One Pot Synthesis Of Metal Phospide/Carbon Nanocomposites And Their Electrochemical Properties

Transition metal phosphides, especially, their mono-phosphorus and poly-phosphorus counterparts have been emerging as functional materials in the field of catalysis and energy storage and conversion, due to their outstanding catalytic and electrochemical properties. At present, developing facile synthetic routes、fabricating novel structures and improving their qualities are the major aspects of the functional materials. Herin, based on the hot solvent method and the chemical vapor deposition method, the thesis reports the one-pot synthesis of carbon coated mono-phosphorus and poly-phosphorus transition metal phosphides nanocomposites. Meanwhile, we also investigate the synergistic effect of nanostructure and carbon coating for their applications in the field of lithium ion battery and hydrogen evolution reaction. The synthetic routes in the work enrich the basic researches for the transition metal phosphides to improve their electrochemical properties. The main parts of the results are summarized as follows:1. Nanorod-FeP@C composites are synthesized via a one-pot solution reaction of ferrocene (Fe(C5H5)2) with excess triphenylphosphine (PPh3) in the sealed vacuum tubes at390℃, in which PPh3is used as both phosphorus source and solvent in the reaction. The structure and lithium storage performance of the as-prepared nanorod-FeP@C composites is intensively characterized, and it is interesting that the composites exhibit an increased capacity during cycling as serving anode materials for lithium-ion batteries (LIBs). Meanwhile, mechanism investigations reveal that the capacity increase of the composites is resulted from a hysteresis lithiation of the nanostructured FeP phase due to the coating of carbon shell in the composites. Moreover, cyclic stability investigation shows that the composites have a very good cyclic stability that shows the potential of the composites as promising long lifespan anode materials for LIBs. Meanwhile, based on the same synthetic routes, FeS@C nanosheets, FeSe@C nanosheets, FeAs@C nanosheets, FeAs2@C nanorods and FeSn@C nanowires are also obtained.2. A series of carbon coated transition-metal phosphide (TMP@C) nanocomposites, including poly-phosphorus phases (CuP2@C, NiP2@C) and mono-phosphorus phases (Ni5P4@C, CoP@C) have been fabricated via a straightforward one-pot route from the reaction of organometallic sources with triphenylphosphine (PPh3) in a sealed quartz tube. The as-prepared TMP@C composites as anode materials for lithium-ion batteries (LIBs) exhibit high lithium-storage capacity with stable cycling and excellent rate capability. In typical, the Ni5P4@C composites present612mA h g-1after100cycles at0.2C,462mA h g-1after200cycles at1.0C and424mA h g-1at5.0C, and the CoP@C composites demonstrate654mA h g-1after100cycles at0.2C,530mA h g-1after200cycles at1.0C, and384mA h g-1at5.0C, respectively. Meanwhile, the NiP2@C composites deliver894mA h g-1after100cycles at0.1C, and360mA h g-1at5.0C. All of these composites would be of great potential for LIBs.3. Phosphorous-rich phase iron diphosphide/carbon tube (FeP2/C) nanohybrids, which are synthesized via a pyrolysis process and composed of heterostructures of orthorhombic FeP2with conical carbon tubes, have been identified as a new anode in lithium-ion batteries. After an annealing treatment to eliminate the excessive hydrogen elements in the carbon tubes, the FeP2/C nanohybrids display good reversible capacity, long cycle life, and excellent rate capability. Specifically, the annealed hybrids exhibit a discharge capacity of602mA h g-1on the second cycle and a discharge capacity of435mA h g-1after100cycles at0.1C (0.137A g-1). Meanwhile, these annealed hybrids exhibit excellent rate capability, such as a reversible capability of510mA h g-1,440mA-h g-1,380mA h g-1,330mA h g-1and240mA h g-1at0.25C,0.5C,1C,2.5C and5C, respectively.4. Taking advantages of the FeP2nanostructuer and good conductivity of conical carbon tubes, the performance of the FeP2/C nanohybrids as a novel non-noble metal electrocatalyst for hydrogen evolution reaction (HER) in0.50M H2SO4is investigated. These nanohybrids show good catalytic activity (without IR compensation, the hybrids show an onset potential of60mV, Tafe slope of66mV dec-1and an overpotential of130mV to obtain a current density of10mA cm-2) and good stability in an acidic medium and might serve as a promising new class of non-noble metal catalysts for practical HER. In addition, a series of FeS/C、FeS2/C、 FeP/C and FeP2/C hybrids with similar structure and size are synthesized. When as catalysts for HER, their catalytic activities can be ranged as FeS/C<FeS2/C<FeP/C <FeP2/C.