Increased Active Sites on Irregular Morphological α-Fe2O3 Nanorods for Enhanced Photoelectrochemical Performance

Understanding Wavelength-Dependent Synergies between Morphology and Photonic Design in TiO2-Based Solar Powered Redox Cells

Solar powered redox cells (SPRCs) are promising for large-scale and long-term storage of solar-energy, particularly when coupled with redox flow batteries (RFBs). While efforts have primarily focused on heterostructure engineering, the potential of synergistic morphology and photonic design has not been carefully studied. Here, we investigate the wavelength-dependent effects of light-absorption and charge transfer characteristics on the performance of gold decorated TiO₂-based SPRC photoanodes operating with RFB-compatible redox couples. Through an in-depth optical and photoelectrochemical characterization of three complementary TiO₂ microstructures, namely nanotubes, honeycombs, and nanoparticles, we elucidate the combined effects of nanometer-scale semiconductor morphology and plasmonic design across the visible spectrum. In particular, thin-walled TiO₂ nanotubes exhibit a ∼ 50% increase in solar-to-chemical efficiency (STC) compared to thick-walled TiO₂ honeycombs thanks to improved charge transfer. Au nanoparticles both increase generation and interfacial charge transfer (above bandgap) and promote hot carrier injection (below bandgap) leading to a further 25% increase in STC. Overall, Au/TiO₂ nanotubes achieve a high photocurrent at 0.098 mA/cm² and an excellent STC of 0.06%, among the highest with respect to the theoretical limit. The incident photon to current efficiency and internal quantum efficiency are also superior to those of bare TiO₂ showing maximum values of 54.7% and 67%, respectively. Overall, nanophotonic engineering that synergistically combines morphology optimization and plasmonic sensitization schemes offer new avenues for improving rechargeable solar-energy technologies such as solar redox flow batteries.

Waste coal cinder catalyst enhanced electrocatalytic oxidation and persulfate advanced oxidation for the degradation of sulfadiazine

Waste coal cinder, a kind of waste cinder discharged from coal combustion of thermal power plants, industrial and civil boilers, and other equipment, was rich in metal oxides with catalytic activity. In this work, waste coal cinder was used to enhance electrochemical coupling peroxymonosulfate (PMS) advanced oxidation degradation of sulfadiazine (SD). The surface morphology, elemental composition, and electrocatalytic activity of waste coal cinder were characterized by various characterization instruments. The results show that compared with simple electrocatalytic oxidation, electrocatalytic oxidation + waste coal cinder and electrocatalytic coupled persulfate oxidation, electrocatalytic oxidation + PMS advanced oxidation + waste coal cinder has the largest removal efficiency (99.95%) and mineralization rates (90.16%) of SD in 90 min, indicating that the introduction of waste coal cinder greatly increases the degradation efficiency. •OH and SO₄^-• were detected during the process of degradation. The optimal degradation process parameters were explored through different voltage, pH, plate spacing, aeration flow rate, potassium peroxymonosulfate sulfate complex salt dose, and Na₂SO₄ dosage. Cycling experiments show waste coal cinder has good structural stability. Through the analysis of triple quadrupole liquid chromatography-mass spectrometry (LC-MS), we put forward three possible ways of SD degradation. This research will provide a novel vision for water treatment.

Integration of biochar into Ag3PO4/α-Fe2O3 heterojunction for enhanced reactive oxygen species generation towards organic pollutants removal

A biochar (BC) harbored Ag₃PO₄/α-Fe₂O₃ type-Ⅰ heterojunction (Ag-Fe-BC) was prepared by a hydrothermal-impregnation method to transfer active center of heterojunctions. The electrochemical and spectroscopic tests demonstrated that BC enhanced the catalytic performance of the heterojunction by enhancing photocurrent, reducing fluorescence intensity, and facilitating separation of electron-hole pairs. The photocatalytic activity showed the Ag-Fe-BC (5:1:3) could degrade Rhodamine B (20 mg/L) by up to 92.7%, which was 3.35 times higher than Ag₃PO₄/α-Fe₂O₃. Tetracycline and ciprofloxacin (20 mg/L) were degraded efficiently by 58.3% and 79.4% within 2 h, respectively. Electron paramagnetic resonance and scavenging experiments confirmed the major reactive oxygen species (ROS) consisted of singlet oxygen (¹O₂) and superoxide (·O₂^-). Excellent RhB adsorption and electrons capturing capacity of BC facilitated electron-hole pairs separation and ROS transferring to target organics followed by elevated degradation. Thus, a facile method was proposed to synthesize a highly efficient visible-light responsive photocatalyst for degradation of various organics in water.

Fabrication of 3D hierarchical Fe2O3/SnO2photoanode for enhanced photoelectrochemical performance

Exploring and fabricating a suitable photoanode with high catalytic activity is critical for enhancing photoelectrochemical (PEC) performance. Herein, a novel 3D hierarchical Fe₂O₃/SnO₂photoanode was fabricated by a hydrothermal route, combining with an annealing process. The morphology, crystal structure were studied by scanning electron microscopy, transmission electron microscopy, x-ray photon spectroscopy, and x-ray diffraction, respectively. The results reveal the successful preparation of Fe₂O₃nanothorns on the surface of SnO₂nanosheets. The as-fabricated 3D Fe₂O₃/SnO₂photoanode yields obviously promoted PEC performance with a photocurrent density of approximate 5.85 mA cm^-2, measured in a mixture of Na₂S (0.25 M) and Na₂SO₃(0.35 M) aqueous solution at 1.23 V (versus reversible hydrogen electrode, RHE). This value of photocurrent is about 53 times higher than that of the bare SnO₂photoanode. The obvious improved PEC properties can be attributed to the 3D Fe₂O₃/SnO₂heterostructures that offer outstanding light harvesting ability as well as improved charge transport and separation. These results suggest that exploring a suitable 3D hierarchical photoanode is an effective approach to boost PEC performance.

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%.