Electrode kinetics of porous Ni-3YSZ cermet operated in fuel cell and electrolysis modes for solid oxide cell application. (1st September 2021)

• Record Type: Journal Article
• Authors: Monaco, Federico; Effori, Elisa; Hubert, Maxime; Siebert, Elisabeth; Geneste, Gregory; Morel, Bertrand; Djurado, Elisabeth; Montinaro, Dario; Laurencin, Jérôme
• Is Part Of: Electrochimica acta. Volume 389(2021)
• Publication Date: 2021-09-01
• Subjects: Reaction mechanism -- Ni-3YSZ cermet -- SOFC -- SOEC -- Modeling -- Electrochemical impedance spectroscopy -- Hydrogen spillover -- Oxygen spillover; 3YSZ Yttria Stabilized Zirconia with 3 mol.% of yttria -- 3Y-TZP Tetragonal Polycrystalline Zirconia stabilized with 3 mol.% of yttria -- 8YSZ Yttria Stabilized Zirconia with 8 mol.% of yttria -- CC Current Collector -- CE Counter Electrode -- CR Chemical Reaction -- DFT Density Functional Theory -- DGM Dusty-Gas Model -- EC Equivalent Circuit -- EIS Electrochemical Impedance Spectroscopy -- ER Electrochemical Reaction -- ESRF European Synchrotron Radiation Facility -- FL Functional Layer -- FLG Finite-Length Gerischer -- GDC Gadolinium-doped Ceria -- LSCF Lanthanum Strontium Cobalt Ferrite -- MD Molecular Dynamics -- OCP Open Circuit Potential -- pFIB Plasma-Focused Ion Beam -- RE Reference Electrode -- ROI Region of Interest -- RVE Representative Volume Element -- SOC Solid Oxide Cell -- SOEC Solid Oxide Electrolysis Cell -- SOFC Solid Oxide Fuel Cell -- TPBls Triple Phase Boundaries lengths -- WE Working Electrode -- YSZ Yttria Stabilized Zirconia; Electrochemistry -- Periodicals; Electrochemistry, Industrial -- Periodicals; 541.37
• DOI: 10.1016/j.electacta.2021.138765
• Languages: English
• ISSNs: 0013-4686

Abstract

Highlights: Electrochemical characterizations of Ni-3YSZ electrode in SOFC and SOEC conditions. Electrochemical impedance spectra measured up to high steam partial pressure. Electrode microstructure reconstructed by synchrotron X-ray holotomography. Dynamic model with a micro kinetic elementary description for porous Ni-3YSZ cermet. Reaction pathways and rate-limiting steps in SOFC and SOEC modes. Abstract: The electrochemical reactions of hydrogen oxidation and steam reduction have been investigated for a porous cermet electrode made of Ni and 3YSZ. The electrochemical characterizations have been performed over a large range of gas compositions at 700°C. It has been shown that the fuel electrode response is activated by the potential under anodic current while a limiting current density appears under cathodic polarization. Moreover, the impedance diagrams exhibit a shape representative of a kind of finite-length Gerischer element with a low-frequency contribution sensitive to the steam content. To interpret these experimental results, a continuous dynamic model has been developed by describing the mass and charge transfers within the electrode. The reaction has been divided into a sequence of elementary steps considering two scenarios of charge transfer based on the oxygen and hydrogen spillover mechanisms. Three-dimensional reconstructions obtained by synchrotron X-ray nano-holotomography have been used to provide the cermet structural properties for the simulations. The numerical computations have shown that the hydrogen spillover scenario is the most appropriate mechanism to reproduce correctly the experiments. Besides, the electrode response is controlled by the charge transfer at triple phase boundary lengths, the oxygen vacancies migration in the 3YSZ network and a pure chemical surface process depending on the polarization. In fuel cell mode, desorption of water molecules from 3YSZ would co-limit the electrode response, while in electrolysis mode, the steam adsorption on Ni would become one of the rate determining steps. Finally, a sensitivity analysis has shown that surface diffusion would also play a key role in the electrode response.