The synergistic effects of solvent interactions with partially dehydrogenated Mg(BH4)2-pyrrolidine complex on the electrochemical properties were investigated. In this system, the pyrrolidine serves two purposes: (1) It facilitates the formation of lower order borane species during dehydrogenation at lower temperatures, and (2) It acts as a boron sink to scavenge the resulting B-H products during the dehydrogenation. Due to this unique behavior, we found that a partially dehydrogenated Mg(BH4)2-pyrrolidine complex possesses enhanced electrochemical properties in five solvents (THF, monoglyme, diglyme, 1,3-Dioxolane, pyrrolidine) when compared to pure Mg(BH4)2 and as prepared Mg(BH4)2-pyrrolidine samples. Cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, and optical spectroelectrochemical techniques were utilized for the characterization of the Mg(BH4)2-pyrrolidine complex in the as prepared and partially dehydrogenated states. The partially dehydrogenated samples showed an ionic conductivity in the range of 2.4–3.1 mS/cm in the five solvents. The THF solvate showed the best electrochemical cycling performance with a magnesium insertion electrode (Mg / Mg(BH4)2-pyrrolidine complex in THF / Li4Ti5O12). This cell showed good stability when cycled at current densities between 25 and 400 mA/g. Extended cycling at 100 mA/g showed good capacity retention (70

In this work, we evaluated two closo-borate salts (Li2B12H12 and Li2B12F12) in propylene carbonate from theoretical and experimental perspectives to understand how the coordination environment influences their spectroscopic and electrochemical properties. The coordination environments of the closo-borate salts were modeled via density functional theory (DFT) and molecular dynamics (MD). Vibrational spectra calculated from the predicted coordination environments are in agreement with experimentally measured steady-state FTIR data. This theoretical investigation also suggested that Li2B12F12 would possess a higher ionic conductivity than Li2B12H12, which was corroborated experimentally. Additionally, an electrochemical cell was designed and fabricated that enabled operando optical and FTIR spectroelectrochemical (OP-IR-SEC) measurements. This allowed for the simultaneous measurement of the relative changes of species at a lithium electrode-liquid electrolyte interface and the visualization of lithium plating at the electrode surface. This technique could provide new chemical insights and potentially link optical changes at the electrode-electrolyte interface to specific chemical species in similar electrochemical systems. The Li2B12F12 electrolyte was found to have a higher thermal stability, which may find utility in applications for batteries that are subject to high-temperature conditions.

Indium Tin Oxide (ITO) thin films are commonly used as transparent conductive layers in the production of solar cells. ITO films are typically heat-treated at temperatures exceeding 200 degrees C after magnetron sputtering to optimize the physical, optical, and electrical characteristics for photovoltaic devices. This high temperature heating procedure greatly limits the use of potential substrates, particularly those comprised of low-temperature-rated polymers. Herein, we examine the physical, optical, and electrical transport effects of oxygen:argon plasmas during radio frequency magnetron sputtering of ITO on glass and flexible polymer surfaces without subsequent heat treatment. ITO thin films were characterized via sheet resistance testing, UV-Vis spectroscopy, X-ray diffraction, and scanning electron microscopy imaging. Sheet resistance measurements revealed an increase in surface resistance with increasing oxygen concentration during sputtering. UV-Vis optical transmittance measurements demonstrated an improvement in optical transmittance with an increase in oxygen concentration reaching a maximum transmittance at an oxygen concentration of 1-2%. Most importantly, it was discovered that producing bilayers of ITO with pure argon sputtered plasmas followed by oxygen:argon plasmas produced ITO thin films with suitable resistance and transmittance without the need for high temperature post annealing. These results highlight a methodology for the deposition of ITO thin films on temperature sensitive substrates for flexible photovoltaics and low-cost module production.

With varying hydrofluoric acid (HF) concentrations under three etching conditions, we presented a comparative study of the effects of both the ordered and randomly ternary mixed terminated Ti3C2Tx surfaces with a wide variation of O/OH/F stoichiometry on the thermodynamic stability and electronic properties. Regardless of the HF concentration, an OH -rich surface is found to be thermodynamically stable and the electrical conductivity of Ti3C2Tx is substantially affected by the OH concentration. The charge density difference and electron localization function demonstrated a significant electron localization at the hydroxyl group on the O/OH/F mixed terminated surface, which could yield a locally induced dipole on the surface that renders favorable reaction sites on the functionalized surface. In addition, a large tunability in the work function (DF ⠁ 3.5 eV) is predicted for Ti3C2Tx. These findings provide a pathway for strategically tuning the electronic and structural properties of Ti3C2 MXenes etched with HF.

The high cost of noble metals is a barrier to widespread commercialization of polymer electrolyte membrane fuel cells. Platinum-group-metal-free catalysts are a promising low-cost alternative for catalyzing the oxygen reduction reaction (ORR). Herein, we report a high activity Fe-N-C cathode catalyst derived from a Fe-porphyrinic framework prepared using low-cost precursors and facile one pot synthesis followed by a single heat treatment. The final product has atomically dispersed iron in proximity to nitrogen groups that share transition metal characteristics, as described by electron energy loss spectrometry and x-ray absorption near edge structure results. Electrochemical studies on a rotating ring-disk electrode indicate a four-electron transfer mechanism for the ORR. Membrane electrode assembly testing of the Fe-porphyrin-derived cathode catalyst shows a high kinetic current density of 22 mA cm^{−2} at 0.9 V in H_{2}-O_{2} fuel cells.

In this work, a two-step hydrothermal/solvothermal process was developed to generate highly fluorescent lawsone polymer dots (LPDs) utilizing an inexpensive and abundant starting material, 2-hydroxy-1,4-napththoquinone (lawsone). This hydrothermal/solvothermal process produces LPDs that have excitation independent emission with well-defined electronic transitions. This two-step protocol provides a straightforward approach to remove unwanted small molecular fluorescence, which has plagued carbon dot systems, without the need for advanced chromatographic purification methods or steps. A series of spectroscopic, electrochemical, and theoretical experiments suggest that this process proceeds via a sequential dehydration and dehydrogenation pathway to cross-link the lawsone into a carbon dot structure. This polymerization process helps to stabilize and favor certain electronic transitions inherently present in the lawsone monomer. The generation of the LPDs results in a 2 order of magnitude increase in the emission intensity and a quantum yield of 37%. This behavior is likely the result of the cross-linked structure shielding these electronic states from deactivation caused by nonradiative processes such as vibrational coupling and excited state quenching from thermal deactivation and solvent collisions. This finding is consistent with a cross-linked enhanced emission (CEE) mechanism, as previously observed for other similar systems. The LPDs were then incorporated into a TiO2 photoanode and utilized as a photosensitizer in a dye-sensitized solar cell (DSSC) which showed an enhancement in photocurrent density over pure TiO2. We also prepared a derivative of the LPDs utilizing a diethylene triamine additive (nitrogen-doped lawsone polymer dots (N-LPDs)) using the same two-step protocol and demonstrated its potential as a fluorescence microscopy dye for imaging MDA-MB-231 cancer cells.

and computational fluid dynamics (CFD) determines the thermal performance of the receiver under the specified heating conditions. Moreover, an in-house MATLAB code is developed to couple SolTrace and ANSYS Fluent. CFD modeling is performed using ANSYS Fluent to predict the thermal performance of the receiver by evaluating radiation and convection heat loss mechanisms. Understanding the effects of variation in heliostat aiming strategy and flow configurations on the thermal performance of the receiver was achieved through parametric analyses. Finally, a receiver thermal efficiency ~85% was predicted and the surface temperatures were observed to be within the allowable limit for the materials under consideration.

A major challenge in the pursuit of higher‐energy‐density lithium batteries for carbon‐neutral‐mobility is electrolyte compatibility with a lithium metal electrode. This study demonstrates the robust and stable nature of a closo‐borate based gel polymer electrolyte (GPE), which enables outstanding electrochemical stability and capacity retention upon extensive cycling. The GPE developed herein has an ionic conductivity of 7.3 × 10−4 S cm−2 at room temperature and stability over a wide temperature range from −35 to 80 °C with a high lithium transference number ( tLi+$t_{{\rm{Li}}}^ + $ = 0.51). Multinuclear nuclear magnetic resonance and Fourier transform infrared are used to understand the solvation environment and interaction between the GPE components. Density functional theory calculations are leveraged to gain additional insight into the coordination environment and support spectroscopic interpretations. The GPE is also established to be a suitable electrolyte for extended cycling with four different active electrode materials when paired with a lithium metal electrode. The GPE can also be incorporated into a flexible battery that is capable of being cut and still functional. The incorporation of a closo‐borate into a gel polymer matrix represents a new direction for enhancing the electrochemical and physical properties of this class of materials.

Deep eutectic electrolytes (DEEs) represent a burgeoning field in electrolytes for energy storage applications. Compared to the more conventionally studied Li-ion electrolyte systems, these electrolytes offer numerous advantages, such as high ion concentration, costs, lower temperature operation, and safety. In this work, the formation of a novel eutectic electrolyte based on lithium salts and methyl carbamate was reported. These DEEs were formed via mixing lithium salts and low-cost methyl carbamate at ratios varying from 1 : 2 to 1 : 5 (mol:mol). The DEE formed from methyl carbamate and lithium hexafluorophosphate (LiPF6) at a 1 : 5 molar ratio generated a 4V stability window and a 25 degrees C conductivity of up to 3.16E(-3) S cm(-1). The DEE formed from methyl carbamate and lithium bis(trifluoromethane)sulfonimide (LiTFSI) at a 1 : 5 molar ratio generated a 3.2 V stability window and a 25 degrees C conductivity of up to 2.87E(-3) S cm(-1). The LiPF6 DEE also demonstrated a discharge capacity of 128 mAh g(-1)after 50 cycles with 93 % discharge capacity retention at moderate cycling rates of 0.5C in a lithium titanate (LTO)/lithium iron phosphate (LFP) full cell. These results demonstrate the potential for methyl carbamate to generate eutectics from lithium salts and offer alternative electrolytes for use in low-temperature Li-ion battery applications.

Porphyrins play pivotal roles in many crucial biological processes including photosynthesis. However, there is still a knowledge gap in understanding electronic and excited state implications associated with functionalization of the porphyrin ring system. These effects can have electrochemical and spectroscopic signatures that reveal the complex nature of these somewhat minor substitutions, beyond simple inductive or electronic effect correlations. To obtain a deeper insight into the influences of porphyrin functionalization, four free-base, meso-substituted porphyrins: tetraphenyl porphyrin (TPP), tetra(4-hydroxyphenyl) porphyrin (THPP), tetra(4-carboxyphenyl) porphyrin (TCPP), and tetra(4-nitrophenyl) porphyrin (TNPP), were synthesized, characterized, and investigated. The influence of various substituents, (-hydroxy,-carboxy, and -nitro) in the para position of the meso-substituted phenyl moieties were evaluated by spectroelectrochemical techniques (absorption and fluorescence), femtosecond transient absorption spectroscopy, cyclic and differential pulse voltammetry, ultraviolet photoelectron spectroscopy (UPS), and time-dependent density functional theory (TD-DFT). Spectral features were evaluated for the neutral porphyrins and differences observed among the various porphyrins were further explained using rendered frontier molecular orbitals pertaining to the relevant transitions. Electrochemically generated anionic and cationic porphyrin species indicate similar absorbance spectroscopic signatures attributed to a red-shift in the Soret band. Emissive behavior reveals the emergence of one new fluorescence decay pathway for the ionic porphyrin, distinct from the neutral macrocycle. Femtosecond transient absorption spectroscopy analysis provided further analysis of the implications on the excited-state as a function of the para substituent of the free-base meso-substituted tetraphenyl porphyrins. Herein, we provide an in-depth and comprehensive analysis of the electronic and excited state effects associated with systematically varying the induced dipole at the methine bridge of the free-base porphyrin macrocycle and the spectroscopic signatures related to the neutral, anionic, and cationic species of these porphyrins.

material, an efficient recycle loop could be set up for converting the decomposition products back into the starting boron-nitrogen hydride. This project is addressing two key challenges facing the exploitation of the boron/nitrogen hydrides (ammonia-borane), as hydrogen storage material: (1) Development of a simple, efficient, and controllable system for extracting most of the available hydrogen, realizing the high hydrogen density on a system weight/volume basis, and (2) Development of a large-capacity, inexpensive, ammonia-borane regeneration process starting from its decomposition products (BNHx) for recycle. During Phase I of the program both catalytic and non-catalytic decomposition of ammonia borane are being investigated to determine optimum decomposition conditions in terms of temperature for decomposition, rate of hydrogen release, purity of hydrogen produced, thermal efficiency of decomposition, and regenerability of the decomposition products. The non-catalytic studies provide a base-line performance to evaluate catalytic decomposition. Utilization of solid phase catalysts mixed with ammonia-borane was explored for its potential to lower the decomposition temperature, to increase the rate of hydrogen release at a given temperature, to lead to decomposition products amenable for regeneration, and direct catalytic hydrogenation of the decomposition products. Two different approaches of heating ammonia-borane are being investigated: (a) 'heat to material approach' in which a fixed compartmentalized ammonia-borane is heated by a carefully controlled heating pattern, and (b) 'material to heat approach' in which a small amount of ammonia-borane is dispensed at a time in a fixed hot zone. All stages of AB decomposition are exothermic which should allow the small 'hot zone' used in the second approach for heating to be self-sustaining. During the past year hydrogen release efforts focused on the second approach determining the amount of hydrogen released, kinetics of hydrogen release, and the amounts of impurities released as a function of AB decomposition temperature in the 'hot zone.'

In this work, we evaluate the electrochemical properties of MBH4-C60 (M = Li+, Na+) nanocomposites for potential use as a solid-state electrolyte in alkali-ion batteries. The enhancement of ionic conductivity for MBH4 was achieved through the addition of C60 and partial dehydrogenation, resulting in an electrolyte with significantly higher ionic conductivity when compared to the pure MBH4. This improvement is attributed to the nanoionic destabilization of the MBH4 salt due to the affinity of the BH4− anion for C60 and partial dehydrogenation of the MBH4 through heating. The LiBH4-C60 nanocomposite was successfully paired with two anodes (graphite and lithium titanate) and two cathodes (LiFePO4 and TiS2) and galvanostatically cycled. The NaBH4-C60 nanocomposite showed nearly a 4-order-of-magnitude increase in ionic conductivity versus pure NaBH4 and demonstrated reversible sodium stripping and plating in a symmetric cell.

The controlled and selective release of hydrogen isotopes from lanthanum-nickel- aluminum (LANA) materials was achieved using an alternating electromagnetic field (AEMF). In the presence of the AEMF, the rate of desorption for D-2 was faster than for H-2. In a closed system, compared to the control experiments with helium, hydrogen-loaded LANA samples showed a significant increase in pressure, which illustrate the desorption of hydrogen from the applied AEMF. An exponential increase in the hydrogen release rate was observed with an increased AEMF strength. Additionally, hydrogen release from LANA confined in a subzero environment (-78 degrees C) using an AEMF was demonstrated. These results demonstrate that the LANA material can be heated directly using alternating electromagnetic fields rather than indirectly to rapidly and selectively desorb hydrogen isotopes. The rapid response and difference in desorption kinetics for different hydrogen isotopes in the presence of the alternating electromagnetic fields provide a promising pathway for applications requiring the controlled release of hydrogen and separation of its isotopes.

The copper-based metal-organic framework (MOF) HKUST-1 adsorbs organic molecules into its pores. When loaded with electron-rich oligothiophenes, the resulting system reacts under heat to initiate oxidative polymerization without the use of any other oxidant or catalyst. This reaction is not observed in the non-redox-active MOF MIL-100(Al). We have characterized the composites by optical and nanoscale microscopy, vibrational and UV-vis spectroscopy, X-ray photoelectron spectroscopy, N2 sorption analysis, and thermogravimetric analysis/residual gas analysis. Unsubstituted oligothiophenes polymerize within MOF pores, while 3,4-ethylenedioxythiophene forms a coating on the MOF surface. MOF composites with conjugated polymer dopants trapped inside their pores undergo profound shifts in the composite electronic structure. Reasoning from time-dependent density functional theory calculations of an HKUST-1 model system bound to monomers, we rationalize the observed reactivity and propose an initiation mechanism based on a ligand-to-metal charge-transfer state.

There is a need to develop high-capacity, stable anode materials for the next generation of lithium ion batteries that will power consumer electronics and automobiles of the future. This report describes a systematic experimental and theoretical evaluation of a series of hydrogenated fullerenes (C60Hx) for use as high-capacity anodes in lithium ion batteries. It was discovered that there is an optimal degree of hydrogenation for C-60 to achieve reversible lithiation. Under the optimized conditions, C60Hx was found to have a stable capacity of 588 mAh/g for over 600 cycles at a current density of 0.05 A/g. Extended cycling studies at higher current densities demonstrated that this material is stable for 2000 cycles. Theoretical modeling of this system determined that electronic structure changes due to hydrogenation is responsible for the favorable interaction of Li+ with C60Hx. This study represents a unique methodology for increasing anode capacity and optimization of an anode's electrochemical properties by controlling the hydrogen content of the active material.

Concentrated solar power (CSP) has been gaining significant attention as a method to produce electricity, but requires a suitable thermal energy storage (TES) system for continuous operation when the sun is unavailable. Thermochemical energy storage systems based on metal hydrides have advantages due to their high energy densities, potential for cost reductions, and higher operating conditions versus commonly utilized molten salts. Higher operational temperatures are desired for CSP power plants to achieve higher efficiencies and therefore lower costs. Herein, we demonstrate the feasibility of CaAl2 as a high temperature thermal energy storage material for concentrated solar power applications. CaAl2 is demonstrated to operate at 600 degrees C and have excellent reversibility, reasonable thermal conductivities, and equilibrium pressures practical for metal hydride based thermal energy storage systems. CaAl2 was determined to hydrogenate in a two-step process mechanism to form CaH2 and Al and dehydrogenate to reform CaAl2 at 600 degrees C by adjusting hydrogen pressure. To our knowledge, this material represents the lowest cost metal hydride TES material capable of operating at or above 600 degrees C. Published by Elsevier B.V.