Surface Potentials of (001), (012), (113) Hematite (α-Fe2O3) Crystal Faces in Aqueous Solution
Abstract
Hematite (α-Fe2O3) is an important candidate electrode for energy system technologies such as photoelectrochemical water splitting. Conversion efficiency issues with this material are presently being addressed through nanostructuring, doping, and surface modification. However, key electrochemical properties of hematite/electrolyte interfaces remain poorly understood at a fundamental level, in particular those of crystallographically well-defined hematite faces likely present as interfacial components at the grain scale. We report a combined measurement and theory study that isolates and evaluates the equilibrium surface potentials of three nearly defect-free single crystal faces of hematite, titrated from pH 3 to 11.25. We link measured surface potentials with atomic-scale surface topology, namely the ratio and distributions of surface protonation/deprotonation site types expected from the bulk structure. The data reveal face-specific points of zero potential (PZP) relatable to points of zero net charge (PZC) that lie within a small pH window (8.35-8.85). Over the entire pH range the surface potentials show strong non-Nernstian charging at pH extremes separated by a wide central plateau in agreement with surface complexation modeling predictions, but with important face-specific distinctions. We introduce a new surface complexation model based on fitting the entire data set that depends primarily only on the proton affinities of twomore »
- Authors:
- Publication Date:
- Research Org.:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Org.:
- USDOE
- OSTI Identifier:
- 1092638
- Report Number(s):
- PNNL-SA-95956
39937; KC0302060
- DOE Contract Number:
- AC05-76RL01830
- Resource Type:
- Journal Article
- Journal Name:
- Physical Chemistry Chemical Physics. PCCP, 15(33):13911-139-21
- Additional Journal Information:
- Journal Name: Physical Chemistry Chemical Physics. PCCP, 15(33):13911-139-21
- Country of Publication:
- United States
- Language:
- English
- Subject:
- Environmental Molecular Sciences Laboratory
Citation Formats
Chatman, Shawn ME, Zarzycki, Piotr P., and Rosso, Kevin M. Surface Potentials of (001), (012), (113) Hematite (α-Fe2O3) Crystal Faces in Aqueous Solution. United States: N. p., 2013.
Web. doi:10.1039/c3cp52592a.
Chatman, Shawn ME, Zarzycki, Piotr P., & Rosso, Kevin M. Surface Potentials of (001), (012), (113) Hematite (α-Fe2O3) Crystal Faces in Aqueous Solution. United States. https://doi.org/10.1039/c3cp52592a
Chatman, Shawn ME, Zarzycki, Piotr P., and Rosso, Kevin M. 2013.
"Surface Potentials of (001), (012), (113) Hematite (α-Fe2O3) Crystal Faces in Aqueous Solution". United States. https://doi.org/10.1039/c3cp52592a.
@article{osti_1092638,
title = {Surface Potentials of (001), (012), (113) Hematite (α-Fe2O3) Crystal Faces in Aqueous Solution},
author = {Chatman, Shawn ME and Zarzycki, Piotr P. and Rosso, Kevin M.},
abstractNote = {Hematite (α-Fe2O3) is an important candidate electrode for energy system technologies such as photoelectrochemical water splitting. Conversion efficiency issues with this material are presently being addressed through nanostructuring, doping, and surface modification. However, key electrochemical properties of hematite/electrolyte interfaces remain poorly understood at a fundamental level, in particular those of crystallographically well-defined hematite faces likely present as interfacial components at the grain scale. We report a combined measurement and theory study that isolates and evaluates the equilibrium surface potentials of three nearly defect-free single crystal faces of hematite, titrated from pH 3 to 11.25. We link measured surface potentials with atomic-scale surface topology, namely the ratio and distributions of surface protonation/deprotonation site types expected from the bulk structure. The data reveal face-specific points of zero potential (PZP) relatable to points of zero net charge (PZC) that lie within a small pH window (8.35-8.85). Over the entire pH range the surface potentials show strong non-Nernstian charging at pH extremes separated by a wide central plateau in agreement with surface complexation modeling predictions, but with important face-specific distinctions. We introduce a new surface complexation model based on fitting the entire data set that depends primarily only on the proton affinities of two site types and the two associated electrical double layer capacitances. The data and model show that magnitudes of surface potential biases at the pH extremes are on the order of 100 mV, similar to the activation energy for electron hopping mobility. An energy band diagram for hematite crystallites with specific face expression and pH effects is proposed that could provide a baseline for understanding water splitting performance enhancement effects from nanostructuring, and guide morphology targets and pH for systematic improvements in efficiency.},
doi = {10.1039/c3cp52592a},
url = {https://www.osti.gov/biblio/1092638},
journal = {Physical Chemistry Chemical Physics. PCCP, 15(33):13911-139-21},
number = ,
volume = ,
place = {United States},
year = {Thu Sep 05 00:00:00 EDT 2013},
month = {Thu Sep 05 00:00:00 EDT 2013}
}