Fast ion-conductive electrolyte based on a doped LaAlO₃ with an amorphous surface layer for low-temperature solid oxide fuel cells

Ion transport in solid oxide electrolytes is a key process involved in advanced green energy conversion devices such as solid oxide fuel cells (SOFCs). Conventional SOFC electrolytes require a high operational temperature (over 700 °C) to maintain considerable bulk and grain boundary diffusion of the ions to enable sufficient ionic conductivity for efficient fuel cell operation. The present study explores a novel ion conduction expressway in an amorphous/crystalline heterostructure, La_0·8Sr_0·2Al_0·8Zn_0·2O_3-δ (LSAZ), which can boost the mobility of ions at a relatively low temperature (450–550 °C) for SOFCs. The LSAZ heterostructure includes an insulating perovskite core and a superionic-conducting amorphous surface layer. This electrolyte exhibits a superior conductivity of 0.319 S cm⁻¹ at 550 °C, and it is employed in a SOFC which demonstrates a remarkable performance of 1296 mW cm⁻² at 550 °C, which is 300 times higher than a SOFC with the LSAZ being densified at 1400 °C for 10 h. A superionic conducting amorphous surface layer enriched by high oxygen vacancy defects facilitates ionic conduction along the grain boundary and interfaces between the nanoparticles of LSAZ. Our finding provides an efficient way to design advanced highly conductive electrolytes for solid oxide fuel cells to be operated at reduced temperatures.