Metal-organic frameworks derived transition metal phosphides for electrocatalytic water splitting

It is critical to synthesize high-efficiency electrocatalysts to boost the performance of water splitting to meet the requirements of industrial applications. Metal-organic frameworks(MOFs) can function as ideal molecular platforms for the design of highly reactive transition metal phosphides(TMPs), a kind of candidates for high-efficiently electrocatalytic water splitting. The intrinsic activity of the electrocatalysts can be greatly improved via modulating the electronic structure of the catalytic center through the MOF precursors/templates. Moreover, the carbon layer converted in-situ by the organic ligands can not only protect the TMPs from being degraded in the harsh electrochemical environments, but also avoid agglomeration of the catalysts, thereby promoting their activities and stabilities. Furthermore,heteroatom-containing ligands can incorporate N, S or P, etc. atoms into the carbon matrixes after conversion, regulating the coordination microenvironments of the active centers as well as their electronic structures. In this review, we first summarized the latest developments in MOF-derived TMPs by the unique advantages in metal, organic ligand, and morphology regulations for electrocatalytic water splitting. Secondly, we concluded the critical scientific issues currently facing for designing state-of-the-art TMP-based electrocatalysts. Finally, we presented an outlook on this research area, encompassing electrocatalyst construction, catalytic mechanism research, etc.

Disclosing the active integration structure and robustness of a pseudo-tri-component electrocatalyst toward alkaline hydrogen evolution

Designing multicomponent integration catalysts(MICs)has been a promising strategy for improving electrocatalytic hydrogen evolution reaction(HER)due to the highly active interfaces as well as electronic synergy.Nevertheless,many fundamental questions such as their actual active species and the influence on long-term stability remain to be answered.Herein,we present the structural evolution from a pseudotri-component electrocatalyst of nitrogen-doped carbon supported nickel/vanadium nitride/vanadium oxide(Ni-VN-V_(2)O_(3)/NC)nanorods to the heterostructural nickel/vanadium nitride(Ni-VN/NC)nanosheets during chemical or electrochemical processes.The self-reconstructed Ni-VN/NC exhibits a robust stability under alkaline conditions,while maintaining initial efficient HER activity with a low overpotential of 76 mV at the current density of 10 mA cm^(-2).Theoretical calculations and quasi-in-situ spectroscopic technology unveil the redistribution of electrons on the synergistic active interface,which synchronously optimizes the affinities for hydrogen,hydroxide,and water molecules,thereby remarkably accelerating the HER kinetics by reducing the barrier of Volmer step.

Thermal-induced reversible ferroelastic phase transition in a new bromethyl-substituted molecular rotor

A new bromethyl-substituted molecular rotor, [Cu(dabco CH2Br)(H2O)Br3](dabco CH2Br+=1-(2-bromethyl)-1,4-diazoniabicyclo[2.2.2]octane cation), which belongs to a family of halomethyl-substituted molecular rotors, was synthesized and structurally characterized. The reversible phase transition at ca. 250 K was well established for this molecular rotor by thermal analyses, variable-temperature X-ray diffraction, and variable temperature dielectric measurements. The order-disorder transformation of the rotator part(dabco moiety) causes ferroelastic phase transition with an Aizu notation of mmm F2/m from hightemperature orthorhombic phase(Pbnm) to low-temperature monoclinic phase(P21/n). More important, in reference to the density functional theory calculations and structural analyses, the key factors to tune the phase transition behaviors were discussed in detail for this family of halomethyl-substituted molecular rotors.

A Crystalline Supramolecular Rotor Functioned by Dual Ultrasmall Polar Rotators

As an extended model of conventional molecular rotors,a conceived construction of novel crystalline molecular rotor that simultaneously contains two discrete polar rotators is presented here.The supramolecular self-assembly of 18-crown-6 host and two rotator-containing ion-pair guests affords a three-in-one cocrystal,(2-NH_(3)-iBuOH)(18-crown-6)[ZnBr_(3)(H_(2)O)],in which the hydroxyl group and aqua ligand both function as ultrasmall polar rotators.On the basis of the variable-temperature single-crystal X-ray diffraction,variable-temperature/frequency dielectric response,density functional theory calculations,and molecular dynamics simulations,it is found that such dual polar rotators experience a gradually enhanced rotation with increasing temperature,and more importantly,could be controlled by a reversible polar-to-polar structural phase transition,i.e.,from a“single-(polar rotator)”state at low-temperature phase to a“mixed-dual-(polar rotator)”state in the vicinity of transition,and to an unusual“synchronized-dual-(polar rotator)”state at high-temperature phase.