Manganese oxide-boron composite porous carbons synthesized from carbon dioxide for electrochemical energy applications

Abstract

This work introduces the derivation of boron-manganese-carbon nanocomposites by $CO_2$ carbonization using sodium borohydride ($NaBH_4$) as a reduction agent at 1 bar, followed by impregnating a manganese oxide (MO) form into boron-doped porous carbon (BPC). The prepared composites (BPCMO) can be used as an advanced electrochemical energy material such as an active electrocatalyst for oxygen reduction reaction (ORR) and an electrode material for supercapacitors. Various spectroscopic and microscopic measurements were carried out to investigate the morphology and structure of the BPCMO. Among many types of manganese oxide, it was confirmed that only $Mn_3O_4$ is embedded into the BPC. Cyclic and linear sweep voltammetry indicated that the BPCMO exhibits a four electron transfer pathway and comparable oxygen reduction reaction (ORR) activity to commercial Pt/C. Galvanostatic charge/discharge and electrochemical impedance spectroscopic measurements showed that the BPCMO provided a remarkable capacitance ($150 F g^{-1}$ at $1.0 A g^{-1}$ and $136 F g^{-1}$ at $10.0 A g^{-1}$) compared to the BPC ($58 F g^{-1}$ at $1.0 A g^{-1}$ and $15 F g^{-1}$ at $10.0 A g^{-1}$) with a highly stable capacitance retention of 93.9 % over 3500 charge/discharge cycles. It was found that the electrochemical performance is enhanced due to the generation of new active sites, the increase in specific surface areas, and the reduced overall resistance through the impregnation of $Mn_3O_4$.