Redox Kinetics and Nonstoichiometry of Ce0.5Zr0.5O2−δ for Water Splitting and Hydrogen Production

Handle URI:
http://hdl.handle.net/10754/626725
Title:
Redox Kinetics and Nonstoichiometry of Ce0.5Zr0.5O2−δ for Water Splitting and Hydrogen Production
Authors:
Zhao, Zhenlong ( 0000-0002-5087-7586 ) ; Uddi, Mruthunjaya; Tsvetkov, Nikolai; Yildiz, Bilge; Ghoniem, Ahmed F.
Abstract:
Water splitting and chemical fuel production as a promising carbon-neutral energy solution relies critically on an efficient electrochemical process over catalyst surfaces. The fundamentals within the surface redox pathways, including the complex interactions of mobile ions and electrons between the bulk and the surface, along with the role of adsorbates and electrostatic fields remain yet to be understood quantitatively. This work presents a detailed kinetics study and nonstoichiometry characterization of Ce0.5Zr0.5O2−δ (CZO), one of the most recognized catalysts for water splitting. The use of CZO leads to >60% improvement in the kinetic rates as compared with undoped ceria with twice the total yield at 700 °C, resulting from the improved reducibility. The peak H2 production rate is 95 μmol g–1 s–1 at 700 °C, and the total production is 750 μmol g–1. A threshold temperature of 650 °C is required to achieve significant H2 production at fast rates. The redox kinetics is modeled using two-step surface chemistry with bulk-to-surface transport equilibrium. Kinetics and equilibrium parameters are extracted, and the model predictions show good agreement with the measurements. The enthalpy of bulk defect formation for CZO is found to be 262 kJ/mol, >40% lower than that of undoped ceria. As oxygen vacancy is gradually filled up, the surface H2O splitting chemistry undergoes a transition from exothermic to endothermic, with the crossover around δ = 0.04 to 0.05, which constrains the further ion incorporation process. Our kinetics study reveals that the H2O splitting process with CZO is kinetics limited at low temperature and transitions to partial-equilibrium with significantly enhanced backward reaction at high temperature. The charge-transfer step is found to be the rate-limiting step for H2O splitting. The detailed kinetics and nonstoichiometric equilibria should be helpful in guiding the design and optimization of CZO as a catalyst, oxygen storage material, as well as oxygen carrier for water-splitting applications.
Citation:
Zhao Z, Uddi M, Tsvetkov N, Yildiz B, Ghoniem AF (2017) Redox Kinetics and Nonstoichiometry of Ce0.5Zr0.5O2−δ for Water Splitting and Hydrogen Production. The Journal of Physical Chemistry C 121: 11055–11068. Available: http://dx.doi.org/10.1021/acs.jpcc.7b00644.
Publisher:
American Chemical Society (ACS)
Journal:
The Journal of Physical Chemistry C
Issue Date:
25-Apr-2017
DOI:
10.1021/acs.jpcc.7b00644
Type:
Article
ISSN:
1932-7447; 1932-7455
Sponsors:
This study is financially supported by a grant from the British Petroleum (BP) and the King Abdullah University of Science and Technology (KAUST) Investigator Award.
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Publications Acknowledging KAUST Support

Full metadata record

DC FieldValue Language
dc.contributor.authorZhao, Zhenlongen
dc.contributor.authorUddi, Mruthunjayaen
dc.contributor.authorTsvetkov, Nikolaien
dc.contributor.authorYildiz, Bilgeen
dc.contributor.authorGhoniem, Ahmed F.en
dc.date.accessioned2018-01-04T07:51:42Z-
dc.date.available2018-01-04T07:51:42Z-
dc.date.issued2017-04-25en
dc.identifier.citationZhao Z, Uddi M, Tsvetkov N, Yildiz B, Ghoniem AF (2017) Redox Kinetics and Nonstoichiometry of Ce0.5Zr0.5O2−δ for Water Splitting and Hydrogen Production. The Journal of Physical Chemistry C 121: 11055–11068. Available: http://dx.doi.org/10.1021/acs.jpcc.7b00644.en
dc.identifier.issn1932-7447en
dc.identifier.issn1932-7455en
dc.identifier.doi10.1021/acs.jpcc.7b00644en
dc.identifier.urihttp://hdl.handle.net/10754/626725-
dc.description.abstractWater splitting and chemical fuel production as a promising carbon-neutral energy solution relies critically on an efficient electrochemical process over catalyst surfaces. The fundamentals within the surface redox pathways, including the complex interactions of mobile ions and electrons between the bulk and the surface, along with the role of adsorbates and electrostatic fields remain yet to be understood quantitatively. This work presents a detailed kinetics study and nonstoichiometry characterization of Ce0.5Zr0.5O2−δ (CZO), one of the most recognized catalysts for water splitting. The use of CZO leads to >60% improvement in the kinetic rates as compared with undoped ceria with twice the total yield at 700 °C, resulting from the improved reducibility. The peak H2 production rate is 95 μmol g–1 s–1 at 700 °C, and the total production is 750 μmol g–1. A threshold temperature of 650 °C is required to achieve significant H2 production at fast rates. The redox kinetics is modeled using two-step surface chemistry with bulk-to-surface transport equilibrium. Kinetics and equilibrium parameters are extracted, and the model predictions show good agreement with the measurements. The enthalpy of bulk defect formation for CZO is found to be 262 kJ/mol, >40% lower than that of undoped ceria. As oxygen vacancy is gradually filled up, the surface H2O splitting chemistry undergoes a transition from exothermic to endothermic, with the crossover around δ = 0.04 to 0.05, which constrains the further ion incorporation process. Our kinetics study reveals that the H2O splitting process with CZO is kinetics limited at low temperature and transitions to partial-equilibrium with significantly enhanced backward reaction at high temperature. The charge-transfer step is found to be the rate-limiting step for H2O splitting. The detailed kinetics and nonstoichiometric equilibria should be helpful in guiding the design and optimization of CZO as a catalyst, oxygen storage material, as well as oxygen carrier for water-splitting applications.en
dc.description.sponsorshipThis study is financially supported by a grant from the British Petroleum (BP) and the King Abdullah University of Science and Technology (KAUST) Investigator Award.en
dc.publisherAmerican Chemical Society (ACS)en
dc.titleRedox Kinetics and Nonstoichiometry of Ce0.5Zr0.5O2−δ for Water Splitting and Hydrogen Productionen
dc.typeArticleen
dc.identifier.journalThe Journal of Physical Chemistry Cen
dc.contributor.institutionDepartment of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United Statesen
dc.contributor.institutionDepartment of Mechanical Engineering, University of Alabama, Tuscaloosa, Alabama 35487, United Statesen
dc.contributor.institutionDepartment of Nuclear Science & Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United Statesen
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