Addressing planar solid oxide cell degradation mechanisms: A critical review of selected components

Abstract

In this review paper, a critical assessment of the main degradation processes in three key components of solid oxide fuel cells and electrolysers (negative and positive electrodes and the interconnect) is undertaken, attempting prioritization of respective degradation effects and recommendation of the best approaches in their experimental ascertainment and numerical modeling.Besides different approaches to quantifying the degradation rate of an operating solid oxide cell (SOC), the latest advancements in microstructural representation (3D imaging and reconstruction) of SOC electrodes are reviewed, applied to the quantification of triple-phase boundary (TPB) lengths and morphology evolution over time. The intrinsic degradation processes in the negative (fuel)This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Multiscale modelling potentialities for solid oxide fuel cell performance and degradation analysis

“…Referring to the most severe degradation processes, a local-level simulation was carried to evaluate the performance failure of an anode supported cell due to anodic Ni agglomeration and Cr poisoning at cathodic active sites in the case of poorly working interconnect barrier layers. 9 Following both experimental and theoretical observations, 23,55 the agglomeration of the Ni–YSZ electrode was modelled using a power law type formulation (eqn (5)). r Ni n ( t ) − r Ni n ( t 0 ) = k ( T ) × (1 − exp − λt )where r Ni is the Ni radius within the cermet, t is the observation time, and n , k and λ are the empirical parameters ( k depends on the temperature).…”

“…5, where main differences between an isothermal and a non-isothermal cell behaviour are reported for 1023 K and 1123 K anodic and cathodic gas inlet temperatures as examples. According to experimental observations, 9 the temperature is one of the main degradation source as conrmed by model results where ∼10-15°increase on the cell plane due to the exothermic reaction was sufficient to have a non-negligible higher performance worsening. For instance, on feeding gas at 1123 K, DR h act changed from 25 V% kh −1 to 29 V% kh −1 for the anodic side and from 9 V% kh −1 to 10 V% kh −1 for the cathodic side, comparing isothermal and nonisothermal results.…”

“…Note that modelled results referred to an ideal case where only Ni-agglomeration and Cr deposition were considered, here these values could not be validated on reference experimental tests where other mechanisms are also observed, such as interconnect oxidation, electrolyte phase transition, secondary phase formation, crack development and layer delamination. 9,20,62 However, their addition went beyond the aim of this work which wanted to show the relevance of the variable local control in having an effective prediction of commercial-scale cells as well as of the simulation being a support for experimental activities where the isolation of single processes is quite difficult when a full cell is tested. Assuming a 1000-h working cell with a gas inlet temperature of 1023 K at both sides, the simulation allowed the estimation of performance worsening as a function of the Ni particle and Cr deposition increase.…”

“…8 This limit derives from significant microstructural variations which involve electrodes as well as interconnects and, to a lesser extent, the electrolyte. 9 Indeed, the state-of-the-art anode consists of a Ni–YSZ (Yttria Stabilized Zirconia) cermet, where the hydrogen reacts at the Triple Phase Boundary (TPB) sites, namely the active zones characterised by the contemporaneous presence of an electron conductor ( i.e. , the metal), an ionic conductor ( i.e.…”

“…8 This limit derives from signicant microstructural variations which involve electrodes as well as interconnects and, to a lesser extent, the electrolyte. 9 Indeed, the state-of-the-art anode consists of a Ni-YSZ (Yttria Stabilized Zirconia) cermet, where the hydrogen reacts at the Triple Phase Boundary (TPB) sites, namely the active zones characterised by the contemporaneous presence of an electron conductor (i.e., the metal), an ionic conductor (i.e., the ceramic) and the gas phase to favour reactant transport. Ni permits the achievement of excellent performance due to its good catalytic activity and electron conductivity, on the other hand this metal becomes unstable under long-lasting operation with observed agglomeration and migration.…”