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Title:Modifications and studies of the anode catalyst layer for the direct formic acid fuel cell
Author(s):Morgan, Robert D.
Director of Research:Masel, Richard I.
Doctoral Committee Chair(s):Kenis, Paul J.A.
Doctoral Committee Member(s):Masel, Richard I.; Miley, George H.; Harley, Brendan A.; Zhao, Huimin
Department / Program:Chemical & Biomolecular Engr
Discipline:Chemical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Fuel Cells
Palladium
Electrochemistry
Formic Acid
corrosion
Carbon Nanotubes
Carbon Monoxide (CO) Poisoning
Abstract:There is a growing awareness of the need to investigate alternative energy sources due to the environmental impact and limitations that fossil fuels have. In this work, electrochemical research is reported that includes studies and modifications of the anode structure for the Direct Formic Acid Fuel Cell. Four different concepts will be discussed. The first is the study of the effect of Nafion® loading in the anode catalyst layer using electrochemical techniques. Nafion®, within the anode and cathode catalyst layers, plays a large role in the performance of fuel cells. Nafion® also serves as a binder to help hold the catalyst nanoparticles onto the proton exchange membrane (PEM). The DFAFC anode temporarily needs to be regenerated by raising the anode potential to around 0.8 V vs. RHE to oxidize CO bound to the surface, but the Pourbaix diagram predicts that Pd will corrode at these potentials. Data will be presented to examine Pd durability at three different Nafion® loadings: 10, 30 and 50 wt. %. Lastly, cyclic voltammetry data will be presented that suggests that the Nafion® adds to the production of CO during oxidation of formic acid for 12 hours at 0.3 V vs. RHE. The resulting data showed that an increase in CO coverage was observed with increasing Nafion® content in the anode catalyst layer. Secondly, data for a palladium-decorated carbon nanotube catalyst prepared on a gas diffusion electrode via vacuum filtration that shows improved electrooxidation of formic acid is discussed. During linear sweep voltammetry, the palladium-decorated CNT showed a current of 0.18 mA cm-2 , while the standard palladium black catalyst only showed a current of 0.082 mA cm-2 at 0.3 V vs. RHE . This is a 120 % improvement. Also during a 12 hour chronoamperogram at 0.3 V vs. RHE, the palladium-decorated CNT catalyst showed a factor of 3.5 improvement at the end of 12 hours. The current was also much more stable for the palladium-decorated CNT. During the last 8.5 hours, the palladium-decorated CNT show a current loss of 36%, whereas the standard palladium black catalyst showed a current loss of nearly 90%. Lastly we report that the palladium-decorated CNT showed better current stability under potential cycling. After 300 cycles in 12 M HCOOH from 0.02 to 1.45 V vs. RHE, the palladium-decorated CNT showed only a 33% current loss when measured at 0.3 V vs. RHE. However, the standard palladium showed a decay of 60% when also measured at 0.3 V vs. RHE. It was also found that antimony doubles the rate of reaction in an electrochemical cell, but the increase is less in real fuel cell conditions. The current that is produced at 0.6 V is approximately 14% greater for the fuel cell containing antimony additions than the palladium anode catalyst. In a constant-current test, it was found that the fuel cell assembled with palladium–antimony anode catalyst produces 18% more voltage than the palladium anode catalyst after 9 h of operation. Lastly, palladium was modified with an electropolymerized aniline layer to attempt to increase the performance of the direct formic acid fuel cell. It was shown in the electrochemical cell that there was a 62% increase in formic acid oxidation current. However, when tested in the fuel cell, the enhancement at 0.6 V was only 10 %. This is likely due to the complicated environment of the fuel cell, which causes the results to not directly translate to the fuel cell. Unfortunately, long term studies indicated that the voltage decay in the polyaniline-modified electrode was steeper than palladium.
Issue Date:2011-08-26
URI:http://hdl.handle.net/2142/26304
Rights Information:Copyright 2011 Robert D. Morgan
Date Available in IDEALS:2011-08-26
2013-08-27
Date Deposited:2011-08


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