Fabrication of Ptru Catalyst Supported on Mo-modified Titania Oxide and Its Methanol Electrooxidation Performance

Author:Li Jia Long

Supervisor:hao su e wang zhen bo


Degree Year:2019





Direct methanol fuel cells(DMFCs)are considered as the most promising new generation of clean energy converter for their merits of high energy densities,ease of transportation and quick launch.However,large scale commercialization of DMFCs is still impeded by lack of key catalyst with reasonable cost and durability.Hence,practical improvements with the manufacturing cost and extended operation durability are imperative.To resolve the paradox of low activity and absence of extended durability in electrocatalyst,this research focuses on the interfacial functionalization and structural architecture of composite support material.Molybdenum-modified interface functionalized Mox Ti1-x-x O2 nanoparticles(IF-MTNPs)with an anatase-type crystalline core were obtained successfully through a postprocessing method of commercialized TiO2(p-TNPs)under the mild alkaline hydrothermal process.The PtRu/IF-MTNPS-C catalyst was prepared by mixing the above composite support and commercial XC-72 carbon black.Due to the improved electron conductivity and enhanced electron interactions with PtRu NPs,the resultant catalyst manifested a mass activity of 0.71 A·mg-1Pt,which is3.4 times higher than that of pristine PtRu/p-TNPs-C catalyst.Moreover,the stability of catalyst after 1000 CV cycles was improved by 9.3%.A one-step synthesis of the modified TiO2 nanocrystallines(iMTNCs)with interfacial functionalization by Mo from tetrabutyl orthotitanate was further proposed.The iMTNCs-C(incorporated with commercial VC-72 carbon black)composite was employed as the functionalized support for PtRu binary catalyst towards methanol electrooxidation.The mass activity of resultant PtRu/iMTNCs-C catalyst was improved by 25.4%in comparison with that of PtRu/IF-MTNPs-C with the similar stability.These improvements in catalytic performance are attributed to the electronic donation from Mo-functionalized interface of iMTNCs to PtRu nanoparticles and ultrafine crystalline architecture of composite support.Furthermore,the electronic transport performance of the modified support and the push-electron effect on precious metals were improved,and the electronic structure of the modified carrier was changed accompanying with the moving down of d-band center,and the anti-toxicity of carbon-containing intermediates(COads)was enhanced in the process of methanol oxidation.In order to further improve the performance of PtRu catalytst,an approach to improve the bonding form of unstable carbon black and interfacial functionalized titanium oxide was proposed for the fabrication of Mo-doped Mox Ti1-x-x O2 nanotubes(C@IF-MTNTs).Through mild hydrothermal reaction with subsequent annealing,synchronous carbon coating and interfacial functionalizing was conducted based on the TiO2 nanotubes(TNTs).The carbon nanotube composite support C@IF-MTNTs with anatase/rutile mixed-phase TiO2 core was prepared by the carbonating at800℃and simultaneous Mo-doping.The obtained PtRu/C@IF-MTNTs catalyst exhibited a mass activity of 1.05 A·mg-1Pt,which is 2 times higher than that of the pristine PtRu/C@TNTs catalyst.The catalyst showed 1.7 times higher in catalytic activity and over 20%higher stability than PtRu/C catalyst.Such superior catalytic performance towards methanol electrooxidation is ascribed to the Mo functionalized interface,concentric multilayered 1D architecture,and anatase/rutile mixed-phase core,which facilitates the charge transport through 1D structural support and electronic interaction between C@IF-MTNTs and ultra-fine PtRu NPs.A core shell structured C@Mox Ti1-x-x O2 nanocrystalline with functionalized interface(C@MTNC-FI)derived from tetrabutyl orthotitanate was fabricated via hydrothermal and subsequent annealing.The mass activity of obtained PtRu/C@MTNCs-FI catalyst was 2.68 times and 1.68 times higher than those of PtRu/C@TNCs and commercial PtRu/C catalyst,respectively,and the stability of catalyst was improved by 24%.The promotion in catalytic performance can be attributed to ultrafine crystalline of TiO2 phase,Mo functionalized interface with enhanced electronic interactions,and in-situ carbon-coated core shell architecture with improved electrical transport.The Mo functionalized TiO2 nanowires coated by the chitosan-derived N-doped C(NC)coated(NC@MTNWs-FI)was obtained through hydrothermal treatment towards pristine TiO2 nanowires and carbon precursor,as well as subsequent annealing treatment.Based on the synergistic effect of electronic donation form N doped C layer and Mo functionalized interface to PtRu NPs,the PtRu/NC@MTNWs-FI catalyst showed a mass activity of 1.23 A·mg-1Pt,which is over 2 times higher than PtRu/NC@TNWs catalyst,and the stability is 15.9%higher stability.The mass activity and stability were improved by 2.24 times and23.2%in comparison with PtRu/C catalyst,respectively.NC coated Mo modified TiO2 nanowires composites derived from polyaniline and polypyrrole were synthesized via in situ polymerization with subsequent annealing.It is concluded that the catalyst with the highest activity is derived from chitosan,which contains the most content of pyridine type N.The catalyst derived from polyaniline is the most stable,which is 5.8%higher than chitosan-derived catalyst.The adsorption mode in two states(top adsorption and face centered cubic adsorption)of Pt/TiO2 slab adsorption model with(001)lattice docking were studied by DFT method.The adsorption energy of the top adsorption state is more than 10 times higher than that of the face centered cubic adsorption state,and it has smaller equilibrium adsorption distance and more charge transfer to the Pt layer.Under top adsorption state,the adsorption energy of Pt/Ti0.75Mo0.25O2 is 500 times higher than that of un-modified Pt/TiO2 model,and has smaller equilibrium adsorption distance and more interface relaxation.The analysis of inter facial electronic structure reveals that the d band center of Pt layer in the top adsorption system of Pt/Ti0.75Mo0.25O2 model moves down than the position of Pt/TiO2 top adsorption state,and the adjacent interface Ti atoms show an obvious Pt-Ti bonding trend under the effect of Mo.