Electrolyte-supported membrane electrode assemblies (MEAs) were fabricated using Cs3H2[BOB(PO4)3] (affectionately dubbed CsBOB) as the electrolyte and membrane separator and tested for proton conduction and power generation at temperatures up to 250 °C. The devices reached steady state ionic conductivities of 0.8-1.8 × 10-5 S cm-1 and produced commensurate power at nominal steady-state power densities of 0.6-1.2 × 10-2 mW cm-2 over the course of 160-h tests, thereby experimentally demonstrating that the CsBOB electrolyte does, in fact, conduct protons and is chemically stable under fuel cell operating conditions on the order of days. Machine-learned interatomic potentials (MLIP) trained on density functional theory calculations were used for molecular dynamics (MD) simulations, providing computational evidence confirming proton motion through bulk CsBOB. Importantly, the MLIP MD, bolstered by solid-state nuclear magnetic resonance (SS-NMR), also revealed that interstitial water plays a significant role in the CsBOB proton conduction mechanism under the operating conditions that were tested, helping provide high proton mobility. However, at these conductivities, electrochemistry is electrolyte limited; a 2-3 order-of-magnitude increase in proton conductivity is necessary for MEAs utilizing CsBOB electrolyte to achieve sufficiently high power densities for use in commercially competitive fuel cells. Future work will focus on improving CsBOB proton conductivity by increasing carrier density.

Herein, we report the results of evaluation of an oxygen reduction reaction (ORR) electrocatalyst comprising ca. 2 nm Pt nanoparticles, confined within a highly porous, amorphous carbon-nitrogen matrix, both at the electrode/electrolyte and electrode/triple-phase boundary interfaces. The catalyst was synthesized by a pyrolytic reduction of Pt(acac)2 nodes in the Pt(acac)2-hexaaminetriphenylene (Pt-HATP) cocrystal at 600 degrees C for 1 h. The pyrolyzed Pt-HATP electrocatalyst, with a Pt loading of 35 wt %, exhibits the electrochemical surface area (ECSA) of 38.8 +/- 4.0 m2 gPt -1 and the area-specific activity of 150 mu A cmPt -2 in thin-film rotating-disk electrode (RDE) experiments, which do not exceed those of commercial 40 wt % Pt/VC. Importantly, it demonstrates superior durability in RDE testing, attributed to lower losses in the ECSA due to suppression of nanoparticle coalescence/agglomeration during potential cycling. Evaluation of Pt-HATP in a membrane-electrode assembly (MEA) fuel-cell configuration shows a higher iR-corrected performance compared to the commercial catalyst. Although the Pt-HATP MEA exhibits significant high-frequency and proton resistances, it benefits from the lower Faradaic resistance manifested by a lower Tafel slope of 86 +/- 10 vs 136 +/- 10 mV for 40 wt % Pt/VC.

Nonoxidative coupling of methane represents a long-standing challenge in heterogeneous catalysis, as it requires activation of the carbon-hydrogen (C-H) bond, controlled carbon-carbon (C-C) bond formation, and effective hydrogen management without relying on oxidants. Here, we report a low-temperature C-H activation and nonoxidative C-C coupling of methane over atomically dispersed titanium-aluminum-boron nanopowder (Ti-Al-B NP) utilizing a catalytic microreactor coupled to synchrotron single-photon photoionization reflectron time-of-flight mass spectrometry. The soft-ionization, in situ probing method detects the nascent reaction products and radical intermediates under operando conditions, including methyl radical, C2 hydrocarbons, and molecular hydrogen. Methane activation is initiated at 800 K, approximately 700 K below the gas-phase decomposition threshold, leading predominantly to ethylene formation with selectivity reaching up to 78% among the C-C coupled products. Electronic structure calculations on model Ti-Al-B clusters elucidate a cooperative catalytic mechanism in which titanium enables methane adsorption and C-H activation, boron acts as a reversible hydrogen reservoir, and aluminum stabilizes methylene intermediates, thereby facilitating selective C-C coupling and dehydrogenation. These findings establish a distinct catalyst architecture for nonoxidative methane coupling based on earth abundant elements alternative to expensive platinum and other noble metal-containing conventional catalysts and provide molecular-level design principles for controlling dehydrogenation and subsequent C-C bond formation in challenging light alkane conversions.

Sonochemically-synthesized atomically-dispersed titanium-aluminum-boron nanopowder (TiAlB NP) exhibits a remarkable low-temperature catalytic activation of aliphatic C-H bonds at 750 K followed by C-C bond activation thus emerging as a potent low-cost alternative to expensive platinum group metals. Here, the model saturated hydrocarbon, exo-tetrahydrodicyclopentadiene (C10H16), undergoes catalytic decomposition on TiAlB NPs in a chemical microreactor to produce 1,3-cyclopentadiene (c-C5H6), cyclopentene (c-C5H8), and molecular hydrogen (H2) as detected in situ via isomer-selective, single-photon ionization time-of-flight mass spectrometry. Extensive electronic structure theory calculations on model clusters of the catalyst decode a unique synergy among the atomic constituents of the catalyst and chemical bonding in this stepwise, retro Diels Alder reaction: Ti, although insensitive to C-H activation in its metallic state, initiates the catalysis via chemisorption of the hydrocarbon, adjacent B centers readily abstract hydrogen atoms and store them during the catalytic cycle, while Al stabilizes the catalyst structure yet providing space for critical docking sites for the departing hydrocarbons.

The presented family of one-dimensional (1D) polyanionic borophosphates is discussed in the context of a growing class of intermediate temperature electrolytes. The borophosphates are noteworthy for exhibiting high thermal stability under a highly reducing H2 atmosphere. Here, we report the electrolyte characteristics observed in rubidium borophosphate (Rb3H2[BOB-(PO4)3]) and cesium borophosphate (Cs3H2[BOB-(PO4)3]) (a new compound) as newly identified members of the proton-conducting 1D borophosphate polyelectrolyte family. Ab initio molecular dynamics simulations of the compounds suggest extremely high H+ mobility correlated with gyrational mobility of the borophosphate chains, which is similar in character to that of previously reported borosulfate proton electrolytes. Particularly noteworthy is the proton conductivity of the Cs3H2[BOB-(PO4)3] variant, which has the highest conductivity of any of the borophosphates so far, found to be on the order of 10 -5 S·cm -1 (250 °C and 0.2 atm of water). Cs3H2[BOB-(PO4)3] was found to be the best-performing 1D borophosphate electrolyte due to the combination of the highest observed proton conductivity, the greatest thermal stability, and attractive mechanical properties. This represents an important advance for intermediate temperature proton conductors and provides a viable path to improve electrolytes for intermediate temperature hydrogen fuel cells.

Vacuum ultraviolet photoionization (VUV-PI) mass spectrometry offers an isomer-selective and universal ionization with minimal fragmentation detection of organics in complex chemical systems such as pyrolysis and combustion. Here, we report a state-of-the-art experimental setup of a universal catalytic microreactor combined with a molecular beam to investigate the thermocatalytic oxidation of a heterogeneous system relevant for probing reactions at gas-solid interfaces. In strong contrast to traditional off-line analytical methods, this technique is capable of identifying and quantifying short-lived species (radicals) as well as stable products to decipher initial reaction steps via the detection of nascent products. The thermocatalytic oxidative degradation of exo-tetrahydrodicyclopentadiene (JP-10), a high energy-density hydrocarbon fuel, over solid titanium-aluminum-boron reactive mixed metal nanopowder (Ti-Al-B RMNP) is exploited to showcase potential applications. Overall, some 59 nascent gas-phase products are identified via photoionization efficiency (PIE) curves, including oxygenated species and hydrocarbons comprising closed-shell molecules and radicals. The critical temperature for complete oxidative decomposition of JP-10 was lowered by 450 K from 1400 K to 950 K, indicating an efficient thermocatalytic action of Ti-Al-B nanoparticles on JP-10. The enabling of a universal chemical microreactor along with VUV-PI mass spectrometry broadens the applicability of this technique to hydrocarbon fuel oxidation and pyrolysis characterization. This isomer-selective sensitive probing along with the detection of radical transients makes the aforementioned technique superior to other conventional analytical techniques such as microflow tube and pyrolysis-gas chromatography coupled with mass spectrometry for investigating similar pyrolysis reactions and comprehensive quantification.

A platinum-containing hexaaminotriphenylene (HATP, 2,3,6,7,10,11-hexaaminotriphenylene, [C18H12N6]) hybrid cocrystal material ([Pt(acac)2][HATP]) has been synthesized and used as a precursor that was pyrolyzed to produce an oxygen reduction reaction (ORR)-active electrocatalyst. The crystalline precursor, pyrolyzed in vacuo and monitored in situ with temperature-variable TEM, was found to form an amorphous carbon network intercalated with crystalline platinum nanoparticles (NPs). The thermal decomposition of the coordinated hexaaminotriphenylene ligand, with loss of the amino groups around 300 degrees C, is concomitant with the reduction of platinum centers from Pt2+ to Pt0, while the pyrolysis time and temperature control the ultimate size of the nanoparticles. Pt nanoparticle growth above 300 degrees C was found to be limited, likely as a result of the nanoparticles being trapped in a carbon network that formed from the HATP molecules during the pyrolytic process. Samples of the pyrolyzed material were investigated by RDE for ORR catalysis in an acidic medium and were found to have a modest electrochemical surface area (38.8 m2/gPt) and a mass-specific activity of 58.5 mA/cmPt 2.

A phosphorus-containing polymer with very high thermo-oxidative stability was synthesized for the first time by addition of silver nitrate to tricyanophosphine (P(CN)(3)). By optimizing the reaction time and silver nitrate concentration to a 1:1 molar ratio, a new polycyanophosphate [p(CP)] was formed as the primary phosphorus-containing product over the competing species, P(CN)(3). The reactions and products were monitored by FT-IR, ICP-OES, NMR, and XPS spectroscopic techniques, which indicated a complicated oxidation reaction that converted the P(III) precursor species to P(V) polyphosphate species with pendant cyano- and isocyano- moieties. The p(CP) resin was found to contain a high (17.6 at.%) amount of phosphorus by ICP-OES, which contributed to its excellent thermo-oxidative resistance with a high char yield of over 60 wt.% at 1000 degrees C (1273 K) in air, indicating that the material could be particularly useful for high-temperature applications.

The ionic conductivity, thermal stability, and general viability for use as electrolytes in fuel cells are examined for two borophosphate polyelectrolyte compounds (e.g., sodium borophosphate (NaBOB, Na5[BOB(PO4)3)]) and ammonium borophosphate (NH4BOB, (NH4)3H2[BOB(PO4)3])). Bulk synthesis methods are presented for laboratory scale reactions (> 5 g) using low-temperature ionic liquid fluxes. Electrochemical impedance spectroscopy (EIS) was used to determine temperature-dependent ionic conductivities of the NH4BOB and NaBOB to be on the order of 2 µS cm−1 and 0.1 µS cm−1 at 200 °C, respectively. Although NH4BOB displays higher ionic conductivity compared to NaBOB at equivalent temperatures, thermal gravimetric analysis (TGA) shows much higher thermal stability for NaBOB, exhibiting no mass loss below 600 °C. The thermal stability of NaBOB was also assessed under reducing ( 1 atm H2) conditions, finding no reductive thermal degradation below 400 °C. Ab initio molecular dynamics (AIMD) simulations show free proton (H+) movement is related to gyrational mobility of the polyanionic borophosphate chains.

Irradiation of aqueous suspensions containing hydrogen-terminated detonation nanodiamond (HND) with sub-bandgap (λexc > 225 nm) excitation leads to the reductive degradation of perfluorooctanesulfonate (PFOS). As evidenced by nanosecond transient absorption spectroscopy (nsTA), we show that 254 nm excitation of HND in water induces the photoemission of electrons producing hydrated electrons (eaq-). A red shift in the eaq- absorption maximum relative to bulk water indicates a disruption in the hydrogen bonding network of the interfacial water layer at the HND surface. A shortening of the eaq- lifetime with the addition of PFOS and accompanying blue shift of the eaq- absorption maximum indicate PFOS reduction and HND/PFOS surface interactions, respectively. Prolonged photolysis of HND/PFOS solutions at 254 nm results in the degradation of PFOS into smaller polyfluoroalkyl derivatives consistent with other advanced reduction processes. The degradation of PFOS by this method is less sensitive to pH than the state-of-the-art UV-sulfite method.

The initial reduction dynamics of perfluoroalkyl substances (PFASs) by the hydrated electron, eaq-, is a topic of great interest and importance due to the pervasive environmental presence of PFAS in soil and waters and the need to remediate the contamination. Understanding how PFAS behaves in water, including the potential effect of aggregation on the apparent PFAS reduction rate constant (kPFAS) is, therefore, of paramount importance. In this publication we re-examine the proposition that submicellar aggregation decreases the apparent kPFAS for sodium perfluorocarboxylates of varying chain lengths (NaPFxA, x = number of carbons in the PFAS backbone, ranging from 4 to 8) using transient absorption spectroscopy. We compare the dynamics for eaq- quenching by NaPFxA in aqueous solutions of ferrocyanide, Fe(CN)64-, and sulfite, SO32-. The results demonstrate that the apparent rate constant depends on the choice of eaq- precursor. We demonstrate that the ionic strength of the solution and the counterion of the PFxA salt both affect the measured rate constant of PFAS reduction by eaq-. The results presented here help to better understand PFAS degradation by advanced reduction processes. Hydrated electron quenching by perfluoroalkyl carboxylates in ferrocyanide and sulfite is examined with nanosecond transient absorption spectroscopy. The results show distinct differences that are influenced by ionic strength and PFAS counterion.

A method is described and demonstrated for imaging the combustion of particle agglomerates for a composite aluminized polymer fuel. The method uses two bandpass filters to distinguish particles that are hot but not reacting from particles that are reacting and producing AlO. For a fuel strand burning in an oxygen crossflow, nonreacting particles are shown detaching from the fuel surface and igniting downstream.

Titanium (Ti), aluminum (Al), and boron (B) reactive mixed-metal nanopowders (Ti-Al-B RMNPs) represent attractive additives to hydrocarbon fuels such as exo-tetrahydrodicyclopentadiene (C10H16; JP-10) enhancing the limited volumetric energy densities of traditional hydrocarbons, but fundamental mechanisms and combustion stages in the oxidation have been obscure. This understanding is of vital significance in the development of next-generation propulsion systems and energy-generation technologies. Here, we expose distinct oxidation stages of single droplets of JP-10 doped with Ti-Al-B-RMNP exploiting innovative ultrasonic levitator technology coupled with time-resolved spectroscopic (UV-vis) and imaging diagnostics (optical and infrared). Two spatially and temporally distinct stages of combustion define a glow flame stage in which JP-10 and nanoparticles combust via a homogeneous gas phase (Al) and heterogeneous gas-surface oxidation (Ti, B) and a slower diffusion flame stage associated with the oxidation of JP-10. These findings enable the development of next-generation RMNP fuel additives with superior payload delivery capabilities.

The origin of thermochromism displayed by the hybrid material [Ni(dieten)2](BF4)2 (dieten = N,N-diethylethylenediamine) is explored by anion substitution of the tetrafluoroborate anions (BF4-) with varying percentages (0-25%) of bromide (Br-). Differential scanning calorimetry and variable-temperature diffuse reflectance spectroscopy indicate that the yellow-orange to orange-red thermochromic transition inherent to undoped [Ni(dieten)2](BF4)2 shifts from 100 to 90 °C as the doping concentration increases from 0 to 25%. Similarly, a 15 nm line broadening of the Kubelka-Munk transformed diffuse reflectance signal (proportional to the absorbance of the complex) and a broadening of the endothermic transition are observed with increasing Br- doping. The structure of the undoped [Ni(dieten)2](BF4)2, determined by single-crystal X-ray diffraction, is presented, and powder X-ray diffraction was used to confirm that the crystal structure and crystallinity of each doped sample remains unchanged from the BF4- phase. We provide evidence for an underlying mechanism of thermochromism that is linked to hydrogen bonding within the crystal structure and which can be manipulated via targeted modulation of lattice anions. The mechanism proposed here is likely applicable to other materials within the family of dieten complexes ([M(dieten)2](X)2, where M = Ni2+, Cu2+ and X = BF4-, ClO4-, NO3-).

Disagreements persist regarding the rate constants for the initial reduction of perfluorooctanoate (PFOA) by the hydrated electron, eaq-, with published values differing by nearly 2 orders of magnitude (between similar to 1 x 107 and similar to 1 x 109 M-1 s-1). In this letter, we demonstrate a nonlinear dependence of the eaq- decay rate on the [PFOA] which we attribute as being a result of aggregation of PFOA at concentrations below the critical micellar concentration. We invoke a kinetic model for the reaction between PFOA and eaq- at concentrations below 1 mM involving dimerization of the PFOA; higher-order aggregates are acknowledged but not modeled. Our kinetic model adequately fits the nanosecond transient absorption data at [PFOA] <= 1 mM providing apparent rate constants for the reduction of PFOA monomers (k1 = 1.4 x 109 M-1 s-1) and dimers (k2 = 1.1 x 107 M-1 s-1) by eaq-. For reasons that are only partially understood, the aggregation of PFOA decreases the probability of the reduction of PFOA by eaq-. These results reconcile the reports of differing rate constants for the initial reduction of PFOA by eaq- suggesting its origin to be related to the aggregation of PFOA even under dilute conditions.

Thermal runaway reactions resulting in catastrophic battery failure and combustion have invigorated a search for non-flammable electrolytes. We report the synthesis of non- flammable inorganic lithiated carbon phosphonitride (Li-C-P-N) amorphous solids in various solvents, their spectroscopic and other characterization aimed at greater molecular structure understanding, and their ionic conductivities. The resin precursor to this polymeric material is the product of reacting solvated P(CN)(3) and LiN(CN)(2) at room temperature. The resulting resin can be cast from various polar aprotic solvents and produces Li-C-P-N films upon drying. The reaction mechanism was studied by time-resolved P-31 solution NMR. A fully cured sample was studied by P-31, C-13 and Li-7 MAS NMR, including variable temperature Li-7 MAS NMR observations of changes in satellite transitions arising from Li (+) ion motions. Films dried at room temperature under inert atmosphere were temperature cycled as high as 250 degrees C to measure conductivity as a function of temperature and thermal curing. Thermally treated, partially solvated Li-C-P-N films cast from pyridine and dimethoxyethane/acetonitrile exhibit ionic conductivities as high as 10(-5) S cm(-1) above 100 degrees C, depending on temperature and cure procedure, although conductivity drops dramatically in films held above 150 degrees C. We propose that the conductivity of Lithorn ions through the films is highly dependent on the presence and identity of tightly-bound solvent, the presence of excess LiN(CN)(2) retained in the Li-C-P-N matrix, as well as the structure of the cross-linked Li-C-P-N network.

A scalable new method for the synthesis of borosulfate compounds in sulfuric acid providing control over product crystallite size is reported as an alternative to traditional methods requiring slow growth from oleum. This new synthetic approach is used to prepare three isostructural, 1D borosulfates: one containing only ammonium cations, another containing only potassium cations, and the third sample with a solid solution of 1:1 ammonium–potassium. Proton conduction in polycrystalline pellets of these borosulfate electrolytes is compared by electrochemical impedance spectroscopy (EIS) and ab initio molecular dynamics (AIMD) simulations. For a given cation (e.g., NH 4 + ), conductivity decreases by three orders of magnitude with decreasing particle size while maintaining constant activation energy, indicating that proton conduction is not primarily a grain‐boundary process. AIMD simulations show that excess proton mobility in K[B(SO 4 ) 2 ] is in line with that of NH 4 [B(SO 4 ) 2 ], being a backbone (not cation) mediated process. Although K[B(SO 4 ) 2 ] exhibits higher activation energy (60.6 ± 2.0 kJ mol −1 ) than NH 4 [B(SO 4 ) 2 ] (33.8 ± 1.0 kJ mol −1 ), at 200 °C it achieves comparable conductivity to NH 4 [B(SO 4 ) 2 ] samples, which is attributable to hydrolytic B–O–H defects being the common source of mobile protons in these materials.

Investigations of the syntheses, structural characterization, and relative stabilities of the cyclopentadienyl, amidinate Zr cycloalkylmethyl complexes, (CPAM)Zr(X)[CH2(cyclo-CmH2m-1)] (CPAM = (eta 5-C5Me5)[(N,N & PRIME;)-kappa 2-N (Et)-C(Me)N(t-Bu)]) for X = Cl and m = 3 (1a), 4 (1b) and 5 (1c) and for X = Me, and m = 4 (2b), and of the corresponding isomeric omega-alkenyl complexes, (CPAM)Zr(Cl)[CH2(CH2)nCH2CH = CH2] for n = 0 (3a), 1 (3b) and 2 (3c), have been conducted. Hydrozirconation of methylenecyclopropane by (CPAM)Zr(X)Cl (X = H or D) (8), which is generated in situ through hydrogenolysis of the Zr-Si bond of (CPAM)Zr(SiMe2Ph)Cl (7), provided a high yield of 3a due to rapid isomerization of transiently generated 1a. In contrast, crystalline 1b could be isolated in high yield via hydrozirconation of methylenecyclobutane by 8, and it has been structurally charac-terized by X-ray crystallography. Thermolysis of 1b in solution provided a quantitative yield of 3b, while quantitative production of 1c was achieved through intramolecular cyclization of 3c by reversible chloride abstraction that was catalyzed by addition of the ion pair, {(CPAM)Zr(Me)}{B(C6F5)4} 10. The cyclobutylmethyl complex 2b was also prepared from 1b through traditional methylation using MeLi, and it too was structurally characterized by X-ray crystallography. In solution, 2b thermally decomposes at 25 C to an intractable mixture. Finally, reaction of 2b with a stoichiometric amount of the borate B1 provided the corresponding ion pair complex, {(CPAM)Zr[CH2CH2CH2CH = CH2]}{B(C6F5)4} (9) in which the terminal alkenyl group is intramo-lecularly coordinated to the transition metal center as determined by 1H NMR spectroscopy. The results of a DFT (B3LYP / LANL2DZ (Zr) / 6-31G**) computational investigation for the 1b to 3b isomerization and for the structure of 9 are also included.