Atomic Layer Deposition of Zirconium Oxide for Fuel

Atomic Layer Deposition of Zirconium Oxide for Fuel Cell Applications UIC REU – Summer 2011 AMRe. L 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

Fossil fuel Fuel Cell Advantages • Provides clean energy – Hydrogen fuel cells – only emit water 2007 Natural Gas 23 % Coal 23 % Nuclear Power 8 % Renewable Energy 6 % • Very efficient – Fuel Values • Hydrogen: 141. 8 k. J/g • Gasoline: 48 k. J/g • Coal: 15 -27 k. J/g Santhanam et al. , Introduction to Hydrogen Technology, 2009, Hoboken, NJ: J. Wiley. Petroleum 40 % Source: US Energy Information Agency Environmentally friendly

Sections of the Fuel Cell • Cathode – Oxygen is reduced SOFC FUEL CELL Electrical Current Fuel In Air In • Electrolyte – Transports the oxygen ions • Anode – Hydrogen is oxidized Excess Fuel and Water Unused Gases Out www 1. 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

Problem with Reducing Temperature • High temperatures needed to transport O 2 - 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) Tri-methyl aluminum Al(CH 3)3(g) Methyl group (CH 3)3(g) Hydroxyl (OH) from surface absorbed H 2 O Reaction of TMA with OH Methane reaction product CH 4 H 2 O www. cambridgenanotech. com/ald

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

ALD System Zy. ALD

Pulse and Purge times required Reactor Temperature: 300°C Bubbler Temperature: 50°C Bubbler Pressure: 10 torr Precursor: Zy. ALD 6 s Precursor Pulse Time: Varied Precursor Purge Time: 10 20 s Varied 1 ss 1. 5 Oxidizer Pulse Time: Varied Oxidizer Purge Time: 17 Varied s Run for 40 cycles Zr Growth Rate (Å/cycle) Growth Rate (Å/cycle) 111 1 0. 95 0. 9 0. 80. 9 0. 85 0. 75 0. 60. 8 0. 75 0. 65 0. 7 0. 4 0. 6 2 20. 2 12 www. cambridgenanotech. com/ald 7 2. 50. 4 133 0. 6 3. 5140. 8 4 1154. 5 1. 2516 12 1. 4 5. 5 171. 6 6 Precursor Purge Time (s) Precursor Oxidizer Pulse Purge. Time(s) 6. 5 1. 8 18

Temperature Window Reactor Temperature: Varied Bubbler Temperature: 50°C Bubbler Pressure: 10 torr Precursor: Zy. ALD 2 Growth Rate (Å/cycle) 1. 8 1. 6 1. 4 1. 2 Temperature Window 1 0. 8 0. 6 Precursor Condensation Precursor Decomposition 0. 4 0. 2 0 50 100 150 200 250 Temperature (°C) 300 350 400

Comparison to Work from another group Growth Rate (Å/cycle) 1. 8 1. 6 1. 4 1. 2 1 0. 8 0. 6 0. 4 0. 2 0 225 Niinistö, et al. , J. Mater. Chem. 18, 5243 (2008). 250 275 300 Temperature (°C) 325 350

Thickness vs. Cycles Run Reactor Temperature: 300°C Bubbler Temperature: 50°C Bubbler Pressure: 10 torr Precursor: Zy. ALD 160 Thickness (Å) 140 120 Slope: . 87 R² = 0. 9973 100 80 60 40 20 0 0 50 100 Number of Cycles Run 150

Future Work 1. Deposit the zirconium oxide on Platinum 2. Run electrochemical analysis Electrolyte: Zirconium Oxide Silicon Platinum Substrate

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