Synergistic dual-phase air electrode enables high and durable performance of reversible proton ceramic electrochemical cells

Reversible proton ceramic electrochemical cells are promising solid-state ion devices for efficient power generation and energy storage, but necessitate effective air electrodes to accelerate the commercial application. Here, we construct a triple-conducting hybrid electrode through a stoichiometry tuning strategy, composed of a cubic phase Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ and a hexagonal phase Ba₄Sr₄(Co_0.8Fe_0.2)₄O_16−δ. Unlike the common 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 achieves strong interactions between hybrid phases, but also can efficiently modifies the phase contents. When operate as an air electrode for reversible proton ceramic electrochemical cell, the hybrid electrode with unique dual-phase synergy shows excellent electrochemical performance with a current density of 3.73 A cm⁻² @ 1.3 V in electrolysis mode and a peak power density of 1.99 W cm⁻² in fuel cell mode at 650 °C.