A Review of MnO₂ Composites Incorporated with Conductive Materials for Energy Storage

Abstract

Manganese dioxide (MnO2) has been widely used in the field of energy storage due to its high specific capacitance, low cost, natural abundance, and being environmentally friendly. However, suffering from poor electrical conductivity and high dissolvability, the performance of MnO2 can no longer meet the needs of rapidly growing technological development, especially for the application as electrode material in metal‐ion batteries and supercapacitors. In this review, recent studies on the development of binary or multiple MnO2‐based composites with conductive components for energy storage are summarized. Firstly, general preparing methods for MnO2‐based composites are introduced. Subsequently, the binary and multiple MnO2‐based composites with carbon, conducting polymer, and other conductive materials are discussed respectively. The improvement in their performance is summarized as well. Finally, perspectives on the practical applications of MnO2‐based composites are presented.

Intrinsically Conducting Polymer Composites as Active Masses in Supercapacitors

“…The insufficient supercapacitor electrode performance of plain metal oxides was stated in [ 7 , 213 ]; it has been attributed to the frequently poor electronic conductance and solubility of the compounds, at least in certain redox states of the active metal ions resulting in fast capacity fading. As a remedy, nanostructuring has been proposed and examined [ 63 , 202 , 214 , 215 , 216 , 217 ]; the preparation of composites, including those with ICPs, has been recommended elsewhere [ 5 , 7 , 71 , 213 , 214 , 218 , 219 , 220 ]. To call such composite-formation a modification may be misleading [ 5 ].…”

Hydrothermal Synthesis of MnO2 Microspheres and Their Degradation of Toluene

“…In this regard, MnO 2 has been widely used in VOC clearance for its unique properties, such as multiple valence of manganese (Mn 2+ , Mn 3+ , and Mn 4+ ), 6,7 strong oxidizability, low cost, and high environmental compatibility. 8 In addition, Mn oxide is a typical metal oxide that contains numerous electron centers, which could adsorb O 2 forming electron-rich species, and gives abundant lattice oxygen to promote the catalytic reaction. 9 Various morphologies of MnO 2 , such as 0D tunnel structure nanoparticles, 10 1D tunnel structure nanowires, nanorods, nanotubes, nanobelts, 11,12 2D layer structure, 13 and 3D mesh structure, 14,15 have been synthesized and used to degrade VOCs.…”

“…Among these methods, the hydrothermal method has been widely applied owing to its no-template and mild hydrothermal conditions in the synthesis process. 8,20 In addition, Ye et al found that MnO 2 -CeO 2 synthesized using the hydrothermal method had higher Hg 0 removal efficiency at lower temperatures. 21 The work reported by Yao et al showed that the MnO x -CeO 2 catalyst synthesized using the hydrothermal method achieved the excellent catalytic performance for NO at low temperatures.…”

“…Hence, it is essential to develop a new catalyst with higher activity, lower cost, and better stabilization performance. In this regard, MnO 2 has been widely used in VOC clearance for its unique properties, such as multiple valence of manganese (Mn 2+ , Mn 3+ , and Mn 4+ ), , strong oxidizability, low cost, and high environmental compatibility . In addition, Mn oxide is a typical metal oxide that contains numerous electron centers, which could adsorb O 2 forming electron-rich species, and gives abundant lattice oxygen to promote the catalytic reaction …”

“…For the synthesis method, coprecipitation, the sol–gel method, and the hydrothermal method have been reported to be used for the preparation of hierarchical 3D MnO 2 materials. Among these methods, the hydrothermal method has been widely applied owing to its no-template and mild hydrothermal conditions in the synthesis process. , …”