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1.
Efficient electrochemical nitrogen fixation at iron phosphide (Fe_2P) catalyst in alkaline medium
Beata Rytelewska, Anna Chmielnicka, Takwa Chouki, Magdalena Skunik-Nuckowka, Shaghayegh Naghdi, Dominik Eder, Aleksandra Michalowska, Tomasz Ratajczyk, Egon Pavlica, Saim Emin, 2023, original scientific article

Abstract: A catalytic system based on iron phosphide (Fe2P) has exhibited electrocatalytic activity toward N2-reduction reaction in alkaline medium (0.5 mol dm−3 NaOH). Based on voltammetric stripping-type electroanalytical measurements, Raman spectroscopic and spectrophotometric data, it can be stated that the Fe2P catalyst facilitates conversion of N2 to NH3, and the process is fairly selective with respect to the competing hydrogen evolution. A series of diagnostic electrocatalytic experiments (utilizing platinum nanoparticles and HKUST-1) have been proposed and performed to control purity of nitrogen gas and to probe presence of potential contaminants such as ammonia, nitrogen oxo-species and oxygen. On the whole, the results are consistent with the view that the interfacial reduced-iron (Fe0) centers, while existing within the network of P sites, induce activation and reduction of nitrogen, parallel to the water splitting (reduction) to hydrogen. It is apparent from Tafel plots and impedance measurements that mechanism and dynamics of nitrogen reduction depends on the applied electroreduction potential. The catalytic system exhibits certain tolerance with respect to the competitive hydrogen evolution and gives (during electrolysis at -0.4 V vs. RHE) the Faradaic efficiency, namely, the selectivity (molar) efficiency, toward production of NH3 on the level of 60%. Under such conditions, the NH3-yield rate has been found to be equal to 7.5 µmol cm−2 h−1 (21 µmol m−2 s−1). By referring to classic concepts of electrochemical kinetic analysis, the rate constant in heterogeneous units has been found to be on the moderate level of 1-2*10−4 cm s−1 (at -0.4 V). The above mentioned iron-phosphorous active sites, which are generated on surfaces of Fe2P particles, have also been demonstrated to exhibit strong catalytic properties during reductions of other electrochemically inert reactants, such as oxygen, nitrites and nitrates.
Keywords: nitrogen reduction, alkaline medium, iron phosphide catalyst, ammonia, electrochemical determinations
Published in RUNG: 30.11.2023; Views: 909; Downloads: 4
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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: 1296; Downloads: 0
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4.
Efficient Iron Phosphide Catalyst as a Counter Electrode in Dye-Sensitized Solar Cells : article
Abdullah Yildiz, Takwa Chouki, Aycan Atli, Moussab Harb, Sammy W Verbruggen, Rajeshreddy Ninakanti, Saim Emin, 2021, original scientific article

Abstract: Developing an efficient material as a counter electrode (CE) with excellent catalytic activity, intrinsic stability, and low cost is essential for the commercial application of dye-sensitized solar cells (DSSCs). Transition metal phosphides have been demonstrated as outstanding multifunctional catalysts in a broad range of energy conversion technologies. Here, we exploited different phases of iron phosphide as CEs in DSSCs with an I–/I3–-based electrolyte. Solvothermal synthesis using a triphenylphosphine precursor as a phosphorus source allows to grow a Fe2P phase at 300 °C and a FeP phase at 350 °C. The obtained iron phosphide catalysts were coated on fluorine-doped tin oxide substrates and heat-treated at 450 °C under an inert gas atmosphere. The solar-to-current conversion efficiency of the solar cells assembled with the Fe2P material reached 3.96 ± 0.06%, which is comparable to the device assembled with a platinum (Pt) CE. DFT calculations support the experimental observations and explain the fundamental origin behind the improved performance of Fe2P compared to FeP. These results indicate that the Fe2P catalyst exhibits excellent performance along with desired stability to be deployed as an efficient Pt-free alternative in DSSCs.
Keywords: Iron phosphide, catalyst, counter electrode, dye-sensitized solar cell, solvothermal synthesis
Published in RUNG: 06.02.2023; Views: 1202; Downloads: 0
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5.
Highly active iron phosphide catalysts for selective electrochemical nitrate reduction to ammonia
Takwa Chouki, Manel Machreki, Iwona A. Rutkowska, Beata Rytelewska, Pawel Jozef Kulesza, Georgi Tyuliev, Moussab Harb, Luis Miguel Azofra, Saim Emin, 2023, original scientific article

Abstract: The electrochemical reduction reaction of the nitrate ion (NO3−), a widespread water pollutant, to valuable ammonia (NH3) is a promising approach for environmental remediation and green energy conservation. The development of high-performance electrocatalysts to selectively reduce NO3− wastes into value-added NH3 will open up a different route of NO3− treatment, and impose both environmental and economic impacts on sustainable NH3 synthesis. Transition metal phosphides represent one of the most promising earth-abundant catalysts with impressive electrocatalytic activities. Herein, we report for the first time 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. Detection of the in-situ formed product was achieved using 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). The recycling tests confirmed that Fe2P and FeP catalysts exhibit excellent stability during the NO3− reduction at − 0.37 V vs. 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. These results indicate that the Fe2P phase exhibits excellent performance to be deployed as an efficient noble metal-free catalyst for NH3 generation.
Keywords: iron phosphide, electrocatalysts, nitrates reduction ammonia, DFT calculations
Published in RUNG: 02.02.2023; Views: 1506; Downloads: 4
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6.
Solvothermal synthesis of iron phosphides and their application for efficient electrocatalytic hydrogen evolution
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 [1]. 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 HER activities of the iron phosphide catalyst were found to be phase dependent. 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 the 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, electrocatalyst, hydrogen evolution, overpotential
Published in RUNG: 13.05.2021; Views: 2356; Downloads: 0
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7.
Synthesis of efficient iron phosphide catalyst for electrocatalytic hydrogen generation
Takwa Chouki, D. Lazarević, B. Donkova, Saim Emin, 2021, original scientific article

Abstract: A solvothermal synthesis of iron phosphide electrocatalysts using triphenylphosphine (TPP) as phosphorus precursor is presented. The synthetic protocol generates Fe2P/FeP phase at 350°C. After deposition of the catalyst onto graphite substrate heat-treatment at higher temperature was carried out. Annealing at 500°C under reductive atmosphere induced structural changes in the Fe2P/FeP samples which yielded a pure Fe2P phase. The electrocatalytic activity of the Fe2P catalyst was studied for hydrogen evolution reaction (HER) in 0.5 M H2SO4. The recorded overpotential for HER was about 130 mV vs. a reversible hydrogen electrode (RHE) at 10 mA cm−2
Keywords: solvothermal synthesis, iron phosphide, electrocatalyst, hydrogen evolution
Published in RUNG: 10.05.2021; Views: 2280; Downloads: 0
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8.
Solvothermal synthesis of iron phosphides and their application for efficient electrocatalytic hydrogen evolution
Takwa Chouki, Manel Machreki, Saim Emin, 2020, original scientific article

Abstract: Abstract In this paper, we present a solvothermal synthesis of iron phosphide electrocatalysts using a triphenylphosphine (TPP) precursor. The synthetic protocol generates 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 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). Pure Fe2P films was prepared under argon atmosphere at 450 °C (Fe2P−450 °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 H2SO4. The HER activities of the iron phosphide catalyst were found to be phase dependent. 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: Solvothermal synthesis, Iron phosphide, Electrocatalyst, Hydrogen evolution, Overpotential
Published in RUNG: 20.07.2020; Views: 2929; Downloads: 0
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