文献汇报ppt课件.ppt

1,Paper Review,李俊乾 化学工程（专） 14102932,Synthesis, characterization and electrochemical studies of nano-structured CaWO4 as platinum support for oxygen reduction reaction(纳米钨酸钙的合成、表征和其负载铂对氧还原反应的电催化),2,Literature source,3,Contents,Introduction,1,2,Experimental section,1,Conclusions,2,3,4,Results and discussion,4,1. Introduction,In recent years, proton exchange membrane fuel cells(PEMFCs) have been recognized as promising devices for portable and transport applications due to their good energy conversion efficiency, high power density, low operating temperature, and easy transport.,PEMFCS working principle:,5,1. Introduction,The cathodic reaction of oxygen reduction reaction (ORR),The anodic reaction of hydrogen oxidation reaction for,H2+2M2MH 2MH2M+2H+2e-,O2+H+M+e-MHO2 MHO2+H+e-MO+H2O MO+H+e-MOH MOH+H+e-M+H2O,Electrocatalytic reaction mechanism:,6,In the fuel cell in the work process, the platinum catalyst active surface area will be gradually reduced, resulting in the attenuation of fuel cell performance.,the properties of Pt/PtM alloy recession schematic diagram,7,Experimental section,2,8,2. Experimental section,Synthesis of nanostructured CaWO4:,80C,pH=7,white precipitates were collected by centrifugation,Na2WO42H2O (5 mM),CaCl26H2O (5 mM),CaWO4,mixed together,dried initially at room temperature,calcinate,500 C for 5 h,9,2. Experimental section,Catalyst preparation:,calcium tungstate(1),Graphite(2),CaWO4/graphite electrode,K2PtCl4（2.5mM）,H 2 SO 4（0.25 M）,the catalyst of Pt/CaWO4-graphite,30 wt.% of n-eicosane,heated,electrochemically precipitated,10,2,3,Results and discussion,11,3. Results and discussion,The approximate crystallite sizes of samples were estimated by the Scherrers formula:,The particle size and morphology of CaWO4 were examined using TEM ，D=1025 nm.,12,3. Results and discussion,These reduction peaks are not symmetric because of depletion of PtCl42-ions in the vicinity of the electrodes in potentials more negative than the peak potentials .,Cyclic voltammograms during electrodeposition Pt on both graphite and nano-CaWO4/graphite.,13,3. Results and discussion,(a) and (b) Scanning electron microscopy images of Pt/CaWO4-graphite.,In these pictures, brighter areas corresponded to Pt and CaWO4 that the platinum particles are dispersed over the surface of the support and graphite sheet.,14,3. Results and discussion,(d)The EDXspectrum,presence of Pt, Ca and W in thePt/CaWO4-graphite catalysts,15,3. Results and discussion,Area indicating that electrochemical activity.,Cyclic voltammograms of CaWO4-graphite, graphite, Pt/CaWO4-graphite and Pt/graphite in a 0.5 M H2SO4 aqueous solution at scan rate of 50 mV/s.,The size of the oxidation and reduction current depends on the value of Pt-dispersion.,16,3. Results and discussion,返回,The oxygen reduction peak current increases linearly with the square root of scan rate, emphasizing on the controlling of the reaction by oxygen diffusion to the electrode surface,Cyclic voltammograms of the Pt/CaWO4-graphite in a 0.5 M H2SO4 at various scan rates.,17,3. Results and discussion,The more positive half wave potential indicates the enhanced electroc-atalytic activity of the catalysts for ORR .,Linear sweeping voltammograms of Pt/CaWO4-graphite and Pt/graphite in O2 saturated 0.5 M H2SO4 solution with a scan rate of 25 mV/s.,18,3. Results and discussion,It is clear that the Pt/CaWO4-graphite shows a lower charge-transfer resistance due to the smaller semicircles diameter compared to Pt/graphite catalyst in 0.5 M H2SO4 solution.,Nyquist plot for Pt/CaWO4-graphite and Pt/graphite in 0.5 M H2SO4 vs. Ag/ AgCl.,19,Conclusions,4,20,4. conclusions,Nano-structured calcium tungstate was synthesized by the co-precipitation .,The application of CaWO4 as a catalyst support for Pt.,Pt/CaWO4-graphite catalyst exhibited better electrochemical activity for oxygen reduction reaction in H2SO4 solutio compared to Pt/graphite.,21,Thank you for your attention!,