1. Iron phosphide electrocatalyst for renewable production of value-added productsTakwa Chouki, Manel Machreki, Iwona A. Rutkowska, Beata Rytelewska, Pawel Jozef Kulesza, Georgi Tyuliev, Moussab Harb, Luis Miguel Azofra, Saim Emin, 2022, published scientific conference contribution abstract (invited lecture) Abstract: The electrochemical reduction reaction of the nitrate ion (NO3) to valuable ammonia (NH3) is a promising green approach. Herein, we report for the the electrocatalytic reduction of NO3 using different phases of iron phosphide. Particularly, FeP and Fe2P phases were successfully demonstrated as efficient catalysts for NH3 generation. The Fe2P catalyst exhibits the highest Faradaic efficiency (96%) for NH3 generation with a yield (0.25 mmol h−1 cm-−2) at −0.55 V vs. reversible hydrogen electrode (RHE). The recycling tests confirmed that Fe2P and FeP catalysts exhibit excellent stability during the NO3 reduction at −0.37 V vs. RHE. These results indicate that the Fe2P phase exhibits excellent performance to be deployed as an efficient noble metal-free catalyst for NH3 generation. In addition to NO3 reduction the iron phosphide phases were used in electrocatalytic H2 generation using water electrolysis. The electrocatalytic activities of heat-treated Fe2P−450°C, Fe3P−500°C, and Fe2P/FeP−500°C catalysts were studied for hydrogen evolution reaction (HER) in 0.5 M H2SO4. The lowest electrode potential of 110 mV vs. a reversible hydrogen electrode (RHE) at 10 mA cm−2 was achieved with a mixed Fe2P/FeP−500°C catalyst.
Keywords: electrochemical reduction, nitrate reduction, iron phosphide catalyst, NH3 generation
Published in RUNG: 10.01.2025; Views: 595; Downloads: 2
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2. In situ treatment of organic pollutants in water using photoelectrocatalysisSaim Emin, Takwa Chouki, Manel Machreki, 2022, published scientific conference contribution abstract (invited lecture) Abstract: The photoelectrochemical (PEC) approach has emerged as a promising advanced oxidation process to remove organic pollutants in water environment. Here, we report a novel method for the preparation of hematite (α-Fe2O3) thin films by using a combination of spin-coating and heat-treatment approaches. Firstly, a solution containing iron precursor was spin-coated on fluorine doped tin oxide substrates and later heat-treated at 750º C to generates a porous film.1 The α-Fe2O3 thin films were studied as a catalyst in PEC water oxidation and textile dye degradation system We applied the α-Fe2O3 thin films in PEC degradation of a textile Basic Blue 41 (B41) dye. Efficient PEC degradation of B41 dye is demonstrated in the presence of reactive chlorine species (RCS) under LED illumination (λex 400 nm, 20 W) and 1.5 V vs. reversible hydrogen electrode applied potential. In addition to Fe2O3, we also grew TiO2 nanotubes on titanium plate using the so-called anodization approach. We applied the obtained TiO2 thin films in PEC degradation of B41 dye. In addition to the B41 textile dye, we used also used the TiO2 nanotubes for degradation of anti-inflammatory drugs. Various operation parameters, including anodic potential, pH, electrolytes and concentration of dye, were investigated to determine the optimal experimental conditions. The degradation of B41 was remarkably enhanced by in situ generated RCS. Recycling test revealed that α-Fe2O3 photoanode shows good activity and excellent stability during B41 degradation. High-performance liquid chromatography analysis coupled with UV-VIS system and gas-chromatography/liquid chromatography coupled to mass spectrometry detector confirmed the degradation of B41 dye and the evolution of by-product. Phytotoxicity test using Lepidium sativum L showed that treated waters are safe to be discharged in the environment.
Keywords: photoelectrocatalysis, Fe2O3 thin films, basic blue dye 41
Published in RUNG: 10.01.2025; Views: 589; Downloads: 2
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3. Photoelectrochemical conversion of biomass alcohols using in-situ Sn-doped ▫$\alpha-Fe_2O_3$▫ thin filmsManel Machreki, Artem Badasyan, Dušan Žigon, Georgi Tyuliev, Saim Emin, 2025, original scientific article Abstract: Transformation of biomass into value-added chemicals and fuels is considered an upcycling process that is beneficial to resource utilization. In this study, we used a photoelectrochemical (PEC) approach for selective oxidation of propane-1,2,3-triol to dihydroxyacetone (DHA) with high efficiency and selectivity (99%) using Sn-doped -Fe2O3 (Sn:-Fe2O3) thin films with intrinsic oxygen vacancies (OVs). DHA is an essential compound utilized in the cosmetic industry. In a similar manner, we conducted the first study of the PEC oxidation of 4-hydroxy-3-methoxybenzyl alcohol under visible light. A kinetic model has been formulated and solved to find the time-dependent generation of the products. Electrochemical impedance analyses and PEC experiments demonstrated a correlation between the concentration of molecules and the catalytic performance of Sn:-Fe2O3. Studies using scavengers indicate that the photogenerated holes (h+), singlet oxygen (1O2), hydroxyl radicals (•OH), and superoxide radicals (•O2–) play key roles in achieving high PEC activity. This work provided a new perspective on designing efficient PEC systems for biomass conversion into energy and value-added chemicals.
Keywords: Sn-doped alpha-Fe2O3, oxygen vacancies, photoelectrochemical oxidation, propane-1, 2, 3-triol, 4-hydroxy-3-methoxybenzyl alcohol
Published in RUNG: 08.01.2025; Views: 621; Downloads: 6
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6. Photoelectrochemical activation of peroxymonosulfate using Sn-doped ▫$α-Fe_2O_3$▫ thin film for degradation of anti-inflammatory pharmaceutical drugManel Machreki, Georgi Tyuliev, Dušan Žigon, Qian Guo, Takwa Chouki, Ana Belén Jorge Sobrido, Stoichko Dimitrov, Saim Emin, 2024, original scientific article Abstract: Introduction of oxygen vacancies (OVs) has been investigated as a promising way to improve the electrical and catalytic characteristics of a hematite (α-Fe2O3) based photoelectrode. In this work, we develop a novel method for preparing porous Sn-doped α-Fe2O3 (Sn:Fe2O3) thin films with intrinsic OVs. The procedure included spin- coating an iron precursor onto a fluorine-doped tin oxide (FTO) substrate, followed by thermal treatment at elevated temperatures. The influence of Sn dopant on the optoelectronic properties of α-Fe2O3 was demonstrated by X-ray photoelectron spectroscopy and photoelectrochemical (PEC) measurements. The combined effect of OVs and Sn doping was found to play a synergistic role in reducing the charge recombination’s. The Sn:Fe2O3 photoanodes were used as a dual catalyst to oxidise water and break down an anti-inflammatory drug called 2-(4- isobutylphenyl)propanoic acid (IBPA). The Sn:Fe2O3 thin film with a 30-minute heat treatment time displayed the highest incident photon-to-current efficiency. For the first time, Sn:Fe2O3 thin films were utilised in the effective PEC degradation of IBPA employing peroxymonosulfate (PMS) under visible light illumination. The hydroxyl radicals (•OH), singlet oxygen (1O2), photogenerated holes (h+), and sulfate radicals (SO4 • ) were discovered to be the main reactive species during PEC degradation. IBPA degradation and the formation of new compounds were verified using liquid chromatography-mass spectrometry. The Lepidium sativum L phytotoxicity test reveals that PEC-treated wastewater with IBPA exhibits decreased toxicity.
Keywords: Sn-doped Fe2O3, oxygen vacancies, photoelectrochemical degradation, 2-(4-isobutylphenyl)propanoic acid, peroxymonosulfate
Published in RUNG: 10.01.2024; Views: 2174; Downloads: 42
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7. Materials for sustainable electrochemical energy conversionSaim Emin, Takwa Chouki, Manel Machreki, 2023, published scientific conference contribution abstract (invited lecture) Abstract: The process of hydrogen evolution reaction (HER) through water electrolysis is an important technology for
establishing the so called "hydrogen economy". Here we will cover different systems for electrocatalytic HER.
Transition metal carbides and metal phosphides are alternative to platinum (Pt) and offer excellent electrocatalytic
activity for HER. Pyrolysis of hexacarbonyl tungsten, W(CO)6, in 1-octadecene has been used to prepare colloidal
tungsten, W, nanoparticles (NPs) [1]. The obtained W NPs has been spin-coated on graphite (C) electrodes. Heat
treatment of the W/C electrodes at elevated temperatures (≥ 900°C) allows the preparation of metallic W and
tungsten carbide (W2C@WC) thin films. The obtained W2C@WC electrodes were used for hydrogen evolution
studies (HER) in 0.5M H2SO4. Cyclic voltammetry tests for 1000 cycles showed that W2C@WC exhibit long term
stability without significant drop in current density. The overpotential defined at 10 mA/cm2
is 310 mV vs. RHE
giving an excellent catalytic activity for HER. Iron phosphide electrocatalysts were synthesized using a
triphenylphosphine (TPP) precursor. Different iron phosphide phases were synthesized at 300°C (Fe2P) and at
350°C ( FeP ) [2]. To enhance the catalytic activities of obtained iron phosphide particles heat-treatments were
carried out at elevated temperatures. Annealing at 500°C under reductive atmosphere induced structural changes
in the samples: (i) Fe2P provided a pure Fe3P phase (Fe3P−500°C) and (ii) FeP transformed into a mixture of iron
phosphide phases (Fe2P/FeP−500°C). The lowest electrode potential of 110 mV vs. a reversible hydrogen electrode
(RHE) at 10 mA cm−2 was achieved with Fe2P/FeP−500°C catalyst
Keywords: Fe2P, electrocatalysis, hydrogen, ammonia
Published in RUNG: 13.12.2023; Views: 2481; Downloads: 5
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8. The role of lattice defects on the optical properties of TiO[sub]2 nanotube arrays for synergistic water splittingManel Machreki, Takwa Chouki, Georgi Tyuliev, Mattia Fanetti, Matjaž Valant, Denis Arčon, Matej Pregelj, Saim Emin, 2023, original scientific article Abstract: In this study, we report a facile one-step chemical method to synthesize reduced titanium dioxide (TiO2) nanotube arrays (NTAs) with point defects. Treatment with NaBH4 introduces oxygen vacancies (OVs) in the TiO2 lattice. Chemical analysis and optical studies indicate that the OV density can be significantly increased by changing reduction time treatment, leading to higher optical transmission of the TiO2 NTAs and retarded carrier recombination in the photoelectrochemical process. A cathodoluminescence (CL) study of reduced TiO2 (TiO2–x) NTAs revealed that OVs contribute significantly to the emission bands in the visible range. It was found that the TiO2 NTAs reduced for a longer duration exhibited a higher concentration of OVs. A typical CL spectrum of TiO2 was deconvoluted to four Gaussian components, assigned to F, F+, and Ti3+ centers.
Keywords: TiO2 nanotubes, defects, cathodoluminescence
Published in RUNG: 13.12.2023; Views: 1962; Downloads: 9
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9. Tuning the activity of iron phosphide electrocatalysts for sustainable energy conversionSaim Emin, Takwa Chouki, Manel Machreki, 2023, published scientific conference contribution abstract (invited lecture) Abstract: Electrocatalysis is a promising approach for the sustainable conversion of renewable energy sources, such as solar and wind power, into chemical energy that can be stored and used on demand. By harnessing renewable electricity to drive electrochemical reactions, we can produce fuels and chemicals in a way that is both clean and cost-effective. As we continue to develop new electrocatalytic materials and improve the efficiency of existing processes, the potential for electrocatalysis to transform our energy system will only continue to grow.
We report the use of iron phosphide (Fe2P, FeP) in several electrocatalytic applications, such as reduction of nitrate ions (NO3), hydrogen and oxygen evolution studies. The electrochemical reduction of the nitrate ion (NO3), a widespread water pollutant, to valuable ammonia (NH3) is a promising approach to achieving green energy conservation. Particularly, FeP and Fe2P phases were successfully demonstrated as efficient catalysts for NH3 generation. Detection of the in-situ formed product using a bi-potentiostat was achieved by electrooxidation of NH3 to nitrogen (N2) on a Pt electrode. The Fe2P catalyst exhibits the highest Faradaic efficiency (96%) for NH3 generation with a yield (0.25 mmol h−1 cm-−2 or 2.10 mg h−1 cm−2) at −0.55 V vs. reversible hydrogen electrode (RHE). To get relevant information about the reaction mechanisms and the fundamental origins behind the better performance of Fe2P, density functional theory (DFT) calculations were performed.
Keywords: Fe2P, FeP, electrocatalysis, NH3 reduction, counter electrode
Published in RUNG: 04.12.2023; Views: 2190; Downloads: 6
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10. Defective ▫$TiO_2$▫ nanotube arrays for efficient photoelectrochemical degradation of organic pollutantsManel Machreki, Takwa Chouki, Georgi Tyuliev, Dušan Žigon, Bunsho Ohtani, Alexandre Loukanov, Plamen Stefanov, Saim Emin, 2023, original scientific article Abstract: Oxygen vacancies (OVs) are one of the most critical factors that enhance the electrical and catalytic characteristics of metal oxide-based photo-electrodes. In this work, a simple procedure was applied to prepare reduced TiO 2 nanotube arrays (NTAs) (TiO 2−x) via a one-step reduction method using NaBH 4. A series of characterization techniques were used to study the structural, optical, and electronic properties of TiO 2−x NTAs. X-ray photoelectron spectroscopy confirmed the presence of defects in TiO 2−x NTAs. Photoacoustic measurements were used to estimate the electron-trap density in the NTAs. Photoelectrochemical studies show that the photocurrent density of TiO 2−x NTAs was nearly 3 times higher than that of pristine TiO 2. It was found that increasing OVs in TiO 2 affects the surface recombination centers, enhances electrical conductivity, and improves charge transport. For the first time, a TiO 2−x photoanode was used in the photo-electrochemical (PEC) degradation of a textile dye (basic blue 41, B41) and ibuprofen (IBF) pharmaceutical using in situ generated reactive chlorine species (RCS). Liquid chromatography coupled with mass spectrometry was used to study the mechanisms for the degradation of B41 and IBF. Phytotoxicity tests of B41 and IBF solutions were performed using Lepidium sativum L. to evaluate the potential acute toxicity before and after the PEC treatment. The present work provides efficient PEC degradation of the B41 dye and IBF in the presence of RCS without generating harmful products.
Keywords: TiO2, nanotube arrays, photoelectrochemical degradation, organic pollutants
Published in RUNG: 12.06.2023; Views: 2506; Downloads: 12
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