Τμήμα Χημικών Μηχανικών (Δημοσ. Π.Π. σε περιοδικά)
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Item Open Access Enhancement of the intrinsic Ni/GDC activity under rSOC operation by means of Fe–Au doping: An electro-kinetic study(International Journal of Hydrogen Energy, 2023-06-22) Ζαραβέλης, Φώτιος; Νιάκολας, Δημήτριος; Zaravelis, Fotios; Niakolas, DimitriosThe investigation dealt with the effect of Fe and Au wt.% concentrations on the enhanced performance and stability of Ni/GDC under rSOC operation. Moreover, it focused on the comparison of the intrinsic electro-kinetics between the best performing Fe–Au-modified cell and Ni/GDC under SOE operation. The rSOC performance and stability of all cells was examined in the temperature range of 900–800 °C. The electro-kinetic measurements took place at 900 °C by varying the pH2O. All Fe–Au–Ni/GDC electrodes exhibited enhanced activity, compared to the SoA Ni/GDC, with variations in their stability after three rSOC cycles. Specifically, the fuel electrode with the lowest wt.% concentration in Fe and Au (0.5Fe–1Au–Ni/GDC) exhibited the highest activity and stability under rSOC operation. By increasing the wt.% loadings to 2 wt.% Fe and 3 wt.% Au, there was rapid degradation of the initially high performance, mainly due to increase of the ohmic resistance. SEM analysis showed higher macro-porosity on the reduced state of the modified electrodes, which in the case of the best performing 0.5Fe–1Au–Ni/GDC was the least affected after rSOC operation. Interestingly, the SOE performance of the examined Fe–Au-modified electrodes was not similarly inhibited by the decrease of temperature, compared to Ni/GDC. This was further clarified through electro-kinetic measurements, aiming to verify the effect from the Fe–Au doping on the intrinsic electrochemical activity of Ni/GDC for the H2O electrolysis reaction. Comparison between the SoA and the best performing 0.5Fe–1Au–Ni/GDC showed an enhancing effect on the intrinsic electro-kinetics of the modified electrode. Specifically, the dependence of the polarization resistance on the pH2O was found to be strongly positive, resulting in a higher apparent reaction order, compared to Ni/GDC.Item Open Access Transition metals in Ni/GDC for the reversible solid oxide cell operation : optimization of the Mo-Au-Ni synergy and further enhancement via substitution of Mo with Fe(Electrochimica Acta, 2023-04-02) Ζαραβέλης, Φώτιος; Σύγκελλου, Λαμπρινή; Σουβαλιώτη, Αθηνά; Νιάκολας, Δημήτριος; Zaravelis, Fotios; Sygellou, Labrini; Souvalioti, Athina; Niakolas, DimitriosThe study focused on the elucidation of the synergistic interaction of different wt.% loadings of Mo and Au in Ni/GDC, with the objective to find their optimum content for enhanced rSOC performance. In addition, the promoting effect of Fe in Ni/GDC was stabilized via co-deposition with Au and there is for the first-time comparison among the transition metal modifications of Mo-Au-Ni vs Fe-Au-Ni. A series of samples was prepared, where the content of Au varied between 1 and 3 wt.% and between 0.4 and 1 wt.% for Mo. Physicochemical characterization took place with XRF, BET, SEM, H2-TPR, TPH2O and in-situ H2O-XPS. The effect of the transition metals interaction on the performance of SoA Ni/GDC was investigated via electrochemical I-V and EIS measurements in rSOC operation, by applying different pH2O/pH2 mixtures in the temperature range of 900 – 800 °C. It was found that high Mo and/or Au wt.% content, results in larger Mo-Au-Ni particles and affects differently the bulk and surface interaction of the samples with H2O, as well as the Rohm and Rpol values of the fuel electrodes. The modified samples were less prone to bulk oxidation by H2O, while they exhibited higher surface oxidation of Ni and higher amount of Ce3+, compared to Ni/GDC. On the surface of the optimum 0.4 wt.% Mo-1 wt.%Au-Ni/GDC: (i) Ni was less oxidized, (ii) Au0 enrichment was more stable and (iii) Mo was more oxidized, overall affecting positively the Rpol versus the electrode with the higher loadings of 1 wt.% Mo-3 wt.% Au. The main degradation factor of the latter cell was ascribed to the increased Rohm. Finally, a new ternary 0.5 wt.% Fe-3 wt.% Au-Ni/GDC electrode is presented, which exhibited superior electrochemical rSOC performance and stability, compared to the optimum Mo-Au-Ni/GDC, highlighting the need for further research in the transition metals effect on SOCs.Item Open Access Effect of the PH2O/PCO2 and PH2 on the intrinsic electro-catalytic interactions and the CO production pathway on Ni/GDC during solid oxide H2O/CO2 co-electrolysis(Elsevier) Niakolas, D.K.; Neophytides, S.G.; Ioannidou, E.; Chavani, M.; Νιάκολας, Δ.The study presents a holistic methodology for the discrimination of the contribution of H2O and CO2 electrolysis reactions, as well as of the RWGS, on the production rate of CO during the solid oxide H2O/CO2 co-electrolysis process. The investigation took place on an electrolyte supported cell with Ni/GDC as the fuel electrode, at 800–900 °C, by applying various PΗ2Ο/PCO2 feed ratios, in the range of 0 ≤ PΗ2Ο/PCO2 ≤ 1, and two PΗ2 values (2 and 21 kPa). Critical combination of physicochemical and electrochemical characterization with electrocatalytic measurements and quantitative analysis of products highlighted a competitive adsorption and electro-reduction between H2O and CO2 on Ni/GDC. Moreover, it is confirmed that the H2O/CO2 co-electrolysis process is determined by: (i) PH2O/PCO2 ratio and (ii) PH2. Specifically, at PΗ2Ο/PCO2 = 1 and high PΗ2 = 21 kPa the adsorption of H2O is favored, compared to CO2, and the electrochemical process is 100% selective towards the electrolysis of H2O. The CO production is catalytically controlled by the RWGS reaction. The electrochemical reduction of CO2 occurs at PΗ2Ο/PCO2 = 0.3, in combination with H2O electrolysis and the RWGS, whereas its contribution is enhanced by decreasing the PΗ2Ο and PΗ2.Item Open Access Iterative multi-frame super-resolution image reconstruction via variance-based fidelity to the data(2014-08-27) Panagiotopoulou, Antigoni; Παναγιωτοπούλου, ΑντιγόνηMulti-frame Super-Resolution (SR) image reconstruction creates a single High-Resolution (HR) image from a sequence of Low-Resolution (LR) frames. Apart from resolution increment, blurring and noise removal is also achieved. In stochastic regularized methods, the SR problem is formulated by means of two terms, the data-fidelity term and the regularization term. In the present work, a novel estimator named Var-norm has been proposed for utilization in the data-fidelity term. This estimator presents a simple mathematical form based on the variance of the SR estimation error, i.e. on the difference between the estimated LR frame and the corresponding measured LR frame. The introduced Var-norm estimator is combined with the Bilateral Total Variation (BTV) regularization to formulate a novel SR method. The SR performance of the proposed method is directly compared with that of two SR techniques existing in the literature. Experimentation proves that the proposed method outperforms the existing methods.