine-doped tin oxide (FTO) glass is reported. Nanorods of diameter about 35 nm and length about 300 nm have been vertically grown on an FTO substrate. Upon calcination, the FeOOH phase could be easily converted to a hematite structure while maintaining the shape of the nanorod array. An interesting abnormal cathodic photocurrent is generated on the FeOOH nanorod-array photoelectrode under illumination, which is totally different from that obtained on a calcined hematite photoelectrode under the same experimental conditions. The cathodic photocurrent density generated on the FeOOH photoelectrode can also be tuned by applying an electrochemical anodic or cathodic treatment. Detailed analysis has revealed that higher valence state Fe(IV) species in the FeOOH photoelectrode play an important role in sacrificing the photoexcited electrons for generation of the cathodic photocurrent. Comparison between the FeOOH and hematite photoelectrodes allows for a better understanding of the interplay between crystal structure, surface reactions, and photocurrent. The findings on this new abnormal phenomenon could also provide guidance for the design of new types of semiconducting photoelectrochemical devices.

Self-Improvement of Ti:Fe2O3 Photoanodes: Photoelectrocatalysis Improvement after Long-Term Stability Testing in Alkaline Electrolyte

“…XPS O 1s spectra of Ti:Fe 2 O 3 after long-term stability testing and as-prepared Ti:Fe 2 O 3 /FeOOH are shown in Figure . The O 1s peaks can be deconvoluted into four peaks at 529.2, 530.9, 531.9, and 534.4 eV, corresponding to Fe–O, Fe–OH, absorbed water, and chemisorbed oxygen species, respectively. , On Ti:Fe 2 O 3 /FeOOH, the intensities of Fe–O and Fe–OH peaks are comparable, indicating the successful FeOOH formation during the PEC deposition process. For Ti:Fe 2 O 3 photoanodes, with the time increasing from 18 to 70 h during the stability testing, the intensity ratio of Fe–OH and Fe–O peaks changes from 18.72% to 28.67%.…”

“…The O 1s peaks can be deconvoluted into four peaks at 529.2, 530.9, 531.9, and 534.4 eV, corresponding to Fe−O, Fe−OH, absorbed water, and chemisorbed oxygen species, respectively. 35,36 On Ti: To understand the inherent mechanism, we tested the 12 h stability of Fe 2 O 3 and Ti:Fe 2 O 3 photoanodes under various electrolyte solutions (Figure 4a). In NaOH, both Fe 2 O 3 and Ti:Fe 2 O 3 photoanodes show a rapid decrease at the initial stage and then a gradual enhancement in photocurrent density during 12 h testing at 1.5 V under visible light of 100 mW cm −2 .…”

α- and γ-FeOOH: Stability, Reversibility, and Nature of the Active Phase under Hydrogen Evolution

“…The Fe–O–H phase diagram shows outstanding complexity, the oxides, hydroxides, and oxide–hydroxides counting at least 16 different compounds and crystal structures. , Iron oxides are widespread compounds in nature as well, occurring in the lithosphere, biosphere, and hydrosphere. Fe–O–H compounds are also of extreme importance for technological applications: indeed, they are used as pigments, catalysts for various reactions such as oxygen evolution reaction (OER), − and adsorbants and, of course, are ubiquitously found as steel corrosion products . Steel is used as cathode for a number of important industrial electrochemical processes, such as for the NaClO 3 production as a precursor for ClO 2 , a bleaching agent with a huge worldwide market.…”