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Zakaria SNA, Hollingsworth N, Islam HU, Roffey A, Santos-Carballal D, Roldan A, Bras W, Sankar G, Hogarth G, Holt KB, de Leeuw NH. Insight into the Nature of Iron Sulfide Surfaces During the Electrochemical Hydrogen Evolution and CO 2 Reduction Reactions. ACS APPLIED MATERIALS & INTERFACES 2018; 10:32078-32085. [PMID: 30028585 DOI: 10.1021/acsami.8b08612] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Greigite and other iron sulfides are potential, cheap, earth-abundant electrocatalysts for the hydrogen evolution reaction (HER), yet little is known about the underlying surface chemistry. Structural and chemical changes to a greigite (Fe3S4)-modified electrode were determined at -0.6 V versus standard hydrogen electrode (SHE) at pH 7, under conditions of the HER. In situ X-ray absorption spectroscopy was employed at the Fe K-edge to show that iron-sulfur linkages were replaced by iron-oxygen units under these conditions. The resulting material was determined as 60% greigite and 40% iron hydroxide (goethite) with a proposed core-shell structure. A large increase in pH at the electrode surface (to pH 12) is caused by the generation of OH- as a product of the HER. Under these conditions, iron sulfide materials are thermodynamically unstable with respect to the hydroxide. In situ infrared spectroscopy of the solution near the electrode interface confirmed changes in the phosphate ion speciation consistent with a change in pH from 7 to 12 when -0.6 V versus SHE is applied. Saturation of the solution with CO2 resulted in the inhibition of the hydroxide formation, potentially due to surface adsorption of HCO3-. This study shows that the true nature of the greigite electrode under conditions of the HER is a core-shell greigite-hydroxide material and emphasizes the importance of in situ investigation of the catalyst under operation to develop true and accurate mechanistic models.
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Affiliation(s)
- Siti N A Zakaria
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , U.K
- Faculty of Science , Universiti Brunei Darussalam , Jln Tungku Link , Gadong BE1410 , Brunei
| | - Nathan Hollingsworth
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , U.K
| | - Husn U Islam
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , U.K
| | - Anna Roffey
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , U.K
| | - David Santos-Carballal
- School of Chemistry , Cardiff University , Main Building, Park Place , Cardiff CF10 3AT , U.K
| | - Alberto Roldan
- School of Chemistry , Cardiff University , Main Building, Park Place , Cardiff CF10 3AT , U.K
| | - Wim Bras
- European Synchrotron Radiation Facility , BP220, Grenoble F38043 , France
| | - Gopinathan Sankar
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , U.K
| | - Graeme Hogarth
- Department of Chemistry , Kings College London , Britannia House, 7 Trinity Street , London SE1 1DB , U.K
| | - Katherine B Holt
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , U.K
| | - Nora H de Leeuw
- Department of Chemistry , University College London , 20 Gordon Street , London WC1H 0AJ , U.K
- School of Chemistry , Cardiff University , Main Building, Park Place , Cardiff CF10 3AT , U.K
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Mejia Likosova E, Collins RN, Keller J, Freguia S. Anodic reactivity of ferrous sulfide precipitates changing over time due to particulate speciation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:12366-12373. [PMID: 24093133 DOI: 10.1021/es402967e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The disposal of ferric phosphate (FePO4) sludge, routinely generated in wastewater and drinking water treatment, has a major impact on the overall treatment cost. Iron sulfide (FeSx) precipitation via sulfide addition to ferric phosphate (FePO4) sludge has been proven to be an effective method for phosphate recovery. Electrochemical oxidation of FeSx can then be utilized to recover ferric iron for reuse back in the phosphate removal process. In this study, the reactivity of FeSx particles for anodic oxidation at pH 4 was studied as a function of time after FeSx precipitate generation at a S/Fe molar ratio of 1.75. Cyclic voltammetry showed high reactivity for fresh FeSx particles, but the reactivity diminished significantly over a period of 1 month. X-ray absorption spectroscopy (XAS) revealed that this reduced reactivity with time is a consequence of the transformation of the FeSx particles in suspension from mackinawite (FeS) to pyrite (FeS2).
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Affiliation(s)
- Elena Mejia Likosova
- The University of Queensland , Advanced Water Management Centre (AWMC), St Lucia, Brisbane, Queensland 4072, Australia
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El Mendili Y, Abdelouas A, Bardeau JF. Insight into the mechanism of carbon steel corrosion under aerobic and anaerobic conditions. Phys Chem Chem Phys 2013; 15:9197-204. [DOI: 10.1039/c3cp50853f] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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