Abstract
Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50°C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6 M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13 mW cm−2, in contrast to MnO2, which produced a maximum power density of 9.2 mW cm−2. The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms.
Highlights
Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution
From the Fourier transformed infrared (FTIR) spectra, it can be concluded that the Graphene oxide (GO) on the MnO2 cathode surface was reduced to electrochemically reduced graphene oxide (ERGO) during cell discharge in 6M KOH, and this finding is in accordance with the electrochemical reduction of GO to ERGO in concentrated alkaline solution[31]
The presence of ERGO is responsible for the lower R2 of the GO on the MnO2 air cathode (GO-MnO2) air cathode after discharge
Summary
Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution. Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6 M KOH solution for GO-MnO2 compared to the MnO2 cathode. On the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms. The oxygen reduction reaction (ORR) is one of the most widely studied reactions, for fuel cell and metal-air battery applications. Different types of graphene, such as graphene nanosheets[1] and porous graphene[2] are good electro-catalysts for ORR in lithium-air cells. The ORR proceeds with a 4 electron reduction pathway for MnO25–7 and graphene[4,8]. A detailed mechanism for the first step (eq 1) on MnO2 in alkaline medium has been proposed[7,9]: Mn4z z e{ < Mn3z ðf astÞ ð3Þ
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