Engineering of B-Metal Exsolution for High Performance Anode Materials in Solid Oxide Fuel Cells

Abstract

B-metal exsolution has great potential to synthesize well-distributed metal nanoparticles (NPs) on the surface of oxide support materials. In previous works, we found the different exsolution tendencies of different kinds of transition metals on double-layered PrBaMn2O5+δ (L-PBMO). In particular, the exsolved NPs showed higher catalytic activity and stability for fuel oxidation, such as dry reforming of methane. To further engineer that concept, we have explored the possibility and detailed mechanism for various kinds of B-metal exsolution on L-PBMO. Based on our density functional theory (DFT) results, we will introduce (1) a possible driving force for B-metal NPs exsolution, (2) thermodynamically favorable mechanism for alloy NPs exsolution, and (3) how to boost B-metal exsolution to further improve cell performance SOFCs with the experimental verifications.In addition to L-PBMO, we also introduce the bond length of B-metal (Co) with lattice oxygen in perovskite structure (Co-doped SrTiO3, STC) as a key descriptor to represent the degree of Co exsolution on STC. Interestingly, we found that the Co exsolution can be facilitated under biaxial tensile strain (larger bond length of Co-O). By examining the bond length of Co-O under different strain states, we demonstrated that the weaker bond strength of Co-O is originated from the larger bond length of Co-O under tensile strain. This results in easier bond breaking between Co and O, thereby facilitating Co exsolution. To confirm our hypothesis (controlling Co-O bond length), we doped the larger ionic radius of A-site cation (Ba) into Sr in STC to induce tensile strain around Co. As we expected, the exsolution of Co is more preferred than than of Ba on STO, which is a more practical way to induce tensile strain than the mechanically applied strategy. As an application of exsolved Co NPs, we showed enhanced catalytic activity for CO oxidation.