Manganese Oxide/Reduced Graphene Oxide Nanocomposite for High-Efficient Electrocatalyst towards Oxygen Reduction Reaction

Abstract

Sluggish kinetics of oxygen reduction reaction (ORR) are the critical challenge for metal-air batteries and fuel cells. To increase the reaction rate, the high-efficient electrocatalysts are needed. Among various catalysts, platinum and its alloys are investigated as the best catalyst for the ORR. However, the use of Pt-based catalysts is still suffered from many disadvantages including excessive cost, scarcity, and poor stability. In this work, lithium-birnessite (Li-bir), reduced graphene oxide (rGO), and Li-bir/rGO nanocomposite were tested as the ORR catalysts. The linear sweep voltammogram (LSV) curves at a scan rate of 10 mV s-1 show that the Li-bir/rGO nanocomposite provides the best catalytic performance with an onset potential of 0.87 V vs. RHE, half-wave potential of 0.72 V vs. RHE, limiting current density of 5.72 mA٠cm-1 (at a rotation rate of 1600 rpm), along with the Tafel slope of 92.5 mV٠dec-1. Furthermore, the electron transfer number per oxygen molecule calculated by Koutechy–Levich (K–L) equation is 3.84, indicating a 4-electron pathway for the ORR suggesting that the Li-bir/rGO nanocomposite can be used as a high-efficient ORR catalyst. More interestingly, a current retention of the Li-bir/rGO nanocomposite remains over 84 % while the current density of the commercial Pt/C decreases to 67 % after 17,000 seconds. The catalyst in this work may be practically used in many applications such as metal-air batteries.