Electrolyzer and fuel cells based on proton-conducting solid oxides (PC-SOEC/FC) are gaining ground in the energy conversion scenario, thanks to fast proton diffusion rates at convenient operating temperatures. However, current performances are curbed by severe limitations of common electrodes [1]. Within this context, here we outline the latest work of our group on the rational design of innovative electrode materials for PC-SOEC/FC applications. With first-principles methods we aimed at providing unbiased explanations and predictions of materials properties and functions, so to assess new design principles based on quantum mechanics.

The desired electrode materials for PC-SOEC/FCs should pair mixed proton/electron conductive (MPEC) features to good catalytic activity. We followed two design strategies: induction of proton conduction to mixed ion-electron conductors to obtain triple conducting oxides [2] or induction of electronic conduction on well-known proton conductor materials [3]. To this end, in bulk solids we evaluated oxygen vacancy formation and water uptake enthalpies, and we characterized the minimum-energy path for proton migration and the corresponding barrier heights. Then, we investigated the catalysis associated to the four proton-coupled electron transfer processes for the oxygen evolution reaction (OER) and reverse oxygen reduction reaction (ORR) at the electrode surfaces. Our calculations revealed the structural and electronic features than are needed for an effective bifunctionality towards the OER and ORR.

Our findings can trigger the targeted experimental synthesis and testing of new single-phase electrodes and can enable the deployment of reversible proton-conducting SOEC/FC devices. Moreover, our analysis can be exploited for the rational design of bifunctional electrocatalytic systems with similar key characteristics.

[1] L. Bi, S. Boulfrad, and E. Traversa, Chem. Soc. Rev. 43 (2014) 8255.

[2] A. B. Muñoz-García and M. Pavone, Chem. Mater. 28 (2016) 490

[3] A. B. Muñoz-García, M. Tuccillo, and M. Pavone, J. Mater. Chem. A 5 (2017) 11825