Effect of electrolyte and carbon material on the electrochemical performance of high-voltage aqueous symmetric supercapacitors

Abstract

The energy storage capability of the aqueous supercapacitors is mainly attributed to the relatively low operating voltage of the device, as the thermodynamic decomposition voltage of water is 1.23 V. Therefore, the extension of the working voltage of the aqueous capacitor beyond the electrolyte decomposition limit is an important subject for the development of environmentally friendly energy storage devices. In this study, a commercial activated carbon (AC) and synthesized phosphorus-doped reduced graphene oxide (P-rGO) were used to gain insight into the influence of both textural properties and the surface chemistry on the electrochemical performance of high-voltage aqueous supercapacitors. Materials on the opposite end of the spectrum (highly porous, undoped AC and heteroatom-rich phosphorus-doped reduced graphene oxide with low porosity) were compared in a symmetric cell, operating in a wide voltage window of 2.0 V in 2 M NaClO4 electrolyte. Additionally, AC-based cell was tested in 1 M Na2SO4 solution to assess the differences in its performance in different sodium-based electrolytes. The obtained results demonstrate that both a porous structure and high contribution of heteroatoms, which improve the hydrophilicity of the electrode, are required to achieve high specific energy density values. However, with increasing current and higher power densities, a developed porous structure is required to maintain good energy storage characteristics. Achieving high operating voltage in the aqueous symmetric full-carbon supercapacitors is a promising energy storage solution. The assembled devices show a good specific energy density of up to 13 Wh kg−1 at a power density of 30 W kg−1. Graphical abstract

Ammonium and Tartrate Salts as Alternatives to Neutral Aqueous Electrolytes for Supercapacitors

“…Impedance experiments were implemented at open circuit potential in the range of 10 mHz to 100 kHz with an amplitude of 10 mV. Diffusion coefficient D [m 2 s À 1 ] was calculated by using equation ( 7) as follows: [43][44][45] D ¼ w=R 2 (7) w is the knee frequency, at which the impedance spectra reveal a capacitive behaviour of the system (change from 45°to 90°). R [cm] is the thickness of electrode and describes the path ions must pass through during charge storage.…”

“…This enables high power densities and high cyclability up to 10 6 cycles [6] . Unfortunately, the energy density of SCs is not yet competitive with that of batteries [7] . Intensive research is therefore being conducted to increase the energy density of SCs.…”

“…[6] Unfortunately, the energy density of SCs is not yet competitive with that of batteries. [7] Intensive research is therefore being conducted to increase the energy density of SCs. According to the equation (Eq.…”

Effect of conductive layer on the performance of gel electrolyte‐based supercapacitors

“…The choice of electrode material and design plays a significant role in determining a supercapacitor's performance, so these factors should also be considered in a performance review 16–18 . Electrolytes with liquid or solid‐state types are a key factor in storing the electrical charge.…”

“…14,15 The choice of electrode material and design plays a significant role in determining a supercapacitor's performance, so these factors should also be considered in a performance review. [16][17][18] Electrolytes with liquid or solidstate types are a key factor in storing the electrical charge. Although the ion diffusion in solid-state electrolytes is not as fast as the liquid electrolyte, they are extremely versatile as a standalone energy source component for certain applications or in combination with batteries as a hybrid system.…”