University of Michigan, Department of Chemical Engineering Atomic Layer Deposition of Zirconium Oxide for Fuel Cell Applications UIC REU – Summer 2011 AMReL Lab, UIC Department of Bioengineering and Department of Chemical Engineering Christine James University of Michigan, Department of Chemical Engineering

Overview Background Atomic Layer Deposition Data Collected Future Work

Fuel Cell Advantages Provides clean energy Very efficient Fossil fuel 2007 Provides clean energy Hydrogen fuel cells only emit water Very efficient Fuel Values Hydrogen: 141.8 kJ/g Gasoline: 48 kJ/g Coal: 15-27 kJ/g Santhanam et al., Introduction to Hydrogen Technology, 2009, Hoboken, NJ: J. Wiley. Natural Gas 23 % Coal 23 % Nuclear Power 8 % Renewable Energy 6 % Source: US Energy Information Agency Petroleum 40 % Environmentally friendly Hydrogen is not the only fuel, there are also other carbohydrides and biofuels

Sections of the Fuel Cell SOFC FUEL CELL Cathode Oxygen is reduced Electrical Current Fuel In Air In Electrolyte Transports the oxygen ions Excess Fuel and Water Unused Gases Out Anode Hydrogen is oxidized www1.eere.energy.gov

Solid Oxide Fuel Cells (SOFCs) Current SOFCs are high temperature Temperature: about 1000 °C Intermediate Temperature Fuel Cells Temperature: 600-800°C Smaller scale applications Allows use of alternate materials Starts and stops faster Reduces corrosion Offers a wide range of possibilities The reduced corrosion improves the durability

Problem with Reducing Temperature High temperatures needed to transport O2- ions Requirement can be as high as 1200° C Low temperatures cause ionic resistance Approach Deposit electrolytes and analyze Samples from atomic to bulk-like thickness Method to be used: Atomic Layer Deposition Deposit oxide layers on silicon then platinum (Pt)

Atomic Layer Deposition (ALD) H2O Tri-methyl aluminum Al(CH3)3(g) Methyl group (CH3)3(g) Hydroxyl (OH) from surface absorbed H2O Reaction of TMA with OH Methane reaction product CH4 www.cambridgenanotech.com/ald

Chosen Precursor www.aloha.airliquide.com Precursors   Growth Temperature Impurities Metal Precursor O source Range (°C) Preferred (°C) Saturation verified C [-at%] H [-at%] at 300 °C ZyALD Ozone 250-400 300 Yes <1 N.R. Niinistö, et al., Advanced Engineering Materials, 2009, 11, No.4, 223.

ALD System ZyALD There are 4 bubblers so that we can use 4 precursors and this is important when depositing all sections of the fuel cell ZyALD

Pulse and Purge times required Reactor Temperature: 300°C Bubbler Temperature: 50°C Bubbler Pressure: 10 torr Precursor: ZyALD Precursor Pulse Time: Precursor Purge Time: Oxidizer Pulse Time: Oxidizer Purge Time: Run for 40 cycles 20 s 10 s Varied 1.5 s Varied 1 s 17 s Varied 6 s Varied Zr www.cambridgenanotech.com/ald

Temperature Window Reactor Temperature: Varied Bubbler Pressure: 10 torr Bubbler Temperature: 50°C Precursor: ZyALD Temperature Window Precursor Condensation Precursor Decomposition

Comparison to Work from another group Niinistö, et al., J. Mater. Chem. 18, 5243 (2008).

Thickness vs. Cycles Run Reactor Temperature: 300°C Bubbler Pressure: 10 torr Bubbler Temperature: 50°C Precursor: ZyALD Slope: .87 R² = 0.9973

Future Work Deposit the zirconium oxide on Platinum Run electrochemical analysis Electrolyte: Zirconium Oxide Silicon Substrate Platinum

Summary Goal is to lower operating temperature of the fuel cell By decreasing electrolyte layer thickness Atomic Layer Deposition (ALD) is being used Have determined some necessary parameters: Pulse and Purge times Temperature Window for ALD Have compared cycles and thickness Proved linear relationship Next Steps: Deposit on Platinum Run Electrochemical analysis

Acknowledgements National Science Foundation EEC-NSF Grant # 1062943 Graduate Mentor: Runshen Xu Professor Takoudis and Professor Jursich