University of Central Florida STARS Electronic Theses and Dissertations, 2004-2019 2011 Comparative Study of Ethanol and Methanol Electro-oxidation on a Platinum/ceria Composite Electrode in Alkaline and Acid Solutions : Electro-catalytic Performance and Reaction Kinetics Carlos Humberto Hidalgo Martinez University of Central Florida Part of the Chemistry Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Masters Thesis (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS. For more information, please contact [email protected]. STARS Citation Hidalgo Martinez, Carlos Humberto, "Comparative Study of Ethanol and Methanol Electro-oxidation on a Platinum/ceria Composite Electrode in Alkaline and Acid Solutions : Electro-catalytic Performance and Reaction Kinetics" (2011). Electronic Theses and Dissertations, 2004-2019. 6628. https://stars.library.ucf.edu/etd/6628 COMPARATIVE STUDY OF ETHANOL AND METHANOL ELECTRO-OXIDATION ON A PLATINUM/CERIA COMPOSITE ELECTRODE IN ALKALINE AND ACID SOLUTIONS: ELECTRO- CATALYTIC PERFORMANCE AND REACTION KINETICS by CARLOS HUMBERTO HIDALGO MARTINEZ B.S. University of North Florida, 1999 M.B.A University of Phoenix, 2003 A thesis subMitted in partial fulfillMent of the requireMents for the degree of Master of Science in the Department of Chemistry in the College of Sciences at the University of Central Florida Orlando, Florida Spring TerM 2011 Major Professor: Diego J. Diaz © 2011 Carlos Humberto Hidalgo Martinez ii ABSTRACT A comparative study of the electro-oxidation of ethanol and methanol was carried out on a Pt/ceria composite electrode prepared by electro-deposition. Modification of the Pt electrode was realized by co-deposition from a 1.0 MM K2PtCl6 solution that also contained a 20 mM suspension of ceria. The electro-catalytic activities and stabilities of the Pt/ceria catalyst towards ethanol electro-oxidation reactions (EOR) and Methanol electro-oxidation reactions (MOR) were investigated by potentiodynamic and potentiostatic methods in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions at various concentrations of ethanol and Methanol. The kinetics of ethanol and Methanol on a Pt/ceria composite electrode were measured in 0.5 M sulfuric acid and 1.0 M sodium hydroxide solutions using a rotating disk electrode (RDE). Cyclic voltammetry was employed in temperatures ranging from 15 to 55°C to provide quantitative and qualitative information on the kinetics of alcohol oxidation. The temperature dependence of the electro-catalytic activities afforded the deterMination of apparent activation energies for ethanol and Methanol oxidation. iii Dedicated to My wife and My parents. Carolina, thank you for your support and motivation through these challenging years of graduate school; it would have been insurmountable without you. To my parents, thank you for laying the foundation of success by providing exceptional secondary education and instilling perseverance, dedication, and hard work. iv ACKNOWLEDGMENTS I offer My deep and eternal gratitude to Dr. Diaz. Thank you for your guidance, knowledge, consideration and patience. Thank you for Making students’ learning experiences a priority. Your focus on the prime goal of graduate education instead of grants, publications, and prestige speaks volumes of your character and sets you apart froM the rest. v TABLE OF CONTENTS LIST OF FIGURES ..................................................................................................................................... VII LIST OF TABLES ....................................................................................................................................... XI 1. INTRODUCTION ....................................................................................................................................... 1 2. EXPERIMENTAL ...................................................................................................................................... 5 2.1 REAGENTS ............................................................................................................................................. 5 2.2 METHODS AND APPARATUS ................................................................................................................... 5 2.3 PREPARATION OF MODIFIED ELECTRODES ............................................................................................ 6 3. ETHANOL ELECTRO-OXIDATION ON A PLATINUM/CERIA COMPOSITE ELECTRODE IN ACID MEDIA ................................................................................................................................................. 7 3.1 THE BARE PLATINUM ELECTRODE AND THE TRUE SURFACE AREA OF AN ELECTRODE......................... 7 3.2 THE PT/CERIA COMPOSITE ELECTRODE ................................................................................................. 9 3.3 EFFECT OF SCAN RATE AND ETHANOL CONCENTRATION .................................................................... 11 3.4 THE TEMPERATURE EFFECT ................................................................................................................ 16 3.5 KINETICS ............................................................................................................................................. 20 4. ETHANOL ELECTRO-OXIDATION ON A PLATINUM/CERIA COMPOSITE ELECTRODE IN ALKALINE MEDIA ..................................................................................................................................... 26 4.1 THE BARE PLATINUM ELECTRODE IN 1 M SODIUM HYDROXIDE ......................................................... 26 4.2 THE PT/CERIA COMPOSITE ELECTRODE ............................................................................................... 27 4.3 EFFECT OF SCAN RATE AND ETHANOL CONCENTRATION .................................................................... 29 4.4 THE TEMPERATURE EFFECT ................................................................................................................ 33 4.5 KINETICS ............................................................................................................................................. 36 5. METHANOL ELECTRO-OXIDATION ON A PLATINUM/CERIA COMPOSITE ELECTRODE IN ACID MEDIA ............................................................................................................................................... 40 5.1 THE PT/CERIA COMPOSITE ELECTRODE ............................................................................................... 40 5.2 EFFECT OF SCAN RATE AND METHANOL CONCENTRATION ................................................................. 41 5.3 THE TEMPERATURE EFFECT ................................................................................................................ 44 5.4 KINETICS ............................................................................................................................................. 46 6. METHANOL ELECTRO-OXIDATION ON A PLATINUM/CERIA COMPOSITE ELECTRODE IN ALKALINE MEDIA ..................................................................................................................................... 50 6.1 THE PT/CERIA COMPOSITE ELECTRODE ............................................................................................... 50 6.2 EFFECT OF SCAN RATE AND METHANOL CONCENTRATION ................................................................. 52 6.3 THE TEMPERATURE EFFECT ................................................................................................................ 55 6.4 KINETICS ............................................................................................................................................. 58 7. CONCLUSIONS ....................................................................................................................................... 61 8. REFERENCES .......................................................................................................................................... 63 vi LIST!OF!FIGURES! Figure 1- Clean Pt electrode in 0.5 M H2SO4 Scan rate 0.1 V/s ......................................... 8 Figure 2: Cyclic voltamMogram for 1 M ethanol on a Pt/CeO2 coMposite electrode recorded in 0.5 M H2SO4 electrolyte at 24 !C, scan rate 50 mV/s ........................... 10 Figure 3: Cyclic voltamMograms for 1 M ethanol on Pt/CeO2 composite electrode in 0.5 M H2SO4 electrolyte at 23!C. Scan rates (v) = 200, 100, 150, 50, 25 mV/sec ........ 12 Figure 4: Peak current vs. square root of scan rate plot for 0.25M ethanol in 0.5 M H2SO4. Both peaks show a linear relationship with the square root of the scan rate indicating a diffusion limited reaction. ..................................................................... 14 Figure 5: Peak current vs. square root of scan rate plot for 0.5 M ethanol in 0.5 M H2SO4. The peak at potential 0.7 V does not show a linear relationship linear with the square root of the scan rate indicating an adsorption process. The peak at 1.1 V has a linear relationship with the square root of the scan rate indicating a diffusion limited reaction. ..................................................................................................................... 14 Figure 6: Peak current vs. square root of scan rate plot for 1 M ethanol