Metal Hydrogen Phosphates Research Articles

Enhancing PA-PBI Composite Membrane with Metal Oxides Incorporation for HT-PEMFC Operating Above 200 oc

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are renowned for their excellent CO tolerance and rapid reaction kinetics [1]. Among the various membrane types, phosphoric acid doped polybenzimidazole (PA-PBI) membranes, phosphoric acd (PA) acts as a proton conductor, facilitating proton transfer through hydrogen bond rearrangement between PA molecules and the PBI backbone [2]. However, the operating temperature of PA-PBI membrane-based HT-PEMFC is constrained by the condensation of PA, limiting their use to below 180 oC and posing a significant challenge for achieving efficient operation above 200 oC.Recent research endeavors have focused on enhancing PA-PBI membranes by incorporating metal oxides to extend their operational temperature range beyond 180 oC. The addition of metal oxides into PA solution leads to the formation of metal hydrogen phosphate, effectively preventing PA evaporation at elevated temperatures ( > 180 oC) and maintaining membrane performance without degradation. Furthermore, the presence of metal oxides facilitates proton transfer to the metal hydrogen phosphate surface, thereby improving ionic conductivity even at temperatures exceeding 200 oC.In this study, we present the synthesis of poly(2,2’-(1,4-phenylene)-5,5’ bibenzimidaozle) (pPBI) composite membranes through an in-situ method, where various metal oxides (SnO2, TiO2, ZrO2) are introduced into the synthesis solution. Through systematic investigation, we evaluate the impact of these metal compounds on fuel cell performance and durability at high temperatures exceeding 200 oC. Our findings shed light on the potential of metal oxide-modified PA-PBI composite membranes for advancing the performance and reliability of HT-PEMFCs in demanding operating conditions.

A reactive and environmentally friendly protocol for expeditious synthesis of various resorcinarenes using zinc hydrogen sulfate

ABSTRACTIn this work, for the first time, metal hydrogen phosphates and sulfates have been studied as effective solid acid catalysts for the condensation of resorcinol with aromatic and aliphatic aldehydes to give tetrameric cyclic products, resorcinarenes, which have major roles in biological and industrial activities. This catalyst has several advantages, it is non-toxic, thermally and mechanically stable, inexpensive and highly resistant against organic solvents. It increases the reaction rate about six fold and makes this method an attractive alternative to the existing methods for resorcinarene formation. Interestingly, the present catalyst exhibited a high turnover number (TON) and turnover frequency (TOF) which were even comparable with that of HCl.

Gas-phase dehydration of glycerol to acrolein catalyzed by hybrid acid sites derived from transition metal hydrogen phosphate and meso-HZSM-5

The dehydration of glycerol to acrolein is a useful approach for the value-added conversion of bio-diesel derived glycerol. To improve the acrolein yield, the transition metal hydrogen phosphates/meso-HZSM-5 hybrid catalysts were synthesized and examined for glycerol dehydration. The commercial HZSM-5 firstly treated with alkaline for introducing mesoporosity and investigated the glycerol dehydration over the various composite catalysts prepared by monohydrogen phosphates (CuHPO4, Mo1/3HPO4, ZnHPO4, NiHPO4, MnHPO4) supported on meso-HZSM-5. The hybrid catalysts presented for improvement of strong acid sites and acrolein yield. Additionally, the studies on the hydrogen number in nickel-hydrogen phosphates demonstrated that the NiHPO4/meso HZSM-5 exhibited higher acrolein yield than Ni3/2PO4/meso-HZSM-5 and Ni1/2H2PO4/meso-HZSM-5 catalyst systems. The activities of the composite catalysts significantly influenced by the pore characteristics of support, types of transition metal hydrogen phosphates, amount and strength of acid sites. The proper arrangement of hybrid catalyst with strong Lewis acid sites is a viable and effective method for design functional solid acid catalyst and develops their catalytic performance in glycerol dehydration to acrolein.

Reclamation of phosphorus from aqueous solutions as alkaline earth metal phosphate in a fluidized-bed homogeneous crystallization (FBHC) process

This investigation studies the crystallization of alkaline earth metal phosphates (Me-PO4, Me=Mg, Ca, Sr, Ba) to recover phosphorus (1000 ppm-P) in a fluidized-bed reactor without the addition of seeds. Experimental results showed that the effluent pHe critically determined the phosphorus removal rate (PR%) and crystallization ratio (CR%). The PR%s that were achieved by the generation of Mg, Ca, Sr and Ba-phosphates with an inlet molar ratio [Me]in/[P]in of 2 were 77.8%, 99.4%, 97% and 98.9% at the pHe values exceeded 7.5, 6.6, 7.2 and 6.4, respectively. However, the CR% was strictly optimized by a pHe that transformed the crystalline phases of granular pellets (0.5–2mm in diameter) from metal hydrogen phosphate (MeHPO4) to hydroxyapatite (Me5(PO4)3(OH)), and maximum CR%s of 54.5%, 78.8%, 79.0% and 89.0% were obtained by the generation of Mg, Ca, Sr and Ba-phosphates. According to estimates of aquatic chemistries and supersolubility behaviors in the effluent, a successful FBHC process operated under a supersaturation that was close to the metastable zone. Finally, a reasonable mechanism of the removal of phosphorus by converting the aqueous phosphorus into highly pure metal phosphate pellets was inferred.

Estimation of composition, coordination model, and stability constant of some metal/phosphate complexes using spectral and potentiometric measurements

AbstractComplexation reactions in a binary metal/phosphate system were studied. Protolytic equilibria of phosphate in the presence of cobalt, nickel, iron, copper, chromium and silver metal ions were investigated by potentiometric titrations in the pH range of 2–11. Stability constants of the metal/phosphate complexes were determined by computer analysis of the potentiometric titration. Potentiometric titrations suggest that the presence of metal phosphate and metal hydrogen phosphate provides the solutions with stability constants logK c 2.21, 2.11, 2.23, 2.34, 1.96, and 2.14 of Co, Ni, Fe, Ag, Cr, and Cu/phosphate, respectively. The results of infrared spectroscopy, X-ray powder diffraction and equilibrium studies were used to reveal the mode of interaction between the metal ions and phosphate. Metal phosphates with a hydrogen phosphate anion and fully nonprotonated phosphate could be isolated under the reaction conditions.

Synthesis of MnNiP2O7 and Nonisothermal Decomposition Kinetics of a New Binary Mn0.5Ni0.5HPO4·H2O Precursor Obtained from a Rapid Coprecipitation at Ambient Temperature

The new binary metal hydrogen phosphate monohydrate Mn05Ni0.5HPO4·H2O was synthesized by a rapid and simple coprecipitation method using phosphoric acid, manganese metal, and nickel carbonate at ambient temperature. The kinetics of dehydration of Mn05Ni0.5HPO4·H2O was studied under nonisothermal heating by thermogravimetry (TG), and its final decomposition product was a binary metal pyrophosphate, MnNiP2O7. The activation energies of the dehydration step of Mn05Ni0.5HPO4·H2O were calculated through the isoconversional methods of Ozawa and Kissinger−Akahira−Sunose (KAS), and the possible conversion functions have been estimated through the Coats−Redfern method. The activation energies calculated for the dehydration of Mn05Ni0.5HPO4·H2O by different methods and techniques were found to be consistent. The possible conversion function of the dehydration reaction for Mn05Ni0.5HPO4·H2O was “spherical symmetry” of a “three-dimensional diffusion mechanism”.

Complementarity of optical and incoherent inelastic neutron scattering spectroscopies in the study of proton conducting materials

With the availability of incoherent inelastic neutron scattering (INS) data over spectral ranges comparable to those in optical vibrational (infrared and Raman) spectroscopies, the methods have become truly complementary, and the combination of information they provide particularly suited to the identification of the nature of protonic entities in proton conducting solids. The use of these techniques to recognise the extent of proton transfer to water in strong acid hydrates (e.g. perchloric acid monohydrate), and in layered solid acid hydrates (e.g. aluminium hydrogen sulphate mono- and tetra-hydrates, tin hydrogen phosphate and tungstophosphoric acid hexahydrate) is illustrated, so allowing the spectral fingerprint of oxonium and diaquahydrogen ions to be established. The application of vibrational spectroscopic methods to organic derivatives of layered proton conductors is also shown, with examples including ammonium-, tetramethylammonium- and aniline-exchanged metal hydrogen phosphates.

Oxidation of cerium(III) phosphate by steam in the presence of lithium halides and its use in thermochemical water-splitting cycles

Thermochemical cycles for water splitting employ thermal energy to drive a cyclic series of chemical reactions, the sum of which is just H/sub 2/O + thermal energy = H/sub 2/ + 1/2 O/sub 2/. It was shown previously that cerium (IV) oxide, CeO/sub 2/, reacts with alkali metal hydrogen phosphates - MH/sub 2/PO/sub 4/ or M/sub 2/HPO/sub 4/, where M = Li, Na, K - at > 600/sup 0/C to produce O/sub 2/(g), cerium(III) phosphate, CePO/sub 4/, and alkali metal orthophosphates, M/sub 3/PO/sub 4/. When M = Na or K, the double phosphate M/sub 3/Ce(PO/sub 4/)/sub 2/ forms from the CePO/sub 4/ and the M/sub 3/PO/sub 4/. In seeking ways to use these reactions in thermochemical cycles, it was discovered that steam will oxidize CePO/sub 4/ to CeO/sub 2/ in the presence of lithium halides - LiX, where X = Cl, Br, I - according to the following reaction: 2CePO/sub 4/(c) + 6LiX(c,l) + 4H/sub 2/O(g) = 2CeO/sub 2/(c) + 2LiPO/sub 4/(c) + 6HX(g) + H/sub 2/(g), (c), (l), and (g) refer respectively to the states crystalline, liquid, and gaseous. This paper describes studies of this reaction and its use in thermochemical cycles based on the Ce(IV)/Ce(III) redox couple.

Infra-red and proton magnetic resonance spectra of solid substances containing very short hydrogen bonds

According to the type of spectra obtained, the substances investigated are divided into two groups. The infra-red spectra of the first group are characterized by the presence of two OH stretching bands in the region 3000 to 1900 cm −1 separated by 300 to 500 cm −1. The PMR signals are strong and narrow (3–5 G) at room temperature and slightly broader at −180°. To this group belong some metal hydrogen phosphates, arsenates, periodates, phthalates and p-nitrobenzoates. The i.r. spectra of the second group are characterized by the absence of the OH stretching band in the region above 1800 cm −1. The PMR signals are narrow and weak or very weak at room temperature and remain essentially unchanged at low temperature. To this group belong potassium hydrogen bisphenylacetate, bisbenzoate, sodium sesquicarbonate and potassium hydrogen maleate. The latter compound shows a particularly weak signal. These experimental results are interpreted in terms of a potential function for the proton motion having two minima of potential energy separated by a barrier of different size in each of the two groups. In the first one, the barrier is sufficiently small to allow for the tunnelling of protons with subsequent splitting of vibrational levels. With regard to PMR such a function results in a short correlation time which is temperature independent at low temperature when the proton is tunnelling at the lowest vibrational level. In the second group the potential barrier is vanishingly small, the hydrogen bond approaching the symmetrical type. The OH stretching frequency becomes small and the characteristic property of the vibration is lost owing to strong vibrational interactions with other modes. In the limiting case the tunnelling motion ceases. As there is no more large proton motion the relaxation time becomes long: the signal is weak and saturation occurs even at low r.f. power. This extreme case seems to be approached by KH-maleate.

Polymerization and Depolymerization Phenomena in Phosphate–Metaphosphate Systems at Higher Temperatures. IV. Condensation Reactions of Alkali Metal Hydrogen Phosphates

Polymerization and Depolymerization Phenomena in Phosphate–Metaphosphate Systems at Higher Temperatures. IV. Condensation Reactions of Alkali Metal Hydrogen Phosphates

Polymerization and Depolymerization Phenomena in Phosphate–Metaphosphate Systems at Higher Temperatures. III. Condensation Reactions of Divalent Metal Hydrogen Phosphates

Polymerization and Depolymerization Phenomena in Phosphate–Metaphosphate Systems at Higher Temperatures. III. Condensation Reactions of Divalent Metal Hydrogen Phosphates