Visualization of the Diffusion Pathway of Protons in (NH4)2Si0.5Ti0.5P4O13 as an Electrolyte for Intermediate-Temperature Fuel Cells

STIMMING, ULRICH; REEB, BERTHOLD; SUN, CHUNWEN; LÓPEZ, CARLOS ALBERTO; CHEN, LANLI; ALONSO, JOSÉ ANTONIO; SHI, SIQI

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2018 vol. 57 p. 676 - 680

0020-1669

We demonstrate that (NH4)2Si0.5Ti0.5P4O13 is an excellent proton conductor. The crystallographic information concerning the hydrogen positions is unraveled from neutron-powder-diffraction (NPD) data for the first time. This study shows that all the hydrogen atoms are connected though H bonds, establishing a two-dimensional path between the [(Si0.5Ti0.5)-P4O132−]n layers for proton diffusion across the crystal structure by breakingand reconstructing intermediate H−O=P bonds. This transient species probably reduces the potential energy of the H jump from an ammonium unit to the next neighboring NH4+ unit. Both theoretical and experimental results support an interstitial-proton-conduction mechanism. The proton conductivities of (NH4)2Si0.5Ti0.5P4O13 reach 0.0061 and 0.024 S cm−1 in humid air at 125 and 250 °C, respectively. This finding demonstrates that (NH4)2Si0.5Ti0.5P4O13 is a promising electrolyte material operating at 150−250 °C. This work opens up a new avenue for designing and fabricating high-performance inorganic electrolytes.