Controllable Fabrication And Active Sites Identification Of Pt/C Electro-Catalysts For Methanol Oxidation

Direct methanol fuel cells(DMFCs)have wide potential applications in portable and mobile equipments due to their several advantages,such as environmental-friendly characteristics,fuel availability,safe operation,excellent energy density and high energy conversion efficiency.Currently,the most commonly used catalyst in DMFCs are a commercial Pt/C one.However,its low Pt atom utilization efficiency and poor stability call for developing highly efficient and stable catalysts to achieve the large-scale application.In this thesis,a series of Pt/CNT nanocatalysts with different Pt particle sizes are prepared by atomic layer deposition using home-made carbon nanotubes as the support.Subsequently,the underlying nature of the structure sensitivity is revealed over Pt/CNT electro-catalyzed methanol oxidation reaction(MOR).Finally,the dominant active sites of these catalysts are discriminated,which could provide guidance for the design and optimization of highly efficient and stable Pt-based MOR catalysts.The main findings are shown below:(1)A catalytic chemical vapor deposition method is employed to synthesize carbon nanotubes(CNT)by catalytic methane cracking of Fe/γ-Al2O3 prepared with a co-precipitation method.The regulation of the CNT yields and microstructures is revealed by changing the reaction parameters.The two as-synthesized CNT samples at 600 and 800℃ for 12 h are chosen as starting support materials,and then they are treated by nitric acid oxidation,in which the resultant supports are donated as CNT-600-12-O and CNT-800-12-O,respectively.These four supports and commercial carbon black are further used to immobilize Pt nanoparticles by an atomic layer deposition technology(ALD).Further combining the catalyst structure characterization and electro-catalytic methanol oxidation results indicates that the CNT-600-12-O supported Pt catalyst shows excellent MOR performance,which is mainly attributed to the more Pt active sites.(2)A series of Pt/CNT-600-12-O nanocatalysts with different Pt particle sizes are prepared by the ALD.It is observed that there are significant Pt size effects on the MOR activity,in which the 1.9 nm sized Pt catalyst shows the highest peak current density of 67 mA·cm-2.Such activity is 3.2 times higher than that of commercial 20 wt%Pt/C catalyst.By further combining with the model calculations,the underlying nature of the Pt particle size effects is revealed,and the Pt corner sites are discriminated as the dominant active sites for the MOR.Meanwhile,the lower Pt electron binding energy,i.e.,the electron-rich Pt catalyst,is beneficial for the improvement of the MOR activity.