Molybdenum Phosphide Quantum Dots Encapsulated by P/N-Doped Carbon for Hydrogen Evolution Reaction in Acid and Alkaline Electrolytes.

A facile and eco-friendly strategy is presented for synthesizing novel nanocomposites, with MoP quantum dots (QDs) as cores and graphitic carbon as shells, these nanoparticles are dispersed in a nitrogen and phosphorus-doped porous carbon and carbon nanotubes (CNTs) substrates (MoP@NPC/CNT). The synthesis involves self-assembling reactions to form single-source precursors (SSPs), followed by pyrolysis at 900 °C in an inert atmosphere to obtain MoP@NPC/CNT-900. The presence of carbon layers on the MoP QDs effectively prevents particle aggregation, enhancing the utilization of active MoP species. The optimized sample, MoP@NPC/CNT-900, exhibits remarkable electrocatalytic activity and durability for the hydrogen evolution reaction (HER). It demonstrates a low overpotential of 155 mV at 10 mA cm-2 , a small Tafel slope of 76 mV dec-1 , and sustained performance over 20 hours in 0.5 M H2 SO4 . Furthermore, the catalyst shows excellent activity in 1 M KOH, with a relatively low overpotential of 131 mV and long-term durability under constant current input. The exceptional HER activity can be attributed to several factors: the superior performance of MoP QDs, the large surface area and good conductivity of the carbon substrates, and the synergistic effect between MoP and carbon species.

Electrochemical Performance of Carbon-Rich Silicon Carbonitride Ceramic as Support for Sulfur Cathode in Lithium Sulfur Battery.

As a promising matrix material for anchoring sulfur in the cathode for lithium-sulfur (Li-S) batteries, porous conducting supports have gained much attention. In this work, sulfur-containing C-rich SiCN composites are processed from silicon carbonitride (SiCN) ceramics, synthesized at temperatures from 800 to 1100 °C. To embed sulfur in the porous SiCN matrix, an easy and scalable procedure, denoted as melting-diffusion method, is applied. Accordingly, sulfur is infiltrated under solvothermal conditions at 155 °C into pores of carbon-rich silicon carbonitride (C-rich SiCN). The impact of the initial porosity and microstructure of the SiCN ceramics on the electrochemical performance of the synthesized SiCN-sulfur (SiCN-S) composites is analysed and discussed. A combination of the mesoporous character of SiCN and presence of a disordered free carbon phase makes the electrochemical performance of the SiCN matrix obtained at 900 °C superior to that of SiCN synthesized at lower and higher temperatures. A capacity value of more than 195 mAh/g over 50 cycles at a high sulfur content of 66 wt.% is achieved.

Single-Source-Precursor Derived Transition Metal Alloys Embedded in Nitrogen-Doped Porous Carbons as Efficient Oxygen Evolution Electrocatalysts.

Carbon supported metallic nanomaterials are of great interest due to their low-cost, high durability and promising functional performance. Herein, a highly active oxygen evolution reaction (OER) electrocatalyst comprised of defective carbon shell encapsulated metal (Fe, Co, Ni) nanoparticles and their alloys supported on in-situ formed N-doped graphene/carbon nanotube hybrid is synthesized from novel single-source-precursors (SSP). The precursors are synthesized by a facile one-pot reaction of tannic acid with polyethylenimine and different metal ions and subsequent pyrolysis of the SSP. Benefiting from the heteroatom doping of carbon and formation of well-encapsulated metal/alloy nanoparticles, the obtained FeNi@NC-900 catalyst possesses lowest overpotentials of 310 mV to achieve a current density of 10 mA cm-2 for OER with a small Tafel slope value of 45 mV dec-1 , indicating excellent catalytic performance due to the following features: (1) A synergistic electronic effect among metal alloy nanoparticles, nitrogen-doped carbon, and entangled carbon nanotubes; (2) penetration of electrolyte is promoted towards the active sites through the porous structure of the formed mesoporous carbon clusters; (3) the unique core-shell nanostructure of the hybrid material effectively curbs the degradation of electrocatalyst by protecting the alloy nanoparticles from harsh electrolyte. This work advances an inexpensive and facile method towards the development of transition metal-based hybrid material for potential energy storage and conversion.

Self-supported nickel-doped molybdenum carbide nanoflower clusters on carbon fiber paper for an efficient hydrogen evolution reaction.

Developing an efficient, stable and low-cost noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER) is an effective way to alleviate the energy crisis. Herein, we report a simple and facile approach to synthesize self-supported Ni-doped Mo2C via a molten salt method. By optimizing the content of Ni, the concentration of Ni(NO3)2, and the annealing time, self-supported nanoflower-like electrocatalysts composed of ultrathin nanosheets on carbon fiber paper (CFP) can be achieved. Such a fluffy and porous nanoflower-like structure has a large specific surface area, which can expose many active sites, and promote charge transfer; moreover, all of the above is beneficial for improving the HER performance. Density functional theory (DFT) calculations reveal that the doping of Ni leads to a down shift of the value of the d band center (εd), so that the adsorbed hydrogen (Hads) is easier to desorb from the catalyst surface, thus leading to an enhanced intrinsic catalytic activity of Ni doped Mo2C based catalysts. As a result, Mo2C-3 M Ni(NO3)2/CFP with a nanoflower-like structure prepared at 1000 °C for 6 h exhibits the best electrocatalytic performance for the HER in 0.5 M H2SO4, with a low overpotential of 56 mV (at j = 10 mA cm-2) and a Tafel slope (27.4 mV dec-1) comparable to that of commercial Pt/C (25.8 mV dec-1). The excellent performance surpasses most of the noble-metal-free electrocatalysts. In addition, the outstanding long-term durability of Mo2C-3 M Ni(NO3)2/CFP is demonstrated by showing no obvious fluctuations during 35 h of the HER testing. This work provides a simple and facile strategy for the preparation of nanoelectrocatalysts with high specific surface areas and high catalytic activities, both of which promote an efficient HER.

Dielectric Properties and Electromagnetic Wave Absorbing Performance of Single-Source-Precursor Synthesized Mo4.8Si3C0.6/SiC/Cfree Nanocomposites with an In Situ Formed Nowotny Phase.

For the first time, dielectric properties and electromagnetic wave (EMW) absorbing performance of single-source-precursor derived Mo4.8Si3C0.6/SiC/Cfree ceramic nanocomposites with a highly electrically conductive intermetallic Nowotny phase (NP, i.e., Mo4.8Si3C0.6) are reported. High-temperature phase evolution of the nanocomposites reveals that free carbon (Cfree) plays a crucial role in the in situ formation of the NP, indicating that the microstructure of the nanocomposites can be tailored via molecular design of the single-source precursors. Compared with SiC/Cfree and MoSi2/SiC/Cfree nanocomposites obtained under the same conditions, the Mo4.8Si3C0.6/SiC/Cfree nanocomposites exhibit significantly enhanced EMW absorbing performance. A minimum reflection loss (RL) of -59 dB was achieved at 8 GHz for the thickness of 2.46 mm, proving the superiority of the Mo4.8Si3C0.6/SiC/Cfree nanocomposite as an outstanding EMW absorbing material. On the basis of our previous discovery that the Mo4.8Si3C0.6 embedded in a SiC-based matrix with high specific surface area exhibits excellent electrocatalytic properties suitable for the electrochemical hydrogen evolution reaction, the present results prove that Mo4.8Si3C0.6/SiC/Cfree nanocomposites have to be considered as novel multifunctional materials with tailorable microstructure and excellent performance in two different fields including electrochemical water splitting and EMW absorption.

Single-source-precursor synthesis of dense SiC/HfC(x)N(1-x)-based ultrahigh-temperature ceramic nanocomposites.

A novel single-source precursor was synthesized by the reaction of an allyl hydrido polycarbosilane (SMP10) and tetrakis(dimethylamido)hafnium(iv) (TDMAH) for the purpose of preparing dense monolithic SiC/HfC(x)N(1-x)-based ultrahigh temperature ceramic nanocomposites. The materials obtained at different stages of the synthesis process were characterized via Fourier transform infrared (FT-IR) as well as nuclear magnetic resonance (NMR) spectroscopy. The polymer-to-ceramic transformation was investigated by means of MAS NMR and FT-IR spectroscopy as well as thermogravimetric analysis (TGA) coupled with in situ mass spectrometry. Moreover, the microstructural evolution of the synthesized SiHfCN-based ceramics annealed at different temperatures ranging from 1300 °C to 1800 °C was characterized by elemental analysis, X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM). Based on its high temperature behavior, the amorphous SiHfCN-based ceramic powder was used to prepare monolithic SiC/HfC(x)N(1-x)-based nanocomposites using the spark plasma sintering (SPS) technique. The results showed that dense monolithic SiC/HfC(x)N(1-x)-based nanocomposites with low open porosity (0.74 vol%) can be prepared successfully from single-source precursors. The average grain size of both HfC0.83N0.17 and SiC phases was found to be less than 100 nm after SPS processing owing to a unique microstructure: HfC0.83N0.17 grains were embedded homogeneously in a ß-SiC matrix and encapsulated by in situ formed carbon layers which acted as a diffusion barrier to suppress grain growth. The segregated Hf-carbonitride grains significantly influenced the electrical conductivity of the SPS processed monolithic samples. While Hf-free polymer-derived SiC showed an electrical conductivity of ca. 1.8 S cm(-1), the electrical conductivity of the Hf-containing material was analyzed to be ca. 136.2 S cm(-1).

Versatile fabrication of arbitrarily shaped multi-membrane hydrogels suitable for biomedical applications.

In this work, arbitrarily shaped multi-membrane hydrogels were successfully fabricated from gel-core templates using the layer-by-layer (LbL) method. Namely, the first gel membrane layer was formed around a gel-core template when the crosslinker loaded gel-core was soaked in a polysaccharide solution, and it was then ripened in a crosslinker solution, in which the crosslinker was loaded for the fabrication of the following layer. The formation and control of the gel membrane layer were studied in detail. The results indicated that a reasonably rapid crosslinking of the polysaccharide was essential for the successful preparation of a multi-membrane hydrogel, irrespective of chemical or physical crosslinking. The formation of a gel membrane layer was found to be controlled by the diffusion of the crosslinker. The chemically and the physically crosslinked multi-membrane hydrogels were characterized, and the chemically crosslinked chitosan multi-membrane hydrogel exhibited a unique sub-layered microstructure. The chitosan multi-membrane hydrogel which was sensitive to pH was fabricated using terephthalaldehyde as the crosslinker, and the hydrogel displayed LbL disintegration in acidic medium. Chondrocytes were cultivated in the presence of the multi-membrane hydrogel, and they could be easily attached to proliferate quickly. Because of the arbitrary shape, solid or hollow structure, pH sensitivity and biocompatibility, the polysaccharide multi-membrane hydrogels are promising materials for biomedical applications.

Microwave-assisted synthesis of poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) tri-block co-polymers and use as matrices for sustained delivery of ibuprofen taken as model drug.

Poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) triblock co-polymers with number-average molar mass (Mn) over 20000 g/mol were prepared by ring-opening polymerization of epsilon-caprolactone initiated by poly(ethylene glycol) under microwave irradiation. This method was proposed as a means to improve in vivo compatibility as no harmful chemicals were involved in the polymerization except epsilon-caprolactone and poly(ethylene glycol). The resulting tri-block co-polymers were characterized by FT-IR, H-NMR, GPC and WAXD. Their Mn and their composition was controlled by the amount and the chain length of the poly(ethylene glycol) macromers involved in the feed. The ability of poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) co-polymers to entrap and deliver drugs was investigated with ibuprofen as a model drug. The release of ibuprofen was significantly influenced by the co-polymer composition and the extent of loading. The in vitro release of ibuprofen was sustained from 3 to 15 days for 10% loading, depending on the ratio of epsilon-caprolactone to ethylene glycol-derived subunits in co-polymer chains. This ratio ranged from 0.97 to 9.78. In the case of the co-polymer whose epsilon-caprolactone molar ratio to ethylene glycol-derived subunits was 2.49, the ibuprofen release was sustained for 2 to 24 days for ibuprofen loads going from 5 to 20 wt%.