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Title: Photo-induced water oxidation at the aqueous GaN (101¯0) interface: Deprotonation kinetics of the first proton-coupled electron-transfer step

Photoeclectrochemical water splitting plays a key role in a promising path to the carbon-neutral generation of solar fuels. Wurzite GaN and its alloys (e.g., GaN/ZnO and InGaN) are demonstrated photocatalysts for water oxidation, and they can drive the overall water splitting reaction when coupled with co-catalysts for proton reduction. In the present work, we investigate the water oxidation mechanism on the prototypical GaN (101¯0) surface using a combined ab initio molecular dynamics and molecular cluster model approach taking into account the role of water dissociation and hydrogen bonding within the first solvation shell of the hydroxylated surface. The investigation of free-energy changes for the four proton-coupled electron-transfer (PCET) steps of the water oxidation mechanism shows that the first PCET step for the conversion of –Ga-OH to –Ga-O˙⁻ requires the highest energy input. We further examine the sequential PCETs, with the proton transfer (PT) following the electron transfer (ET), and find that photo-generated holes localize on surface –NH sites is thermodynamically more favorable than –OH sites. However, proton transfer from –OH sites with subsequent localization of holes on oxygen atoms is kinetically favored owing to hydrogen bonding interactions at the GaN (101¯0)–water interface. We find that the deprotonation of surface –OHmore » sites is the limiting factor for the generation of reactive oxyl radical ion intermediates and consequently for water oxidation.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [3] ;  [2]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States); Yale Univ., New Haven, CT (United States)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. Yale Univ., New Haven, CT (United States)
Publication Date:
OSTI Identifier:
1183858
Report Number(s):
BNL--107983-2015-JA
Journal ID: ISSN 2155-5435; R&D Project: CO045; KC0301020
Grant/Contract Number:
SC00112704
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:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY water oxidation; density functional theory; GaN; photocatalysis; aqueous interface; AIMD