Visualization of the diffusion pathway of protons in (NH4)2Si0.5Ti0.5P4O13 as an electrolyte for intermediate temperature fuel cells

Sun, C; Chen, L; Shi, S; Reeb, B; Lopez, CA; Alonso, JA; Stimming, U

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

Lookup NU author(s): Professor Ulrich Stimming

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Abstract

We demonstrate that (NH₄)₂Si_0.5Ti_0.5P₄O₁₃ is an excellent proton conductor. The crystallographic information concerning the hydrogen positions is for the first time unraveled from neutron powder diffraction (NPD) data. This study shows that all the hydrogen atoms are connected though H-bonds, establishing a two-dimensional path between [(Si_0.5Ti_0.5)P₄O₁₃^2-]_n layers for the 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 ^oC and 250 ^oC, respectively. This finding demonstrates that (NH₄)₂Si_0.5Ti_0.5P₄O₁₃ is a promising electrolyte material operating at 150-250^oC. This work opens up a new avenue for designing and fabricating high-performance inorganic electrolytes.

Publication metadata

Author(s): Sun C, Chen L, Shi S, Reeb B, Lopez CA, Alonso JA, Stimming U

Publication type: Article

Publication status: Published

Journal: Inorganic Chemistry

Year: 2018

Volume: 57

Issue: 2

Pages: 676-680

Print publication date: 16/01/2018

Online publication date: 02/01/2018

Acceptance date: 20/12/2017

Date deposited: 21/12/2017

ISSN (print): 0020-1669

ISSN (electronic): 1520-510X

Publisher: American Chemical Society

URL: https://doi.org/10.1021/acs.inorgchem.7b02517

DOI: 10.1021/acs.inorgchem.7b02517

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