Nitrogen Doped Superactivated Carbons Prepared at Mild Conditions as Electrodes for Supercapacitors in Organic Electrolyte

María José Mostazo-López,Soshi Shiraishi,Diego Cazorla-Amorós,Ramiro Ruiz-Rosas,Yoshikiyo Hatakeyama,Tomomi Tagaya,Emilia Morallón

doi:10.3390/c6030056

María José Mostazo-López, Soshi Shiraishi + Show 5 more

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https://doi.org/10.3390/c6030056

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Abstract

Nitrogen functionalization of a highly microporous activated carbon (SBET > 3000 m2/g), to be used as electrode of electric double layer capacitor (EDLC), was carried out by different methods based on organic chemistry protocols at low temperature and selective thermal post-treatments under inert atmosphere. The combination of both methods allowed the production of carbon materials with very similar surface area (2400–3000 m2/g) and different surface chemistry. The nitrogen functionalization by chemical methods produce the attachment of 4 at. % N (XPS) by consumption of oxygen functional groups. The thermal treatments rearrange the surface chemistry by decreasing and converting both nitrogen and oxygen moieties. The effect of surface chemistry on the performance of these materials as electrodes for symmetric supercapacitors was analyzed in organic electrolyte (1M TEMABF4/propylene carbonate). The devices showed high gravimetric capacitance (37–40 F/g) and gravimetric energy density (31–37 Wh/kg). The electrochemical stability of the EDLC was evaluated by a floating test under severe conditions of voltage and temperature. The results evidence an improvement of the durability of nitrogen-doped activated carbons modified by chemical treatments due to the decrease of detrimental oxygen functionalities and the generation of nitrogen groups with higher electrochemical stability.

Highlights

Electrochemical capacitors are energy storage devices of great interest mainly due to their high power density, durability and broad operation temperature range [1,2]
We have developed nitrogen functionalization methods at mild conditions that allow the incorporation of a wide range of nitrogen functionalities while preserving the structure of the pristine carbon material, even when using carbon materials with extraordinary microporosity [9,28]
We propose the synthesis of nitrogen-doped activated carbons with high apparent surface area by combining functionalization methods based on wet methods at low temperatures and post-thermal treatments at different temperatures, whose combination allows a selective modification of the surface chemistry

Summary

Introduction

Electrochemical capacitors (supercapacitors) are energy storage devices of great interest mainly due to their high power density, durability and broad operation temperature range [1,2]. It is necessary to increase their energy density for enabling their use in a wider range of applications. This requires the use of electrode materials and electrolytes able to increase both the capacitance and the operation voltage of electrochemical capacitors. The use of excessively high operation voltage dramatically affects the performance of the electrodes, since carbon materials undergo reactions with the electrolyte that decrease their electrochemical stability, and diminish the cycle life of the device [7,8,9]. The development of carbon materials with improved electrochemical stability and durability is highly needed for their use in electrochemical capacitors

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