Solid Oxide fuel cells (SOFC) require high operating temperatures, typically 800-1000^oC, which can affect the stability and durability of SOFC materials. Because of this, research is being directed towards reducing the operating temperature of SOFCs. A promising answer could be the use of proton-conducting solid oxide fuel cells (H⁺-SOFC), as these devices operate at lower temperatures 500^oC < T < 700^oC.

The search for air electrode (cathode) materials with fast transfer kinetics is an important issue in developing H⁺-SOFCs.  The air electrode plays a critical role in proton conducting fuel cells because the electrochemical reaction that combines protons (H⁺), electrons from the external circuit (which gives the electrical power) and oxygen (from the air) occurs here - producing water as the waste product. Double perovskite oxides possess excellent electrochemical properties correlated with their mixed ionic and electronic conductivity and are being considered as potential cathodes in H⁺-SOFCs .  Their fast oxygen transport kinetics and the high level of oxygen vacancies they can accommodate are needed to allow the dissociation of water molecules and the formation of protonic defects, however the presence of structural protons in these systems has not yet been demonstrated.

In situ neutron diffraction data collected on the high-flux POLARIS diffractometer at ISIS exploited the sensitivity of neutron diffraction to light atoms to determine atomic positions and site occupancies. The double perovskites NdBaCo_2-xMn_xO_5+δ (x = 0 and 0.5) were investigated using high temperature neutron powder diffraction in dry argon and wet atmospheres. This enabled researchers to search for the presence of protons, monitor the oxygen vacancy formation and assess the stability and structural behaviour of NdBaCo_2-xMn_xO_5+δ under operating conditions consistent with cathodes in H⁺-SOFCs.

Chloe Johnson and Ron Smith

Research date: August 2015

Further Information

The full article is available here.

M Bahout, SS Pramana, JM Hanlon, V Dorcet, RI Smith, S Paofai, SJ Skinner. (2015) “Stability of NdBaCo22-xMnxO5+δ (x = 0, 0.5) layered perovskites under humid conditions investigated by high-temperature in situ neutron powder diffraction". J. Mater. Chem. A, 2015, 3, 15420-15431

For more information, please contact Ron Smith.​