The Controlled Synthesis Of Binary Metal Phosphide And Investigation Of Their Electrocatalytic Properties For Hydrogen Evolution

As a renewable energy carrier,hydrogen is gaining more and more attention.Water electrolysis is a CO2-free route to generate H2 and is ordinarily implemented in alkaline or neutral solution.Pt and Pt-based materials have excellent electronic structure and have emerged as the hydrogen evolution reaction?HER?electrocatalysts with the greatest promise so far.Nevertheless,high cost and low terrestrial abundance of Pt-group metals prevent their further large scale applications as HER electrocatalysts for hydrogen production.Therefore,studies on non-precious metal or metal-free electrocatalysts are being performed with more attention and interest.Metal phosphide is a kind of outstanding catalyst for Hydrodesulfurization?HDS?.Owing to the HDS and HER have the similar process for hydrogen adsorption,TMP could also be a promising catalysts for HRE,which have excellent catalytic activity and stability.In this thesis,nano-engineering and metal doping are the main strategies to improve the catalytic ability for hydrogen evolution of TMP in alkaline or neutral solution.Taking ZIF-67 as template,double metal phosphide?NiCoP?with hollow quasi-polyhedron structure was prepared by acidic etching and low temperature phosphorization treatment,their electrocatalytic properties for hydrogen evolution were investigated;using the hydrothermal synthesized nickel cobalt bimetallic carbonate hydroxide salt as template,the urchin-like Ni0.5Co0.5P was prepared via topological transformation,their electrocatalytic properties were surveyed in alkaline or neutral media.;via microwave assisted polyol reduction method,a small amount of Pt was deposited on the above prepared CoP.The relative electrocatalytic properties of Pt modified CoP were surveyed in alkaline or neutral media.The detailed work of this thesis is as follows:?1?Double metal phosphide?NiCoP?with hollow quasi-polyhedron structure was prepared by acidic etching and precipitation of ZIF-67 polyhedra and further phosphorization treatment with NaH2PO2.The morphology and microstructure of NiCoP quasi-polyhedron and its precursors were investigated by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,and a micropore and chemisorption analyzer.Electrocatalytic properties were examined by typical electrochemical methods,such as linear sweep voltammetry,cyclic voltammetry,chronoamperometry,and electrochemical impedance spectroscopy in 1.0 M KOH aqueous solution.Results reveal that,compared with CoP hollow polyhedra,NiCoP hollow quasi-polyhedra exhibit better electrochemical properties for hydrogen evolution with a low onset overpotential of 74 mV and a small Tafel slope of 42 mV dec-1.When the current density is 10 mA cm-2,the corresponding overpotential is merely 124 mV,and 93%of its electrocatalytic activity can be maintained after 12 h.?2?The urchin-like nickel cobalt bimetallic carbonate hydroxide salt was firstly synthesized via hydrothermal method,then double metal phosphide?Ni0.5Co0.5P?with hollow quasi-polyhedron structure was prepared by low temperature oxidation and subsequent phosphorization.The morphology,structure,specific surface area,pore size distribution,surface valence and compositions of the Ni0.5Co0.5P catalyst have been characterized by SEM?TEM?EDS?XRD?BET and XPS,respectively.The results show that NiCoP well inherited the morphology of the precursor and there is plenty of mesoporous structure in the 1D nanowires.Furthermore,CV,LSV,EIS and I-t technologies were used to examine the hydrogen evolution performance of Ni0.5Co0.5P in 1M KOH and 1M PBS solution,respectively.The results indicate that Ni0.5Co0.5P is an excellent electrocatalyst for hydrogen evolution in alkaline aqueous solution.Its onset overpotential is 26 mV and the Tafel slope is 58 mv dec-1.It only needs the overpotential of 87 mV to reach the current density of 10 mA cm-2 and can remain the current density nearly unchanged after 25 h amperometric test.In addition,the same catalyst also exihibits good electrocatalytic properties and durability for hydrogen evolution in PBS solution?pH=7?.?3?The CoP hollow polyhedron was prepared by calcination and phosphorization with the ZIF-67.Then,by microwave assisted polyol reduction method,a small amount of Pt was deposited on the above prepared CoP.That is to say,the Pt modified CoP polyhedron was synthesized.Then,SEM?TEM?XRD and BET and XPS was executed to characterize and analyse the morphology,structure,specific surface area and pore size distribution of the Pt modified CoP and its precursor.The results suggest that the Pt modified CoP has the similar morphology with that of CoP and its surface was filled with plenty of mesopores.Moreover,CV,LSV,EIS and I-t technologies were used to evaluate the hydrogen evolution performance of Pt modified CoP.It turned out that the Pt modified CoP exhibit excellent electrocatalytic capacity and durability in 1M KOH and 1M PBS solution,respectively.In 1 M KOH,its ?₁₀is merely 48 mV and b is 58 mv dec-1.After 44 h constant potential electrolysis,the current density shows the less attenuation.Meanwhile,in 1 M PBS,its ?₁₀is 88 mV and 91%of its electrocatalytic activity can be maintained for 44 h.