Surface Self-Transforming FeTi-LDH Overlayer in Fe2 O3 /Fe2 TiO5 Photoanode for Improved Water Oxidation.

Integrating hematite nanostructures with efficient layer double hydroxides (LDHs) is highly desirable to improve the photoelectrochemical (PEC) water oxidation performance. Here, an innovative and facile strategy is developed to fabricate the FeTi-LDH overlayer decorated Fe2 O3 /Fe2 TiO5 photoanode via a surface self-transformation induced by the co-treatment of hydrazine and NaOH at room temperature. Electrochemical measurements find that this favorable structure can not only facilitate the charge transfer/separation at the electrode/electrolyte interface but also accelerate the surface water oxidation kinetics. Consequently, the as-obtained Fe2 O3 /Fe2 TiO5 /LDH photoanode exhibits a remarkably increased photocurrent density of 3.54 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE) accompanied by an obvious cathodic shift (≈140 mV) in the onset potential. This work opens up a new and effective pathway for the design of high-performance hematite photoanodes toward efficient PEC water oxidation.

How titanium and iron are integrated into hematite to enhance the photoelectrochemical water oxidation: a review.

Hematite has been considered as a promising photoanode candidate for photoelectrochemical (PEC) water oxidation and has attracted numerous interests in the past decades. However, intrinsic drawbacks drastically lower its photocatalytic activity. Ti-based modifications including Ti-doping, Fe2O3/Fe2TiO5 heterostructures, TiO2 passivation layers, and Ti-containing underlayers have shown great potential in enhancing the PEC conversion efficiency of hematite. Moreover, the combination of Ti-based modifications with various strategies towards more efficient hematite photoanodes has been widely investigated. Nevertheless, a corresponding comprehensive overview, especially with the most recent working mechanisms, is still lacking, limiting further improvement. In this respect, by summarizing the recent progress in Ti-modified hematite photoanodes, this review aims to demonstrate how the integration of titanium and iron atoms into hematite influences the PEC properties by tuning the carrier behaviours. It will provide more cues for the rational design of high-performance hematite photoanodes towards future practical applications.

N and Sn Co-Doped hematite photoanodes for efficient solar water oxidation.

Surface electron-hole recombination and low conductivity have significantly hindered the photoelectrochemical water oxidation performance of hematite. Here we report a surface N and Sn co-incorporation in hematite for efficient water oxidation, which shows a greatly enhanced photocurrent density of 2.30 mA/cm2 at 1.23 V vs. RHE when compared to the pristine hematite (0.89 mA/cm2). Moreover, after the subsequent loading of Co-Pi cocatalyst, a further improved photocurrent density of 2.80 mA/cm2 at 1.23 V vs. RHE can also be achieved. The excellent performance can be attributed to the synergistic effect of N and Sn in hematite, in which the surface Sn-doping could increase the donor density of hematite while the N-incorporation could adjust the amount of Sn in hematite to suppress the surface charge recombination and further increase the donor density. To the best of our knowledge, it should be the first report to reveal the synergistic effect of non-metal element N and metallic element Sn in hematite for high performance, which could be a feasible way towards the development of efficient hematite photoanodes.

Novel broad-spectrum-driven oxygen-linked band and porous defect co-modified orange carbon nitride for photodegradation of Bisphenol A and 2-Mercaptobenzothiazole.

Here, we successfully synthesized the oxygen-linked band and porous defect co-modified orange carbon nitride (AF-C3N4) using a simple method. Further, the band structure calculation of its simulated structure is performed by DFT, which shows that the introduction of oxygen-linked band can adjust its band structure. The photocatalytic degradation rates of 0.3AF-C3N4 for bisphenol A and 2-mercaptobenzothiazole were 8 times and 2.73 times that of the original g-C3N4, respectively. Moreover, 0.3AF-C3N4 also shows photocatalytic activity under different wavelength light (blue, green and red light), which indicates that the synthesized materials have a broad spectrum of photocatalytic activity. Further, we proposed a possible photocatalytic degradation pathway by HPLC-MS analysis. Free radical quenching test and ESR spectra show that the generated superoxide radicals (•O2-), hydroxyl radicals (•OH) and holes (h+) cause photodegradation, while enhancing singlet oxygen (1O2) and weaken the content of hydrogen peroxide has further proved that active oxygen groups play an important role in the photocatalytic degradation process. Additionally, the 0.3AF-C3N4 can also be a photoelectrochemical sensor to detect the concentration of bisphenol A (λ ≥ 550 nm). This study provides a new strategy for the synthesis of orange carbon nitride by oxygen-linked band and porous defect co-modification for photocatalytic applications.

Graphene quantum dots modified flower like Bi2WO6 for enhanced photocatalytic nitrogen fixation.

Graphene quantum dots modified Bi2WO6 (GQD/Bi2WO6) composites is applied to photocatalytic N2 fixation. The as-prepared GQD/Bi2WO6 samples showed considerable increase in photocatalytic nitrogen fixation compared to the pure Bi2WO6 and GQD. The results revealed that GQD uniformly placed on the surface of Bi2WO6 and tight junction between the two samples helped to boost the photocatalytic activity. The PL, photocurrent and EIS analyses further demonstrated that the composite had the low recombination rate of photo-generated charges. Photocatalytic nitrogen fixation test indicated that GQD/Bi2WO6 with 10 wt% GQDs exhibited the highest ammonia synthesis rate in the presence of visible light, which is 8.88-fold and 33.8-fold higher than pure Bi2WO6 and GQD. Simultaneously, the GQD/Bi2WO6 sample has high stability.

Efficient Photoelectrochemical Water Oxidation on Hematite with Fluorine-Doped FeOOH and FeNiOOH as Dual Cocatalysts.

An effective cocatalyst is usually required to improve the performance of photoelectrochemical (PEC) water splitting catalysts. A fluorine-doped FeOOH (F:FeOOH) cocatalyst on a hematite photoanode was used to lower the onset potential by 140 mV and significantly improve the PEC performance. Moreover, a more effective dual cocatalytic system was prepared by subsequent loading of a FeNiOOH cocatalyst, which resulted in a further decrease of the onset potential by 270 mV. The final onset potential of the Fe2 O3 /F:FeOOH/FeNiOOH photoanode was lowered to 0.45 V versus the reversible hydrogen electrode (RHE), which is one of the lowest onset potential values ever reported for hematite photoanodes. The photocurrent also dramatically increased by a factor of approximately 3 to 0.9 mA cm-2 at 1.0 V versus RHE. Based on the structural, chemical, and electrochemical impedance spectroscopy characterization, the enhanced performance was attributed to the F:FeOOH overlayer, which reduced the surface recombination and accelerated the oxygen evolution reaction activity, and the FeNiOOH cocatalyst, which further enhanced the reaction kinetics. The facile preparation of the F:FeOOH cocatalyst and the design of the dual cocatalytic system will allow the development of high-performance hematite photoanodes.

Loading the FeNiOOH cocatalyst on Pt-modified hematite nanostructures for efficient solar water oxidation.

A FeNiOOH-decorated hematite photoanode has been prepared using a facile electrodeposition method, with a significant cathodic shift of the onset potential (up to 190 mV) compared to the pristine sample. Synchrotron radiation based techniques have been used to identify the composition of the catalyst indicating the presence of FeOOH and NiOOH (FeNiOOH). The enhanced performance can be attributed to the better oxidation evolution reaction kinetics with the FeNiOOH cocatalyst. The FeNiOOH-decorated hematite is very stable for a long time. Moreover, the cocatalyst can be well coupled to the Pt-modified hematite photoanode achieving a high photocurrent of 2.21 mA cm(-2) at 1.23 V vs. RHE. The good catalytic properties and the facile preparation method suggest that the decoration of FeNiOOH is a favorable strategy to improve the performance of hematite.

Thin-Layer Fe2TiO5 on Hematite for Efficient Solar Water Oxidation.

A thin Fe2TiO5 layer was produced on hematite either by evaporating a TiCl4 solution on FeOOH or by a simple HF-assisted Ti treatment of FeOOH, both followed by annealing. The prepared Fe2TiO5-hematite heterostructure showed a significant enhancement in photocurrent density compared to that of the pristine hematite. For example, the sample after HF-assisted Ti treatment exhibited a significantly enhanced photocurrent of 2.0 mA/cm(2) at 1.23 V vs RHE. Moreover, the performance of the Fe2TiO5-hematite heterostructure can be further improved by coupling with Co-Pi catalysts, achieving a higher photocurrent of 2.6 mA/cm(2) at 1.23 V vs RHE. Synchrotron-based soft X-ray absorption spectroscopy analyses clearly revealed the existence of an Fe2TiO5 structure on hematite forming a heterojunction, which reduced the photogenerated hole accumulation and then improved the performance.

Direct observation and spectroscopy of nanoscaled carboxylated carbonaceous fragments coated on carbon nanotubes.

The coating of nanoscaled carboxylated carbonaceous fragments on carbon nanotubes (CNTs) has been directly observed in chemical imaging with a concurrent identification of their electronic structure by scanning transmission X-ray microscopy. The coating also shields the detection of the CNT/nanoparticle interaction.