Effects of Electronic and Ionic Conductivities of Layered Perovskites on Solid Oxide Electrolyser Performances

Abstract

The climate change crisis is causing an exponentially increase in demand for green hydrogen. When run in electrolysis mode, solid oxide electrochemical reactors (SOERs) are one of the systems that can generate green hydrogen with high efficiencies, due to their high operating temperatures. In SOERs, the rate-determining steps for the overall reaction come from oxygen reduction (ORR) in fuel cell mode and oxygen evolution (OER) in electrolyser mode. For the enhancement of catalytic activity for ORR/OER, recent studies have been focused on layer perovskite materials for positive electrodes to increase SOER performances. The distinctive arrangement of cations in their structures leads to higher oxygen vacancy concentrations, thereby promoting catalytic activity for ORR/OER.We shall report OER kinetics of two layered perovskites: PrBaCo1.6Fe0.4O5+δ (PBCF) and NdBaCo1.6Fe0.4O5+δ (NBCF) which have been studied as materials exhibiting major differences in oxide ion and electronic conductivities. Electrolyser performances were determined of both water vapour (→2H2 + O2) and CO2 (→2CO + O2), on which the effects were investigated of those differences in ionic / electronic conductivities. For water vapour electrolysis at the thermoneutral potential difference of 1.285 V, the current density was 144 mA cm-2 at 700 ℃ for the cell with a PBCF positive electrode, which exhibited current densities 1.42 times higher than for the cell with a NBCF positive electrode, for reasons we shall explain.