1. Electrochemical determination of ammonia at low concentrations : detection of N[sub]2-electroreduction product in alkaline mediumBeata Rytelewska, Anna Chmielnicka, Takwa Chouki, Saim Emin, Iwona A. Rutkowska, Pawel Jozef Kulesza, 2025, original scientific article Abstract: A Pt nanoparticle catalyst supported on partially-defective CeO₂ was developed for sensitive voltammetric detection of ammonia (NH₃) in alkaline media (0.5 mol dm⁻³ NaOH), achieving a detection limit of 2–3 μmol dm⁻³. This system enables in situ NH₃ monitoring during nitrogen electroreduction at an Fe₃P catalyst, without medium transfer, minimizing contamination. The Pt-based electrode also serves as a diagnostic tool to confirm electrolyte and gas purity. Selective NH₃ formation with negligible hydrazine or hydroxylamine by-products was confirmed via voltammetry and spectrophotometry.
Keywords: electrochemical analysis, ammonia determination, alkaline medium, nitrogen electroreduction, iron phosphide, electroanalytical control experiments, ceria, platinum nanoparticles, rhodium nanoparticles
Published in RUNG: 21.05.2025; Views: 364; Downloads: 2
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2. Efficient electrochemical nitrogen fixation at iron phosphide (Fe_2P) catalyst in alkaline mediumBeata 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: 3078; Downloads: 5
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