Facile Proton Transport in Ammonium Borosulfate—An Unhumidified Solid Acid Polyelectrolyte for Intermediate Temperatures

Abstract

metal-organic frameworks (MOFs), [12-18] and finally covalent organic frameworks (COFs). [19-23] Typically, solid acids display high proton conductivity above a superprotonic transition temperature occurring at >135 °C, [8] but are virtually insulating at lower temperatures, and are often susceptible to degradation under operating conditions. [9] Impregnated organic polymers such as PBI-H 3 PO 4 generally operate at 150-200 °C and show good fuel tolerance, but suffer from acid leaching. [11] Development of CP/MOF electrolytes has led to the discovery of a number of materials that exhibit proton conductivities of 10-100 mS cm −1 under conditions that require active humidification; however, materials that operate under anhydrous conditions are uncommon. [24] Here, we present the discovery that ammonium borosulfate, NH 4 [B(SO 4) 2 ], a solid acid coordination polymer, is a good ionic conductor at modest temperatures (100-200 °C), without active humidification (ambient, <2.5 % RH). As a condensed salt of the molecular superacid H[B(HSO 4) 4 ], its crystal structure presents an infinite, hydrogen-bonded NH•••O•••HN network between interstitial NH 4 + cations and 1D anionic chains of 1 ∞ [B(SO 4) 4/2 ] − that upon initial examination appears promising for long-range proton transfer. [25] According to previously reported calculations of borosulfate pK a values, NH 4

High Enhancement in Proton Conductivity by Incorporating Sulfonic Acids into a Zirconium-Based Metal–Organic Framework via “Click” Reaction

“…Thermogravimetric analyses (TGA) of the all samples were then carried out to check their thermal stabilities and the results revealed that the click postmodified UiO-66-SO 3 H as all other samples shows a high thermal stability under the operating temperature (usually below 150 °C) of PEM fuel cells (Figure S2). − After the sample of the click postmodified UiO-66-SO 3 H was soaked in hot water for 24 h, PXRD measurements were also performed to check their humidity stabilities and the measurement results showed that the PXRD profiles are still consistent well with that of the UiO-66 (Figure a), indicating the frameworks are maintained after water soaking. The TGA and PXRD measurements revealed that the click modified UiO-66-SO 3 H show high thermal and humidity stabilities under the operating conditions of PEM fuel cells.…”

“…Massive greenhouse-gas emissions from the consumption of traditional restricted carbon-based fuels have led to severe environmental issues. Hydrogen has been considered as clean and sustainable energy carriers to replace fossil energy and permanently solve these issues. , With hydrogen as fuel, the proton-exchange-membrane (PEM) fuel cell has been developed, which can directly convert the chemical energy of hydrogen to electricity in high efficiency with nearly zero-emission. − Proton conductivity of proton-exchange membranes plays a key role in the overall performance of the PEM fuel cells. − Various materials, such as inorganic and organic sulfate salts, − tungstate clusters, − graphynes, , and the porous organic polymer (POPs) or covalent organic frameworks (COFs), − have been synthesized and tested as PEM candidates in the fuel cells. Although among these diverse promising candidates, Nafion, a perfluorinated sulfonated organic polymer, has been already commercial available, − fabricating robust proton-conductive electrolytes with higher proton conductivity and long-life reusability for the application in the technology of PEM fuel cells still a long-term and arduous task toward the worldwide scientists.…”

Polycations Stabilised by Borosulfates: [Au3Cl4][B(S2O7)2] and the One‐Dimensional Metal [Au2Cl4][B(S2O7)2](SO3)

“…Synthesis of [Au 3 Cl 4 ][B(S 2 O 7 ) 2 ] and [Au 2 Cl 4 ][B(S 2 O 7 ) 2 ](SO 3 ): AuCl 3 (30 mg (0.1 mmol), synthesised according to ref. [1]) and H 3 BO 3 (75 mg (1.21 mmol), Carl Roth, Karlsruhe, Germany, ≥99.8 %) were loaded into a thick‐walled glass ampoule ( l =200 mm, ø=16 mm, thickness of the tube wall=1.8 mm) and attached to a specially designed apparatus for the generation, handling and titration of SO 3 under inert atmosphere. To generate SO 3 , Oleum (20 % SO 3 , Sigma–Aldrich) was added dropwise to an excessive amount P 4 O 10 (97 %, Merck).…”

“…In recent years, interest in borosulfates has been growing steadily, not only due to their structural versatility but also for their potential applications in the fields of solid acid electrolytes [1] and materials with nonlinear optical properties [2] . The anionic substructures of conventional borosulfates are similar to silicates and consist of vertex connected (BO 4 ) and (SO 4 ) tetrahedra.…”

Ag[B(S2O7)2]: The First Transition Metal Borosulfate Featuring Disulfate Groups

“…Besides the structural evolution, especially optical properties were investigated showing a weak coordination behavior of the borosulfate anions [3–5] or even second harmonic generation responses [6] . A striking prospect for borosulfate chemistry, however, could be as electrolytes for solid acid fuel cells, since a high proton conductivity for the ammonium borosulfates NH 4 [B(SO 4 ) 2 ] was reported, recently [7] . Next to proton conductivity, theoretical calculations on solid state Li‐ion conductors revealed Li 5 [B(SO 4 ) 4 ] as a potential fast‐ion conductor [8] .…”