High Stable Non-platinum and Platinum Catalysts Based on the Modification of Molybdenum/titanium Compounds

Author:Zhang Yan

Supervisor:zuo jian bing


Degree Year:2017





Pt supported on carbon black(Pt/C)catalyst is the most commonly used electrocatalyst in low temperature fuel cells.It has the catalytic activity for hydrogen evolution reaction(HER),methanol oxidation reaction(MOR)and oxygen reduction reaction(ORR),which are essential reactions in new energy equipment such as fuel cells and water splitting.However,the price of Pt/C is high,and carbon supports are prone to be oxidized under the electrochemical condition as well as the migration and agglomeration of Pt nanopartricles,leading to a decrease in the lifetime of catalyst.In view of the above problems,this paper presented two technical paths.Among them,molybdenum as a carbide-forming element was used to deposite onto the surface of carbon black to form carbide,which can chemically bond with carbon black.The metal catalyst on the surface of carbon black was strongly bonded to carbon black by means of the formed carbides to form stable non-Pt and Pt catalysts.Another path was the use of nano-silicon carbide(SiC)and silicon nitride whisker(Si3N4)with high chemical stability instead of carbon black as support.And metal titanium was used to coat Si C and Si3N4 to form titanium carbide or titanium nitride interface layer,making a strong combination of Pt with SiC and Si3N4.The details are as follows:1.Ni and Mo hydroxides were deposited on the surface of carbon black by microwave-assisted reduction method.Then MoNi,MoNi4 and Mo2C modified carbon black was obtained after the carbonthermal reduction process at 800°C for 1 h.The final product Ni Mo-Mo2C/C can be used as catalyst material for HER.The results of electrochemical experiments showed that Ni Mo-Mo2C/C catalyst had a high catalytic activity for HER with onset overpotential of-90 mV.The as-prepared NiMo-Mo2C/C supported Pt(10 wt%)10Pt/Ni Mo-Mo2C/C electrocatalyst was synthesized through a microwave-assistedreductionmethod.Theelectrocatalyticactivityof10Pt/NiMo-Mo2C/C for MOR,ORR and HER was close to or higher than that of 20Pt/C with 20 wt%Pt loading.The stability test showed that the stability of10Pt/NiMo-Mo2C/C was significantly higher than that of 20Pt/C,which was attributed to the anchoring effect of Mo2C between Pt and carbon black.2.A mixture of carbon black and metallic Mo powder was placed in a discharge plasma sintering system by spark plasma coating at 870°C for 40 min.The metal Mo was activated and reacted with carbon black to form Mo2C during the process of heat treatment.The molybdenum compounds(Mo2C and MoO2)modified carbon black particles(Mo/C)were finally obtained.The formed Mo/C non-platinum catalyst showed high catalytic activity and stability for HER.The 10Pt/Mo/C catalyst obtained by the loading of 10 wt%Pt on the surface of Mo/C had a similar catalytic activity with 20Pt/C due to the synergistic effect of Pt,MoO2 and Mo2C.Mo2C as an intermediate layer can anchor carbon black and Pt,so that 10Pt/Mo/C catalyst showed much higher stability than 20Pt/C.3.SiC and Si3N4 were modified with metal titanium using vacuum deposition method.In addition,nitriding was carried out during the preparation of Ti/SiC to obtain titanium nitride modified SiC(TiN/SiC).Pt/Ti/SiC,Pt/TiN/SiC and Pt/TiN/Si3N4catalysts were prepared using the above materials as the support and exhibited similar or even slightly better MOR and ORR catalytic activity than Pt/C.Morover,Pt/Ti/SiC,Pt/TiN/SiC and Pt/TiN/Si3N4 can effectively prevent the loss of catalyst due to oxidative corrosion,and show a much higher stability than Pt/C.