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The bifunctional electrocatalytic activities of birnessite-type layered manganese oxide with lithium ion as an intercalated cation (Li-bir) and its composite with reduced graphene oxide (Li-bir/rGO) toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were investigated. The enhanced catalytic activity of the Li-bir/rGO composite can be ascribed to the elevated electrical conductivity of the birnessite suggested via a lower charge transfer resistance obtained from the electrochemical impedance spectroscopy.Moreover, the local oxidation states of Mn in the Li-bir/rGO were investigated by in situ X-ray absorption spectroscopy during the ORR and OER processes. Interestingly, the generated oxygen gas from the OER process observed via the in situ gas chromatography of the Li-bir/rGO is 5.44 mmol g-1 which is higher than that of the pristine Li-bir (4.98 mmol g-1). These results suggest that the Li-bir/rGO can be further utilized as a bifunctional electrocatalyst for high-performance metal-air batteries. [ABSTRACT FROM AUTHOR]

To enhance the specific energy of electrochemical capacitors, several methods have been introduced including complex electrode modification as well as asymmetric cell development. Herein, an alternative approach to enhance both specific energy and power of N-doped reduced graphene oxide aerogel electrochemical capacitor via the introduction of hybrid redox electrolyte is proposed. The electrochemical properties of the hybrid electrolyte composing of 1-butyl-1-methylpyrrolidinium dicyanamide ionic liquid with 100mMferrocenemethanol redox additive were studied via cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The combination between a unique nanostructure of N-doped reduced graphene oxide aerogel and novel hybrid electrolyte results in an excellent specific capacitance and specific energy of 112.1 F g-1 and 34.2 Wh kg-1, respectively, as compared to 76.7 F g-1 and 23.5 Wh kg-1 of the neat 1-butyl-1-methylpyrrolidinium dicyanamide electrolyte. The remarkable improvements can be explained by the emerging of the Faradaic-redox activity of the ferrocene methanol at the electrode-electrolyte interface. This simple approach could demonstrate another feasible route to improve the performance of ionic liquid-based electrochemical capacitors. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene aerogel (NGae) with a three-dimensional (3D) interconnected structure with ca. 3.5 at% of nitrogen content was synthesized by a hydrothermal reduction of graphene oxide with hydrazine and a following freezing-dry method. The 3D morphology of conductive NGae provides fast ion diffusion leading to nearly steady specific capacitances (ca. 450 F g-1) when increasing scan rates (10-100 mV-1) or applied currents (0.5-2.5 A g-1). Not only can the nitrogen-containing groups improve the electrical conductivity of NGae but also they can store charges via their reversible surface redox reactions. The as-fabricated symmetric supercapacitor of NGae in 1 M H2SO4 electrolyte provides a maximum specific energy and power of 42 Wh kg-1 and 2077 W kg-1, respectively. In addition, incorporating pseudocapacitor materials i.e., MnO2 and polyaniline to NGae structure can also provide higher specific energy owing to surface redox reactions. The as-fabricated supercapacitors in this work may be practically used in high energy and power applications. [ABSTRACT FROM AUTHOR]

An energy storage device having both high energy and power density is crucial for many applications such as electric vehicles and mobile phones. Herein, pre-lithiated three-dimensional (3D) nitrogen-doped reduced graphene oxide aerogel (N-rGO aerogel) was introduced as a negative electrode to overcome the kinetic sluggish of lithium ions and activated carbon (AC) was used as a positive electrode of lithium-ion capacitor (LIC). The electrochemical property of electrode materials was studied in a three-electrode system using a hydrodynamic rotating disk electrode at different rotation rates confirming the lithium ion chemisorption on the N-rGO aerogel. The as-fabricated LIC tested in a cell voltage window of 2.0-4.0 V can provide a maximum specific energy of 170.28 Wh kg-1 (144.79 Wh L-1), a maximum specific power of 25.75 kW kg-1 (21.89 kW L-1) with ~100% capacity retention and 100% coulombic efficiency over 2000 cycles. The excellent performance stems from the nitrogen-containing group and 3D interconnected structure of the N-rGO aerogel. The LIC in this work may be used in many high energy and power applications. [ABSTRACT FROM AUTHOR]