Density Functional Theory Study Of Stability Of Pt Based Catalyst For Fuel Cells

Noble metal Pt remains the best Proton Exchange Membrane Fuel Cells(PEMFC)catalyst, but prohibitively high costs and limited supplies are major hurdles for PEMFCapplications. Wide efforts are being made to replace or reduce the usage of precious Ptcatalyst as the cathode of PEMFC. At present, the most widely used cathode catalystsystem is platinum in the form of small nanoparticles supported on amorphouscarbon-particle aggregates(Pt/C).Based above problems, in this work, theory calculation is applied to study thenature chemistry reason behind the experimental phenomena in the experiment,providing a theoretical basis for the feasibility of the experiment.(1) Given that the stability and catalytic oxygen reduction activity of Pt/C catalysthad been greatly enhanced after covered polyaniline (PANI), Density Functional Theorycalculation was carried out to investigate the essential reason behind this phenomenon.The theoretical calculations suggested that the number of hole in PANI increased withthe transfer of electrons from PANI to support C. It caused PANI partial oxidation andthus strengthened the electric conductivity of PANI. PANI interacted with Pt/C mainlyvia3C atoms or1N atom and2C atoms within the same benzene ring. The systemenergy decreased markedly with the coverage of PANI on the Pt/C. It means that thePt/C@PANI was more stable than Pt/C. The lifted HOMO energy level and lowered dband center of Pt/C@PANI compared with Pt/C were all conductive for (i) electrontransfer between Pt/C@PANI and O2due to the reduced gap between the HOMO ofPt/C@PANI and the LUMO of oxygen and (ii) the desorption of intermediate species onthe surface of the catalysts and releasing fresh catalytic sites for the subsequent reaction.(2) Experimental phenomenon shows that the stability of catalyst Pt for ORR wasenhanced by Ti3C2support. Based on the phenomenon, density function theory (DFT)was used to elucidate the cause behind the difference in catalysis caused by supports.The difference in activities of Pt/Ti3C2and Pt/C catalysts for the ORR could becorrelated with the oxygen and oxygen atom adhesion energies and the d band center ofthe catalysts. PDOS research shows that the interaction of the Ti3C2with Pt leads to thedownward shift of the d-orbital of Pt atoms relative to the Fermi level result in catalystsystem more stable and indicates that the Pd-d and Ti-d states share a matching energyfrom-6eV to0eV, which also accompanied by an electron transfer from Ti to Pt. The adsorption behavior of the CO molecule on the Pt/Ti3C2surface was compared withthose obtained on the Pt(111) surface with a surface structure similar to thePt(111)/Ti3C2surface. An obvious elongation of the Pt-C distance and a decrease in COadsorption energy show that the Pt(111)/Ti3C2surface, relative to the Pt(111) surface,exhibits much improved resistance to CO poisoning.