Nitrogen doped highly ordered mesoporous carbon as catalyst and catalyst support for oxygen reduction

PhD ThesisFuels such as hydrogen, produced from renewable resources and efficiently utilized in environment friendly fuel cells are crucial to long term energy security. However, the lack of cost-effective catalysts, with a performance similar to that of platinum, is a major obstacle to the development of the fuel cell technology. This work researched cheap and environmental friendly oxygen reduction catalysts, based on carbon, which can replace platinum for oxygen reduction reaction (ORR) in the cathode of alkaline and microbial fuel cells. Nitrogen doped mesoporous carbon was prepared by pyrolyzing 1,2-diaminobenzene in a template of highly ordered mesoporous silica (KIT-6) at 700, 800 and 900 oC. Manganese oxides are active catalysts for ORR and as they are an earth abundant metal with widespread availability, this offsets a key drawback of the platinum group metals (PGM). A simple chemical deposition method (using KMnO4) and physical deposition followed by heat treatment (using Mn(NO3)2) was used to prepare amorphous and crystalline manganese oxides which were separately deposited on ordered mesoporous nitrogen doped carbon (OMNC) and on ordered mesoporous carbon (OMC) without nitrogen doping respectively. The catalysts were characterized by Transmission Electron Microscopy (TEM), X-ray powder diffraction (XRD), Raman Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS) and nitrogen adsorption-desorption. Cyclic voltammetry and linear sweep voltammetry (LSV) with a rotating-ring disk electrode (RRDE) were used for electrochemical characterisation of the iv oxygen reduction reaction (ORR). They were also tested as cathode catalysts in a microbial fuel cell. The best catalysts in alkaline media (0.1 M KOH) were amorphous manganese oxide on OMNC and OMC. They had onset potentials of 1.04 V and 1.05 V (RHE); half-wave potentials of 0.83 V and 0.82 V (RHE) respectively. This behaviour may be because the amorphous oxide maintained the ordered pore structure of the catalysts by depositing a thin coating of nanoparticle catalysts within them, thus causing a fast three phase reaction and excellent catalyst utilization. In the microbial fuel cell, the best catalysts were the amorphous MnO2 on OMC and on nitrogen doped carbon pyrolyzed at 900oC with equal power densities of.the Petroleum Technology Development Fund (PTDF) Nigeri

A two-phase flow and non-isothermal agglomerate model for a proton exchange membrane (PEM) fuel cell

A two dimensional, across the channel, steady-state model for a proton exchange membrane fuel cell (PEMFC) is presented in which the non-isothermal model for temperature distribution, the two-phase flow model for liquid water transport and the agglomerate model for oxygen reduction reaction are fully coupled. This model is used to investigate thermal transport within the membrane electrode assembly (MEA) associated with the combinational water phase-transfer and transport mechanisms. Effective temperature distribution strategies are established aim to enhance the cell performance. Agglomerate assumption is adopted in which the ionomer and liquid water in turn cover the agglomerate to form the ionomer and liquid water films. Ionomer swelling is associated with the non-uniform distribution of the water content. The modelling results show that heat accumulates within the cathode catalyst layer under the channel. Higher operating temperature improves the cell performance by increasing the kinetics, reducing the liquid water saturation on the cathode and increasing the water carrying capacity of the anode gas. Applying higher temperature on the anode and enlarging the width ratio of the channel/rib could improve the cell performance. Higher cathode temperature decreases the oxygen mole fraction, resulting in an insufficient oxygen supply and a limitation of the cell performance