Cross-linked solid-liquid interfaces enable a fast proton transport in the aluminate heterostructure electrolyte

Having a highly-conductive protonic electrolyte is an essential requirement of developing solid ceramic fuel cell (SCFC) operated below 600 °C. Proton transport in solid electrolyte structure occurs via a bulk conduction mechanism in conventional SCFC, which may not be so efficient; therefore we have developed a fast proton conducting NaAlO₂/LiAlO₂ (NAO-LAO) heterostructure electrolyte, achieving the ionic conductivity of 0.23 S cm^-1 thanks to its rich cross-linked solid-liquid interfaces; the SCFC employing this new developed electrolyte showed a maximum power density of 844 mW cm^-2 at 550 °C, and the fuel cell could still operate at even lower temperatures down to 370 °C, although the output reduced to 90 mW cm^-2. The proton-hydration liquid layer promoted the formation of cross-linked solid-liquid interfaces in the NAO-LAO electrolyte, which promoted the construction of solid-liquid hybrid proton transportation channels and effectively reduced polarization loss, leading to high proton conduction at even lower temperatures. This work provides an efficient design approach for developing enabling electrolytes with high proton conductivity for SCFCs to be operated at relatively lower temperatures (300-600 °C) than traditional solid oxide fuel cells which operate above 750 °C.