Imparting Stable and Ultrahigh Proton Conductivity to a Layered Rare Earth Hydroxide via Ion Exchange

Proton conductors are essential functional materials with a wide variety of potential applications in energy storage and conversion. In order to address the issues of low proton conductivity and poor stability in conventional proton conductors, a simple and valid ion-exchange method was proposed in this study for the introduction of stable and ultrahigh proton conductivity in layered rare earth hydroxides (LRHs). Test analyses by solid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, and powder X-ray diffraction revealed that the exchange of H₂PO₄^- not only does not disrupt the layered structure of LRHs, but also creates more active proton sites and channels necessary for proton transport, thereby creating a high-performance proton conductor (LRH-H₂PO₄^-). By utilizing this ion-exchange method, the proton conductivity of LRHs can be significantly enhanced from a low level to an ultrahigh level (>10^-2 S·cm^-1), while maintaining excellent long-term stability. Moreover, through methodically manipulating the guest ions and molecules housed within the interlayers of LRHs, a comprehensive explanation has been presented regarding the proficient mechanism of proton conduction in LRH-H₂PO₄^-. As a result, this investigation presents a feasible and available approach for advancing proton conductor.