Flash‐Induced Ultrafast Production of Graphene/MnO with Extraordinary Supercapacitance

Abstract

MnO 2 ) electrodes (1110 F g −1 ), [10,11] which indicates its potential to further improve the capacitance of carbon-based electrodes. In 2013, Liao et al. [10] proposed the fabrication of vertically-aligned graphene@MnO nanosheets as high-performance SC electrodes through a hydrothermal process, and increased the specific capacitance of electrode to 790 F g −1 . Later, other fabrication approaches such as carbon-coating of self-assembly of MnO nanoparticles, direct electrospinning on carbon nanofibers, and thermal plasma deposition of MnO onto porous carbon materials have also been investigated to synthesize MnO/carbon electrodes. [11][12][13] However, although nano-MnO has been synthesized and deposited in carbon-based electrodes, the process is relatively complicated and usually requires multiple steps. This is because nano-MnO suffers from agglomeration of the particles during the synthesis process, which leads to loss of surface active sites and thus a decrease in electrochemical activity. As a result, the reported capacitances of MnO/carbon electrodes are generally less than 800 F g −1 , which are far below the theoretical limit of MnO (only approximately 60% is achieved). Therefore, it remains challenging to well anchor the MnO homogeneously onto carbon networks through a facile and simple process to produce high capacitance SC electrodes.Flash reduction is considered as one promising solution to the production of graphene/MnO electrodes in a green and facile manner. The irradiation of intensive flash light pulse triggers fierce reduction and exfoliation of graphene oxide (GO) films due to efficient photothermal effect, leaving highly conductive and porous flash reduced graphene oxide (frGO) electrodes with excellent electrochemical performances. [14][15][16][17] Large amount of gases such as carbon monoxide (CO), carbon dioxide (CO 2 ), water vapor (H 2 O), and hydrogen (H 2 ) are released from the reduction of GO, coupled with instant temperature rise within GO films after flash irradiation, which provides an ideal environment for the reduction of MnO 2 to MnO. [18,19] In this paper, we report, for the first time, a green and simple co-reduction method for producing high-performance graphene/MnO electrodes via ultrafast flash reduction process within several milliseconds. We tailor the reducing gases (CO and H 2 ) generated from flash reduction of GO to fully transform the pre-deposited MnO 2 nano-needles into MnO without agglomeration simultaneously during the production of high-quality porous graphene materials. Through rational control the feeding ratio guided by simulation studies, optimal Production of high-capacitance electrodes beyond the theoretical limit of 550 F g −1 of pure graphene materials is highly desired for energy storage applications, yet remains an open challenge, especially with a facile and simple process. By rational design of reaction condition guided by theoretical analysis, the ultrafast (within millisecond) fabrication of highperformance graphene/MnO electrodes via a low-cost ...

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