The Simulation And Design Of The High Efficient,low Cost Fuel Cell Electrode Nanomaterials Supported On Titanium Carbide

Due to the energy crisis and environment problems,fuel cells are receiving considerable attention both in the industry and the science.Among different kinds of fuel cells,the proton exchange membrane fuel cells?PEMFCs?have been recognized as potential future power sources for many applications such as the zero/low-emission vehicles and portable power stations.The traditional electrode catalysts for PEMFC are typically Pt nanoparticles supported on carbon.Carbon can be easily corroded in the electrochemical environment.Pt-based catalysts encounter the stability problem and are easily poisoned by CO.The over-dependence of Pt limits the application of PEMFC in the traditional industry.To this end,cheaper and more effective electrocatalysts are therefore needed for the further development of fuel cell technology.The nano-materials supported on transition mental carbide?TMC?would be a good solution to overcome the problems through optimizing the substrate and supported metals.First-principles methods based on the density functional theory are employed to investigate the stability and activity of Ti C with the consideration of the surfaces orientation,chemical potential and surface vacancy defects.Then,the supporting of small Pt_n?n=1⁵?clusters on the Ti C?001?,the interaction between them and the variations of the electronic properties are elucidated.Finally,the Pd monolayer supported on Ti C?001?is designed,what is more,the adsorption,diffusion,and dissociation of O₂ on it are calculated.Our findings provide a guidance for designing high efficient and low cost catalysts.The main work performed and results reached are as follows:?1?The surface energy of Ti C is investigated with the consideration of the variations of the surface orientation,termination and carbon chemical potential,as well as the influence of surface vacancy defects of various concentrations.We found that the surface relaxation results in rumpling of the?001?and?110?surfaces and the contraction of the?111?surfaces.The relative stability of the low-index surfaces of Ti C varies with the carbon chemical potential,surface defects and vacancy concentrations,which will have an effect on the nanoparticles morphology and catalytic performance in practice.?2?The interactions between the small platinum clusters?Pt_n,n=1⁵?and the Ti C?001?surface is investigated.The results show that a single Pt atom prefers to be adsorbed at the C-top site,while a Pt₂ cluster prefers dimerization and a Pt₃ cluster forms a linear structure on the Ti C?001?.As for Pt₄ cluster,the three-dimensional distorted tetrahedral structure and the two-dimensional square structure almost have equal stability.In contrast with the two-dimensional isolated Pt₅ cluster,the adsorbed Pt₅ cluster prefers a three-dimensional structure on Ti C?001?.Substantial charge transfer takes place from Ti C?001?surface to the adsorbed Pt_n clusters,resulting in the negatively charged Pt_n clusters.At last,the d-band centers of the adsorbed the Pt atoms are studied,predicting that 2D Pt_n/Ti C might be an ideal candidate for the electrocatalyst.?3?The adsorption,diffusion and dissociation of O₂ on the palladium monolayer supported on Ti C?001?surface are elucidated.We found that the interaction strength between Pd and C is large enough to maintain the monolayer configuration avoiding clustering.The presence of the Ti C?001?will strongly modify the electronic structure.The supported ML Pd has a d-band center of 2.38 e V below the Fermi level,which is almost the same as that of Pt?111?.What is more,the combination of MLPd with Ti C?001?substrate can improve the efficiency for the adsorption of oxygen molecule and weaken the oxygen atom binding strength simultaneously.The dissociation barriers of oxygen are relatively small and less depend on the oxygen coverage.The diffusion of O₂ and O between the adjacent Hollow sites is easy on MLPd/Ti C?001?.Hence,the model of MLPd/Ti C?001?may be a high efficient ORR catalyst.