Charge storage mechanisms of manganese oxide nanosheets and N-doped reduced graphene oxide aerogel for high-performance asymmetric supercapacitors.

Pawin Iamprasertkun,Pinit Kidkhunthod,Somlak Ittisanronnachai,Jumras Limtrakul,Atiweena Krittayavathananon,Montree Sawangphruk,Anusorn Seubsai,Santi Maensiri,Narong Chanlek,Winyoo Sangthong,Panvika Pannopard,Rattikorn Yimnirun,Sukanya Nilmoung,Kanokwan Kongpatpanich

doi:10.1038/srep37560

Abstract

Although manganese oxide- and graphene-based supercapacitors have been widely studied, their charge storage mechanisms are not yet fully investigated. In this work, we have studied the charge storage mechanisms of K-birnassite MnO2 nanosheets and N-doped reduced graphene oxide aerogel (N-rGOae) using an in situ X-ray absorption spectroscopy (XAS) and an electrochemical quart crystal microbalance (EQCM). The oxidation number of Mn at the MnO2 electrode is +3.01 at 0 V vs. SCE for the charging process and gets oxidized to +3.12 at +0.8 V vs. SCE and then reduced back to +3.01 at 0 V vs. SCE for the discharging process. The mass change of solvated ions, inserted to the layers of MnO2 during the charging process is 7.4 μg cm−2. Whilst, the mass change of the solvated ions at the N-rGOae electrode is 8.4 μg cm−2. An asymmetric supercapacitor of MnO2//N-rGOae (CR2016) provides a maximum specific capacitance of ca. 467 F g−1 at 1 A g−1, a maximum specific power of 39 kW kg−1 and a specific energy of 40 Wh kg−1 with a wide working potential of 1.6 V and 93.2% capacity retention after 7,500 cycles. The MnO2//N-rGOae supercapacitor may be practically used in high power and energy applications.

Highlights

Manganese oxide- and graphene-based supercapacitors have been widely studied, their charge storage mechanisms are not yet fully investigated
The results provide further understanding on the charge storage mechanisms of MnO2 nanosheets and N-doped reduced graphene oxide aerogel (N-rGOae)
The N-rGOae was synthesized using a hydrothermal process by reducing graphene oxide with hydrazine and used as the negative electrode

Summary

Introduction

Manganese oxide- and graphene-based supercapacitors have been widely studied, their charge storage mechanisms are not yet fully investigated. They have high specific power (~10 kW kg−1) and long cycle life (up to 500,000 cycles)[3] when compared with batteries[4] This is because the charge storage mechanisms of supercapacitors are mainly at the solid-liquid interface via electrochemical double layer capacitive (EDLC) and pseudocapacitive behaviors. The recent effort has been devoted to developing the electrode materials of the advanced ASCs. Recently, the ASC of the polypyrrole nanotubes (positive electrode)//N-doped carbon nanotubes (negative electrode) can provide a wide working potential of 1.4 V, a specific energy of 28.95 Wh kg−1 with a specific power of 7.75 kW kg−1 and a cyclic stability of ca. New advanced ASCs have been fabricated using MnO2 nanosheets and nitrogen-doped reduced graphene oxide aerogel (N-rGOae) as positive and negative electrodes, respectively. It can be concluded here that the charge storage mechanisms of MnO2-based supercapacitors are not yet fully clear

Methods

Results

Conclusion