Optimization of a Reference Kinetic Model for Solid Oxide Fuel Cells

Abstract

Solid oxide fuel cells (SOFCs) stand out among other fuel cell types because of their specific characteristics. The high operating temperature permits to reach optimal conductivity and favours kinetics without requiring noble metal catalysts. The SOFC behaviour analysis is fundamental to optimise operating conditions and to obtain the best performance. For this purpose, specific models are studied to investigate the electrochemical kinetics, which is the most critical aspect in the simulation. This is closely linked to cell materials and structure, as well as to operating conditions (feed composition and temperature above all) that influence cell polarization effects. The present work aims at evaluating these contributions by means of a semi-empirical kinetic formulation based on both theoretical and experimental approaches. A dedicated experimental campaign on an anode-supported NiYSZ/8YSZ/GDC-LSCF button cell is performed to identify experimental parameters. Each working variable is changed singularly to understand its specific effect, avoiding the overlap of multiple effects. The studied kinetics is validated using a 0D model to evaluate global cell operation, and a 1D model to estimate occurring mechanisms along anode thickness. The comparison between experimental and simulated data allows a preliminary validation of the proposed model, providing a base for subsequent more specific studies.

Solid Oxide Fuel Cell Performance Analysis through Local Modelling

“…The pre-exponential coefficients are specific to the electrocatalytic materials used (i.e., Ni/8YSZ-cermet as anode and LSCF as cathode), yet the detected values are comparable with the range in the literature (γ an 5.5 × 10 8 − 5.5 × 10 10 A/m 2 , γ cat 7 × 10 8 − 7 × 10 10 A/m 2 ) [30]. The requested parameters for concentration overpotential are presented in previous works [31,33], while the micro-structural cell features are derived from post-experimental characterization of different layers (refer to Section 4.4).…”

“…The anodic term is derived from the Butler-Volmer equation, considering that the exchange current density diverges in this case. 1D material balance is developed along the electrode thickness to detect the gas profile (Equation (11); for the complete explication, refer to [31] (11) The diffusion coefficients are the combination of molecular contributions, consisting of interactions among different particles, and the Knudsen term due to molecule-wall collisions. The first is evaluated through the Chapman-Enskog approach for a binary mixture (Equation ( 12)), corrected in order to consider the presence of more compounds (Equation ( 13)) [32].…”

Electrochemical Characterization and Modelling of Anode and Electrolyte Supported Solid Oxide Fuel Cells

“…Their averages allowed for identifying global cell parameters. The used equations are represented in Table 2; their rigorous formulation was described in detail in authors' previous works (Bianchi et al, 2020a;Bianchi et al, 2020b). For each reactant gas stream (a H 2 -rich feed at fuel electrode and a N 2 -O 2 mixture at air electrode), material balances along the feed flow directions were solved deriving the electrochemical reaction rate from Faraday's law.…”

Operating Principles, Performance and Technology Readiness Level of Reversible Solid Oxide Cells

“…In both fuel cell and electrolysis operation, high-temperature solid oxide cells usually have a good efficiency since the kinetics depends on thermally activated processes [46]. In fuel cell mode, the common efficiency, η SOFC , is around 50-60%, nevertheless, 70% is also obtained in specific operating conditions.…”