Optimizing the Proton Conductivity of Fe-Diphosphonates by Increasing the Relative Number of Protons and Carrier
Xiao-Fan Jiang1, Yu-Juan Ma1, Ji-Xiang Hu1,2
1College of Chemistry and Chemical Engineering, Qingdao University, Qingdao, Shandong 266071, China.
Abstract:
Proton conductive materials have attracted extensive interest in recent years due to their fascinating applications in sensors, batteries, and proton exchange membrane fuel cells. Herein, two Fe-diphosphonate chains (H4-BAPEN)0.5·[FeIII(H-HEDP)(HEDP)0.5(H2O)] (1) and (H4-TETA)2·[FeIII2FeII(H-HEDP)2(HEDP)2(OH)2]·2H2O (2) (HEDP = 1-hydroxyethylidenediphosphonate, BAPEN = 1,2-bis(3-aminopropylamino)ethane, and TETA = triethylenetetramine) with different templating agents were prepared by hydrothermal reactions. The valence states of the Fe centers were demonstrated by 57Fe Mössbauer spectra at 100 K, with a high-spin FeIII state for 1 and mixed high-spin FeIII/FeII states for 2. Their magnetic properties were determined, which featured strong antiferromagnetic couplings in the chain. Importantly, the proton conductivity of both compounds at 100% relative humidity was explored at different temperatures, with 2.79 × 10-4 S cm-1 at 80 °C for 1 and 7.55 × 10-4 S cm-1 at 45 °C for 2, respectively. This work provides an opportunity for improving proton conductive properties by increasing the relative number of protons and the carrier density using protonated flexible aliphatic amines.
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