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Deconvolution of strain and ligand

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This slide describes about Hydrogen Evolution Reaction and effect of Cu substitution in enhancing the activity. Deconvolution of strain and ligand effect is explained in the slide and in the respective paper.

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Deconvolution of strain and ligand

  1. 1. “Inverse Strain Effect in Atomic Scale” - Enhanced Hydrogen Evolution Activity and Durability in Cu substituted Palladseite Saurav Chandra Sarma 14/11/2018 S.C. Sarma, V. Mishra, K.A. Ann Mary, S. Roy, S.C. Peter, ACS Energy Letters, (2018) 1
  2. 2. Introduction Pd17Se15 (CuPd)17Se15 +Cu Standard colloidal synthesis Hydrogen has the highest energy content per unit mass. Feedstock for fuel cell Ease of production from highly abundant water Why Hydrogen..?? Where does Cu substitute in Pd17Se15 lattice? How does Cu substitution affect structure and oxidation state? What is the driving force for the enhancement of the electrocatalytic activity? 2
  3. 3. Where does Cu substitute in Pd17Se15 lattice? +Cu 3 Decrease in the (330) plane intensity with Cu substitution Left shift in the PXRD peak position instead of right shift  Inverse Strain Effect Cu 128 pm Pd 163 pm Se 190 pm
  4. 4. How does Cu Substitution affect Pd17Se15 lattice? (0) (-2) XAFS experiment performed at P64 Beamline, PETRA III, DESY, Germany 4
  5. 5. Electrochemical Hydrogen Evolution Reaction (HER) Onset improved after Cu substitution High current density at lower overpotential Pd17Se15 13.08 s-1 @200 mV (CuPd)17Se15 126.3 s-1 @200 mV 5
  6. 6. Stability and Faradaic Efficiency Calculation Time (mins) 6
  7. 7. Driving Force for Enhancement of Activity Change in Surface Area No significant contribution from surface area 7 Cdl α Surface Area
  8. 8. Substitution Effect Ligand Effect: Strain Effect: Ensemble Effect: Depends on the nature of the substituent Depends on the size of the substituent Depends on the coordination environment How to DECONVOLUTE these effects..?? 8
  9. 9. Deconvoluting Strain and Ligand Effect a=b=c=8 Å a=b=c= 9 Å a=b=c= 8 Å a=b=c= 9 Å Ligand Effect Strain Effect +Cu  Constrained lattice parameter to A  Cu- substituted  Constrained lattice parameter to B  No substitution (CuPd)17Se15 (B) Pd17Se15 (A) Change in d-band center = (d – Pd17Se15) ɛavg= 𝐸𝜌 𝐸 𝑑𝐸 𝐸𝑓 −∞ 𝜌 𝐸 𝑑𝐸 𝐸𝑓 −∞ 9
  10. 10. Deconvoluting Strain, Ligand and Ensemble Effect Selective-site blocking 10 • Pd2+ is not a good H2 adsorbing material. • Se gets activated because of tensile strain as well as Cu leaching.
  11. 11. Conclusion 11 Effect of Cu substitution Stability for 30000 Cycles Reason for enhancement of activity Site of Cu substitution High TOF of 126.3 s-1. Enhancement of activity after Cu substitution Faradaic efficiency close to 100 % was achieved. Reason for expansion of unit cell H2O

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