Department of Chemical Engineering Nara National College of Technology

1. Department of Chemical Engineering Nara National College of Technology Electrochemical Stability of Au sub-ML on Pt/QC Electrode Nara National college of technology Takanori KOBAYASHI, Atsuhiro KAWAMURA, Katsumi KATAKURA, Hirohisa YAMADA

2. Introduction Department of Chemical Engineering Nara National College of Technology Form of the next-generation energy Next-generation energy device for smart grid society Conventional large-scale power generation Smart grid society • Solar power • Wind generation • Accumulator • Fuel cell • Nuclear power generation • Hydraulic power generation • Thermal power generation It is a next-generation energy device including the Fuel cell to support smart grid society.

3. Introduction Department of Chemical Engineering Nara National College of Technology Energy conversion a battery Electrical Energy Chemical Energy direct conversion Rotation (heat-engine) generation Burn Kinetic energy Thermal energy 燃焼 Thermal power generation The battery can convert chemical energy into electrical energy without having the carneau limitation.

4. Introduction Department of Chemical Engineering Nara National College of Technology Polymer Electrolyte Fuel Cells (PEFCs) O2(air) Reformed H2 e- Pt nanoparticle H+ Separetor Anode reaction Cathode reaction Total reaction Electrolyte Pt catalyst CP(Carbon Paper) Carbon black Fig. 2 Schematic illustration for Pt/C catalyst. Fig. 1 Schematic illustration for PEFCs.

5. Change the design Department of Chemical Engineering Nara National College of Technology Objective work Pt dissolution is one of the most important issue for the commercialization in PEFCs. Gold is most stable material in noble metals. Adzic et. al. reported that Au sub-ML suppress the Pt dissolution. In the experiment In this study, we focused the effect of Au role for the suppression of Pt dissolution, and investigated by the EQCM and RRDE technique. Fig. 3 Schematic illustration for Aumonolayer/Pt/C core-shell catalyst.

6. Experimental Department of Chemical Engineering Nara National College of Technology EQCM technique Fig. 4 Three-electrode glass cell for ORR measurements. • Electrolyte ： 0.05 M H2SO4 • Working electrodes ： Au on QC • (10MHz, • Counter electrode ： Pt • Reference ： RHE • Temperature ： 25℃ P.G.S. QCM Sauerbreyequation :Mass change :Frequency change :Shear stress of the quartz crystal ) :Surface area [] :Density of the quartz crystal ( :Overtone order :Nominal frequency ()

7. Experimental Department of Chemical Engineering Nara National College of Technology RDE technique Fig. 5 Hydrodynamic voltammograms of oxygen reduction current at disk. Rotating rate: 400 – 3600 rpm. Fig. 4 Three-electrode glass cell for ORR measurements. Koutecky－Levichequation • Electrolyte ： 0.1 M HClO4 • Working electrodes ： RDE • Disk: catalyst (Pt/C TKK, 46.8 wt.%) on GC • () • Counter electrode ： Pt-wire • Reference ： RHE • Temperature ： 25℃ • Rotating rate ： 400 – 3600 rpm : the diffusion limiting current n: the number of electron involved in ORR : the Faraday constant : the geometric surface area of the electrode C0*: the equilibrium concentration of dissolve O2 in the solution D0: the diffusion coefficient of dissolve O2 in the solution : the kinematic viscosity of the solution : the angular frequency of rotation water

8. Experimental Department of Chemical Engineering Nara National College of Technology Under Potential Deposition(UPD)method 0.05M H2SO4 + 2mM CuSO4 Cu monolayer(ML) was UPDed on Ptat 0.328V for 10 min. Pt / C 2mM HAuCl4 Cu ML / Pt / C Au ML/Pt/C catalyst was prepared by replacement of CuUPD atoms with Au atoms. 3Cu0 + 2Au3+3Cu2+ + 2Au0 Au ML / Pt / C Fig. 6 Schematic illustration for Au ML/Pt/C preparation.

9. Results and Discussion Department of Chemical Engineering Nara National College of Technology Durability of Pt/QC and Au 1ML/Pt/QC Electrode Square durability on Pt/QC electrode Fig. 7 CV and EQCM measurements on Pt on QC electrode. Scan rate: 50mVs-1. • Typical, Pt peaks (e.g.. Hydrogen adsorption/desorption and PtOx formation/reduction) were observed in CV and EQCM measurements.

10. Results and Discussion Department of Chemical Engineering Nara National College of Technology Durability of Pt/QC and Au 1ML/Pt/QC Electrode Square durability on Pt/QC electrode The amount of Pt dissolution Table.1 The mass of Pt dissolutions per step calculated. Fig. 8 The mass change of Pt measured by EQCM technique during square wave durability tests. Pt dissolution • Pt dissolved into electrolyte above 1.1 V. • The amount of dissolved Pt increased with the increase of upper limit potential. Potential holding time: 3sec 1.0 ~ 1.2 V 0.6 V Square wave

11. Results and Discussion Department of Chemical Engineering Nara National College of Technology Durability of Pt/QC and Au 1ML/Pt/QC Electrode Preparation of Au ML on Pt/QC electrode Fig. 10 CVs on Bare Pt and Au ML on Pt/QC electrodes. Scan rate: 50mVs-1. OCV3min 0.328 V 10min Ptcoveragecalculatedfrom ECSA was ca. 80%. Fig. 9 The frequency change during the preparation of Au ML on Pt/QC electrode. • The atomic ratio calculated from EQCM measurement was larger than theoretically estimated atomic ratio. In addition, surface coverage of Au ML was larger than this ratio. Therefore, Au atoms displaced not only to UPD-Cu but also to surface Pt?? Atomic ratio EQCM : Theoretical:

12. Results and Discussion Department of Chemical Engineering Nara National College of Technology Durability of Pt/QC and Au 1ML/Pt/QC Electrode Square durability on Au ML/Pt/QC electrode Table.2 The mass of Pt dissolutions per step calculated. The amount of Pt dissolution Fig. 11 The mass change on Au ML/Pt/QC measured by EQCM technique during square wave durability tests. Pt dissolution • Pt and/or Au dissolution occurred above 1.2V upper potential than on Pt/QC. • Au ML/Pt/QC dissolved on 1.2 V, but the amount of dissolved Pt was suppressed by Au ML. The durability of Pt dissolution was enhanced by Au 1ML?

13. Results and Discussion Department of Chemical Engineering Nara National College of Technology Effects of Au ML on Activity and Durability in Oxygen Reduction Reaction q= 27.8% Fig. 12 CVs of Pt/C on GC electrode. Scan rate: 50mVs-1. • The coverage of Au sub-monolayer on Pt/C lower than that on Pt/QC.

14. Results and Discussion Department of Chemical Engineering Nara National College of Technology Effects of Au ML on Activity and Durability in Oxygen Reduction Reaction Durability test Pt/C Au 1ML/Pt/C [] Fig. 14 CVs of Pt/C on GC electrode plotted against cycle number. Scan rate: 50mVs-1. Fig. 13 CVs on Au ML/Pt/C and Pt/C on GC electrodes during durability tests . Scan rate: 50mVs-1. • ECSA decreased with increase of potential step. • Au ML/Pt/C had better durability than Pt/C.

15. Results and Discussion Department of Chemical Engineering Nara National College of Technology Effects of Au ML on Activity and Durability in Oxygen Reduction Reaction ORR activity Fig. 15 Activities of Pt/C, Au 1ML/Pt/C at 0.9 V for ORR in 0.1 M HClO4. • Au ML had larger durability than Pt/C, and SA increased after durability test.

16. Department of Chemical Engineering Nara National College of Technology Conclusions • Au ML/Pt/QC and Au xML(x=1 or 2)/Pt/C electrodes were successfully prepared by UPD technique. • Au displacement not only to UPD-Cu, but also to surface Pt was observed in EQCM measurement. • However, the coverage of Au xML(x=1, 2)/Pt/C was much lower than that of Au ML/Pt/QC electrode. • It shows that Au suppressed Pt dissolution during durability test by EQCM and RDE studies. • The durability of Au xML/Pt/C has greater than that of Pt/C in . • This means that Au might suppressed Pt dissolution, and enhanced the SA for ORR after the durability test.