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Published September 14, 2015 | Accepted Version + Supplemental Material
Journal Article Open

Molecular Mixed-Metal Manganese Oxido Cubanes as Precursors to Heterogeneous Oxygen Evolution Catalysts

Abstract

Well-defined mixed-metal [CoMn₃O₄] and [NiMn₃O₄] cubane complexes were synthesized and used as precursors for heterogeneous oxygen evolution reaction (OER) electrocatalysts. The discrete clusters were dropcasted onto glassy carbon (GC) and indium tin oxide (ITO) electrodes, and the OER activities of the resulting films were evaluated. The catalytic surfaces were analyzed by various techniques to gain insight into the structure-function relationships of the electrocatalysts' heterometallic composition. Depending on preparation conditions, the Co-Mn oxide was found to change metal composition during catalysis, while the Ni–Mn oxides maintained the NiMn₃ ratio. XAS studies provided structural insights indicating that the electrocatalysts are different from the molecular precursors, but that the original NiMn₃O₄ cubane-like geometry was maintained in the absence of thermal treatment (2-Ni). In contrast, the thermally generated 3-Ni develops an oxide-like extended structure. Both 2-Ni and 3-Ni undergo structural changes upon electrolysis, but they do not convert into the same material. The observed structural motifs in these heterogeneous electrocatalysts are reminiscent of the biological oxygen-evolving complex in Photosystem II, including the MMn₃O₄ cubane moiety. The reported studies demonstrate the use of discrete heterometallic oxide clusters as precursors for heterogeneous water oxidation catalysts of novel composition and the distinct behavior of two sets of mixed metal oxides.

Additional Information

© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Received: March 20, 2015. Article first published online: 4 Aug. 2015. This work was supported by Caltech, the NSF CAREER grant CHE-1151918 and the NIH grant R01 GM102687A (T.A.). T.A. is a Sloan, Cottrell, and Dreyfus fellow. Rotating-disk voltammetry and 2 h stability measurements are based on work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under award no. DESC0004993. Portions of this research were carried out at the SSRL, operated by Stanford University for the U.S. DOE Office of Science, and supported by the DOE and NIH. X-ray spectroscopy studies were supported by the NIH (R.T.) and by the Director of the OBES, Division of Chemical Sciences, Geosciences, and Biosciences, DOE (J.Y.). We thank James D. Blakemore for helpful discussions, Nathan Dalleska for assistance in ICP-MS data acquisition, and Tim Davenport for assistance in TGA studies. We thank Dr. Jordi Cabana and Dr. Ulrike Boesenberg for providing the NiO reference spectrum. Research was in part carried out at the Molecular Materials Research Center of the Beckman Institute of the California Institute of Technology. This project benefited from the use of instrumentation made available by the Caltech Environmental Analysis Center.

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Accepted Version - nihms785201.pdf

Supplemental Material - chem_201501104_sm_miscellaneous_information.pdf

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August 22, 2023
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October 23, 2023