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An in situ proton filter covalent organic framework catalyst for highly efficient aqueous electrochemical ammonia production
Kayaramkodath C. Ranjeesh, Sukhjot Kaur, Abdul K. Mohammed, Safa Gaber, Divyani Gupta, Khaled Badawy, Mohamed Aslam, Nirpendra Singh, Tina Škorjanc, Matjaž Finšgar, 2023, original scientific article

Abstract: The electrocatalytic nitrogen reduction reaction (NRR) driven by renewable electricity provides a green synthesis route for ammonia (NH3) production under ambient conditions but suffers from a low conversion yield and poor Faradaic efficiency (F.E.) because of strong competition from hydrogen evolution reaction (HER) and the poor solubility of N2 in aqueous systems. Herein, an in situ proton filter covalent organic framework catalyst (Ru-Tta-Dfp) is reported with inherent Ruthenium (Ru) sites where the framework controls reactant diffusion by suppressing proton supply and enhancing N2 flux, causing highly selective and efficient catalysis. The smart catalyst design results in a remarkable ammonia production yield rate of 2.03 mg h−1 mgcat−1 with an excellent F.E. of ≈52.9%. The findings are further endorsed with the help of molecular dynamics simulations and control COF systems without in situ proton filter feasibility. The results point to a paradigm shift in engineering high-performance NRR electrocatalysts for more feasible green NH3 production.
Keywords: covalent organic frameworks, ammonia, electrochemical synthesis, electrochemistry, nitrogen reduction reaction, ruthenium
Published in RUNG: 11.12.2023; Views: 680; Downloads: 6
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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: 774; Downloads: 4
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Performance of copper - based catalysts for electrochemical CO2 reduction
Stefan Popović, 2023, doctoral dissertation

Abstract: The industrial era has brought a never-ending problem to civilization through the emission of greenhouse gases (GHGs) while extracting energy from fossil fuels for a variety of processes. Among different GHGs, carbon dioxide (CO2) stood out as one of the most impactful and dangerous gases causing climatic disasters around the globe. However, CO2 as the abundant C1 building block, through the conversion pathways gives a plethora of opportunities to convert it into a wide range of commercial products and applications. The holistic approach among different conversion pathways is the electrochemical reduction of CO2 (eCO2R), ideally powered by renewable energy from intermittent sources such as wind and solar power. A silver bullet of the process is to find a catalyst that is active, selective, and stable. Copper has been recognized as the only monometallic catalyst that can produce products that require a transfer of >2e-. However, in recent years the increased awareness of its reconstructive nature under eCO2RR-relevant conditions multiplied the complexity of the parameters that can influence the reaction. Therefore overall thesis's approach to studying copper-based catalysts is based to understand the reconstructive aspect and the stability of Cu-based catalysts, and deeply comprehend their relationship with the activity/selectivity. Chapter 1 gives an introduction to the recent activities in the field of carbon capture, utilization and storage (CCSU) technologies, the fundaments of CO2 as a molecule, and its pathway toward state-of-the-art discoveries in the eCO2 R reaction. Afterward, the thesis focuses on the main experimental technique to produce nanostructured copper-based materials, namely, electrodeposition (Chapter 2). A big part of the thesis focuses on the establishment of an electrochemical setup for activity/selectivity measu rement. The setup consists of two parts: 1) construction of the custom-made gas-tight sandwich-type electrochemical cell and 2) optimization of the online gas and ex-situ liquid product detection. After the establishment of the reliable electrochemical setup, Chapter 3 focuses on electrochemically -grown Cu2O nanocubes catalyst and how the reconstructive nature induced by a particular electrochemical protocol influences on boost in activity/selectivity for methane production. The last part of the thesis consists contribution to the fundamental understanding of the degradation mechanisms and stability of Cu -based catalysts under eCO2RR conditions. A unique ex-situ approach, mirrored in identical location scanning electron microscopy (IL-SEM) method is employed to study electrodeposited spherical half-micron particles on the glassy carbon rotating disk electrode (GC-RDE). With this evidence, we could interpret the observed structural changes as two separate electrochemical processes occurring one after another, namely copper dissolution from pre-oxidized native nanoparticles and subsequent (electro -) redeposition of the dissolved copper species in a form of n ew smaller Cu fragments.
Keywords: electrocatalysts, electrochemical CO2 reduction, copper nanoparticles, IL-SEM, stability, degradation
Published in RUNG: 14.11.2023; Views: 947; Downloads: 16
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