Unique Proton Transportation Pathway in a Robust Inorganic Coordination Polymer Leading to Intrinsically High and Sustainable Anhydrous Proton Conductivity

• Published in: Journal of the American Chemical Society Vol. 140; no. 19; pp. 6146 - 6155
• Main Authors: Gui, Daxiang, Dai, Xing, Tao, Zetian, Zheng, Tao, Wang, Xiangxiang, Silver, Mark A, Shu, Jie, Chen, Lanhua, Wang, Yanlong, Zhang, Tiantian, Xie, Jian, Zou, Lin, Xia, Yuanhua, Zhang, Jujia, Zhang, Jin, Zhao, Ling, Diwu, Juan, Zhou, Ruhong, Chai, Zhifang, Wang, Shuao
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16.05.2018
• Subjects: ammonium; coordination polymers; electric power; encapsulation; fuel cells; hydrogen bonding; molecular dynamics; neutrons; nuclear magnetic resonance spectroscopy; phosphates; power generation; protons; simulation models; X-ray diffraction; zirconium
• DOI: 10.1021/jacs.8b02598
• ISSN: 0002-7863; 1520-5126

Although comprehensive progress has been made in the area of coordination polymer (CP)/metal–organic framework (MOF)-based proton-conducting materials over the past decade, searching for a CP/MOF with stable, intrinsic, high anhydrous proton conductivity that can be directly used as a practical electrolyte in an intermediate-temperature proton-exchange membrane fuel cell assembly for durable power generation remains a substantial challenge. Here, we introduce a new proton-conducting CP, (NH4)3[Zr­(H2/3PO4)3] (ZrP), which consists of one-dimensional zirconium phosphate anionic chains and fully ordered charge-balancing NH4 + cations. X-ray crystallography, neutron powder diffraction, and variable-temperature solid-state NMR spectroscopy suggest that protons are disordered within an inherent hydrogen-bonded infinite chain of acid–base pairs (N–H···O–P), leading to a stable anhydrous proton conductivity of 1.45 × 10–3 S·cm–1 at 180 °C, one of the highest values among reported intermediate-temperature proton-conducting materials. First-principles and quantum molecular dynamics simulations were used to directly visualize the unique proton transport pathway involving very efficient proton exchange between NH4 + and phosphate pairs, which is distinct from the common guest encapsulation/dehydration/superprotonic transition mechanisms. ZrP as the electrolyte was further assembled into a H2/O2 fuel cell, which showed a record-high electrical power density of 12 mW·cm–2 at 180 °C among reported cells assembled from crystalline solid electrolytes, as well as a direct methanol fuel cell for the first time to demonstrate real applications. These cells were tested for over 15 h without notable power loss.