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Electrochemical nanogravimetric studies of platinum in acid and neutral media

Electrochemical nanogravimetric studies of platinum in acid and neutral media. György Inzelt , Balázs Berkes and Ákos Kriston Department of Physical Chemistry, Eötvös Loránd University, Budapest, Hungary RSE-SEE, Belgrade, 2010. Electrochemical quartz crystal nan obalance measurements.

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Electrochemical nanogravimetric studies of platinum in acid and neutral media

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  1. Electrochemical nanogravimetric studies of platinum in acid and neutral media György Inzelt, Balázs Berkes and Ákos Kriston Department of Physical Chemistry, Eötvös Loránd University, Budapest, Hungary RSE-SEE, Belgrade, 2010

  2. Electrochemical quartz crystal nanobalance measurements Working electrode: 5 MHz AT-cut crystal coated with platinum.The geometrical and piezoelectrically active area of the working electrode were1.22 cm2 and 0.33 cm2, respectively. Counter electrode: platinum wire. Reference electrode: a sodium chloride saturated calomel electrode (SCE).

  3. Relationship between frequency and surface mass Df – frequency change Cf – integral sensitivity Dm – mass change A – surface area f0 – fundamental frequency mk – shear modulus of quartz ρk – density of quartz νtr – wave speed in quartz Lk – thickness of the quartz Df = - Cf Cf = 3.43 x 107 Hz cm2g-1(5 MHz) 5 MHz crystal: 9 ng= 1 Hz Ageom = 1.22 cm2, Apiezo = 0.33 cm2

  4. Df = - (mol cm-2) ρF – density of the contacting liquid ηF – viscosity of the contacting liquid Q – charge consumed n – charge number of the electrode reaction M – molar mass Γ – surface concentration Ar = frAgeom fr – roughness factor Effect of immersion in liquid Electrochemical relationships

  5. General observations Platinum, H2SO4

  6. General observations Pt + H2O PtOH + H+ + e- Pt-H  Pt + H+ + e- M = 14-20 g mol-1 M = 4-20 g mol-1 PtO + 2 H+ + 2 e- → Pt + H2OEo = 0.98 V

  7. Effect of scan rate, Pt-Pt,0 oC

  8. Peak current vs. Scan rate

  9. Effect of the platinization and roughness factor Pt-Pt, 1 M H2SO4, v = 10mV s-1, 20 oC, - 0.22 V – + 1.0 V, fr (1) = 24, fr (2) = 52,

  10. Effect of the platinization and roughness factor Pt-Pt, 1 M H2SO4, v = 10mV s-1, 20 oC, fr (1) = 24, fr (2) = 52

  11. Effect of temperature Smooth vacuum-deposited Pt, 3rd, 12th, 16th and 21st cycles1 M H2SO4, v = 100 mV s-1

  12. Effect of temperature Pt-Pt,1 M H2SO4,v = 10 mV s-1,Df (Pt-deposition) = - 1950 Hz,4th, 13th and 20th cycles

  13. The hydrogen region and the double layer region

  14. M = 4-20 (n = 1)

  15. Anion adsorption

  16. Voltradiometric and cyclic voltammetric curvesPt-Pt, 1.7 x 10-3 M H235SO4 in 1 M HClO4, v = 0.25 mVs-1(The potential values are referred to RHE) Horányi (1987)

  17. Effect of the concentration of sulfuric acid

  18. The effect of the concentration of sulfuric acid on the cyclic voltammetric response (a) at a platinized platinum electrode (fr = 19.4) in contact with (1) 0.1, (2) 0.5, (3) 1, and (4) 4 mol dm-3 H2SO4

  19. The effect of the concentration of sulfuric acid on the EQCN frequency response (b) detected simultaneously with the CVs at the platinized platinum electrode shown in (a) in contact with (1) 0.1, (2) 0.5, (3) 1, and (4) 4 mol dm-3 H2SO4

  20. The effect of the concentration of sulfuric acid on the EQCN frequency response ( Δf vs. E curves) detected simultaneously with the CVs at the platinized platinum electrode shown in (a) in contact with (1) 0.1, (2) 0.5, (3) 1, and (4) 4 mol dm-3 H2SO4

  21. Cation adsorption Effect of the concentration of Cs2SO4

  22. The effect of the concentration of Cs2SO4 on the cyclic voltammetric (a) response (1) 0.0 (2) 0.029, (3) 0.056, (4) 0.1, (5) 0.12, and (6) 0.136 mol dm-3Cs2SO4

  23. The effect of the concentration of Cs2SO4 on the simultaneously detected EQCN frequency (b) response (1) 0.0 (2) 0.029, (3) 0.056, (4) 0.1, (5) 0.12, and (6) 0.136 mol dm-3Cs2SO4

  24. The effect of the concentration of Cs2SO4 on the simultaneously detected EQCN frequency (c) response (( Δf vs. E curves) (1) 0.0 (2) 0.029, (3) 0.056, (4) 0.1, (5) 0.12, and (6) 0.136 mol dm-3Cs2SO4

  25. The excess frequency difference (Δf) as a function of the concentration of Cs+ ions. Δf is the difference of the frequencies measured at – 0.28 V vs. SCE and those calculated from the density and the viscosity of the respective solutions The continuous lines are fitting curves by using a Langmuir-type equation: y = a×b×x / (1 + b×x).

  26. The difference between the charges measured for the oxidative removal of adsorbed hydrogen in the absence (S) and presence of Cs+ ions (Cs) in H2SO4 solutions related to that of the pure sulfuric acid (S) as a function of the concentration ratio of Cs+ and H+ ions. The continuous lines are fitting curves by using a Langmuir-type equation: y = a×b×x / (1 + b×x).

  27. The mass change as a function of the charge consumed in the hydrogen upd region and double layer region. The calculated values of the apparent molar masses (M)of the adsorbed species are indicated. (1) 0.05 and (2) 0.5 mol dm-3 H2SO4,(3) 0.136 mol dm-3 Cs2SO4 + 0.127 mol dm-3 H2SO4 solution.

  28. Potential step experiment from -0.2 to 0.2 V, H oxidation M = 9.8±0.1 (n = 1) M = 5.5±0.1 (n = 1) M = 2.8±0.1 (n = 1) Pt-Pt, fr = 64,1 M H2SO4; 50 oC;

  29. Potential step experiment from 0.25 to - 0.2 V, H+ reduction, Pt-Pt, 1 M H2SO4 , 60 °C M = 8.7±0.1 (n = 1) M = 8.4±0.2 (n = 1)

  30. The hydrogen evolution region pH and cation dependence

  31. Pt – Pt, 1 M H2SO4, v = 10 mV s-1

  32. Pt – Pt, H2SO4 – K2SO4 (pH 2), v = 10 mV s-1

  33. Oxide region Effect of the concentration of H2SO4andCs2SO4

  34. The effect of the concentration of sulfuric acid on the cyclic voltammetric response (a) for the potential region including the formation of platinum oxide. Concentrations: (1) 0.1, (2) 0.5, (3) 1, and (4) 4 mol dm-3 H2SO4. Scan rate: 10 mV s-1.

  35. The effect of the concentration of sulfuric acid.The ∆f vs. E plots (b) for the potential region including the formation of platinum oxide. Concentrations: (1) 0.1, (2) 0.5, (3) 1, and (4) 4 mol dm-3 H2SO4. Scan rate: 10 mV s-1.

  36. Potential step experiment.Oxide formationPt-Pt, 0.35 V – 1.3 V, 1 M H2SO4, 60 oC M = 18.6 g mol-1

  37. The effect of the concentration of Cs2SO4 on the cyclic voltammetric (a) response for the potential region including the formation of platinum oxide. Concentrations: (1) 0.0 (2) 0.029, (3) 0.1, (4) 0.12, and (5) 0.136 mol dm-3 Cs2SO4. Scan rate: 10 mV s-1.

  38. The effect of the concentration of Cs2SO4 on the simultaneously obtained EQCN frequency response (b) for the potential region including the formation of platinum oxide. Concentrations: (1) 0.0 (2) 0.029, (3) 0.1, (4) 0.12, and (5) 0.136 mol dm-3 Cs2SO4. Scan rate: 10 mV s-1.

  39. Cathodic dissolution of platinum

  40. Effect of the positive potential limit and scan rate I. „Smooth”, vacuum-deposited Pt, fr = 4, 0.5 M H2SO4, v = 50 mV s-1, 20 oC, - 0.22 V – + 1.1 V

  41. Effect of the positive potential limit and scan rate II. „Smooth”, vacuum-deposited Pt, fr = 4, 0.5 M H2SO4, v = 50 mV s-1, 20 oC, - 0.22 V – + 1.25 V

  42. Effect of the positive potential limit and scan rate III. „Smooth”, vacuum-deposited Pt, fr = 4, 0.5 M H2SO4, v = 10 mV s-1, 20 oC, - 0.22 V – + 1.2 V

  43. Effect of the positive potential limit and scan rate IV. „Smooth”, vacuum-deposited Pt, fr = 4, 0.5 M H2SO4, v = 5 mV s-1, 20 oC, - 0.22 V – + 1.2 V

  44. Effect of the positive potential limit and scan rate V. „Smooth”, vacuum-deposited Pt, fr = 4, 0.5 M H2SO4, v = 5 mV s-1, 20 oC, - 0.22 V – + 1.2 V (1) 5th, (2) 12th cycles

  45. Effect of the positive potential limit and scan rate V. „Smooth”, vacuum-deposited Pt, fr = 4, 0.5 M H2SO4, v = 5 mV s-1, 20 oC, - 0.22 V – + 1.2 V (1) 5th, (2) 12th cycles

  46. Cathodic dissolution of platinum PtO2 + 4 H+ + 2 (2-x) e-  x Pt2+ + (1-x) Pt + 2 H2O PtO2 + 2 H+ + 2 e-  Pt(OH)2 Pt(OH)2 + 2 H+ Pt2+ + 2 H2O

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