Inkjet printing for solid oxide electrochemical reactors

The increasing reliance of electricity grids globally on intermittent renewable energy resources necessitates large-scale energy storage to balance supply and demand. This could be achieved by converting surplus electrical energy into chemical bonds, and sequentially vice versa, using high-temperature, reversible solid oxide electrochemical reactors (SOERs). However, SOER performances are limited by irreproducible and unpredictable electrode microstructures when fabricated by conventional composite powder-mixing. Hence, this project aimed to test the hypothesis that inkjet printing, a potentially more environmentally benign fabrication technique, could achieve geometrically reproducible SOER microstructures with predictable, and ultimately enhanced, electrochemical performances. Aqueous-based colloidally stable and printable inks were developed for the conventional SOER materials: yttria-stabilised zirconia (YSZ), gadolinium-doped ceria (CGO), lanthanum strontium manganite (LSM), and NiO. Inkjet-printed LSM deposits from the aqueous-based ink were destroyed by heat treatment, so a butanol-based LSM ink formulation was developed. Inkjet-printed YSZ electrolytes for the SOER: CO/CO2|Ni-YSZ|YSZ (printed)|YSZLSM|LSM|O2 achieved 0.78 A cm-2 at 809 C in electrolysis mode, a performance comparableto that with electrolytes fabricated by powder-mixing. Inkjet printed composite YSZ-LSM electrodes resulted in enhanced electrochemical performances compared to conventionally fabricated electrodes in fuel cell and electrolyser modes with H2 and CO/CO2, respectively; at 788 C, a fuel cell peak power density of 0.69 W cm-2 and an electrolyser current density of 3.3 A cm-2 at the thermoneutral potential difference of ca. 1.5 V, were achieved. To steer 3D geometries to be printed, spatial distributions of overpotentials, gas compositions, and current densities were predicted using finite element models. Inkjet-printed YSZ pillar arrays with diameter and height of ca. 35 and 140 m, respectively, were subsequently inkjet printed with LSM to fabricate the oxygen-electrodes. Their electrochemical performance was ca. 50 % lower than that of the composite YSZ-LSM electrodes, due to LSM detaching from the electrolyte during sintering. To replace the composite electrode support, NiO and LSM inks were used to fabricate the SOER: Ni(O) (printed)|YSZ|LSM (printed). Electrochemical performance was limited by Ni coarsening, but a YSZ pillar support could solve this problem, enabling future SOERs to be completely inkjet-printed.