Holey graphene/MnO ₂ nanosheets with open ion channels for high‐performance solid‐state asymmetric supercapacitors

Abstract

Holey graphene/MnO2 (HG/MnO2) composites with open ion channels are synthesized by an electrostatic self‐assembly method. The HG with rich in‐plane nanopores is prepared via a mild etching reaction first, followed by modified with poly‐diallyldimethylammoniumchloride (PDDA) to transfer the surface charge of HG nanosheets from negative to positive, which are eventually assembled on the negatively charged MnO2 nanosheets via electrostatic attraction. As a result, the HG allows ions to pass through the graphene sheet, improving the ion transport channels. Besides, the electrostatic self‐assembly between HG and MnO2 enables the composite a high conductivity, providing effective electron transport pathways. The HG and MnO2 sheets are observed to be tightly bounded by the transmission electron microscope (TEM), and the HG content in the composites is determined to be 9.6% to 20% by the thermogravimetric (TG) test. The HG/MnO2‐2 electrode with the HG content of around 14.8% displays the large specific capacitance of 219.3 F g−1 at 0.5 A g−1 and the high rate capacity of 134.7 F g−1 at 10 A g−1. Furthermore, the as‐prepared solid‐state asymmetric supercapacitors (SSAS) achieve a wide stable operating voltage of 1.8 V, a high energy density of 16.8 Wh kg−1 at the power density of 224.6 W kg−1, and low capacitance degradation of only 6.3% after 5000 cycles.

Perspective Chapter: Graphene Based Nanocomposites for Supercapacitor Electrodes

“…At 0.5 A/g, the obtained HG/MnO 2 composite electrode containing a 14.8% holey graphene composition shows a specific capacitance of about 219.3 F g −1 , and also at 10 A/g, it shows good capacity retention of more than 61.4%. [28].…”

Advances in Mn‐Based MOFs and Their Derivatives for High‐Performance Supercapacitor

“…However, the inherent semiconductor property of MnO x leads to a significantly lower actual capacitance than that of theoretical value. [140] The inherently poor electrical conductivity of MnO x can be improved by combining with carbon matrix at the nanoscale, [28,140] which can also induce additional electrochemically active sites and shorten the electrons and ions transport path way, and thus improving the rate capability and extending the service life of the device. [142,143] Since the metal nodes in MOFs skeleton can be converted into metal NPs and the organic linkers converted to carbon materials during carbonization, MOFs is an ideal precursor for derived metal oxide/carbon composites.…”

“…[26,27] In 2018, we successfully prepared carbon-coated MnO 2 nanospheres with high specific capacitance and cycle stability using a supramolecular host-guest encapsulation strategy. [13] In 2020, our research group adopted advanced structural control strategies to obtain Holey graphene/MnO 2 nanosheets, [28] silver-decorated MnO 2 hollow microsphere, [29] and Mn 3 O 4 anchored nitrogen-doped reduced graphene oxide [30] with excellent supercapacitor performance. Recently, we used a self-template combined "self-oxidation" strategy to prepare hollow MnO 2 nanoboxes (H-MnO 2 -TEA) for the first time without adding any oxidants.…”