Construction of CoS/NiS@CuS with dandelion flower-like heterostructures as efficient catalysts for overall urea splitting

The exploration of efficient and inexpensive electrocatalysts is of great importance for sustainable hydrogen production by water splitting. In this paper, we reported a simple preparation method for in situ growth of NiCoOOH@CuO on nickel foam by a two-step hydrothermal method to generate CoS/NiS@CuS with a dandelion-like heterostructure after a one-step sulfidation. The CoS/NiS@CuS electrode has excellent electrochemical properties for urea oxidation reactions, oxygen evolution reactions and urea electrolysis. Electrochemical performance was tested in alkaline solution, the overpotential of CoS/NiS@CuS is only 190 mV for the oxygen evolution reaction, the potential of CoS/NiS@CuS is only 1.35 V for urea oxidation, and the overpotential of CoS/NiS@CuS is only 110 mV at 10 mA cm⁻² for the hydrogen evolution reaction, which are one of the best activities reported so far. Density functional theory calculations show that CoS₂ exhibits the minimum Gibbs free energy of hydrogen, which plays an important role in promoting the reaction rate. The presence of CoS₂ increases the electrical conductivity of the material, and synergistic effect of NiS and CuS makes the material exhibit superior hydrogen production properties. Our work proves that transition-metal sulfides have great potential in the direction of urea splitting, which provides new ideas and directions for subsequent exploration in the direction of transition-metal sulfides.     

Mixed-valence molybdenum ion incorporated graphitic carbon nitride with high photocatalytic H2 evolution activity

The graphitic carbon nitride (CN) incorporated with mixed-valence molybdenum ion has been prepared via in-situ copolymerization to improve the photocatalytic H₂ evolution performance. The introduced Mo species existed in mixed valence of Mo⁴⁺ and Mo²⁺ state and its content could be tuned by simply adjusting amount of added MoCl₅ in the preparation procedure. The incorporated mixed-valence Mo ions contributed to narrowed band gap, increased electron density and elevated electron motion kinetics, resulting in extended visible light response, promoted separation and transportation of photoexcited charge carriers. The obtained CN–Mo photocatalyst with an optimal content of Mo ions (0.41 wt%) exhibited a robust H₂ production activity up to 1.44 mmol h⁻¹ g⁻¹, 18 times higher than that of pristine counterpart.     

Effect of water on the thermal stability of alpha-aluminum hydride

Water can significantly enhance the thermal spontaneous combustion and explosion hazard of alpha-aluminum hydride (α-AlH₃). Thermal analysis suggested that, as the water content increased from 10% to 40%, the total reaction heat was increased by 68.3%. α-AlH₃ with different water contents (10%–40%) underwent hydrolysis reaction and oxidation reaction with the activation energy of 57.9–68.7 kJ/mol and 88.3–107.6 kJ/mol, respectively. As the heating rate increased from 0.2 to 2 °C/min, the onset temperature, the peak temperature, and the maximum heat flow of the exothermic reaction were increased. As the storage temperature increased from 45 to 65 °C, the time to maximum reaction rate decreased from 5.16 to 0.84 h. Combining the results of SEM, XRD, XPS and thermal analysis, the reaction mechanism of α-AlH₃ and water under isothermal and non-isothermal conditions was revealed.     

Excellent temperature stability of strain in PZ-PT-BNT ternary ceramics

Lead-based Pb(Zr, Ti)O₃ ceramics have been widely applied in piezoelectric actuators, and yet high temperature stability and large strain have been pursued for further application. In this work, a novel PbZrO₃–PbTiO₃-(Bi_0.5Na_0.5)TiO₃ (PZ-PT-BNT) piezoelectric ceramic is designed and prepared by solid-state route. It is found that the introduction of BNT constituent enhances the relaxation behavior of PZ-PT ceramic, inhibits the abrupt change in dielectric properties near Curie temperature, and increases the proportion of tetragonal phase with high temperature stability. Meanwhile, the patterns of electric domains are intentionally modified by adjusting composition of PZ-PT-BNT. Short and broad electric domains in PZ-PT-0.03BNT ceramic are observed by piezoresponse force microscopy, which are insensitive to temperature and have faster response under electric field, contributing to strain characteristics. As a result, through integrating phase structure and electric domain configuration, a strain of 0.21% and excellent temperature stability where the variation of strain is less than 8% in the temperature range of 25–250 °C are achieved in PZ-PT-0.03BNT ceramic. The findings provide an effective strategy for improving the strain stability of PZ-PT-based piezoelectric ceramics, and demonstrate that PZ-PT-BNT ceramics have potential application prospects in high-temperature piezoelectric actuators.     

Microwave-assisted synthesis of edge-grafted carbon nitride by triazole rings for efficient photocatalytic hydrogen evolution

Copolymerization of conjugated nitrogen heterocycles within carbon nitride nowadays is proven to be a successful strategy to promote charge separation. Here, a novel edge-grafted carbon nitride nanosheets by triazole rings were synthesized from the copolymerization of dicyandiamide and 3-amino-1, 2, 4-triazole via microwave-assisted heating with improved yield. Based on the building of a feasible donor-acceptor (D-A) system by such edge grafting, the rapid charge transfer pathways were formed. Benefiting from the thin-layer structure of carbon nitride via microwave-assisted heating and abundant π electrons by intramolecular doping, the system showed enhanced visible light absorption from n-π1 electrons transition, facile charge separation and transfer, and then an increased H₂ evolution rate (637.58 μmol h⁻¹ g⁻¹), which is 17.43 times than the triazole modified sample from conventional thermal condensation method. This work enlightens an innovative pathway for the regulation of carbon nitride photocatalysts by conjugated nitrogen heterocycles for efficient solar energy conversion applications.     

Porous fiber paper and 3D patterned electrodes composed high-sensitivity flexible piezoresistive sensor for physiological signal monitoring

Science China Technological Sciences - The research on flexible pressure sensors has drawn widespread attention in recent years, especially in the fields of health care and intelligent robots. In...     

MnNi2O4-MWCNTs as a nano-electrocatalyst for methanol oxidation reaction

Metal oxides as inexpensive and stable materials in electrochemical processes have been noticed by researchers. In this work, we synthesized a nanocatalyst based on nickel oxide and manganese oxide in the form of binary transition metal oxides (BTMOs), as well as a hybrid of this nanocatalyst with multi-walled carbon nanotubes (MWCNTs) by hydrothermal method. The efficiency of this nanocatalyst was checked for methanol oxidation reaction (MOR). After confirming the successful synthesis of the proposed nanocatalysts with detailed physical characterization and then performing cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrical impedance spectroscopy (EIS) tests, both MnNi₂O₄ and MnNi₂O₄- MWCNTs nanocatalysts showed relatively good capabilities in the MOR process. The results showed that adding MWCNTs to the nanocatalyst structure, in addition to increasing electrical conductivity, also increases the active surface of the nanocatalyst. Thus MnNi₂O₄- MWCNTs nanocatalyst with an exchange current of 3.74 × 10⁻⁵ mA/cm² and 98% cyclic stability compared to MnNi₂O₄ with an exchange current of 8.61 × 10⁻⁸ mA/cm² and 91% cycle stability, is more efficient in the MOR process. Synthesized nanocatalysts can be cheap, stable, and attractive options for MOR.     

Metal-introduced NiCuAl-LDH using chelating agent for steam reforming of methanol

In this study, we focus on NiCuAl-LDH and introduce various metal ion species (Ga, Ni, Fe, Nd, Zn, Mg, and Cu) using a chelating agent into calcined NiCuAl-LDH. We obtained a maximum methanol conversion of 82.6% and H₂ yield of 53.5%. In addition, we found that the metal surface area of Ni and Cu increased compared to NiCuAl-LDH. On the other hand, results demonstrated that the presence of Ni(OH)₂ and Cu(OH)₂ on the catalyst surface had a positive effect on the MSR. We also tested the catalytic stability, introducing Cu by EDTA into calcined NiCuAl-LDH.