Abstract
Traditional noble metal platinum (Pt) is regarded as a bifunctional oxygen catalyst due to its highly catalytic efficiency, but its commercial availability and application is often restricted by high cost. Herein, a cheap and effective catalyst mixed with α-MnO2 and nitrogen-doped Ketjenblack (N-KB) (denoted as MnO2-SM150-0.5) is examined as a potential electrocatalyst in oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). This α-MnO2 is prepared by redox reaction between K2S2O8 and MnSO4 in acid conditions with a facile hydrothermal process (named the SM method). As a result, MnO2-SM150-0.5 exhibits a good catalytic performance for ORR in alkaline solution, and this result is comparable to a Pt/C catalyst. Moreover, this catalyst also shows superior durability and methanol tolerance compared with a Pt/C catalyst. It also displays a discharge voltage (~1.28 V) at a discharge density of 50 mA cm−2 in homemade Al–air batteries that is higher than commercial 20% Pt/C (~1.19 V). The superior electrocatalytic performance of MnO2-SM150-0.5 could be attributed to its higher Mn3+/Mn4+ ratio and the synergistic effect between MnO2 and the nitrogen-doped KB. This study provides a novel strategy for the preparation of an MnO2-based composite electrocatalyst.
Highlights
The efficiency of oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) are critical to the energy conversion efficiency of metal air batteries because of their sluggish reaction kinetics [1]
This study examines the morphology, structure, and electrochemical properties of MnO2 samples by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical testing
Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) ORR were performed using a RDE as working electrode, a double fluid boundary Ag/AgCl electrode as the reference electrode, and a platinum wire as the counter electrode in 0.1-M of KOH solution saturated with oxygen on a CHI760E electrochemical workstation
Summary
The efficiency of oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) are critical to the energy conversion efficiency of metal air batteries because of their sluggish reaction kinetics [1]. Pt-based materials have been developed as typical catalysts for ORR/OER with high catalytic activity [2,3,4]. Their widespread application in commerce is seriously hindered, because the noble metal Pt is very expensive, and its reserves in earth are scarce. Manganese-based materials have good electrocatalytic performance as reported, the superiority of synergic catalysts cannot be neglected. MnO2 spheres are synthesized by the redox reactions between K2 S2 O8 and MnSO4 in acid conditions (denoted as the SM method) These MnO2 spheres mixed with nitrogen-doped Ketjenblack (N-KB) are used as a catalyst for ORR/OER application. This work offers a new strategy for the scalable preparation of more efficient MnO2 bifunctional oxygen catalysts for ORR and OER
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