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1.
Materials for sustainable electrochemical energy conversion
Saim 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: 875; Downloads: 3
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2.
Tuning the activity of iron phosphide electrocatalysts for sustainable energy conversion
Saim 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: 786; Downloads: 4
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3.
Self-adaptive amorphous ▫$CoO_xCl_y$▫ electrocatalyst for sustainable chlorine evolution in acidic brine
Mengjun Xiao, Qianbao Wu, Ruiqi Ku, Liujiang Zhou, Chang Long, Junwu Liang, Andraž Mavrič, Lei Li, Jing Zhu, Matjaž Valant, 2023, original scientific article

Abstract: Electrochemical chlorine evolution reaction is of central importance in the chlor-alkali industry, but the chlorine evolution anode is largely limited by water oxidation side reaction and corrosion-induced performance decay in strong acids. Here we present an amorphous CoOxCly catalyst that has been deposited in situ in an acidic saline electrolyte containing Co2+ and Cl- ions to adapt to the given electrochemical condition and exhibits ~100% chlorine evolution selectivity with an overpotential of ~0.1 V at 10 mA cm−2 and high stability over 500 h. In situ spectroscopic studies and theoretical calculations reveal that the electrochemical introduction of Cl- prevents the Co sites from charging to a higher oxidation state thus suppressing the O-O bond formation for oxygen evolution. Consequently, the chlorine evolution selectivity has been enhanced on the Cl-constrained Co-O* sites via the Volmer-Heyrovsky pathway. This study provides fundamental insights into how the reactant Cl-itself can work as a promoter toward enhancing chlorine evolution in acidic brine.
Keywords: catalyst synthesis, electrocatalysis, chlorine evolution
Published in RUNG: 04.09.2023; Views: 1242; Downloads: 6
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4.
Stable seawater oxidation with a self-healing oxygen-evolving catalyst
Xiaojian Zhang, Chao Feng, Zeyu Fan, Beibei Zhang, Yequan Xiao, Andraž Mavrič, Nadiia Pastukhova, Matjaž Valant, Yi-Fan Han, Yanbo Li, 2023, original scientific article

Abstract: Direct seawater electrolysis is key to massive hydrogen fuel production without the depletion of precious freshwater resources and the need for high-purity electrolytes. However, the presence of high-concentration chloride ions (Cl−) and alkaline-earth metal ions (Mg2+, Ca2+) poses great challenges to the stability and selectivity of the catalysts for seawater splitting. Here, we demonstrate a self-healing oxygen evolution reaction (OER) catalyst for long-term seawater electrolysis. By suppressing the competitive chlorine evolution reaction and precipitating the alkaline-earth metal ions through an alkaline treatment of the seawater, stable seawater oxidation is achieved owing to the self-healing ability of the borate-intercalated nickel–cobalt–iron oxyhydroxides (NiCoFe-Bi) OER catalyst under highly-alkaline conditions. The self-healing NiCoFe-Bi catalyst achieves stable seawater oxidation at a large current density of 500 mA cm−2 for 1000 h with near unity Faraday efficiency. Our results have demonstrated strong durability and high OER selectivity of the self-healing catalyst under harsh conditions, paving the way for industrial large-scale seawater electrolysis.
Keywords: chemistry, electrocatalysis, seawater oxidation, oxygen evolution reaction
Published in RUNG: 08.05.2023; Views: 1336; Downloads: 4
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5.
Colloidal nanoparticles for photo(electro)catalytic water splitting studies
Saim Emin, Manel Machreki, Takwa Chouki, 2022, published scientific conference contribution abstract

Keywords: nanoparticles, electrocatalysis, water splitting
Published in RUNG: 10.02.2023; Views: 1528; Downloads: 0
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6.
Iron phosphide as an efficient electrocatalysts for hydrogen evolution : abstract
Takwa Chouki, Manel Machreki, Saim Emin, 2020, published scientific conference contribution abstract

Abstract: We report the solvothermal synthesis of iron phosphide electrocatalysts using a low-cost phosphorus precursor. The synthetic protocol allows for the preparation of a Fe2P phase at 300°C and FeP phase at 350°C. To enhance the catalytic activities of obtained iron phosphide particles, heat-treatments were carried out at elevated temperatures. Annealing at 500°C 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 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 sulfuric acid (H2SO4). The lowest recorded overpotential of 110 mV at 10 mA cm−2 vs. a reversible hydrogen electrode was achieved with Fe2P/FeP−500°C catalyst. The present approach allows preparation of immobilized iron phsphide catalyst onto carbon support which is essential for application purpose. The procedure developed by us is an elegant approach to tune the composition of iron phosphide catalyst and control the morphology of particles
Keywords: solvothermal synthesis iron phosphide electrocatalysis HER
Published in RUNG: 06.02.2023; Views: 1312; Downloads: 0
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7.
Electrocatalytic Hydrogen Evolution with Transition Metal Based Compounds : abstract
Saim Emin, Takwa Chouki, Manel Machreki, 2021, published scientific conference contribution abstract

Abstract: Electrocatalytic water splitting is one of the cleanest and sustainable way to generate hydrogen. Transition metal based electrocatalysts like iron phosphides (Fe2P, FeP), molybdenum diselenides (MoSe2), and tungsten carbides (W2C, WC) have unique advantages including competitive cost compared to platinum, controllable active sites, and electronic structures that could significantly enhance the hydrogen evolution reaction (HER). Here, we present a combination of approaches for preparing catalyst materials. As an elegant technique, colloidal synthesis was used to synthesize Mo and W nanoparticles. Combined with selenization and carbidation approaches at elevated temperature, it allowed to synthesize MoSe2, W2C, and WC thin films. The syntheses of Fe2P and FeP catalyst were achieved in one-stage using triphenylphosphine precursor. The obtained catalysts were applied in electrocatalytic HER studies.
Keywords: iron phosphides molybdenum diselenide tungtsen carbides electrocatalysis hydrogen evolution
Published in RUNG: 06.02.2023; Views: 1235; Downloads: 0
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8.
Synthesis and application of transition metal phosphide nanomaterials as electrocatalysts for water splitting and chemical transformations : dissertation
Takwa Chouki, 2022, doctoral dissertation

Abstract: In this thesis, we will focus on the solvothermal synthesis of iron phosphides (FeP, Fe2P) using triphenylphosphine (TPP) as an inexpensive and stable phosphorus source. The obtained iron phosphides were applied as electrocatalysts in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), Rhodamine B (RhB) degradation, Escherichia coli (E. coli) inactivation, nitrates reduction reaction (NO3RR) to ammonia (NH3), and as counter electrodes in dye-sensitized solar cells (DSSCs). Detailed characterizations of catalysts were carried out to investigate the correlations between the material structure and catalytic activity. The first part of the thesis gives an introduction to the topic which cover overview of literature about the use of transition metal phosphide as efficient electrocatalysts in water splitting studies, NO3RR to NH3 and DSSCs. The second part is a description of the experimental methods. The third part discusses the solvothermal synthesis of FeP and Fe2P catalysts using TPP precursor. The phase conversion of iron phosphides at elevated temperatures under reductive atmosphere was reported. Structural characterizations of the obtained materials were achieved using multiple techniques. The electrocatalytic activities of heat-treated iron phosphide films for HER were studied in acidic environment. The fourth part discusses the use of Fe2P nanoparticles (NPs) for OER. The fifth part outlines the use of Fe2P precatalyst in water treatment studies. Using a thin film of Fe2P precatalyst, RhB degradation and E. coli inactivation in the presence of in-situ generated reactive chlorine species were reported. Characterization of Fe2P electrocatalysts before and after the test was carried out using different techniques. The sixth part shows for the first time the use of FeP and Fe2P as a noble metal-free electrocatalysts for NO3RR to NH3. In this chapter we will emphasize the nitrate reaction pathways, which are highly complex and poorly understood. The seventh part demonstrates the use of FeP and Fe2P catalysts as robust and efficient counter electrodes in DSSCs.
Keywords: solvothermal synthesis, iron phosphides, electrocatalysis, HER, OER, RhB degradation, E. coli inactivation, NO3RR to NH3, DSSCs, dissertations
Published in RUNG: 29.08.2022; Views: 2146; Downloads: 104
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9.
Effect of the Morphology of the High-Surface-Area Support on the Performance of the Oxygen-Evolution Reaction for Iridium Nanoparticles
Leonard Moriau, Marjan Bele, Živa Marinko, Francisco Ruiz-Zepeda, Gorazd Koderman, Martin Šala, Angelija Kjara Šurca, Janez Kovač, Iztok Arčon, Primož Jovanovič, Nejc Hodnik, Luka Suhadolnik, 2021, original scientific article

Abstract: The development of affordable, low-iridium-loading, scalable, active, and stable catalysts for the oxygen-evolution reaction (OER) is a requirement for the commercialization of proton-exchange membrane water electrolyzers (PEMWEs). However, the synthesis of high-performance OER catalysts with minimal use of the rare and expensive element Ir is very challenging and requires the identification of electrically conductive and stable high-surface-area support materials. We developed a synthesis procedure for the production of large quantities of a nanocomposite powder containing titanium oxynitride (TiONx) and Ir. The catalysts were synthesized with an anodic oxidation process followed by detachment, milling, thermal treatment, and the deposition of Ir nanoparticles. The anodization time was varied to grow three different types of nanotubular structures exhibiting different lengths and wall thicknesses and thus a variety of properties. A comparison of milled samples with different degrees of nanotubular clustering and morphology retention, but with identical chemical compositions and Ir nanoparticle size distributions and dispersions, revealed that the nanotubular support morphology is the determining factor governing the catalyst’s OER activity and stability. Our study is supported by various state-of-the-art materials’ characterization techniques, like X-ray photoelectron spectroscopy, scanning and transmission electron microscopies, Xray powder diffraction and absorption spectroscopy, and electrochemical cyclic voltammetry. Anodic oxidation proved to be a very suitable way to produce high-surface-area powder-type catalysts as the produced material greatly outperformed the IrO2 benchmarks as well as the Ir-supported samples on morphologically different TiONx from previous studies. The highest activity was achieved for the sample prepared with 3 h of anodization, which had the most appropriate morphology for the effective removal of oxygen bubbles.
Keywords: electrocatalysis, oxygen-evolution reaction, TiONx-Ir powder catalyst, iridium nanoparticles, anodic oxidation, morphology−activity correlation
Published in RUNG: 04.01.2021; Views: 2799; Downloads: 0
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10.
ORR stability of Mn–Co/polypyrrole nanocomposite electrocatalysts studied by quasi in-situ identical-location photoelectron microspectroscopy
Patrizia Bocchetta, Belen Aleman, Matteo Amati, Mattia Fanetti, Andrea Goldoni, Luca Gregoratti, Maya Kiskinova, Claudio Mele, Hikmet Sezen, Benedetto Bozzini, 2016, original scientific article

Abstract: The stability of pyrolyzed Mn–Co/polypyrrole (PPy) nanocomposites towards the Oxygen Reduction Reaction (ORR) in alkaline solution, was studied with a close-knit group of complementary microscopic and space-resolved spectroscopic approaches: Atomic Force Microscopy (AFM), Scanning and High-Resolution Transmission Electron Microscopy (SEM, HRTEM) and identical-location Scanning PhotoElectron Microscopy (SPEM). Tracking quasi-in situ the morphochemical evolution of the Mn–Co/PPy catalyst upon electrochemical aging under ORR conditions by this multi-technique approach, has allowed to clarify the key physico-chemical processes underlying the dramatic impact of Co additions to stability improvement.
Keywords: Mixed manganese oxides, Polypyrrole, Oxygen reduction, Electrocatalysis, Nanocomposites, X-ray photoelectron microspectroscopy
Published in RUNG: 25.07.2016; Views: 5511; Downloads: 0
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