Surface and Structural Investigation of a MnOx Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions |
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Authors: | Benjamin J Deibert Jingming Zhang Paul F Smith Dr Karena W Chapman Dr Sylvie Rangan Debasis Banerjee Kui Tan Hao Wang Nicholas Pasquale Prof Feng Chen Prof Ki‐Bum Lee Prof G Charles Dismukes Prof Yves J Chabal Prof Jing Li |
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Institution: | 1. Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA);2. X‐ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (USA);3. Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA);4. Department of Material Science & Engineering, University of Texas at Dallas, Richardson, TX 75080 (USA);5. Department of Chemistry, Biochemistry, and Physics, Rider University, Lawrenceville, NJ 08648 (USA);6. The Waksman Institute, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (USA) |
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Abstract: | Catalytically active MnOx species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnOx catalysts form without supports in situ under photocatalytic conditions. Our most active 4MnOx catalyst (~0.84 mmol O2 mol Mn?1 s?1) forms from a Mn4O4 bearing a metal–organic framework. 4MnOx is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m2g?1) and small regions of crystallinity and layer flexibility. In contrast, the SMnOx formed from Mn2+ salt gives an amorphous species of lower surface area (80 m2g?1) and lower activity (~0.15 mmol O2 mol Mn?1 s?1). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p3/2 core levels detects enriched Mn3+ and Mn2+ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria. |
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Keywords: | birnessite structure manganese oxide metal– organic frameworks water oxidation catalyst water splitting |
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