1. Investigation of the Catalytic Activity of Plasma-Treated Fe, Ni, and Co Foil for Water Splitting Nick Lavrov, Olivia Watson

2. Introduction Increasing evidence for climate change, increasing cost of fossil fuels, and diminishing natural resources motivate today’s alternative energy research. An ideal alternative energy would be cost-effective and renewable. Our project focuses on storing solar energy in chemical bonds, using the body of research in surface science and electrochemical catalysis as our platform. 2

3. Introduction A common mechanism used to store energy from sunlight is called the water splitting reaction H 2 O  O 2 + H 2 (E 0 =1.23 V) Reactive groups called oxides and (oxy)hydroxides can improve the efficiency of oxygen production Plasma (ionized gas) can be used to grow thin layers of these materials on metal electrode surfaces 3

4. Sample Processing Procedure ●Measure, cut and clean foils by sonication in acetone, ethanol, and water, then load and ground sample. ●Turn on water cooling, leak in Ar gas, and ignite plasma to sputter. ●Main treatment: ○Leak in Ar or O 2, then H 2 O ○Heat sample with resistive heating. ○Turn up ion energy and treat for 5-15 minutes. ●Break vacuum with N 2 gas between runs. 4

5. Electrochemistry Electrolyte solution was a solution of 1M NaHCO 3 (NaHCO 3 solid dissolved in DI water). Sample mounted as the working electrode, platinum coil counter electrode, Ag/AgCl (4 M KCl) reference electrode Active area of samples marked off using chemically-resistant tape from 3M 5

6. Results For each foil, we implemented some of the following characterization techniques: Linear Sweep Voltammetry Raman Spectroscopy X-ray Photoelectron Spectroscopy (XPS) Scanning Electron Microscopy (SEM) 6

7. Linear Sweep Voltammetry Current at working electrode is measured while potential between the working electrode and the reference electrode is swept linearly in time. 7

8. Tafel Plot Voltammetry data is converted to fit the Tafel equation. From the graph we can extract the Tafel slope and exchange current density parameters. 8

9. Raman Spectroscopy “Fingerprinting” method to identify the unique inelastic scattering of monochromatic light by chemical bonds Instrument contains optical microscope, useful for initial assessment of changes in surface appearance 9

10. X-ray Photoelectron Spectroscopy (XPS) Analysis technique that focuses X-ray beam on a surface to eject electrons Energy of ejected electron gives information about how tightly it was bound to its atom Every atom has a specific corresponding pattern of electrons at various energy levels 10

11. Scanning Electron Microscopy Special type of microscope that focuses an electron beam on a surface to give a topographical image of a sample SEM has many advantages over light microscopes including: greater depth of field, allow more of a surface image to be in focus at once; very high resolution; very high magnification 11

12. Fe Foil Color Changes At RT, unchanged At 200°C and 250°C, gold At 300°C and 450°C, blue Tempering colors due to thin film interference of iron oxide. 12

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16. SEM: Fe surfaces 50 000x ; 5x5 μm Very strong morphological differences between untreated Fe and hematite; hematite grain size ~160 nm. No obvious morphological difference in magnetite. 16 Untreated FeHematiteMagnetite

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18. SEM: Ni surfaces No obvious morphological differences 18 Untreated Ni 25 000x 10x10 μm Treated Ni 20 000x 13 x 13 μm

19. Ni: X-ray Photoelectron Spectroscopy oxide XPS data confirms an increasing presence of oxidized Ni with samples treated with O 2 /H 2 O plasma. An increased XPS oxide peak corresponds to a small cathodic shift in water oxidation onset potential. 19

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24. Co: Raman Spectroscopy expected peaks at 191, 470, 510, 608, 675 cm -1 24

25. Co: Raman Spectroscopy Co sample 5Co blankCo sample 4 Images taken at 10x magnification during Raman spectroscopy 25

26. SEM: Co surfaces There are many scattered grains across the surface of sample 4, compared to sample 5, which has none. Co sample 4 25,000 x 10 x 10 µm Co sample 5 25,000 x 10 x 10 µm 26

27. SEM: Co surfaces There are not any obvious morphological differences between the two Co samples at a higher magnification. Co sample 4 50,000 x 5 x 5 µm Co sample 5 50,000 x 5 x 5 µm 27

28. Conclusions Plasma treatment seems to be localized to surface and thus too thin to be characterized with Raman spectroscopy Plasma treatment is complex, with many parameters to optimize Future experiments would involve exploring other regimes of plasma treatment including increasing sputtering time, hydrogen plasma, chamber pressure. 28

29. Appendix

30. Gen2 Tectra ® Plasma Source ●Microwave plasma source with magnets at 0.0875T to enhance plasma by ECR. ●Hybrid mode. ●One positive grid to accelerate ions to grounded sample by controlling ion energy. ●High vacuum chamber kept at 10^(-6) Torr. FARADAY CUP ●Aperture of 3mm^2 ●Biased to 54V ●Connected in series to picoammeter to measure current at sample location in relation to ion energy and pressure. ●Materials: stainless steel, sapphire ceramic, tantalum wire. 30

31. Ion Beam Characterization ●Variables: ○Gas: argon, oxygen, water vapor ○Gas mixture ○Partial and total pressure ( 0 - 1.0 mTorr ) ○Ion Energy Ar (mTorr)O 2 (mTorr)H 2 O (mTorr) 1:10.460.450.42 2:30.460.30.75 31

32. Pure Plasma Results Sputtering Conditions: - 1 kV - 10 minutes - 0.46 mTorr - Room Temperature - Used water contact angle to confirm surface cleaning. 32

33. Mixed Plasma Ion Flux 33