Characteristics and properties of a magnetron sputtered gadolinia-doped ceria barrier layer for solid oxide electrochemical cells

Abstract

Gadolinia-doped ceria (GDC) films are synthesized by direct current magnetron sputtering under reactive conditions for hydrogen production by high temperature electrolysis (HTE). First, the sputtering process is investigated by varying the reactive gas flow rate. Working conditions in elemental sputtering mode (ESM) are adjusted to ensure a high incorporation of oxygen while keeping a high deposition rate. Heat treatments in air are found necessary to stabilize the sub-stoichiometric deposited oxide. The main characteristics of the films (crystallinity, chemical composition, porosity, etc.) are studied by Rutherford backscattering spectroscopy (RBS), optical transmission spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and scratch test and are compared to that of a conventional 2 μm thick GDC layer deposited by screen printing. The sputtered layer appears dense and adherent but kind of blisters are observed when deposited on half-cells. Performances of a thin GDC barrier layer (below 500 nm) sputter deposited on half cells are evaluated. Encouraging results are obtained since performances (i.e. about −1.70 A·cm−2 at 1.3 V and 800 °C in HTE mode) are slightly higher to that typically achieved with a classical manufactured cell (i.e. about −1.65 A·cm−2 at 1.3 V and 800 °C). A degradation rate of about 9% for 1000 h operation (at 800 °C with a current density of −0.5 A·cm−2, GDC layer thickness of 425 nm) is achieved.