Kinetic analysis of the synergistic effect of NaBH4 treatment and Co-Pi coating on Fe2O3 photoanodes for photoelectrochemical water oxidation

Degradation of thiamphenicol by La-Fe2O3/DBD/HCP synergistic catalytic system

In this study, a highly efficient La-Fe2O3/dielectric barrier discharge (DBD)/honeycomb ceramic plate synergistic catalytic system was successfully constructed by using modified iron oxide (Fe2O3) catalyst coating assisted DBD plasma, and the prepared catalytic coating was fully characterized by various techniques. The results indicate that the lanthanum (La) is efficiently and uniformly doped in Fe2O3, and the modified La-Fe2O3 catalyst exhibited a better photocatalytic performance. The overuse of Thiamphenicol (TAP), as a typical chloramphenicol antibiotic, has led to its accumulation in the aquatic environment. Accordingly, TAP was selected as the target contaminant to evaluate the catalytic activity of the synergistic system. The results confirmed that the catalytic ability of the synergistic catalytic system was significantly improved, and the data showed that the degradation rate of the synergistic system reached 99.1% under the same conditions compared with 68.2% for the single DBD plasma, which effectively improved low energy efficiency limitations of the single DBD technology. Through quantitative measurements of the concentrations of dissolved ozone (O3) and hydrogen peroxide (H2O2) in the system and radical trapping experiments, combined with emission spectroscopy, the mechanism of synergistic system degradation of TAP was analyzed. The intermediates in the degradation process were characterized by high-resolution mass spectrometry, and the degradation pathway of TAP was proposed based on the analysis of the intermediates and their combination with theoretical calculations. This study presents a theoretical basis for the improvement of DBD technology and a technical guide for the removal process of antibiotics from industrial wastewater.

Introducing Oxygen Vacancies into a WO3 Photoanode through NaH2PO2 Treatment for Efficient Water Splitting

WO3, with a high light absorption capacity and a suitable band structure, is considered a promising photoanode material for photoelectrochemical water splitting. However, the poor photoinduced electron-hole separation efficiency limits its application. Herein, we report an effective strategy to suppress electron-hole recombination by introducing oxygen vacancies (OV) on the surface of a WO3 photoanode through NaH2PO2 treatment. An OV-enriched amorphous surface layer with a thickness of 4 nm is formed after NaH2PO2 treatment, which increases the charge carrier density and enlarges the electrochemical surface area of the photoanode. The charge separation and surface injection efficiencies are both improved after NaH2PO2 treatment, and the charge transfer process of the photoanode is accelerated consequently. The current density of the modified WO3 photoanode reaches 0.96 mA cm-2 at 1.23 V.

Effect of acid treatment on boosting the photoelectrochemical performance of doped and codoped α-Fe2O3 photoanodes

Acid treatment of Ti-doped α-Fe₂O₃ photoanode can reduce the onset potential and promote the photocurrent density for photoelectrochemical (PEC) water splitting reaction. However, the inner mechanism of how this occurs has not yet been clarified. This report compares the effect of HCl hydrothermal treatment on α-Fe₂O₃ photoanodes doped with Ge, Pt, Ti, and Sn or codoped with TiGe, TiPt, and TiSn. The findings show that the promotion effect of HCl hydrothermal treatment was far less significant on the Ge-, Pt-, and Sn-doped α-Fe₂O₃ than on the Ti-doped one. In contrast, the codoped photoanodes could realize a lift in the photocurrent of up to 39% at 1.23 V_RHE (versus the reversible hydrogen electrode) and a reduction in the potential onset by ∼60 mV after HCl hydrothermal treatment. Anatase TiO₂ was detected by Raman spectroscopy on the Ti-doped α-Fe₂O₃ with adequate treatment in HCl solution. Thus, the performance promotion by acid treatment was ascribed to the surface-concentrated Ti-O bonds acting as a passivation layer that could increase the charge-capture capacity and reduce the charge-transfer resistance, as demonstrated by the potential-modulated electrochemical impedance spectroscopy results. HCl treatment of the in situ-doped α-Fe₂O₃ and an excessive treatment time for the ex situ-doped α-Fe₂O₃ caused an inhibition in the PEC performance, which could be attributed to the adverse effect of lattice defects induced by acid corrosion. The application scope of HCl treatment on the doped α-Fe₂O₃ was determined by revealing its working mechanism.

Coupling effect between hole storage and interfacial charge transfer over ultrathin CoPi-modified hematite photoanodes

Understanding the functionality of the modification layer in regulating the charge transfer process at the semiconductor/electrolyte interface is of great significance to the rational design of photoelectrocatalytic water oxidation systems. Herein, by systematically investigating and comparing the charge transfer kinetics behaviors over ferrihydrite (Fh)- and cobalt phosphate (CoPi)-modified hematite (Fe₂O₃) photoanodes, we unveiled the essential relation between photocurrent enhancement and the charge transfer process. With the hole-storage material Fh as a reference, it was found that CoPi demonstrates high hole-storage capacity at a low bias region (<1.0 V vs. RHE) due to the effective release of Fermi level pinning. Afterwards, the stored holes would be timely injected into the electrolyte for water oxidation, caused by the enhanced charge separation in the presence of CoPi. In contrast, the decoration of Fh can only slightly passivate the surface states and promote hole injection in the high potential region. Subsequently, superior hole-storage capacity in the low-potential region is recognized as a crucial factor for photocurrent enhancement. These combined results provide new insights into the understanding of interfacial charge transfer kinetics.

Sustainable photoanode for water oxidation reactions: from metal-based to metal-free materials

Sunlight affords an inexhaustible and primary energy for Earth. A photoelectrochemical system can efficiently harvest solar energy and convert it into chemicals. However, sophisticated processes and expensive raw materials are...

A semiconductor/molecular catalyst hybrid photoanode with FeOOH as an electron transfer relay

A Fe₂ O₃ /FeOOH/poly-Ru(bda)(vpy) (bda = 2,2'-bipyridine-6,6'-dicarboxylate,vpy = 4-vinylpyridine) photoanode has been fabricated by electropolymerization of molecular Ru(bda)(vpy) catalyst on FeOOH modified Fe₂ O₃ , in which a thin layer of FeOOH replicates the role of tyrosine residue in PSII as an efficient electron transfer mediator. The ternary hybrid photoanode produced a 2.4 times higher photocurrent density than that of previously reported Fe₂ O₃ /poly-Ru(bda)(vpy) under AM 1.5 G illumination and displayed a negative shift on the onset potential by 100 mV. In addition, the Fe₂ O₃ /FeOOH/poly-Ru(bda)(vpy) exhibited long-term stability for at least 10 h with a Faraday efficiency of ∼96%. The high performance shown here was attributed to the improved charge separation between excited semiconductor and the catalyst caused by FeOOH mediated electron transfer on the electrode surface.

Improving light absorption and photoelectrochemical performance of thin-film photoelectrode with a reflective substrate

The charge separation/transport efficiency is relatively high in thin-film hematite photoanodes in which the distance for charge transport is short, but simultaneously the high loss of light absorption due to transmission is confronted. To increase light absorption in thin-film Fe₂O₃:Ti, commercial substrates such as Cu foil, Ag foil, and a mirror are adopted acting as back-reflectors and individually integrated with the Fe₂O₃:Ti electrode. The promotion effect of the commercial back-reflectors on the light absorption efficiency and photoelectrochemical (PEC) performance of the hydrothermally prepared Fe₂O₃:Ti electrodes with a variety of film thicknesses is investigated. As a result, Ag foil and the mirror show favorable and equal efficacy while the promoting effect of Cu foil is limited. In addition, the photocurrent increment achieved by the Ag back-reflector decreases linearly along with the logarithmic of the film thickness and the optimized film thickness of the Fe₂O₃:Ti electrode is decreased from 520 to 290 nm. The high durability of Ag foil in the alkaline electrolyte during solar light irradiation is demonstrated. Furthermore, the reflective substrate also shows a promotion effect on the BiVO₄ photoanode and CuBi₂O₄ photocathode, as well as the unbiased photocurrent from a tandem cell constituted by TiO₂ and CuBi₂O₄.

The charge separation/transport efficiency is relatively high in thin-film hematite photoanodes in which the distance for charge transport is short, but simultaneously the high loss of light absorption due to transmission is confronted.

Effect of morphology and impact of the electrode/electrolyte interface on the PEC response of Fe2O3 based systems - comparison of two preparation techniques

The present study is a comparative account of Fe₂O₃ based photoelectrodes prepared by two different techniques, namely spray pyrolysis and electrochemical deposition, followed by photoelectrochemical analysis at pH 13 (highly alkaline) and pH 8 (near neutral) in 0.1 M NaOH solution for solar hydrogen generation. The study also investigates the influence of morphology at the semiconductor electrode/electrolyte interface along with quantitative determination of the morphological parameters of the rough electrode surface affecting the photoelectrochemical response using power spectral density analysis. Studies revealed that the Fe₂O₃ sample (E_100cy) prepared with 100 cycles of electrochemical deposition showed the highest photocurrent density of 2.37 mA cm^-2 and 1.18 mA cm^-2 at 1 V vs. SCE at pH 13 and 8 respectively. Power spectral density analysis exhibited that E_100cy possesses smallest surface features contributing to the PEC response with a lower cut off length scale of 17.23, upper cut off length scale of 150.45, maximum fractal dimension of 2.62 and maximum average rms roughness of 17.52 nm, offering the maximum surface area for charge transfer reactions at the electrode/electrolyte interface. The sample E_100cy exhibited the highest ABPE of 1.29% and IPCE of 37.5%.