Optimization Strategy in Hydrogen Storage Performance of Ti─V─Cr─Mn Alloys via LiAlH4.

V-based solid solution materials hold a significant position in the realm of hydrogen storage materials because of its high hydrogen storage capacity. However, the current dehydrogenation temperature of V-based solid solution exceeds 350 °C, making it challenging to fulfill the appliance under moderate conditions. Here advancements in the hydrogen storage properties and related mechanisms of TiV1.1Cr0.3Mn0.6 + x LiAlH4 (x = 0, 5, 8, 10 wt.%) composites is presented. According to the first principle calculation analysis, the inclusion of Al and Li atoms will lower the binding energy of hydride, thus enhancing the hydrogen absorption reaction and significantly decreasing the activation difficulty. Furthermore, based on crystal orbital Hamilton population (COHP) analysis, the strength of the V─H and Ti─H bonds after doping LiAlH4 are reduced, leading to a decrease of the hydrogen release activation energy (Ea) for the V-based solid solution material, thus the hydrogen release process is easier to carry out. Additionally, the structure of doped LiAlH4 exhibits an outstanding hydrogen release rate of 2.001 wt.% at 323 K and remarkable cycling stability.

Interfacial Engineering of Fluorinated TiO2 Nanosheets with Abundant Oxygen Vacancies for Boosting the Hydrogen Storage Performance of MgH2.

The interaction between fluorinated surface in the partially reduced nano-crystallite titanium dioxide (TiO2-x (F)) and MgH2 is studied for the first time. Compared with pristine MgH2 (416 °C), the onset desorption temperature of MgH2 +5 wt.% TiO2-x (F) composite can be dramatically lowered to 189 °C. In addition, the composite exhibits remarkable dehydrogenation kinetics, which can release 6.0 wt.% hydrogen thoroughly within 6 min at 250 °C. The apparent activation energy for dehydriding is decreased from 268.42 to 119.96 kJ mol-1 . Structural characterization and theoretical calculations indicate that the synergistic effect between multivalent Ti species, and the in situ formed MgF2 and MgF2-x Hx is beneficial for improving the hydrogen storage performance of MgH2 . Moreover, oxygen vacancies can accelerate the electron transportation and facilitate hydrogen diffusion. The study provides a novel perspective on the modification of MgH2 by fluorinated transition metal oxide catalyst.

Superior Dehydrogenation Performance of α-AlH3 Catalyzed by Li3 N: Realizing 8.0 wt.% Capacity at 100 °C.

The high dehydrogenation temperature of aluminum hydride (AlH3 ) has always been an obstacle to its application as a portable hydrogen source. To solve this problem, lithium nitride is introduced into the aluminum hydride system as a catalyst to optimize the dehydrogenation drastically, which reduces the initial dehydrogenation temperature from 140.0 to 66.8 °C, and provides a stable hydrogen capacity of 8.24, 6.18, and 5.75 wt.% at 100, 90, and 80 °C within 120 min by adjusting the mass fraction of lithium nitride. Approximately 8.0 wt.% hydrogen can be released within 15 min at 100 °C for the sample of 10 wt.% doping. Moderate dehydrogenation temperature slows down the inevitable self-dehydrogenation process during the ball-milling process, and the enhanced kinetics at lower temperature shows the possibility of application in the fuel cell.

Co-Incorporated NiV2O6/Ni(HCO3)2 nanoflake arrays grown on nickel foam as a high-performance supercapacitor electrode.

Co-Incorporated NiV2O6/Ni(HCO3)2 arrays with different morphologies can grow on nickel foam (NF) via a mild one-step hydrothermal method. Among them, S-0.5-20 and S-0.25-20 were obtained at a 1 : 1 : 20 molar ratio of Co/V/urea with 0.5 and 0.25 mmol Co(NO3)2, respectively. They demonstrate high areal capacities of 0.99 mA h cm-2 (7.94 F cm-2) and 0.56 mA h cm-2 (4.48 F cm-2) at 1 mA cm-2, respectively, which are superior to that of Co-incorporated Ni(HCO3)2/NF synthesized in the absence of Na3VO4. S-0.25-20 possesses good rate capability with 82.1% retention when the current density is increased 20-fold, and it shows superior long-term durability with 106.2% retention of the initial capacity after 10 000 charging/discharging cycles at 100 mA cm-2. These results are associated with the porous and orderly hierarchical Co-incorporated NiV2O6/Ni(HCO3)2 nanoflake arrays directly grown on the Ni foam. Moreover, due to the synergetic effect of the individual components, electrons can be transferred from V centers to Ni active sites, thus improving the stability of the vanadate. The generation of more active species, such as Co3+, during cycling could account for the increased capacity. A S-0.25-10//activated carbon (AC) asymmetrical supercapacitor shows a high energy density of 0.533 mW h cm-2 at a power density of 0.232 mW cm-2 (0.415 mW h cm-2 at 4.983 mW cm-2). Furthermore, the formation mechanism of the Co-incorporated NiV2O6/Ni(HCO3)2 nanoflake arrays is proposed.

Competitive reaction pathways of C2Cl3 + NO via four-membered ring and bicyclic ring intermediates.

The products and mechanisms of the atmospherically and environmentally important reaction, C(2)Cl(3) + NO, are investigated comprehensively by step-scan time-resolved Fourier transform infrared emission spectroscopy and the CCSD(T)/6-311+G(d)//B3LYP/6-311G(d) level of electronic structure calculations. Vibrationally excited products of Cl(2)CO, ClNCO, CCl(3)NCO and NCO have been observed in the IR emission spectra. Cyclic intermediates are found to play important roles leading to the rich variety of the chemical transformations of the reaction. Mainly two competitive reaction pathways are revealed: the four-membered ring intermediate pathway leading to the products Cl(2)CO + ClCN which is essentially barrierless and the bicyclic ring intermediate pathway leading to the product channels of ClNCO + CCl(2,) CCl(3)NCO and CCl(3) + NCO which is rate-limited by a barrier of 42.9 kJ mol(-1) higher than the reactants. By photolyzing the precursor at 248 and 193 nm, respectively, C(2)Cl(3) radicals with different internal energy are produced to observe the product branching ratios as a function of reactant energy. The Cl(2)CO channel via the four-membered ring intermediate pathway is shown to be overwhelmingly dominant at low energy (temperature) but become less important at high energy while the ClNCO and CCl(3)NCO channels via the bicyclic ring intermediate pathway are greatly enhanced and compete effectively. The experimental observation of the products and their branching ratios varying with reactant energy is well consistent with the calculated potential energy profiles.

Adiabatic and nonadiabatic reaction pathways of the O(3P) with propyne.

For the reaction of O((3)P) with propyne, the product channels and mechanisms are investigated both theoretically and experimentally. Theoretically, the CCSD(T)//B3LYP/6-311G(d,p) level of calculations are performed for both the triplet and singlet potential energy surfaces and the minimum energy crossing point between the two surfaces are located with the Newton-Lagrange method. The theoretical calculations show that the reaction occurs dominantly via the O-addition rather than the H-abstraction mechanism. The reaction starts with the O-addition to either of the triple bond carbon atoms forming triplet ketocarbene (3)CH(3)CCHO or (3)CH(3)COCH which can undergo decomposition, H-atom migration or intersystem crossing from which a variety of channels are open, including the adiabatic channels of CH(3)CCO + H (CH(2)CCHO + H), CH(3) + HCCO, CH(2)CH + HCO, CH(2)CO + CH(2), CH(3)CH + CO, and the nonadiabatic channels of C(2)H(4) + CO, C(2)H(2) + H(2) + CO, H(2) + H(2)CCCO. Experimentally, the CO channel is investigated with TR-FTIR emission spectroscopy. A complete detection of the CO product at each vibrationally excited level up to v = 5 is fulfilled, from which the vibrational energy disposal of CO is determined and found to consist with the statistical partition of the singlet C(2)H(4) + CO channel, but not with the triplet CH(3)CH + CO channel. In combination with the present calculation results, it is concluded that CO arises mainly from the singlet methylketene ((1)CH(3)CHCO) dissociation following the intersystem crossing of the triplet ketocarbene adduct ((3)CH(3)CCHO). Fast intersystem crossing via the minimum energy crossing point of the triplet and singlet surfaces is shown to play significant roles resulting into nonadiabatic pathways for this reaction. Moreover, other interesting questions are explored as to the site selectivity of O((3)P) atom being added to which carbon atom of the triple bond and different types of internal H-atom migrations including 1,2-H shift, 3,2-H shift, and 3,1-H shift involved in the reaction.

Reaction mechanisms of C2Cl3 + NO2 via nitro and nitrite adducts.

The atmospherically and environmentally important reaction of chlorinated vinyl radical with nitrogen dioxide (C 2Cl 3 + NO 2) is investigated by step-scan time-resolved Fourier transform infrared emission spectroscopy and electronic structure calculations. Vibrationally excited products of CO, NO, Cl 2CO, and NO 2 are observed in the IR emission spectra. Geometries of the major intermediates and transition states along the potential energy surface are optimized at the B3LYP/6-311G(d) level, and their energies are refined at the CCSD(T)/6-311+G(d) level. The reaction mechanisms are characterized to be barrierless addition-elimination via nitro (C 2Cl 3-NO 2) and nitrite (C 2Cl 3-ONO) adducts. Four energetically accessible reaction routes are revealed, i.e., the decomposition of the nitrite adduct forming C 2Cl 3O + NO and its sequential dissociation to CO + NO + CCl 3, the elimination of ClNO from the nitrite adduct leading to ClNO + Cl 2CCO, the Cl-atom shift of the nitrite adduct followed by the decomposition to CCl 3CO + NO, and the O-atom shift of the nitro adduct followed by C-C bond cleavage forming ClCNO + Cl 2CO. In competition with these reactive fluxes, the back-decomposition of nitro or nitrite adducts leads to the prompt formation of vibrationally excited NO 2 and the long-lived reaction adducts facilitate the vibrational energy transfer. Moreover, the product channels and mechanisms of the C 2Cl 3 + NO 2 reaction are compared with the C 2H 3 + NO 2 reaction to explore the effect of chlorine substitution. It is found that the two reactions mainly differ in the initial addition preferentially by the N-attack forming nitro adducts (only N-attack is plausible for the C 2H 3 + NO 2 reaction) or the O-attack forming nitrite adducts (O-attack is slightly more favorable and N-attack is also plausible for the C 2Cl 3 + NO 2 reaction). The addition selectivity can be fundamentally correlated to the variation of the charge density of the end carbon atom of the double bond induced by chlorine substitution due to the electron-withdrawing effect of chlorine groups.

Multichannel reaction of C2Cl3 + O2 studied by time-resolved Fourier transform infrared emission spectroscopy.

The multichannel reaction of the C(2)Cl(3) radical with O(2) has been studied thoroughly by step-scan time-resolved Fourier transform infrared emission spectroscopy. Vibrationally excited products of Cl(2)CO, CO, and CO(2) are observed and three major reaction channels forming respectively ClCO + Cl(2)CO, CO + CCl(3)O, and CO(2) + CCl(3) are identified. The vibrational state distribution of the product CO is derived from the spectral fitting, and the nascent average vibrational energy of CO is determined to be 59.9 kJ/mol. A surprisal analysis is applied to evaluate the vibrational energy disposal, which reveals that the experimentally measured CO vibrational energy is much more than that predicted by statistical model. Combining previous ab initio calculation results, the nonstatistical dynamics and mechanism are characterized to be barrierless addition-elimination via short-lived reaction intermediates including the peroxy intermediate C(2)Cl(3)OO* and a crucial three-member-ring COO intermediate.

The reactions of O(3P) with terminal alkenes: the H2CO channel via 3,2 H-atom shift.

The step-scan time-resolved FTIR emission spectroscopy is used to characterize systematically the H(2)CO channel for the reactions of O((3)P) with various alkenes. IR emission bands due to the products of CO, CO(2), and H(2)CO have been observed in the spectra. H(2)CO is identified to be the primary reaction product whereas CO and CO(2) are secondary reaction products of O((3)P) with alkenes. A general trend is observed in which the fraction yield of the H(2)CO product increases substantially as the reactant alkene varies from C(2)H(4), C(3)H(6), 1-C(4)H(8), iso-C(4)H(8), to 1-C(5)H(10). The formation mechanism of the H(2)CO is therefore elucidated to arise from a 3,2 H-atom shift followed by breaking of the C(1)-C(2) bond in the initially formed energized diradical RCH(2)CHCH(2)O*. The 3,2 H-atom shift may become the dominant process with the more rapid delocalization of the energy when the hydrocarbon chain of the alkene molecule is lengthened.