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Title: Platinum nanoparticle during electrochemical hydrogen evolution: Adsorbate distribution, active reaction species, and size effect

For small Pt nanoparticles (NPs), catalytic activity is, as observed, adversely affected by size in the 1–3 nm range. We elucidate, via first-principles-based thermodynamics, the operation H* distribution and cyclic voltammetry (CV) during the hydrogen evolution reaction (HER) across the electrochemical potential, including the underpotential region (U ≤ 0) that is difficult to assess in experiment. We consider multiple adsorption sites on a 1 nm Pt NP model and show that the characteristic CV peaks from different H* species correspond well to experiment. We next quantify the activity contribution from each H* species to explain the adverse effect of size. From the resolved CV peaks at the standard hydrogen electrode potential (U = 0), we first deduce that the active species for the HER are the partially covered (100)-facet bridge sites and the (111)-facet hollow sites. Upon evaluation of the reaction barriers at operation H* distribution and microkinetic modeling of the exchange current, we find that the nearest-neighbor (100)-facet bridge site pairs have the lowest activation energy and contribute to ~75% of the NP activity. Edge bridge sites (fully covered by H*) per se are not active; however, they react with neighboring (100)-facet H* to account for ~18% of themore » activity, whereas (111)-facet hollow sites contribute little. As a result, extrapolating the relative contributions to larger NPs in which the ratio of facet-to-edge sites increases, we show that the adverse size effect of Pt NP HER activity kicks in for sizes below 2 nm.« less
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [1]
  1. Institute of High Performance Computing, Singapore (Singapore)
  2. Iowa State Univ., Ames, IA (United States)
Publication Date:
OSTI Identifier:
1227220
Report Number(s):
IS-J--8649
Journal ID: ISSN 2155-5435
Grant/Contract Number:
AC02-07CH11358
Type:
Accepted Manuscript
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 5; Journal Issue: 4; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY first-principles; cluster expansion; adsorption isotherm; hydrogen evolution; hydrogen oxidation; cyclic voltammetry; catalysis; platinum; electrochemistry