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Title: Facet-Dependent Kinetics and Energetics of Hematite for Solar Water Oxidation Reactions

Abstract

Currently, the performance of a photoelectrochemical (PEC) system is highly dependent on the charge separation, transport and transfer characteristics at the photoelectrode|electrolyte interface. Of the factors that influence the charge behaviors, the crystalline facets of the semiconductor in contact with the electrolyte play an important role but has been poorly studied previously. Here, we present a study aimed at understanding how the different facets of hematite affect the charge separation and transfer behaviors in a solar water oxidation reaction. Specifically, hematite crystallites with predominantly {012} and {001} facets exposed were synthesized. Density functional theory (DFT) calculations revealed that hematite {012} surfaces feature higher OH coverage, which was confirmed by X-ray photoelectron spectroscopy (XPS). These surface OH groups act as active sites to mediate water oxidation reactions, which plays a positive role for the PEC system. These surface OH groups also facilitate charge recombination, which compromises the charge separation capabilities of hematite. Moreover, intensity modulated photocurrent spectroscopy (IMPS) confirmed that hematite {012} surfaces exhibit higher rate constants for both charge transfer and recombination. Open circuit potential (OCP) measurements revealed that the hematite {012} surface reflects a greater degree of Fermi level pinning effect. Our results shed light on how different surfacemore » crystal structures may change surface kinetics and energetics. The information is anticipated to contribute to efforts on optimizing PEC performance for practical solar fuel synthesis.« less

Authors:
 [1];  [2]; ORCiD logo [1];  [1]; ORCiD logo [3]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [1]
  1. Boston College, Chestnut Hill, MA (United States)
  2. Yale Univ., New Haven, CT (United States)
  3. Boston College, Chestnut Hill, MA (United States); Yale Univ., New Haven, CT (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC); Yale Univ., New Haven, CT (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
OSTI Identifier:
1543691
Grant/Contract Number:  
[FG02-07ER15909]
Resource Type:
Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
[ Journal Volume: 11; Journal Issue: 6]; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; hematite; photoelectrochemistry; water splitting; kinetics; energetics; facet

Citation Formats

Li, Wei, Yang, Ke R., Yao, Xiahui, He, Yumin, Dong, Qi, Brudvig, Gary W., Batista, Victor S., and Wang, Dunwei. Facet-Dependent Kinetics and Energetics of Hematite for Solar Water Oxidation Reactions. United States: N. p., 2018. Web. doi:10.1021/acsami.8b05190.
Li, Wei, Yang, Ke R., Yao, Xiahui, He, Yumin, Dong, Qi, Brudvig, Gary W., Batista, Victor S., & Wang, Dunwei. Facet-Dependent Kinetics and Energetics of Hematite for Solar Water Oxidation Reactions. United States. doi:10.1021/acsami.8b05190.
Li, Wei, Yang, Ke R., Yao, Xiahui, He, Yumin, Dong, Qi, Brudvig, Gary W., Batista, Victor S., and Wang, Dunwei. Thu . "Facet-Dependent Kinetics and Energetics of Hematite for Solar Water Oxidation Reactions". United States. doi:10.1021/acsami.8b05190. https://www.osti.gov/servlets/purl/1543691.
@article{osti_1543691,
title = {Facet-Dependent Kinetics and Energetics of Hematite for Solar Water Oxidation Reactions},
author = {Li, Wei and Yang, Ke R. and Yao, Xiahui and He, Yumin and Dong, Qi and Brudvig, Gary W. and Batista, Victor S. and Wang, Dunwei},
abstractNote = {Currently, the performance of a photoelectrochemical (PEC) system is highly dependent on the charge separation, transport and transfer characteristics at the photoelectrode|electrolyte interface. Of the factors that influence the charge behaviors, the crystalline facets of the semiconductor in contact with the electrolyte play an important role but has been poorly studied previously. Here, we present a study aimed at understanding how the different facets of hematite affect the charge separation and transfer behaviors in a solar water oxidation reaction. Specifically, hematite crystallites with predominantly {012} and {001} facets exposed were synthesized. Density functional theory (DFT) calculations revealed that hematite {012} surfaces feature higher OH coverage, which was confirmed by X-ray photoelectron spectroscopy (XPS). These surface OH groups act as active sites to mediate water oxidation reactions, which plays a positive role for the PEC system. These surface OH groups also facilitate charge recombination, which compromises the charge separation capabilities of hematite. Moreover, intensity modulated photocurrent spectroscopy (IMPS) confirmed that hematite {012} surfaces exhibit higher rate constants for both charge transfer and recombination. Open circuit potential (OCP) measurements revealed that the hematite {012} surface reflects a greater degree of Fermi level pinning effect. Our results shed light on how different surface crystal structures may change surface kinetics and energetics. The information is anticipated to contribute to efforts on optimizing PEC performance for practical solar fuel synthesis.},
doi = {10.1021/acsami.8b05190},
journal = {ACS Applied Materials and Interfaces},
number = [6],
volume = [11],
place = {United States},
year = {2018},
month = {5}
}

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