An all-lithium-metal-oxides-based low temperature solid oxide fuel cell with triple (H+/O2−/Li+) conducting electrolyte

Abstract

Fast ionic transportation is in high demand for developing low-temperature solid oxide fuel cells (LT-SOFCs). Facing this challenge, a new H+/O2−/Li+ triple conductor is designed in this study from a lithium-metal oxide, spinel Li4Ti5O12 (LTO). First-principle calculation based on density functional theory (DFT) reveals the proton transport barrier in LTO can be as low as 0.37 eV while the barrier for oxygen ion transportation is 0.94 eV. Using the designed LTO as the electrolyte and a typical cathode of lithium-ion battery, LiNi0.8Co0.15Al0.05O2-δ, as the symmetrical electrodes, an all-lithium-metal-oxides-based LT-SOFC is constructed. High performance is achieved by the SOFC at 550–425 °C, i.e. 625 mW cm−2 at 550 °C, and a low activation energy of 0.60 eV is found with respect to the ionic conductivity of LTO at 550–475 °C. Further study confirms the dual O2−/H+ conduction of LTO via the application of proton and oxygen ion filters as well as the transference number test. Additionally, particular attentions are paid to the transport behavior of Li+ in the cell via a charging process study and from XRD results. The possible contribution of triple conduction on fuel cell performance is discussed. This work demonstrates the great promise of triple H+/O2−/Li+ conducting lithium-metal oxides for LT-SOFC electrolyte development.