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

Abstract

Fuels 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.