Mechanical mixtures of metal oxides and phosphorus pentoxide as novel precursors for the synthesis of transition-metal phosphides

Effect of Temperature on the Hydrotreatment of Sewage Sludge-Derived Pyrolysis Oil and Behavior of Ni-Based Catalyst

The high-energy potential of wastewater sewage sludge (SS) produced in large amounts around the world makes it an attractive feedstock for fuels and energy sectors. Thermochemical valorization relying on pyrolysis of SS followed by hydrotreatment of pyrolysis oil (Py-SS) might even allow the integration of SS into existing oil refineries. In the present study, catalytic hydrotreatment of Py-SS was performed over a NiCuMo-P-SiO2 catalyst in a batch reactor at temperatures in the range of 200–390 °C. Due to sulfur presence in the feed, the increasing reaction temperature induced in situ transformation of metallic Ni into Ni3S2 in the catalyst. In contrast, the Ni3P active phase possessed remarkable stability even at the harshest reaction conditions. The oxygen content in the reaction products was decreased by 59%, while up to 52% of N and 89% of S were removed at 390 °C. The content of free fatty acids was greatly reduced by their conversion to n-alkanes, while the larger amount of volatile aromatics was generated from high molecular mass compounds. The quality of oil-derived products greatly changed at elevated temperatures, providing strong evidence of effective upgrading via decarboxy(ny)lation, hydrogenation, and hydrocracking transformations.

Transition metal trifluoroacetates (M = Fe, Co, Mn) as precursors for uniform colloidal metal difluoride and phosphide nanoparticles

We report a simple one-pot synthesis of uniform transition metal difluoride MF₂ (M = Fe, Mn, Co) nanorods based on transition metal trifluoroacetates (TMTFAs) as single-source precursors. The synthesis of metal fluorides is based on the thermolysis of TMTFAs at 250–320 °C in trioctylphosphine/trioctylphosphine oxide solvent mixtures. The FeF₂ nanorods were converted into FeF₃ nanorods by reaction with gaseous fluorine. The TMTFA precursors are also found to be suitable for the synthesis of colloidal transition metal phosphides. Specifically, we report that the thermolysis of a cobalt trifluoroacetate complex in trioctylphosphine as both the solvent and the phosphorus source can yield 20 nm long cobalt phosphide nanorods or, 3 nm large cobalt phosphide nanoparticles. We also assess electrochemical lithiation/de-lithiation of the obtained FeF₂ and FeF₃ nanomaterials.

Solvothermal water-diethylene glycol synthesis of LiCoPO4and effects of surface treatments on lithium battery performance

Olivine-structured LiCoPO₄ is prepared via a facile solvothermal synthesis, using various ratios of water/diethylene glycol co-solvent, followed by thermal treatment under Ar, air, 5%H₂/N₂ or NH₃. The diethylene glycol plays an important role in tailoring the particle size of LiCoPO₄. It is found that using a ratio of water/diethylene glycol of 1 : 6 (v/v), LiCoPO₄ is obtained with a homogenous particle size of ∼150 nm. The bare LiCoPO₄ prepared after heating in Ar exhibits high initial discharge capacity of 147 mA h g⁻¹ at 0.1C with capacity retention of 70% after 40 cycles. This is attributed to the enhanced electronic conductivity of LiCoPO₄ due to the presence of Co₂P after firing under Ar. The effects of carbon, TiN and RuO₂ coating are also examined. Contrary to other studies, it is found that the solvothermally synthesised LiCoPO₄ samples produced here do not require conductive coatings to achieve good performance.

Solvothermal water-diethylene glycol synthesis of LiCoPO₄, followed by thermal treatment under Ar, air, 5%H₂/N₂ or NH₃ was investigated.

Polyoxometalate Compound-Derived MoP-Based Electrocatalyst with N-Doped Mesoporous Carbon as Matrix, a Cathode Material for Zn-H+ Battery

H₂ is confirmed as a perfect substitute for traditional fossil energy, which can be obtained through hydrogen evolution reaction (HER) after electrocatalytic H₂O decomposition. High-performance electrocatalysts play a significant role in HER. Here, with coordination complex-modified Standberg-type polyoxometalate and peach juice as precursors, MoP-based electrocatalysts with N-doped mesoporous carbon as a matrix (MoP@NMC) were obtained. Remarkably, during synthesis, the extremely poisonous PH₃ and highly explosive H₂ were avoided. MoP@NMC exhibits very excellent electrocatalytic activity in acidic electrolytes. To get 10 mA·cm^-2 current, MoP@NMC only requires 92 mV overpotential with Tafel slope 56 mV·dec^-1. It also possesses perfect long time stability and durability in HER. More importantly, with MoP@NMC as the cathode and the Zn plate serving as the anode, a new type of battery, Zn-H⁺ battery, is assembled. In this Zn-H⁺ battery, Zn provides electrons, which pass through an external circuit and reach the cathode. Under the catalysis of MoP@NMC, the H⁺ ions are reduced by these electrons and form H₂. The open circuit voltage of the Zn-H⁺ battery is 1.19 V. Its peak power density is 89.7 mW·cm^-2. The energy density of this Zn-H⁺ battery arrives at 809 W h·kg^-1 at 10 mA·cm^-2. This work establishes a new piece of research field for HER.

Encapsulating Co2 P@C Core-Shell Nanoparticles in a Porous Carbon Sandwich as Dual-Doped Electrocatalyst for Hydrogen Evolution

A highly efficient and pH-universal hydrogen evolution reaction (HER) electrocatalyst with a sandwich-architecture constructed using zero-dimensional N- and P-dual-doped core-shell Co₂ P@C nanoparticles embedded into a 3 D porous carbon sandwich (Co₂ P@N,P-C/CG) was synthesized through a facile two-step hydrothermal carbonization and pyrolysis method. The interfacial electron transfer rate and the number of active sites increased owing to the synergistic effect between the N,P-dual-doped Co₂ P@C core-shell and sandwich-nanostructured substrates. The presence of a high surface area and large pore sizes improved the mass-transfer dynamics. This nanohybrid showed remarkable electrocatalytic activity toward the HER in a wide pH range with good stability. The computational study and experiments revealed that the carbon atoms close to the N and P dopants on the shell of Co₂ P@N,P-C were effective active sites for HER catalysis and that both Co₂ P and the N,P dopants gave rise to an optimized binding free energy of H on the active sites.

Composition-controlled synthesis of Ni2−xCoxP nanocrystals as bifunctional catalysts for water splitting

NaBH₄-assistant composition-controlled synthesis of Ni_2−xCo_xP nanocrystals with high catalytic activity.

Molybdenum phosphide as a novel and stable catalyst for dry reforming of methane

A novel MoP catalyst exhibited high coking and oxidation resistance for dry reforming of CH₄with CO₂.