New views of the surface electrochemistry of platinum

Transcription

1 New views of the surface electrochemistry of platinum Marc Koper Leiden University (NL) CINF Summerschool Gilleleje (DK), 7-12 August 2016

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4 Outline How to understand basic voltammetry of platinum interaction of Pt with H 2 O, H, OH and O. New surface chemistry of platinum at (not so) very negative potential, and how to make nanoparticles Why is hydrogen evolution on platinum in alkaline media slow?

5 Blank CV of poly-pt in H 2 SO 4 H 3 O + + e - + * H ads + H 2 O Pt + H 2 O PtOx + H + + e - H UPD 1. Surface area/roughness 2. Surface structure 3. Surface porosity?

6 Nature of third H-peak (?) i (µa) E for oxide formation vs. RHE 1.5 V V 1.2 V 1.1 V 1.0 V 0.9 V 0.8 V 0.7 V 0.6 V Ep (V vs. RHE) E (V vs. RHE) Scan rate (V s -1 ) Depends on extent of previous surface oxidation Slow H formation (in contrast to other H UPD peaks) Disappears after cycling in double layer region Special unstable site in porous Pt surface layer? M.P.Sumino, S.Shibata, Electrochim.Acta 14 (1992) 2629 O.Diaz-Morales, M.T.M. Koper, in preparation

7 H ads and OH ads on Pt(111) H 2 O + e - + * H ads + OH - OH - + * OH ads + e - H 3 O + + e - + * H ads + H 2 O H 2 O + * OH ads + H + + e -

8 Comparison to DFT OH ads j / μa cm -2 H ads double layer region J. Rossmeisl, J.K. Nørskov, C.D. Taylor, M.J. Janik, M. Neurock, J. Phys. Chem. B 110 (2006) C.D. Taylor, R.G. Kelly, M. Neurock, J. Electrochem. Soc. 154 (2007) F217 M.T.M.Koper, Electrochim.Acta 56 (2011) 10645

9 H upd /Pt(111) The H upd is well described by the Frumkin isotherm G.Jerkiewicz, Prog.Surf.Sci.57 (1998) 137 exp./fit DFT G ads /ev ε nn /ev M.T.M.Koper, J.J.Lukkien, J.Electroanal.Chem. 485 (2000) 161 G.S.Karlberg et al., Phys.Rev.Lett. 99 (2007)

10 H and OH on stepped platinum 3.0x10-5 H on (110) steps 2.0x10-5 Pt(111) Pt( ) OH on terraces j / A cm x M NaOH -1.0x x10-5 H on terraces H on (100) steps -3.0x E / V RHE 1. Why is there only one step-related peak? 2. Why are the terrace-related peaks broad, and are the step-related peaks sharp? 3. Why is there a difference between acid and alkaline?

11 Charge of step peak About 1 e transferred per Pt step atom, both in acid and alkaline media H + + e H ads J. Clavilier, K. El Achi, and A. Rodes, J. Electroanal. Chem. 272 (1989) 253 J. Clavilier, K. El Achi, and A. Rodes, Chem. Phys. 141 (1990) 1 M.J.T.C.van der Niet, N.Garcia-Araez, J.Hernandez, J.M.Feliu, M.T.M.Koper, Catal.Today 202 (2013) 105

12 ph dependence of step peak anomalous 10 mv RHE /ph (regular 0 mv RHE /ph for terrace) excludes simple H + + e H ads M.J.T.C.van der Niet, N.Garcia-Araez, J.Hernandez, J.M.Feliu, M.T.M.Koper, Catal.Today 202 (2013) 105

13 Why the step peak is sharp Sharp peak implies: Attractive interactions between H on steps (unlikely) Adsorbate replacement reaction: H ads + x H 2 O x OH ads + (1+x) H + + (1+x) e - H covered Pt(100) 1ML The effective interaction energy for competing adsorbates may be negative (i.e., attractive) if the interparticle repulsion exceeds the sum of the intraparticle repulsions. Br covered Pt(100) 0.5 ML Typically satisfied if a smaller adsorbate competes with a bigger adsorbate. N.Garcia-Araez, J.J.Lukkien, M.T.M.Koper, J.M.Feliu, J.Electroanal.Chem. 588 (2006) 1

14 Further evidence: effect of Li Pt (111) Pt (15,15,14) Na + Li + Na + Be Pt(111) Pt(15,15,14) j / µa cm Pt (554) j / µacm Pt(554) 40 Pt (553) 50 Pt(553) Pt (110) 50 Pt(110) E / V vs RHE E / V vs RHE C.Stoffelsma, G.Garcia, P.Rodriguez, N.Garcia-Araez, D.Strmncik, N.M.Markovic, M.T.M.Koper, J.Am.Chem.Soc. 132 (2010) 16127

15 ph dependence of the step peak Negatively charged water on steps Co-adsorbed cation weakens OH bond K.Schwarz, B.Xu, Y.Yan, R.Sundaraman, Phys.Chem.Chem.Phys. 18 (2016) I.T.McCrum, M.J.Janik, ChemElectroChem (2016), in press

16 New water structures at steps DFT prediction of water tetragons near steps UHV-STM image of double lines of water near steps of a Pt(553) surface M.J.Kolb, R.G.Farber, J.Derouin, C.Badan, F.Calle-Vallejo, L.B.F.Juurlink, D.R.Killelea, M.T.M.Koper, Phys.Rev.Lett. 116 (2016)

17 H OPD H UPD DL OH ads O ads 3D oxide/ α-pto 2 4 Current /µa 2 0 J. F. Li, et al, Nature 2010, 464, Nichols & Bewick JEAC Potential /V (vs. RHE)

18 SHINERS of Pt(111)/HClO 4 Intensity /a.u. υ Cl-O Raman Shift /cm -1 Bulk 0.60 V 0.65 V 0.70 V 0.75 V 0.80 V 0.85 V 0.90 V 0.95 V 1.00 V Intensity /a.u. 2D 3D 2D Raman Shift /cm V 1.0 V 1.1 V 1.3 V 1.4 V 1.7 V 1.8 V Normalized Intensity /a.u Potential /V (vs. RHE) Intensity PtO 2 xh 2 O PtO Raman Shift /cm V 1.8 V 1.1 V 1.0 V Y.-F.Huang, P.J.Kooyman, M.T.M.Koper, Nature Comm. 7 (2016) 12440

19 Two-dimensional Pt-(su)peroxide? Species Bond Length /Å υ Pt-O2 / cm -1 υ O-O / cm -1 oxygen atom / Charge on a.u. Pt(111)(OH) 2 -O [Pt(111)(OH) 2 -O 2 ] [Pt(111)-(O 2 ) 2 ] Y.-F.Huang, P.J.Kooyman, M.T.M.Koper, Nature Comm. 7 (2016) A.Panchenko, M.T.M.Koper, T.E.Shubina, S.J.Mitchell, E.Roduner, J.Electrochem.Soc. 151 (2004) A 2016

20 SHINERS of Pt(100)/HClO 4 H UPD OH ads α-pto 2 Current /µa Potential /V (vs. RHE) 0.9 V Intensity /a.u Raman Shift /cm V 0.2 V Intensity /a.u Raman Shift /cm V 1.80 V 1.40 V 1.30 V 1.20 V 1.10 V 1.00 V 0.95 V 0.90 V 0.85 V

21 What happens to Pt at -10 Volt? Before Twenty fold increase in surface area After A.I.Yanson, P.Rodriguez, N.Garcia-Araez, R.V.Mom, F.D.Tichelaar, M.T.M.Koper, Angew.Chem.Int.Ed. 50 (2011) 6346

22 ac voltage generates nanoparticles

23 TEM Size distribution nm More

24 Mechanism of cathodic corrosion Works for every metal we tried It is not hydride formation (with only H + it does not work) It is not alloying by alkali (organic cations work as well) It is not physical disintegration (it starts at ca V!) Our hypothesis: it involves the formation of short-lived metallic anions (Zintl ions?) as intermediates A.I.Yanson, P.Rodriguez, N.Garcia-Araez, R.V.Mom, F.D.Tichelaar, M.T.M.Koper, Angew.Chem.Int.Ed. 50 (2011) 6346

25 Works for alloys Pt (-----) Pt90Rh10 (-----) Pt70Rh30 (-----) Pt20Rh80 (-----) Rh (-----) Nitrate reduction P.Rodriguez, F.D.Tichelaar, M.T.M.Koper, A.I.Yanson, J.Am.Chem.Soc. 133 (2011) 17626

26 Onset of cathodic corrosion Corrosion treatment in 10 M NaOH; characterization in 0.5 M H 2 SO 4 T.J.P.Hersbach, A.I.Yanson, M.T.M.Koper, Nature Comm. 7 (2016) 12653

27 Anisotropic etching -0.2 V -0.4 V -0.5 V -0.6 V -0.6 V -0.8 V T.J.P.Hersbach, A.I.Yanson, M.T.M.Koper, Nature Comm. 7 (2016) 12653

28 Can tune size and shape 100 counts b 25µA/cm ma 290 ma 220 ma 180 ma 125 ma 85 ma 33 ma 25 ma 17 ma 15 ma E (V vs RHE) More 100 terraces with higher current Larger size with higher (average) current A.I.Yanson, P.Antonov, P.Rodriguez, M.T.M.Koper, Electrochim.Acta 113 (2013) 913

29 Gives pretty pictures

30 What about kinetics?

31 Kinetics of H and OH adsorption acid alkaline H upd formation in alkalineis slow; H upd formation in acidic is fast K.J.P.Schouten, M.J.T.C. van der Niet, M.T.M.Koper, Phys.Chem.Chem.Phys. 12 (2010) 15217

32 ph dependent hydrogen evolution j / µa.cm E / V RHE ph 1 ph 11 ph 12 ph 13 H 2 evolution in alkalineis slow; H 2 evolution in acidic is fast I.Ledezma-Yanez, W.D.Z.Wallace, P.Sebastian Pascual, V.Climent, J.M.Feliu, M.T.M.Koper, in preparation

33 ph dependent Tafel slope Tafel slope (IR corrected) / mv.dec ph Rate-determining step of H 2 evolution is ph dependent I.Ledezma-Yanez, W.D.Z.Wallace, P.Sebastian Pascual, V.Climent, J.M.Feliu, M.T.M.Koper, in preparation

34 Potential of zero total charge

35 Proton transfer through solvent layer Proton transfer is slow through solvent layer polarized by electric field O.Pecina, W.Schmickler, Chem.Phys. 228 (1998) 265

36 HER and H-UPD on Pt(111)/Ni(OH) 2 a) HER b) H-UPD mv.dec -1 Pt(111) Pt(111)/Ni(OH) 2 4 E / V RHE Pt(111), ph 13 Pt(111)/Ni(OH) 2, ph 13 Pt(111), ph 1 37 mv.dec mv.dec ct / ms R log i E / V RHE Ni(OH) 2 on the Pt(111) surface enhances HER and H-UPD in alkaline D.Strmcnik et al. Nature Chem. 5 (2013) 300 I.Ledezma-Yanez, W.D.Z.Wallace, P.Sebastian Pascual, V.Climent, J.M.Feliu, M.T.M.Koper, in preparation

37 Pzc/pme of Pt(111) and Ni-Pt(111) Blank Pt(111) Ni(OH) ML 0.2 ML Ni(OH) 2 i / A After measurement TJT E / V Pd Potential of maximum entropy close to V (vs RHE) Potential of maximum entropy close to V (vs RHE) I.Ledezma-Yanez, W.D.Z.Wallace, P.Sebastian Pascual, V.Climent, J.M.Feliu, M.T.M.Koper, in preparation

38 Shift in thermal coefficient ph 10 j / µ µa.cm Pt(111) a) Pt(111)/Ni(OH) Pt(111) b) c) Pt(111)/Ni(OH) Pt(111) E / V RHE d) E / mv -2-4 (δe/δt) M / mv.k -1 Pt(111)/Ni(OH) E / V RHE V V V V t /µs I.Ledezma-Yanez, W.D.Z.Wallace, P.Sebastian Pascual, V.Climent, J.M.Feliu, M.T.M.Koper, in preparation

39 PT through interfacial water In acidic media, H upd and H 2 evolution happen close to the pztc/pme: water is less ordered and easy to reorganize during charge transfer through the double layer In alkaline media, H upd and H 2 evolution happen far from the pztc/pme: water is more ordered and difficult to reorganize during charge transfer through the double layer Promoters shift the pztc/pme

40 Conclusions We still don t fully/really understand the blank voltammetry of platinum and the surface processes involved There is a phenomenon called cathodic corrosion that we don t really understand We don t really understand ph effects in hydrogen evolution; maybe our new model can help (?)

41 Acknowledgements Janneke van der Niet, Yi-Fan Huang, Manuel Kolb, Ludo Juurlink, Federico Calle-Vallejo, Isis Ledezma-Yanez, David Wallace, Alex Yanson, Paramaconi Rodriguez, Thom Hersbach, Oscar Diaz-Morales Paula Sebastian, Victor Climent, Juan Feliu (University of Alicante) Rachel Farber, Dan Killelea (Loyola University, Chicago) Netherlands Organization for Scientific Research (NWO) National Research School Catalysis (NRSC) Hitachi High Technologies European Commission Marie Curie Fellowship