Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 11, Issue 6, Pages 5616-5622Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.8b05190
Keywords
hematite; photoelectrochemistry; water splitting; kinetics; energetics; facet
Funding
- Boston College
- NSF [CBET 1703663, 1703655]
- U.S. Department of Energy (DOE), Chemical Sciences, Geosciences, and Biosciences Division, Office of Science, Office of Basic Energy Sciences (BES) [DEFG02-07ER15909]
- Div Of Chem, Bioeng, Env, & Transp Sys
- Directorate For Engineering [1703655] Funding Source: National Science Foundation
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The performance of a photoelectrochemical (PEC) system is highly dependent on the charge separation, transport and transfer characteristics at the photoelectrodel 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. Indeed, 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 exhibits 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 expected to contribute to efforts on optimizing PEC performance for practical solar fuel synthesis.
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