MoS2 becomes an efficient and durable nonprecious-metal electrocatalyst for the hydrogen evolution reaction (HER) when it contains multifunctional active sites for water splitting derived from 1T-phase, defects, S vacancies, exposed Mo edges with expanded interlayer spacings. In contrast to previously reported MoS2 -based catalysts targeting only a single or few of these characteristics, the all-in-one MoS2 catalyst prepared herein features all of the above active site types. During synthesis, the intercalation of in situ generated NH3 molecules into MoS2 sheets affords ammoniated MoS2 (A-MoS2 ) that predominantly comprises 1T-MoS2 and exhibits an expanded interlayer spacing. The subsequent reduction of A-MoS2 results in the removal of intercalated NH3 and H2 S to form an all-in-one MoS2 with multifunctional active sites mentioned above (R-MoS2 ) that exhibits electrocatalytic HER performance in alkaline media superior to those of all previously reported MoS2 -based electrocatalysts. In particular, a hybrid MoS2 /nickel foam catalyst outperforms commercial Pt/C in the practically meaningful high-current region (>25 mA cm-2 ), demonstrating that R-MoS2 -based materials can potentially replace Pt catalysts in practical alkaline HER systems.

Efficient Hydrogen Evolution Reaction Catalysis in Alkaline Media by All‐in‐One MoS2 with Multifunctional Active Sites

Polypropylene (PP), one of five general-purpose plastics, is widely used in many fields. However, the intrinsic alkane structure of PP makes it relatively easy to burn, leading to limiting its scope of application. Here, this article reviews the most commonly flame retarding strategies used in PP matrices, including the flame-retardant compounds, application methods as well as flame-inhibition mechanism and also focuses on recent advances and foresees the future outlook of such applications. It is seen that traditional flame retardants and some new compounds are considered in modifying the fire behaviors of PP. At present, with the enhancement of environmental awareness, the application frequency of novel materials in this field is increasing. Thus, the harmonious combination of traditional flame retardants with the newly derived flame retardants has broadened the choice of researchers to come up with novel strategies for improving the fire performance of PP matrices.

Flame retardant treatments for polypropylene: Strategies and recent advances

Fabrication of cellulose-based halogen-free flame retardant and its synergistic effect with expandable graphite in polypropylene.

Synergistic effect between a novel triazine-based flame retardant and DOPO/HPCP on epoxy resin

Cytosine pyrophosphate (PPA-C) was prepared by using pyrophosphoric acid (PPA) and cytosine (C). The structure, morphology and thermal stability of PPA-C were analyzed by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and thermogravimetric analysis (TGA). The PPA-C was used as acid and gas source and pentaerythritol (PER) as charring agent to form an intumescent flame retardant (IFR) system which was applied to improve the flame retardancy of polypropylene (PP). The flame retardancy and thermal degradation behaviors of PP/IFR composites were investigated by vertical combustion (UL-94), limiting oxygen index (LOI) and cone calorimeter (cone), TGA etc. The PPA-C and PER have good synergistic effects on improving the flame retardancy of PP which is better than that of commercial ammonium polyphosphate (APP) and PER system. The PP/IFR composites with 18 wt% PPA-C/PER (3:1) achieves the UL-94 V-0 rating and a LOI value of 28.8 vol%. The PPA-C reacts with PER to form -P-O-C and -P-C- during combustion which helps the formation of intumescent char layer. In addition, the IFR makes PP degrade in advance and form more char residues at high temperature. Proper ratio and amount of PPA-C/PER promotes the formation of intumescent char layer without defects during combustion, reduces the heat release rate and delays the thermal degradation of PP composites, thus improves the flame retardancy of PP.

Chengle Wang

Papers

Roles of supermolecule structure of melamine phosphomolybdate in intumescent flame retardant polypropylene composites