ORALS

SESSION: PhysicalThuAM-R10	Vayenas International Symposium on Physical Chemistry and its applications for sustainable development
Thu Oct, 24 2019 / Room: Aphrodite B (100/Gr. F)
Session Chairs: Antonio de Lucas Consuegra; Dimitrios Niakolas; Session Monitor: TBA

12:35: [PhysicalThuAM04]
Transition Metal Elements as Ni/GDC Dopants for the H2O Electrolysis Process in SOECs; Fe-Ni vs Au-Mo-Ni Interaction
Dimitrios Niakolas¹ ; Stylianos G. Neophytides² ; Evangelia Ioannidou¹ ; Charalampos Neofytidis¹ ; ¹Foundation for Research and Technology, Institute of Chemical Engineering Sciences (FORTH/ICEHT), Patras, Greece; ²FORTH ICE-HT, PATRAS, Greece;
Paper Id: 146 [Abstract]

High quality H₂ can be produced through water electrolysis at low or high temperatures. In this respect, solid oxide electrolysis cells (SOECs) are a promising and fast growing technology [1, 2] for H₂O electrolysis above 500°C. SOECs have identical configuration with SOFCs, but reverse operations and currently novel modified Ni-based fuel electrodes are under investigation for H₂O, CO₂ and H₂O⁺ CO₂ electrolysis applications [1, 3]. The presented study focuses on the effect of transition metal elements as dopants of the commercial NiO/GDC powder for the Solid Oxide H₂O electrolysis. Specifically, the experimental comparison is between Au [1], Mo and Fe doping. Comparative electrocatalytic measurements with I-V curves and electrochemical impedance spectra (EIS) analyses are presented in the range of 800-900°C between electrolyte-supported cells with Ni/GDC, 3Au-Ni/GDC [1], 3Mo-Ni/GDC, 3Au-3Mo-Ni/GDC, 2Fe-Ni/GDC and 0.5Fe-Ni/GDC, as the fuel electrode. Complementary physicochemical characterization was also performed both in the form of powders and as half cells with ex-situ and in-situ techniques, including specific redox stability measurements in the presence of H₂O. In summary, the cell comprising the ternary 3Au-3Mo-Ni/GDC electrode and that with 0.5Fe-Ni/GDC performed significantly better compared to the rest. The superior performance of the ternary sample is primarily ascribed to the enrichment of the surface with Au [1] and of the bulk phase with Mo, through the formation of Ni-Au-Mo solid solution [3, 4]. The involved elements act in synergy and modify the physicochemical properties of the electrode, improving the: (i) H₂O re-oxidation rate, (ii) electronic conductivity and (iii) electrochemical interface. In regards to Fe-doping, the wt.% content in iron is one key parameter. The 0.5wt.% loading of Fe results in an electrode of similar high performance to that of the Au-Mo-Ni electrode, having the great advantage of not containing gold in its composition.

References:
[1] E. Ioannidou, Ch. Neofytidis, L. Sygellou, D.K. Niakolas, Applied Catalysis B: Environmental 236 (2018) 253-264.
[2] P. Mocoteguy, A. Brisse, Int. J. Hydrogen Energy 38 (2013) 15887-15902.
[3] Ch. Neofytidis, E. Ioannidou, L. Sygellou, M. Kollia and D.K. Niakolas, Journal of Catalysis (2019), Accepted, In Press.
[4] D.K. Niakolas, C.S. Neofytidis, S.G. Neophytides, Frontiers in Environmental Science 5 (78) (2017) 1-20.

SESSION: PhysicalThuPM2-R10	Vayenas International Symposium on Physical Chemistry and its applications for sustainable development
Thu Oct, 24 2019 / Room: Aphrodite B (100/Gr. F)
Session Chairs: Vasileios Kyriakou; Dimitrios Zagoraios; Session Monitor: TBA

16:20: [PhysicalThuPM210] Keynote
New Low Loading Pt Based Nano-Materials for Fuel Cell Applications
Stylianos G. Neophytides¹ ; Maria Daletou² ; ¹FORTH ICE-HT, PATRAS, Greece; ²FORTH-ICE/HT, patras, Greece;
Paper Id: 159 [Abstract]

Pt supported on carbon electrocatalysts are the most efficient and stable materials for both the oxygen reduction reaction (ORR) at the cathode and the hydrogen oxidation reaction (HOR) at the anode of polymer electrolyte membrane fuel cells (PEMFCs) (1). In this respect, there is increasing demand to reduce cost and therefore, the amounts of Pt used. This can be achieved by increased catalyst activity and/or utilization (2). To reach this goal, there are two approaches: (a) enhancing the specific activity or (b) increasing the specific surface area of the catalyst by forming a fine dispersion. The performance and stability of the (electro) catalysts strongly depends on the physicochemical characteristics, such as the surface area, the crystalline structure, the size and shape of the particles, and the interactions with the support. Both approaches for Pt reduction can be followed separately or combined by exploiting the differentiations induced to the metal by the surface chemistry of the support to result in customized properties and control its performance. When the dispersion of the metal is high, its metal atom is accessible to reactants and available for catalysis, maximizing the efficiency of the metal and minimizing the cost. Reducing the size of the metal in atoms or small groups of atoms can significantly increase both the active surface and the activity of the catalyst through diversification or strengthening of the metal-support interactions3. In this work, we have developed Pt/f-MWCNTs (f-MWCNTs=covalently functionalized MWCNTs) based electrocatalysts with different surface functionalities and Pt loadings. The deposition of the metal was achieved by using the polyol synthetic procedure: reduction of metal precursor salts in an ethylene glycol solution. Through a structural and chemical characterization study of the materials, the introduction of certain groups on the sidewalls of the carbon support resulted in differentiation of the properties, not only in terms of quantitative deposition and dispersion, but also with respect to metal-support interactions, platinum crystal properties and/or oxidative states. The present work addresses scientific issues regarding the most challenging core component of a PEM fuel cell: the Pt based electrocatalyst. This work proposes a comprehensive effort to explore a new approach and exploit the differentiations induced on the metal by the surface chemistry of the support. The introduction of pyridines on the sidewalls of the carbon support can differentiate the metal deposition, not only in terms of dispersion and the obtained morphology, but also with respect to metal-support interactions on platinum properties and its oxidative state. The aim is the interpretation of the catalyst’s electrochemical behavior through a structural and physicochemical characterization study. It is shown that the substrate can play a decisive role on the size and functionality of the electrochemical interface. This approach constitutes a promising route for developing materials with innovative features aiming to a serious reduction in the Pt loads, thus resulting into increased catalyst activity and metal utilization.

References:
1. Yang C., Costamagna P., Srinivasan S., Benziger J., Bocarsly A.B. (2001). J Power Sources, 103:1-9.
2. Notter A D., Kouravelou K., Karachalios T., Daletou M.K., Haberland N.T. (2015). Energy Environ Sci, 8:1969-1985.
3. Flytzani-Stephanopoulos M., Gates B.C. (2012). Annu. Rev. Chem. Biomol. Eng., 3:545-574.