Protonic ceramic electrochemical cells hold the promise to be operated below 600 o C 1,2 . Although the high proton conductivity of the bulk electrolyte has been demonstrated, it cannot be fully utilized in electrochemical full cells due to unknown causes 3 . Here we showed that it all comes from poor contacts between the low-temperature processed oxygen electrode-electrolyte interface.We demonstrated that a simple acid treatment can effectively rejuvenate the high-temperature annealed electrolyte surface, resulting in reactive bonding between the oxygen electrode and the electrolyte and improved electrochemical performance and stability. This enables exceptional protonic ceramic fuel-cell performance down to 350 o C, with peak power densities of 1.6 W cm −2 at 600 o C, 650 mW cm −2 at 450 o C, and 300 mW cm −2 at 350 o C, as well as stable electrolysis operations with current densities above 3.9 A cm −2 at 1.4 V and 600 o C. Our work highlights the critical role of interfacial engineering in ceramic electrochemical devices and offers new understanding and practices towards sustainable energy infrastructure.

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The key challenge for high-performance sodium-ion batteries is the exploitation of appropriate electrode materials with a long cycling stability and high rate capability. Here, we report SbS nanoparticles (∼5 nm) uniformly encapsulated in three-dimensional (3D) porous graphene foam, which were fabricated by a facile hydrothermal coassembly strategy, as a high-performance anode material for sodium-ion batteries. The as-prepared composite can be directly used as electrodes without adding a binder or current collector, exhibiting outstanding electrochemical performance with a high reversible capacity (845 mA h g at 0.1 A g), ultralong cycling life (91.6% capacity retention after 300 cycles at 0.2 A g), and exceptional rate capability (525 mA h g at 10.0 A g). This is attributed to fast Na ion diffusion from the ultrasmall nanoparticles and excellent electric transport between the active material and 3D porous graphene, which also provide an effective strategy for anchoring the nanoparticles. Experimental results show that the SbS undergoes a reversible reaction of SbS + 16Na ↔ 5NaS + 2NaSb during sodiation/desodiation. Moreover, a full cell with Na(VO)(PO)F/C cathode and the as-prepared composite anode was assembled, displaying high output voltage (∼2.2 V) with a stable capacity of 828 mA h g for anode material (with 100 cycles at 0.1 A g), showing the potential for practical application.

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