Luke Sperrin

There is currently a large motivation to lower operating temperatures of solid oxide fuel cells (SOFCs) due to benefits associated with reduced degradation, a reduction in design complexity and cheaper cell components. This is being achieved through using solid electrolytes that exhibit proton conduction between electrodes instead of O anion conduction. In the 1960s, Stotz and Wagner were the first to discover that some oxides could host protons as minor charge carriers. In the 1980s, Iwahara demonstrated that perovskite based materials, already known for oxygen anion conduction, showed proton conductivity. The most promising perovskite-based materials discovered to date include BaZr1-xMxO3-x/2, BaCe1-xMxO3-x/2, and SrCe1-xMxO3-x/2 where M is a large trivalent ion. Generally, the highest conductivity values are obtained for low M3+ substitution levels, typically between 5 and 20%. BaZr1-xYxO3-x/2 has received particular attention over the last few years due to its relatively high proton conductivity and stability under CO2 and H2O atmospheres.
 
The pure BaZrO3 phase crystallizes in a cubic perovskite (ABO3) structure. Yttrium (Y3+) can substitute for zirconium (Zr4+) on the B site, leading to the solid-solution BaZr1-xYxO3-x/2 and oxygen vacancies due to charge compensation. On hydration, the O vacancies formed due to Y substitution are filled by OH groups leading to the chemical formula of BaZr1-xYxO3-x/2-y(OH)2y. Protons then hop between oxygens through the electrolyte resulting in long range protonic conduction.
 
My research focuses on investigating the local structure around the defects by combining experimental NMR with DFT total energy and NMR calculations. A study of local structure should contribute ultimately to an understanding of the high proton conductivities achieved in the hydrated phases. Understanding of the conduction mechanism allows us to discover and design materials with better properties.