Graphene/Ni Wire Foam with Multivalent Manganese Oxide Catalysts for Li-O 2 Battery Cathode
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Graphene/Ni Wire Foam with Multivalent Manganese Oxide Catalysts for Li-O2 Battery Cathode Chueh Liu1, Changling Li1, Zafer Mutlu1, Cengiz S. Ozkan1,3 and Mihrimah Ozkan1,2 1 Materials Science and Engineering Program, University of California, Riverside, CA, USA. 2 Department of Electrical Engineering, University of California, Riverside, CA, USA. 3 Department of Mechanical Engineering, University of California, Riverside, CA, USA.
ABSTRACT Herein, commercial Ni foam coated with self-assembled and linearly-aligned Ni wires is utilized as a cost-effective current collector for application in Li-O2 battery. The Ni wires are furthered deposited with graphene layers (g-Ni wire) to improve electrical conductivity. Multivalent Mn oxides consisting of Mn3O4, Mn2O3 and MnCO3 are used as effective oxygen reduction (ORR) and evolution reaction (OER) catalysts deposited on g-Ni wire current collectors. Specific capacities are respective ~100 and ~170 mAh g-1 without or with O2 introduction into the cell. The relative facile synthesis process requiring merely solution-based synthesis at ambient pressure, low temperature and short process time renders the Mn oxides/gNi wire electrode promising for Li-O2 battery application. INTRODUCTION Energy storage systems, such as hydrogen fuel cells [1,2], supercapacitors [3] and Li-ion batteries [4-10], are widely utilized in diversified fields, such as 3C products, electric vehicles and stationary grid stations [11]. Amongst the alternatives, Li-ion batteries are ubiquitous owing to the stability and moderate energy densities. Nonetheless, even though the capacity of novel Si anodes is completely utilized, the overall capacity is mainly limited by the oxide cathodes. Accordingly, Li-air batteries utilizing O2 conversion reactions providing higher capacities than traditional LiCoO2 cathode are introduced. However, low-priced yet effective ORR and OER catalysts are indispensable for the air cathode. Ni-based catalysts have been utilized as effective ORR and OER catalysts [12]. The accessible surface area plays an important role in Li-air cathodes. Nanomaterials production methods, such as electrospinning [13-15], atomic layer deposition [16,17] and self-assembly [6,7,11], should be optimized and carefully chosen to fit mass manufacturing requirement. In addition, two dimensional materials have been extensively researched owing to their superior electronic properties [18-20]. In this study, self-assembled Ni wire is covered with thin graphene layer (g-Ni wire) in order to eliminate the effects of Nicontaining native oxides (Ni2O3 and NiO) [6] for the oxygen reduction and evolution reactions. The g-Ni wire is further deposited with multivalent Mn oxides, including Mn3O4, Mn2O3 and MnCO3, which demonstrate the cheap ORR and OER catalysts are feasible options for future Liair cathodes. EXPERIMENT
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