Citation: Gan, Y.X.; Tran, A.B.; Rivera, A.; Wu, R.; Sukkoed, N.; Yu, Z.; Gan, J.B.; Dominguez, D.; Chaparro, F.J. Manganese Oxide Loaded Carbon Fiber for Solar Energy Harvesting and Oil Decomposition. C 2023, 9, 26. https://doi.org/10.3390/c9010026 Academic Editors: Jesús Iniesta and Alicia Gomis-Berenguer Received: 30 January 2023 Revised: 19 February 2023 Accepted: 22 February 2023 Published: 26 February 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Journal of Carbon Research C Article Manganese Oxide Loaded Carbon Fiber for Solar Energy Harvesting and Oil Decomposition Yong X. Gan 1, * , Anh B. Tran 1 , Alexander Rivera 1 , Ryan Wu 1 , Natnichar Sukkoed 1 , Zhen Yu 2 , Jeremy B. Gan 3 , Dominic Dominguez 4 and Francisco J. Chaparro 4 1 Department of Mechanical Engineering, California State Polytechnic University Pomona, 3801 W Temple Avenue, Pomona, CA 91768, USA 2 Department of Electrical and Computer Engineering, California State Polytechnic University Pomona, 3801 W Temple Avenue, Pomona, CA 91768, USA 3 Department of Chemical and Biomolecular Engineering, University of California Los Angeles, 405 Hilgard Ave, Los Angeles, CA 90095, USA 4 Nanoscience Instruments & Nanoscience Analytical, Inc., 10008 S. 51st Street Suite 110, Phoenix, AZ 85044, USA * Correspondence: yxgan@cpp.edu; Tel.: +1-(909)-869-2388 Abstract: In this work, a manganese oxide electrode, containing carbon nanofiber composites (MnO 2 /CNF), has been made through electrospinning, oxidization, and partial carbonization high- temperature treatment. Scanning electron microscopy (SEM) was used to observe the morphology of the nanofiber and analyze the composition of the fiber. The fiber size range and element distribution were determined. The oxide nanoparticles were modeled as electrorheological suspensions in the poly- acrylonitrile polymer solution during electrospinning. The dielectrophoretic behavior of the particles subjected to non-uniform electric fields were analyzed and the motion of the oxide particles under the actions from fluctuating electric fields was investigated to explain the sporadic distribution of nanoparticles within the composite nanofibers. A photoactive anode was made from the composite nanofiber and the decomposition of spilled oil was performed under sunlight illumination. It was observed that the manganese oxide containing carbon nanofiber composite electrode can generate electricity and clean the spilled oil under sunlight. Both energy conversion and environment cleaning concepts were demonstrated. Keywords: nanofiber; manganese oxide nanoparticle; biophoton fuel cell; solar energy; energy conversion; water oil separation; spilled oil cleaning and decomposition 1. Introduction Manganese oxides are versatile transition metal oxides due to the multiple valence val- ues of manganese. Depending on processing conditions, such as temperature, time, and atmosphere or oxygen partial pressure, manganese oxides may take the forms of MnO, Mn 2 O 3 , Mn 3 O 4 , Mn 5 O 8 , and MnO 2 [1]. Important applications were reported on various manganese oxides. All forms of manganese oxides are good catalysts. Mn 2 O 3 is an active combustion catalyst for propene and propane oxidation [2]. Mn 3 O 4 serves as the catalyst for methane oxidation [3]. In addition to being a catalyst, MnO 2 has been studied widely as an electrode material for supercapacitors because of its high electrochemical performance and low cost. It is not poisonous. In addition, the preparation of MnO 2 is relatively easy. For example, the sol-gel method was used for producing MnO 2 through the reduction of NaMnO 4 with fumaric acid [4]. A hydrothermal synthesis approach was also used to synthesize man- ganese oxide (MnO 2 ) nanorod for supercapacitor electrode fabrication [5]. The capacitance values were in the range of 72 to 168 F/g. Toupin, Brousse, and Bélanger [6] investigated the charge storage mechanism of MnO 2 electrodes in aqueous electrolytes. It has been found that only a very thin layer of MnO 2 is involved in the charge storage process. C 2023, 9, 26. https://doi.org/10.3390/c9010026 https://www.mdpi.com/journal/carbon