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Mefford JT, Akbashev AR, Kang M, Bentley CL, Gent WE, Deng HD, Alsem DH, Yu YS, Salmon NJ, Shapiro DA, Unwin PR, Chueh WC. Correlative operando microscopy of oxygen evolution electrocatalysts. Nature 2021; 593:67-73. [PMID: 33953412 DOI: 10.1038/s41586-021-03454-x] [Citation(s) in RCA: 175] [Impact Index Per Article: 58.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 03/15/2021] [Indexed: 11/09/2022]
Abstract
Transition metal (oxy)hydroxides are promising electrocatalysts for the oxygen evolution reaction1-3. The properties of these materials evolve dynamically and heterogeneously4 with applied voltage through ion insertion redox reactions, converting materials that are inactive under open circuit conditions into active electrocatalysts during operation5. The catalytic state is thus inherently far from equilibrium, which complicates its direct observation. Here, using a suite of correlative operando scanning probe and X-ray microscopy techniques, we establish a link between the oxygen evolution activity and the local operational chemical, physical and electronic nanoscale structure of single-crystalline β-Co(OH)2 platelet particles. At pre-catalytic voltages, the particles swell to form an α-CoO2H1.5·0.5H2O-like structure-produced through hydroxide intercalation-in which the oxidation state of cobalt is +2.5. Upon increasing the voltage to drive oxygen evolution, interlayer water and protons de-intercalate to form contracted β-CoOOH particles that contain Co3+ species. Although these transformations manifest heterogeneously through the bulk of the particles, the electrochemical current is primarily restricted to their edge facets. The observed Tafel behaviour is correlated with the local concentration of Co3+ at these reactive edge sites, demonstrating the link between bulk ion-insertion and surface catalytic activity.
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Affiliation(s)
- J Tyler Mefford
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA. .,Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
| | - Andrew R Akbashev
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA.,Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
| | - Minkyung Kang
- Department of Chemistry, University of Warwick, Coventry, UK
| | | | - William E Gent
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA
| | - Haitao D Deng
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA
| | | | - Young-Sang Yu
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | | | - David A Shapiro
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Patrick R Unwin
- Department of Chemistry, University of Warwick, Coventry, UK
| | - William C Chueh
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA. .,Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
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Incorporation of tetracarboxylate ions into octacalcium phosphate for the development of next-generation biofriendly materials. Commun Chem 2021; 4:4. [PMID: 36697512 PMCID: PMC9814588 DOI: 10.1038/s42004-020-00443-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Accepted: 12/07/2020] [Indexed: 01/28/2023] Open
Abstract
Octacalcium phosphate (OCP; Ca8(HPO4)2(PO4)4 ∙ 5H2O) is a precursor of hydroxyapatite found in human bones and teeth, and is among the inorganic substances critical for hard tissue formation and regeneration in the human body. OCP has a layered structure and can incorporate carboxylate ions into its interlayers. However, studies involving the incorporation of tetracarboxylic and multivalent (pentavalent and above) carboxylic acids into OCP have not yet been reported. In this study, we investigate the incorporation of pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), a type of tetracarboxylic acid, into OCP. We established that pyromellitate ions could be incorporated into OCP by a wet chemical method using an acetate buffer solution containing pyromellitic acid. The derived OCP showed a brilliant blue emission under UV light owing to the incorporated pyromellitate ions. Incorporation of a carboxylic acid into OCP imparted new functions, which could enable the development of novel functional materials for biomedical applications.
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