Study on Controllable Preparation,and Catalytic Performance of Electrolyzed Water for Transition Metal Phosphides and Their Composite Nanomaterials

Author:Wang Zuo Zuo

Supervisor:zhong wei


Degree Year:2019





The increasing demand for enersy and the limited reserves of fossil energy,as well as the increasing environmental problems,have driven the development of renewable clean energy.Compared with the intermittent and localized nature of and tidal energy,the hydrogen that can be produced by simple electrolysis of water is undoubtedly the new energy with the greatest development potential In order to further reduce the production cost and power loss ot hydrogen produced by electrolyzed water,various non-noble metal catalysts have been successively synthesized in recent years.The transition metal phosphide is a kind of interstitial compound formed by the phosphorus atom entering the transition metal lattice.The unique platinum-like property makes it theoretically excellent iin catalytic performance.This paper focuses on the controllable preparation of transition metal phosphides,and optimized the electronic structure and morphology through elemental doping or composite nanostructures,realizing the efficient synthesis of catalysts with high performance.In addition,a reference is also provided for farther understanding the catalytic mechanism of transition metal phosphides.The main research contents are as follows:1.The rod-like Co3S4/CoP hybrid with a core-shell structure was synthesized by a two-step method using Co(COs)0.5(OH)0.1 IH2O as precursor,and its catalytic hydrosen evolution performance was evaluated in an acidic electrolyte.Compared to binary Co3S4 and CoP catalysts,Co3S4/CoP hybrid exhibits lower onset overpotential(34 mV),smaller Tafel slope(45 mV dec-1)and larger exchange current density(150μA cm-2).It is confirmed that there is a synergetic coupling effect between the Co3S4 core and the CoP shell,hich enables it to provide more active sites for proton adsorption.In addition,the 1D porous structural feature also play a key role in increasing the rate of charge transfer and promoting the adsorption/desorption of reactants or products in the catalytic hydrogen evolution reaction.2.The structure that random CoPS nanoparticles(Size:4-12 nm)anchored on ultrathin amorphous Al2O3 nanosheet(CoPS/Al2O3)are directly synthesized by in-suit transformation of ultrathin cobalt aluminum layered double hydroxide(CoAl-LDH)nanosheets with crossed structure feature in phosphorus/sulfidation process.Thanks to the small particles size and a large number of P2-liuands with electron donor properties and Co3-with octahedral coordination,the CoPS catalytic host is given a relatively ideal hydrogen adsorption free energy and a large number of efficient active sites.Electrochemical tests have further demonstrated the catalytic ability of CoPS/Al2O3 for hydrogen evolution(onset overpotential:-67 mV,Tafel slope:53.6 mV dec-1)and catalytic oxygen evolution(onset overpotential:250 mV,Tafel slope:68.4 mV dec-1).This study introduces a new method for synthesizing ultrathin LDH nanosheets and provides a promisins candidate toward highly active electrocatalysts for overall water splitting.3.Combined with electrodeposition and hypophosphorous thermal decomposition method,molybdenum doped nickel phosphide(Mo-Ni2P/NF)nanostructure that composed of amorphous nanosheets and crystalline nanoparticles was synthesized using 3D interconnected porous nickel foam as substrate.Amorphous nanosheets act as active sites while anchoring the nanoparticles from aggregation and inactivation,and proper contact between the nanoparticles can in turn increase the charge transfer rate,which compensates for the weak conductivity of amorphous nanosheets.In addition,the Mo doping serves to refine the nanoparticles,optimize the electronic structure,enhance the oxidation resistance and increase the charge transfer rate.More importantly,Mo doping also increases the inherent catalytic ability of a single active site.When Mo-Ni2P/NF is used as a hydrogen evolution and oxygen evolution catalyst,overpotential of 450 mV and-310 mV is required to achieve a current density of±150 mA cm-2.