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Opis: 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.
Ključne besede: electrochemical reduction, nitrate reduction, iron phosphide catalyst, NH3 generation
Objavljeno v RUNG: 10.01.2025; Ogledov: 587; Prenosov: 2
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Opis: In a bifunctional Ni/ZSM-5 zeolite type catalyst, catalytic properties are usually tuned via varying Al and Ni contents [1]. Here we present a systematic structural study of the Ni/ZSM-5 materials by Ni K-edge XANES and EXAFS analyses, to monitor the changes of local structure and chemical state of Ni species in the catalysts as a function of Al and Ni content. A series of Ni/ZSM-5 type zeolites with different Al to Si and Ni to Si molar ratios were synthesized by a “green”, template free technique [2]. With a combination of XAS, XRD and TEM we resolved the changes in the local environment of Ni species induced by the different Al contents in the Ni/ZSM-5 catalysts. Ni species in Ni/ZSM-5 exist as NiO nanocrystals and as charge compensating Ni2+ cations. The Ni K-edge XANES and EXAFS results enabled the quantification of Ni-containing species. At a low Al to Si ratio (nAl/nSi < 0.04), the NiO nanoparticles predominate in the samples and account for over 65% of Ni phases. However, NiO is outnumbered by Ni2+ cations attached to the zeolite framework in ZSM-5 with a high Al to Si ratio (nAl/nSi = 0.05) due to a higher number of framework negative charges imparted by Al. The obtained results show that the number of highly reducible and active NiO nanocrystals is strongly correlated with the framework Al sites present in Ni/ZSM-5 zeolites.
Ključne besede: Ni EXAFS, XANES Ni/ZSM-5 catalyst
Objavljeno v RUNG: 05.07.2024; Ogledov: 1508; Prenosov: 4
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Opis: 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.
Ključne besede: catalyst synthesis, electrocatalysis, chlorine evolution
Objavljeno v RUNG: 04.09.2023; Ogledov: 3344; Prenosov: 8
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Opis: 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.
Ključne besede: Iron phosphide, catalyst, counter electrode, dye-sensitized solar cell, solvothermal synthesis
Objavljeno v RUNG: 06.02.2023; Ogledov: 2497; Prenosov: 0
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Opis: Industrial Cu/ZnO/Al2O3 or novel rate catalysts, prepared with a photochemical deposition method, were studied under functional CH3OH synthesis conditions at the set temperature (T) range of 240–350 °C, 20 bar pressure, and stoichiometric carbon dioxide/hydrogen composition. Analytical scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray adsorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) methods were systematically utilized to investigate the interfaces, measured local geometry, and chemical state electronics around the structured active sites of commercially available Cu/ZnO/Al2O3 material or synthesized Cu/ZnO. Processed Cu K-edge EXAFS analysis suggested that various Cu atom species, clusters, metallic fcc Cu, Cu oxides (Cu2O or CuO) and the Cu0.7Zn2 alloy with hexagonal crystalline particles are contained after testing. It was proposed that in addition to the model’s Cu surface area, the amount, ratio and dispersion of the mentioned bonded Cu compounds significantly influenced activity. Additionally, XPS revealed that carbon may be deposited on the commercial Cu/ZnO/Al2O3, forming the inactive carbide coating with Cu or/and Zn, which may be the cause of basicity’s severe deactivation during reactions. The selectivity to methanol decreased with increasing T, whereas more Cu0.7Zn2 inhibited the CO formation through reverse water–gas shift (RWGS) CO2 reduction.
Ključne besede: CH3OH synthesis, Cu/ZnO-based catalyst, XPS, XANES, EXAFS analyses, Catalyst selectivity and activity
Objavljeno v RUNG: 03.06.2021; Ogledov: 3849; Prenosov: 0
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