S1 Supporting Information Solvent-Assisted Modification to Enhance Proton Conductivity and Water Stability in Metal Phosphonates Zhenni Que, † Yingxiang Ye, † Yisi Yang, † Fahui Xiang, † Shimin Chen, † Jiali Huang, † Yunbin Li, † Chulong Liu,* ,† Shengchang Xiang, †,‡ and Zhangjing Zhang* ,†,‡ † Fujian Provincial Key Laboratory of Polymer Materials, College of Chemistry and Materials Science, Fujian Normal University, 32 Shangsan Road, Fuzhou 350007, PR China ‡ State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, 350002, People’s Republic of China Corresponding authors E-mail: liucl@fjnu.edu.cn; zzhang@fjnu.edu.cn.