Promotion Effect Of Cao,Pt,Pd Modification On Oxygen Reduction Reaction In Solid Oxide Fuel Cell

Energy shortage and environmental pollutions are the problems that the whole world is now facing for the sustainable development,thus it is imminent for the movement toward more efficient and cleaner sources of energy.Solid oxide fuel cells(SOFCs)are energy conversion device that converts the chemical energy in hydrocarbon and hydrogen fuels to electrical energy with negligible emissions.The performance of SOFCs is usually dominated by the oxygen reduction reaction(ORR)in the cathodes.The research in this thesis aims to improve the cathode performance.Firstly,the influence of CaO modification on La0.6Sr0.4Co0.2Fe0.8O3-?(LSCF)electrode oxygen reduction reaction rate is studied.Then in the second part,the impacts of Pd and Pt modification on surface exchange reaction of La0.7Sr0.3MnO3(LSM)films with different orientations.In chapter two of this article,CaO modified LSCF cathode obtained by impregnation method to study the influence of CaO on the LSCF cathode performance.Firstly,Ca(NO3)2 solution was dropped onto the porous LSCF and soaked into the LSCF pores,followed by heating at 800 ? for 1 h to form CaO nanoparticles modified LSCF(LSCF-SDC)electrode.Impedance spectrum analysis demonstrates that the CaO nanoparticles can effectively reduce the area specific interfacial polarization resistances(ASR)for LSCF electrodes,and the lowest resistance is obtained with 5.18 wt.%CaO.For example,ASR at 650 ? is 0.310?·cm2 for CaO-LSCF/SDC/CaO-LSCF symmetrical cells,which is smaller than 0.510 ?·cm2 for the bare LSCF electrode.And the impedance spectrum is analyzed using the distribution of relaxation time(DRT)method,the results indicate that CaO could accelerate the charge transfer process corresponding to the decrease in medium-high frequency resistance.Further,CaO can increase the oxygen surface exchange coefficient(Kchem)by an order of magnitude,as demonstrated with electrochemistry relaxation(ECR)measurement.At 700?,Kchem for the bare LSCF is 1.80 × 10-5 cm·s-1,and it is increased to 2.81 × 10-4 cm·s-1 with 0.07 mg·cm-2 CaO particles,indicating that CaO accelerates the ORR kinetics on LSCF surface.Performance of the CaO impregnated LSCF cathode is further investigated using single cells with Ni-SDC anode and SDC electrolytes.A maximum power density increases from 600 to 800 mW·cm-2 with the addition of CaO at 650 ? using humidified H2 as the fuel.In chapter three of this article,dense single crystal LSM films with different orientations modified by Pd and Pt nanoparticles was used to explore the influnce of metal modification on surface exchange reaction of LSM films with different orientations.Firstly,(001)-,(110)-,and(111)-oriented LSM films are prepared by pulsed laser deposition(PLD),then Pt and Pd are deposited on the LSM film surface using sputtering method with sputter coater,respectively.Kchem is investigated using ECR method for with/without Pt and Pd decorated(001)-,(110)-,and(111)-oriented LSM films at the temperature in the range from 500? to 650? It is interesting to note that Kchem is not equal for differently oriented bare LSM films and the lowest Kchem is observed for(110)-LSM,suggesting that the surface reaction kinetics is not the same for the three surfaces.Compared with the bare LSM film,larger Kchem is observed with the Pd and Pt nanoparticles decorated LSM films,indicating the surface exchange kinetics of Pd and Pt decorated LSM films is greatly increased.What's more,Pd and Pt promotion effect is different,and the promotion factor is different for the three orientated film.The promotion factor is largest on both Pd and Pt decorated(110)-LSM surface.Pt nanoparticles decorated on(110)-LSM promotes the surface exchange rate to a factor up to 129,about 5 times higher than the Pd decorated(110)-LSM.