Investigation On The Stability Of Pt/Carbon Nanotube Catalysts And Novel Methods For The Preparation Of The Electrodes For PEMFC

Proton exchange membrane fuel cells (PEMFC) have been receiving increasing attention due to its high energy efficiency and being environmentally friendly. However, PEMFCs'wide application and commercialization is hindered by two serious issues: poor durability or short life time, and high cost. Carbon nanotubes (CNT) are new promising materials of catalyst supports for PEMFCs. Previous studies reveal that CNTs supported catalysts show enhanced catalytic activity towards oxygen reduction reaction (ORR) and methanol oxidation.The effect of their diamters on the electrochemical stability of CNTs is investigated and CNTs with the diameter between 10~20 nm (D1020) show the most strong resistance to electrochemical oxidation among all the investigated CNTs. So it is selected in the following work. The electrochemical stability of CNTs and Vulcan XC-72 carbon black is investigated using an accelerated degradation test (ADT) by applying a fixed potential of 1.2 V (vs. reversible hydrogen electrode, RHE) on the two electrodes in 0.5 mol·L-1 H2SO4 for 120 h at room temperature. Cyclic voltammetry (CV) and X-ray Photoelectron Spectroscopy (XPS) analysis show that more surface oxygen is formed on the surface of Vulcan XC-72 during the electrochemical oxidation under the same conditions, which indicates that CNTs are more resistant to electrochemical oxidation than Vulcan XC-72. The strong stability of CNTs is attributed to their specific structures.The electrochemical stability of Pt/CNT and Pt/Vulcan XC-72 is investigated by applying a constant potential of 1.2 V on the two electrodes in 0.5 mol·L-1 H2SO4 for 192 h (8 days) at room temperature. Transmission Electron Microscope (TEM) images show that the sintering of Pt nanoparticles is more pronounced for Pt/Vulcan XC-72 than that for Pt/CNT. XPS analysis indicates that the oxidation degree of Vulcan XC-72 is higher than that of CNTs. The electrochemical surface area (ESA) of Pt/Vulcan XC-72 electrode decreases by 49.8% after ADT, while only 26.1% for Pt/CNT, which means that PT/CNT is more stable than Pt/Vulcan XC-72 under electrochemical operation. The enhanced stability of Pt/CNT is attributed to the specific interaction between Pt nanoparticles and CNTs and CNTs'high stability under electrochemical conditions. The electrochemical stability of Pt/CNT is closely...