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

Chunwen Sun; Lanli Chen; Siqi Shi; Berthold Reeb; Carlos Alberto López; José Antonio Alonso; Ulrich Stimming

doi:10.1021/acs.inorgchem.7b02517

Visualization of the Diffusion Pathway of Protons in (NH₄)₂Si_0.5Ti_0.5P₄O₁₃ as an Electrolyte for Intermediate-Temperature Fuel Cells

Inorg Chem. 2018 Jan 16;57(2):676-680. doi: 10.1021/acs.inorgchem.7b02517. Epub 2018 Jan 2.

Authors

Chunwen Sun^{1

2}, Lanli Chen³, Siqi Shi³, Berthold Reeb⁴, Carlos Alberto López⁵, José Antonio Alonso⁶, Ulrich Stimming^{4

7

8}

Affiliations

¹ CAS Center for Excellence in Nanoscience, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences , Beijing 100083, China.
² School of Nanoscience and Technology, University of Chinese Academy of Sciences , Beijing 100049, P. R. China.
³ School of Materials Science and Engineering, Shanghai University , Shanghai 200444, China.
⁴ Bavarian Center for Applied Energy Research (ZAE Bayern) , Division Energy Storage, Walther-Meißner-Straße 6, Garching D-85748, Germany.
⁵ Instituto de Investigaciones en Tecnología Química (INTEQUI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis , Chacabuco y Pedernera, San Luis 5700, Argentina.
⁶ Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas (CSIC) , Cantoblanco, Madrid 28049, Spain.
⁷ School of Chemistry, Bedson Building, Newcastle University , Newcastle upon Tyne NE1 7RU Newcastle, United Kingdom.
⁸ TUM CREATE , 1 CREATE Way, #10-02 CREATE Tower, Singapore 138602, Singapore.

PMID: 29292990
DOI: 10.1021/acs.inorgchem.7b02517

Abstract

We demonstrate that (NH₄)₂Si_0.5Ti_0.5P₄O₁₃ 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 [(Si_0.5Ti_0.5)P₄O₁₃^2-]_n layers for proton diffusion across the crystal structure by breaking and 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)₂Si_0.5Ti_0.5P₄O₁₃ reach 0.0061 and 0.024 S cm^-1 in humid air at 125 and 250 °C, respectively. This finding demonstrates that (NH₄)₂Si_0.5Ti_0.5P₄O₁₃ 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.