A synergistic dual-phase air electrode enables ultrahigh and durable performance of reversible proton ceramic electrochemical cells

Abstract

Abstract Reversible proton ceramic electrochemical cells (R-PCECs), as solid-state ion devices capable of efficient power generation and energy storage in the medium temperature range, are expected to transform the global pattern of over-dependence on fossil fuels. A major obstacle to their commercial application is the lack of suitable air electrodes that can function effectively and stably in both fuel cell and electrolysis modes. Here, we report a novel triple-conducting (e−/O2−/H+) hybrid electrode, composed of a cubic perovskite phase Ba0.5Sr0.5Co0.8Fe0.2O3−δ and a hexagonal phase Ba4Sr4(Co0.8Fe0.2)4O16−δ, which may meet the stringent requirements of R-PCECs in terms of activity, conductivity, and durability as an air electrode. Specifically, the corresponding single cell achieves an exciting current density of 3.73 A cm− 2 @ 1.3 V in electrolysis mode and an ultrahigh peak power density of 1.99 W cm− 2 in fuel cell mode at 650°C. Such hybrid electrode can be facilely created through tuning the ratio of A-site to B-site element contents in (Ba0.5Sr0.5)xCo0.8Fe0.2O2+x−δ precursor. In contrast to the widely applied method of creating self-assembled hybrids by breaking through material tolerance limits, the strategy of adjusting the stoichiometric ratio of the A-site/B-site not only allows for strong interactions and correlations between hybrid phases, but also efficiently modifies the phases content. A synergistic effect between the cubic and hexagonal phases presents in the hybrid electrode, which enhances the oxygen reduction and evolution reaction activity and the protonic conductivity and suppresses the thermal expansion, making it outstanding performance in terms of both oxygen activation and durability.