The Research Of Shape And Composition Controlled Synthesis Of High-Performance PEMFC Cathode Catalyst

As a new power supply, fuel cells can directly convert the chemical energy storedin the fuel into electricity. Fuel cells are considered to be the Energy Star in the21stcentury because they are not subject to the limitation of the Carnot cycle and theenergy conversion efficiency is as high as60%-80%. Pt-based catalyst is one of theimportant materials of the fuel cell, and it costs1/3of the total expense of the fuel cell.Pt is very expensive and a scarce resource, how to further enhance its activity,utilization and durability has become the key to this research area. Studies haveshown that, the performance of the Pt-based catalyst is related to its morphology andcomposition. The morphology of the catalyst decides the coordination andarrangement state of the surface atoms, and alloying can adjust the electronic structureof the catalyst. In all, they can effectively improve the activity, utilization and increasedurability of the catalyst.In order to investigate the influence of morphology on performance, we proposed tosynthesize the three-dimensional branched nano-submicron Pt-based catalyst （3DB-Pt） through a simple reflux reaction using Pluronic F127as a weak reducing agent.The structure of the3D B-Pt was characterized by transmission electron microscopy（TEM） and high resolution transmission electron microscopy （HRTEM）, and thecatalytic performance was measured with the electrochemical methods. The3D B-Pthas many roles, multilateral and multi-crystalline. Its electrochemically active area（ECSA） is1.56times greater than that of the commercial Pt black, which improvesthe Pt utilization, effectively. There are numerous of step, suspension atoms anddislocations on the3D B-Pt, which caused by the synthesis process of crystalnucleation and anisotropy coexist. These low coordination number of the active sitesimproved oxygen reduction reaction （ORR） activity significantly. The JK（ECSA）of the3D B-Pt is2.03times higher than that of the commercial Pt/C. The three-dimensionalstructure of the B-Pt is benefit to the anisotropic transmission of the electrons in thereaction. The J_K（M）of the3D B-Pt is1.82times higher than that of the Pt black. Inaddition,3D branched structure is also effective to prevent the reunion among theparticles and to improve their durability.We also study the influence of composition on performance, in this paper. Thenanodandelion Pt-Cu catalyst （ND Pt-Cu） was synthesized through hydrothermal reaction at160℃with octadecylamine （ODA） as the reducer and the protector. In theelectrochemical activation process, lots of Pt vacancies were formed on the surface ofthe Pt-Cu catalyst accompanied with the continuous dissolution of Cu atoms, andappearing many step and suspension atoms, and Pt atoms below the surface also hadthe opportunity to act as surface atoms to increase the content of the surface Pt atoms.These trigger effects are beneficial to the adsorption of H atoms, thereby improvingthe performance of the catalyst. The ECSA of the ND Pt-Cu after200laps of CVactivation is2.36times greater than that of the commercial Pt black, which improvesthe Pt utilization effectively. The J_K（M）of the ND Pt-Cu at0.95V based on the ORRcurve is2.73times higher than that of the Pt black, which improves ORR activity,significantly. In the durability experiment, the surface Pt atoms of the ND Pt-Cu areconsecutive rearrangement until the system reaches the minimum excess free energystate, which drove by the lowest energy principle. After1500cycles of CV durabilitytest, the ECSA loss rate of the ND Pt-Cu is far less than that of the Pt black, showingefficient durability.