Engineers Australia : New cathode material could create fuel cell opportunities

Australian and Chinese researchers have collaborated on research investigating the possible synergistic effects of a new perovskite cathode material for a low-temperature solid-oxide fuel cell.

The team from ANSTO, University of Queensland, Shandong University and Nanjing Tech University have shown that the co-doping of a promising cathode material, strontium cobalt oxide (SrCoO) with niobium (Nb5+) and tantalum (Ta5+), led to improved performance.

Historically, the performance of the cathode in low-temperature solid-oxide fuel cells (LT-SOFC) has been limited by the surface oxygen exchange kinetics of the oxygen-reduction reaction (ORR) as well as the mobility of oxide ion in the bulk.

New cathode materials, which form oxide ions by the reduction of oxygen, have been explored because the low operating temperature of SOFCs results in sluggish kinetics and limits the performance of the battery.

Because the crystal structure of perovskite oxides is not stable below 900°C, they are doped with rare-earth or alkaline-earth elements.

In the study, strontium cobalt oxide was doped with niobium and tantalum to produce the cathode material SrCoNbTaO(SCNT) and isostructural species.

A cubic perovskite structure makes oxygen vacancies in the lattice migrate freely among equivalent oxygen sites.

In SCNT, the niobium and tantalum have the same valence state and very similar ionic radii as the cobalt, and replace some of the cobalt ions.

The researchers believe the niobium and tantalum may be decreasing the energy barrier for oxygen migration, causing the neighbouring cobalt ions to become more active for charge transfer.

A range of other techniques were used in the synthesis of the material, structural characterisation, analysis of conductivity, characterisation of the ORR, and performance.

The SCNT cathode outperformed the other isostructural cathode compositions at and below 500°C and surpassed the target of 500 mW/cm2for SOFCs, suggesting the possibility of operation even below 450°C.

[A schematic of the minimum energy migration pathway for an oxygen vacancy in SCNT. Image: ANSTO]