Optimizing the Proton Conductivity of Fe-Diphosphonates by Increasing the Relative Number of Protons and Carrier Densities

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·[FeIII 2FeII(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.

Hybrid Photochromic Lanthanide Phosphonate with Multiple Photoresponsive Functionalities

“…The maximum value for the conductivity is 2.66 × 10 –4 S cm –1 at 80 °C, and the conductivity increases by twofold with enhanced temperature, indicating that 1 has a valid proton transfer path and its proton conductance exhibits a clear temperature dependence. The conductivity value of 1 is comparable to those of the previously reported TM-HEDP and other metal phosphonate. ,− In order to further study the proton conduction mechanism of 1 , the activation energy ( E a ) was calculated to be 0.174 eV via applying the Arrhenius equation of σ T = σ 0 exp­( E a / kT ) to the conductivity value (Figure S8), which is in line with the typical Grotthuss ( E a < 0.4 eV) mechanism. , …”

Organoamine Templated Multifunctional Hybrid Metal Phosphonate Frameworks: Promising Candidates for Tailoring Electrochemical Behaviors and Size-Selective Efficient Heterogeneous Lewis Acid Catalysis

“…The bulkier 1,4-bis­(3-aminopropyl)­piperazine unit is disordered along with the solvent molecule (DMF) in compound IV . Such disorder of amine molecules is commonly observed in reported amine templated open frameworks. ,,,,− …”

“…Exploration of higher-dimensional and robust multifunctional framework solids through the accumulation of hybrid inorganic–organic building units has been an intriguing topic of intense research over past few decades. , In this area, a large number of various crystalline systems such as metal–organic frameworks (MOFs), coordination polymers (CPs), and polyoxometalates have been usually developed, but hybrid open-framework compounds can also be considered as prominent outcomes equipped with distinguished features such as an easy synthesis process, low-cost preparation, rich structural diversity, tunable porosity, and so forth. − Among the hybrid framework systems, transition metal phosphonates are a well-exploited subclass due to their fascinating structural advantages along with diverse physiochemical properties such as proton conductivity, molecular magnetism, photochromism, catalysis, and so on. − Particularly, the phosphonate-based hybrid open-framework materials often display versatile architectures and interesting topologies through the diverse coordination modes of oxygen-rich organophosphonate molecules as compared to earlier investigated common inorganic network building units such as phosphate, sulfate, thiosulfate, borate, and silicate tetrahedra. − Therefore, numerous research efforts have been made to develop the template-assisted metal phosphonates architectures accompanied by different nitrogen-containing aliphatic or heterocyclic organic linkers over the years. − Nonetheless, the chemistry of template-assisted metal phosphonates is just a beginning theme of research, and there is still rising interest for the search of novel architectures with exciting applications for the open-framework phosphonate-based materials.…”

Charge Separated One-Dimensional Hybrid Cobalt/Nickel Phosphonate Frameworks: A Facile Approach to Design Bifunctional Electrocatalyst for Oxygen Evolution and Hydrogen Evolution Reactions

“…Of late, the advancement of transition-metal-based materials such as oxides, nitrides, sulfides, selenides, hydroxides, phosphides, phosphates, and various composite materials are considered as excellent catalysts for boosting electrochemical water splitting performance by replacing precious platinum/iridium catalysts. − The selection of flexible phosphonate groups along with incorporation of variable templated organoamines in hybrid metal phosphonate structures not only lead to a variety of structures but also serve as charge separators with modulated catalytic activity. − Interestingly, the lower dimensional transition metal phosphonate are often exciting for their strange magnetic behaviors and field-induced transitions. − However, among plentiful stimulating properties of hybrid metal phosphonates, the electrocatalytic water splitting reaction remains less explored so far. − With our continuous effort with metal phosphonates, − herein we have isolated two new hybrid one-dimensional transition-metal phosphonate chain structures with templated TETA through a hydrothermal pathway (i.e., [H 2 TETA]­[M­(H 2 hedp) 2 ]·2H 2 O, where M = Co for I , Ni for II ; H 4 hedp = 1-hydroxyethane-1,1-diphosphonic acid; TETA = triethylenetetramine) for the investigation of their electrochemical behaviors toward OER and HER. The present study not only explores the potential of any low cost bifunctional OER/HER catalyst designed by organophosphonate ligands but also exposes a promising avenue to explore stable, efficient, and precious-metal-free lower-dimensional framework structures as electrocatalysts.…”