A porous crystal family has been explored as alternatives of Nafion films exhibiting super-proton conductivities of ≥10-2 S cm-1 . Here, the proton-conduction natures of a solution-processed film of nanoparticles (NPs) have been studied and compared to those of a Nafion film. A mono-particle film of Prussian-blue NPs is spontaneously formed on a self-assembled monolayer substrate by a one-step solution process. A low-temperature heating process of the densely packed, pinhole-free mono-particle NP film enables a maximum 105 -fold enhancement of proton conductivity, reaching ca. 10-1 S cm-1 . The apparent highest conductivity, compared to previously reported data of the porous crystal family, remains constant against humidity changes by an improved water-retention ability of the film. In our proposed mechanism, the high-performing solution-processed NP film suggests that heating leads to the self-restoration of hydrogen-bonding networks throughout their innumerable grain boundaries.
Keywords: Prussian blue; grain-boundary free proton conduction; metal-organic frameworks; nanoparticles; super-proton conductivity.
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