Three-Dimensional Analysis of Solid Oxide Fuel Cell Ni-YSZ Anode Interconnectivity

Abstract

A method is described for quantitatively analyzing the level of interconnectivity of solid-oxide fuel cell electrode phases. The method was applied to the three-dimensional microstructure of a Ni-Y2O3-stabilized ZrO2 (Ni-YSZ) anode active layer measured by focused ion beam scanning electron microscopy. Each individual contiguous network of Ni, YSZ, and porosity was identified and labeled according to whether it was contiguous with the rest of the electrode. It was determined that the YSZ phase was 100% connected, whereas at least 86% of the Ni and 96% of the pores were connected. Triple-phase boundary (TPB) segments were identified and evaluated with respect to the contiguity of each of the three phases at their locations. It was found that 11.6% of the TPB length was on one or more isolated phases and hence was not electrochemically active.

Fundamentals of electro- and thermochemistry in the anode of solid-oxide fuel cells with hydrocarbon and syngas fuels

“…The exchange current density i 0 is a measure of the electrocatalytic activity of the electrode/electrolyte interface for a given electrochemical reaction. It depends on charge-transfer kinetics (which are generally unknown and not well understood), the concentrations of reactants and products at the TPB, temperature, pressure, and microstructure of the electrode (also unknown, though recent efforts 19,44,[65][66][67][68][69][70] have shed some light on this). Determining the dependence of the exchange current density on reactant and product concentrations from a detailed electrochemical reaction mechanism will reveal the apparent reaction order, which might not always be evident based on a global oxidation reaction.…”

“…Due to the complex microstructure of typical Ni-YSZ cermet anodes, the three phases (i.e., metal, oxide, and pore/gas) are composed of various interconnected networks. 19,68,70 These networks form a highly convoluted structure marked by TPB regions that cannot easily be probed by experiment. Since the TPB is where current-producing reactions occur, exposing this area to study is necessary to make clear the reaction path in the anode.…”

Effective transport properties of the porous electrodes in solid oxide fuel cells

“…The construction of porous heterogeneous media can be based on a mathematical model or statistical correlation [15][16][17][18][19][20][21][22]. Another useful methodology is the reconstruction of a three-dimensional (3D) geometry using information obtained from a series of two-dimensional (2D) micrograph images of the microstructure followed by data image processing approaches [23][24][25][26][27][28][29][30][31]. The medium can, for example, be a random packing of spheres [32][33][34][35][36], a dispersion of particles [37], or a digitized image [17,25,38,39].…”

What Happens Inside a Fuel Cell? Developing an Experimental Functional Map of Fuel Cell Performance

“…Wilson et al [113] were the first to report 3D reconstruction of an SOFC electrode: using a focused ion beam (FIB) technique, the electrode structure can be sequentially milled and imaged to obtain a sequence of 2D images that can be effectively recombined in 3D space. Subsequently, FIB tomography has been more widely adopted for geometrical and modelling studies of a variety of SOFC anode [114][115][116][117][118] and cathode materials. [119][120][121][122] The resolution of conventional X-ray computed tomography (CT) has traditionally limited its application to the study of electrode microstructures.…”