NaBH4-induced phase transition of CoSe_(2) with abundant Se deficiency for acidic oxygen reduction to hydrogen peroxide

Electrocatalytic oxygen reduction(ORR)via the 2e−pathway to form H_(2)O_(2) in acidic medium has attracted extensive attention.However,the low activity,insufficient selectivity and high cost of catalysts have been the bottlenecks.Herein,CoSe_(2) with abundant Se deficiency was synthesized by a simple hydrothermal method,and the addition of NaBH4-induced CoSe_(2) phase transition from orthorhombic to cubic phase with more Se deficiency.The cubic phase CoSe_(2) with abundant Se deficiency can effectively regulate the surface electronic structure with suitable binding energies of*OOH and*O,which shows high activity,selectivity and long-term stability for acidic ORR to H_(2)O_(2).The onset potential is as low as 0.73 V vs.reversible hydrogen electrode(RHE),the H_(2)O_(2) selectivity is 84%(0 V vs.RHE),and the average electron transfer number is about 2.3.Furthermore,the H_(2)O_(2) yield measured using a flow cell is as high as 115.92 mmol·gcat.^(−1)·h^(−1) and the Faradaic efficiency is 70%at 0 V vs.RHE,which presents high potential in electrocatalytic acidic ORR to H_(2)O_(2) and organic pollutant degradation using the electron-Fenton process.

Liquid crystal character controlled by complementary discotic molecules mixtures： Columnar stacking type and mesophase temperature range

In this work, the mesophase properties were tuned via mixing two discotic molecules with structural complementarity. Compared with the liquid crystalline hexakis（n-hexyloxy）triphenylene（H6TP）materials（columnar hexagonal phase from 53 ℃ to 91 ℃）, mesophase types as well as phase transition temperatures varied with the introduction of crystalline hexaazatriphenylene derivative（PBH）molecules. The introduction of less than 33% amount of PBH disrupted the columnar hexagonal phase formed by H6 TP remarkably, followed by the decreased clearing temperatures of liquid crystals. As the PBH amount was further increased, the destroyed columnar hexagonal phase was turned into the columnar rectangular phase, in which H6 TP and PBH molecules together formed the columnar mesophase. The formation of new mesophase contributed to the enlarged mesophase temperature（from44 ℃ to 144 ℃）. We speculated that the alkyl chains interaction induced by the PBH component competed with the strong p–p stacking between H6 TP molecules, thus altering the liquid crystalline properties including mesophase types and phase transition temperatures.

Crystal structure and phase transition of 2-methoxyanilinium perchlorate-18-crown-6

A new phase transition compound,2-methoxyanilinium perchlorate-18-crown-6（1） {（oCH3OC6H4NH3）＋（18-crown-6） ClO4 },has been synthesized and separated as crystals.Differential scanning calorimetry（DSC） measurements show a pair of sharp peaks at 225 K（heating） and 210 K（cooling）,indicating the phase transition is first-order.Dielectric anomalies observed at 225 K（heating）and 210 K（cooling） further confirm the phase transition.The crystal structures determined at 298 K and123 K are both triclinic in P 1.The most distinct difference between room-temperature and lowtemperature structures is the order–disorder transition of the host 18-crown-6 molecule,which is the driving force of the phase transition.

Synthesis,characterization,and phase transition of an inorganic-organic hybrid compound,[(3-nitroanilinium^＋)(18-crown-6)][IO4^-](CH3OH)

A novel inorganic-organic hybrid supramolecular compound,[（3-nitroanilinium^＋）（18-crown-6）][IO4]（CH3OH）（1）,was discovered as phase-transition materials displaying dielectric anomalous behaviors.The yellow block crystal formed by N-H…O hydrogen bonding that made contact through the cavity of 18-crown-6 was characterized by single-crystal X-ray diffraction,elemental analysis,infrared analysis,thermogravimetric analysis,differential scanning calorimetry,and potential-energy calculations.Differential scanning calorimetry measurements indicate that the compound experiences a reversible phase transition at around 220 K.Temperature-dependent dielectric measurements further confirm the phase transitions.Potential-energy calculations demonstrate that the phase transition occurs due to the molecular order-disorder rotation of CH3OH,whereas the space grouping of the crystal remains unchanged.

Enhanced αγ′ Transition of Poly(vinylidene fluoride) by Step Crystallization and Subsequent Annealing

Poly（vinylidene fluoride）（PVDF） exhibits pronounced polymorphs. Its γ phase is attractive due to the electroactive properties. The γ-PVDF is however difficult to obtain under normal crystallization condition. In a previous work, we reported a simple melt-recrystallization approach for producing γ-phase rich PVDF thin films through selective melting and subsequent recrystallization. We reported here another approach for promoting the αγ′ phase transition to prepare γ-phase rich PVDF thin films. To this end, a stepwise crystallization and subsequent annealing process was used. The idea is based on a quick generation of a large amount of α-PVDF crystals with some of their γ-PVDF counterparts at suitable crystallization temperature and then annealing at a temperature above the crystallization temperature for enhancing the molecular chain mobility to overcome the energy barrier of phase transition. It was found that crystallizing the PVDF melt first at 152 °C for 4 h, then quenching to room temperature and finally annealing the sample at 160 °C for 100 h was the most efficient to produce γ-PVDF rich films. This is related to the melting and recrystallization of the α-PVDF crystals produced during quenching in the annealing process at 160 °C, which favors the formation of γ-PVDF crystals for triggering the αγ′ phase transition.

Optical nature of non-substituted triphenylmethyl cation:Crystalline state emission,thermochromism,and phosphorescence

Since the discovery of the triphenylmethyl(trityl)cation 120 years ago,a variety of aromatic cations having various colors and luminescence properties have been rigorously studied.Many,differently substituted trityl cations have been synthesized,and their optical properties have been elucidated.However,the optical properties of the parent,non-substituted and highly reactive trityl cation,which was observed to be very weakly luminescent,have not been subjected to detailed investigation.In the effort described herein,we explored the optical nature of non-substituted trityl hexafluorophosphate(PF_(6))in the crystalline state.Trityl PF_(6) was found to exist as two crystal polymorphs including a yellow(Y)and an orange(O)form.Moreover,we observed that these crystalline forms display crystalline-state emission with different colors.The results of X-ray crystallographic analysis showed that the two polymorphs have totally different molecular packing arrangements.Furthermore,an investigation of their optical properties revealed that the O-crystal undergoes a distinct color change to yellow upon cooling as a consequence of a change in the nature of the charge transfer interaction between the cation and PF6 anion,and that both the Y-and O-crystal exhibit phosphorescence.

Investigation of Structural, Electronic and Mechanical Properties of Rubidium Metal Hydrides RbMH_4(M=B, Al, Ga)

Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of rubidium metal hydrides RbMH4（M = B, Al, Ga） for five different crystal structures, namely hexagonal（P63mc）, tetragonal（P42/nmc）, tetragonal（P421c）, orthorhombic（Pnma） and monoclinic（P21/c）. Among the considered structures, tetragonal（P421c） phase is found to be the most stable one for these metal hydrides at normal pressure. A pressure-induced structural phase transition from tetragonal（P421c） to monoclinic（P21/c） phase is observed in all the three metal hydrides. The electronic structure reveals that these hydrides are wide band gap semiconductors. The calculated elastic constants indicate that these alkali metal tetrahydrides are mechanically stable at normal pressure.