Carbon nanofiber layers on metal and carbon substrates : PEM fuel cell and microreactor applications

摘要

This thesis describes the preparation of CNF layers on flat and porous substrates and their application as catalyst supports for chemical and electrochemical gas‐liquidsolid (G‐L‐S) catalytic reactions. Metal nanoparticles growing CNFs on flat metal substrates at 600°C are easily formed from NiO, in contrast to Fe and Co oxides, leading to higher carbon deposition rates. However, high activity towards total carbon deposition is generally detrimental for obtaining well‐attached and homogenously distributed CNFs. Dense carbon (C) and entangled CNF layers are deposited on Ni foils at 450°C after either oxidation or oxidation‐reduction pretreatments. The preparation of stable and thick CNF layers involves a compromise between the deposition of a thick C layer and the amount of weakly attached CNFs. The addition of 5% H2 produces thicker, rougher and more porous CNF layers than when 1% H2 is used. The water wetting properties of the samples are more significantly influenced by the CNF layer thickness than both surface roughness and porosity. A CNF layer is also grown on a porous stainless steel substrate. Pd nanoparticles deposition on the CNFs is performed for the catalytic reduction of nitrite with H2 in an aqueous solution. The presence of the CNFs on the stainless steel surface had a significant effect on the reactor performance. Even without the presence of H2 and Pd, the NO2‐ ions were successfully reduced. A CNF layer and subsequent Pt nanoparticles deposition is performed on a carbon paper substrate for the electrocatalytic oxygen reduction reaction (ORR). The Pt electrochemical surface area, when deposited on CNFs, is much higher than that obtained for commercial Pt/Vulcan. The external oxygen diffusion is higher for Pt/CNFs, as compared to Pt/Vulcan, due to the intrinsic morphology of the CNFs that allow a better accessibility to oxygen diffusion.