TY - JOUR A1 - Rautenberg, Max A1 - Bhattacharya, Biswajit A1 - Das, Chayanika A1 - Emmerling, Franziska T1 - Mechanochemical Synthesis of Phosphonate-Based Proton Conducting Metal-Organic Frameworks JF - Inorganic Chemistry N2 - Water-stable metal−organic frameworks (MOFs) with proton-conducting behavior have attracted great attention as promising materials for proton-exchange membrane fuel cells. Herein, we report the mechanochemical gram-scale synthesis of three new mixed-ligand phosphonate-based MOFs, {Co(H2PhDPA)(4,4′-bipy)H2O)·2H2O}n (BAM-1), {Fe(H2PhDPA)(4,4′-bipy) (H2O)·2H2O}n (BAM-2), and {Cu(H2PhDPA)(dpe)2(H2O)2·2H2O}n (BAM-3) [where H2PhDPA = phenylene diphosphonate, 4,4′-bipy = 4,4′-bipyridine, and dpe = 1,2-di(4-pyridyl)ethylene]. Single-crystal X-ray diffraction measurements revealed that BAM-1 and BAM-2 are isostructural and possess a three-dimensional (3D) network structure comprising one-dimensional (1D) channels filled with guest water molecules. Instead, BAM-3 displays a 1D network structure extended into a 3D supramolecular structure through hydrogenbonding and π−π interactions. In all three structures, guest water molecules are interconnected with the uncoordinated acidic hydroxyl groups of the phosphonate moieties and coordinated water molecules by means of extended hydrogen-bonding interactions. BAM-1 and BAM-2 showed a gradual increase in proton conductivity with increasing temperature and reached 4.9 × 10−5 and 4.4 × 10−5 S cm−1 at 90 °C and 98% relative humidity (RH). The highest proton conductivity recorded for BAM-3 was 1.4 × 10−5 S cm−1 at 50 °C and 98% RH. Upon further heating, BAM-3 undergoes dehydration followed by a phase transition to another crystalline form which largely affects its performance. All compounds exhibited a proton hopping (Grotthuss model) mechanism, as suggested by their low activation energy. KW - Mechanochemistry KW - Metal-organic-frameworks KW - Proton conductivity PY - 2022 DO - https://doi.org/10.1021/acs.inorgchem.2c01023 VL - 61 SP - 10801 EP - 10809 PB - ACS Publications AN - OPUS4-55448 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rautenberg, Max A1 - Akhmetova, Irina A1 - Das, Chayanika A1 - Bhattacharya, Biswajit A1 - Emmerling, Franziska T1 - Synthesis and In Situ Monitoring of Mechanochemical Preparation of Highly Proton Conductive Hydrogen-Bonded Metal Phosphonates JF - ACS Omega N2 - Crystalline porous materials are recognized as promising proton conductors for the proton exchange membrane (PEM) in fuel cell technology owing to their tunable framework structure. However, it is still a challenging bulk synthesis for real-world applications of these materials. Herein, we report the mechanochemical gram-scale synthesis of two isostructural metal hydrogen-bonded organic frameworks (MHOFs) of Co(II) and Ni(II) based on 1-hydroxyethylidenediphosphonic acid (HEDPH4) with 2,2′-bipyridine (2,2′-bipy): Co(HEDPH3)2(2,2′-bipy)·H2O (1) and Ni(HEDPH3)2(2,2′-bipy)·H2O (2). In situ monitoring of the mechanochemical synthesis using different synchrotron-based techniques revealed a one-step mechanism – the starting materials are directly converted to the product. With the existence of extensive hydrogen bonds with amphiprotic uncoordinated phosphonate hydroxyl and oxygen atoms, both frameworks exhibited proton conduction in the range of 10–4 S cm–1 at room temperature under humid conditions. This study demonstrates the potential of green mechanosynthesis for bulk material preparation of framework-based solid-state proton conductors. KW - Mechanochemistry KW - Proton conductivity KW - Metal Organic Frameworks PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-577777 DO - https://doi.org/10.1021/acssuschemeng.2c07509 VL - 8 IS - 19 SP - 16687 EP - 16693 PB - ACS Publications AN - OPUS4-57777 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Karafiludis, Stephanos A1 - Bhattacharya, Biswajit A1 - de Oliveira Guilherme Buzanich, Ana A1 - Fink, Friedrich A1 - Feldmann, Ines A1 - ten Elshof, J. E. A1 - Emmerling, Franziska A1 - Stawski, Tomasz T1 - Thermally processed Ni-and Co-struvites as functional materials for proton conductivity JF - Dalton Transactions N2 - We present how mesoporosity can be engineered in transition metal phosphate (TMPs) materials in a template-free manner. The method involves the transformation of a precursor metal phosphate phase, called M-struvite (NH4MPO4·6H2O, M = Mg2+, Ni2+, Co2+, NixCo1−x2+). It relies on the thermal decomposition of crystalline M-struvite precursors to an amorphous and simultaneously mesoporous phase, which forms during degassing of NH3 and H2O. The temporal evolution of mesoporous frameworks and the response of the metal coordination environment were followed by in situ and ex situ scattering and diffraction, as well as X-ray spectroscopy. Despite sharing the same precursor struvite structure, different amorphous and mesoporous structures were obtained depending on the involved transition metal. We highlight the systematic differences in absolute surface area, pore shape, pore size, and phase transitions depending on the metal cation present in the analogous M-struvites. The amorphous structures of thermally decomposed Mg-, Ni- and NixCo1−x-struvites exhibit high surface areas and pore volumes (240 m2 g−1 and 0.32 cm−3 g−1 for Mg and 90 m2 g−1 and 0.13 cm−3 g−1 for Ni). We propose that the low-cost, environmentally friendly M-struvites could be obtained as recycling products from industrial and agricultural wastewaters. These waste products could be then upcycled into mesoporous TMPs through a simple thermal treatment for further application, for instance in (electro)catalysis. KW - Struvite KW - Phosphates KW - Transition metals KW - Proton conductivity PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-575862 DO - https://doi.org/10.1039/D3DT00839H SN - 1477-9226 SP - 1 EP - 13 PB - Royal Society of Chemisty (RSC) CY - London/Cambridge AN - OPUS4-57586 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Karafiludis, Stephanos A1 - de Oliveira Guilherme Buzanich, Ana A1 - ten Elshof, Johan E. A1 - Emmerling, Franziska A1 - Stawski, Tomasz T1 - Recycled transition metal phosphates as functional materials for electrochemistry N2 - In the last decade transition metal phosphates (TMPs) captured major interest due to their high electrochemical activity useful for electrode materials, supercapacitors or batteries. Importantly, TMPs are known to exhibit high proton conductivity of the order of >10-2 -10-5 S/cm from 25°C to temperatures as high as 400°C. The crucial milestone in the research on the applicational use of TMPs in all their varieties is an ability to obtain, explore and optimize different compositions and structures, both crystalline and amorphous. Thus, we elucidate the structures of amorphous and crystalline Ni- and Co phosphate phases, as they develop upon heating. This method relies on the thermal decomposition of a crystalline M-struvite precursor, i.e. NH4MPO4•6H2O (M = Mg, Ni, Co, NixCo1-x etc. Here, coincidently volatile components such as H2O or NH3 degas out of the compound resulting in a phase transformation to amorphous or crystalline metal phosphate phases depending on the reaction conditions. For this we used a suite of advanced methods such as FTIR, FT-RS and synchrotron-based XAS. Ni-struvite transforms to amorphous phases over a broad range of temperatures (90°C < T < 600°C) in which it remains in an octahedral coordination environment. On the other hand, Co-struvite treatment leads to multiple crystalline phases with only small amounts of short-lived amorphous phases. Importantly, the occurring amorphous phases exhibit uniform mesoporous frameworks (2–5 nm wide pore channels, specific surface area of 100 m2g−1 and a pore volume of 0.13 cm3g−1) at low temperatures (<200°C) while the crystalline compounds can be used as proton conductors demonstrating values of >10-4 S/cm at 25°C. Consequently, we investigated the amorphization/evolution of mesoporosity, the proton-conducting properties and the complex local structure with in- and ex-situ approaches during thermal treatment. Additionally, to this low cost, environmentally friendly and simple one pot synthesis, the precursor M-struvites could grow as a recovery product from industrial waste waters. In such a way, they would to a recycling economy of sought-after commodities like phosphorus or transition metals. T2 - E-MRS Spring Conference 2023 CY - Strasbourg, France DA - 29.05.2023 KW - Struvite KW - Transition metals KW - Phosphates KW - Functional materials KW - Mesoporosity KW - Proton conductivity PY - 2023 AN - OPUS4-57587 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -