3D Printing of Functional Layers for Solid Oxide Fuel Cells and Electrolysers

Energy conversion efficiencies of solid oxide fuel cells (SOFCs) and electrolysers (SOEs) can be increased, principally by increasing the density of triple phase boundaries (electrode | electrolyte | reactant gas in pores) where reactions occur. SOFCs and SOEs with infiltrated-scaffold composite electrode structures have been shown to have greater densities of triple phase boundaries (TPBs), and enhanced control of particle size and porosity compared with structures derived from powder mixing ^[1]. However, methods that fabricate reproducible and explicitly tailored scaffolds with micrometre length scales have yet to be reported. Hence, we are developing 3D inkjet printing, using a Ceradrop X-Series inkjet printer with three multi-nozzle print heads, to fabricate reproducible, structured ceramic frameworks with ca. 5 µm resolution, prior to sintering. Ultimately, this should enable fabrication of percolated (porous) cathode | (non-porous) electrolyte | (porous) anode structures much more reproducibly and with greater definition than hitherto, to achieve increased energy conversion performances. The reproducible geometries will also enable more facile comparison of experimental performance and model predictions ^[2].

One prerequisite is the development of stable dispersions (‘inks’) of sub-micrometre sized metal oxide particles (i.e. (ZrO₂)_0.92(Y₂O₃)_0.08, NiO, La_1-xSr_xMnO_3-δ) in liquid phases with suitable solids fractions and physical properties, for which results will be presented (Fig.1a). These inks have been used to print the functional layers of SOFCs/SOEs (Fig.1b). However, geometries of electrode | electrolyte structures are subject to limitations imposed by the requirement to minimise the spatial distributions of potential and current densities. Hence, results will also be presented for predictions (Fig.2) of those parameters, modelled using finite element software, and preliminary current density-potential difference data for a printed SOE.

Firstly, yttria-stabilized zirconia (YSZ) particles were deposited onto a planar YSZ | NiO substrate, as pre-cursors to a thin (ca. 10 µm), gas-tight electrolyte, formed by heating the green structure to ca. 500°C to burn out organics used to stabilise ink particles against aggregation, followed by sintering YSZ at ca. 1400°C. Subsequently, YSZ and NiO nanoparticles were co-printed with an organic polymer to fabricate porous electrode structures on non-porous YSZ electrolyte layers.

Reference

1. M. Kishimoto, M. Lomberg, E. Ruiz-Trejo, N.P. Brandon, Enhanced triple-phase boundary density in infiltrated electrodes for solid oxide fuel cells demonstrated by high-resolution tomography, J. Power Sources, 266 (2014) 291-5.
2. U. Doraswami, P. Shearing, N. Droushiotis, K. Li, N.P. Brandon and G.H. Kelsall, Modelling the Effects of Measured Anode Triple-Phase Boundary Densities on the Performance of Hollow Fiber SOFCs, Solid State Ionics, 192 (2011) 494–500.