Synthesis and Characterization of Carbon Catalyst Substrates for Fuel Cell Applications

Abstract

The work in this thesis addresses the synthesis and characterization of porous carbonsubstrates, and their electrochemical and fuel cell evaluation. The approach involvesusing porous carbon materials of different pore characteristics as electrocatalystmaterials for use as cathode catalyst substrates in direct methanol fuel cells (DMFC).In this work, a porous carbon, known as carbonaceous Celatom or C-Celatom, wasprepared by template synthesis using a widely abundant, inexpensive macroporoussilica structure diatomaceous earth (Celatom FW-80). Ordered mesoporous carbonCMK-3 was also produced by template synthesis of mesoporous silica SBA-15.Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used toconfirm the synthesis of the desired carbon structures.Three different platinum deposition techniques were investigated for electrocatalystsynthesis, an incipient wetness technique, as ethylene glycol reduction technique, andan alkoxide reduction technique. Transmission electron microscopy (TEM) and SEManalysis of the catalysts formed using the incipient wetness and ethylene glycoltechniques showed that the synthesized catalysts were not suitable for fuel cell use.Optimization of the alkoxide reduction technique resulted in a deposition technique thatresulted in a well-dispersed catalyst with small, uniform particle sizes (2.1 - 3.1 nm).The synthesized electrocatalysts were evaluated electrochemically and found to havehigh electrochemically active surface areas (ESA) of 33.38 m2 g-1 for Pt/Vulcan XC-72, 22.45 m2 g-1 for Pt/CMK-3 and 20.51 m2 g-1 for Pt/C-Celatom.The oxygen reduction (ORR) activity was evaluated by linear sweep voltammetry(LSV). The Pt/C-Celatom exhibited the greatest activity towards the oxygen reductionreaction, and the greatest number of active sites for the ORR. Assessment of thematerial by electrochemical impedance spectroscopy (EIS) also showed that an MEAwith C-Celatom as the cathode catalyst has the lowest combines charge transfer andmass transport resistance.Single cell DMFC testing was carried out with each of the experimental substrates. Thesynthesized catalysts demonstrated high performance over a range of temperatures andfeed molarity concentrations. The C-Celatom MEA exhibited the greatest power outputof the synthesized catalysts for low molarity operation, with peak power densities of25.8 and 32.6 mW cm-2 with 0.5M and 1M feed respectively.

Date of Award	31 Dec 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Edward Roberts (Supervisor) & Stuart Holmes (Supervisor)