Pseudo capacitors

In the third paper by French and Ukrainian scientists (Khomenko et al.), the authors focus on high performance a-MnCVcarbon nanotube composites as pseudo-capacitor materials. Somewhat surprisingly, this paper teaches to use carbon nanotubes for the role of conductive additives, thus suggesting an alternative to the carbon blacks and graphite materials - low cost, widely accepted conductive diluents, which are typically used in todays supercapacitors. The electrochemical devices used in the report are full symmetric and optimized asymmetric systems, and are discussed here... 

Zhang, Y. Q., L. Li, S. J. Shi et al. 2014. Synthesis of porous Coj04 nanoflake array and its temperature behavior as pseudo-capacitor electrode. Journal of Power Sources 256 200-205. 

Kim et al. electrochemically deposited PPy on a CNT/silica film substrate using a potential cycling method at room temperature. After removal of silica with hydrofluoric acid (HF), CNT/PPy composites with controlled pore size in a three-dimensional (3D) entangled structure of a CNT film were prepared as electrode materials for a pseudo-capacitor [36]. The pore size of the final CNT/PPy composite film could be controlled by changing the amount of silica in the mixed suspension of CNTs and nanosize silica. The SC of the CNT/PPy composite with 83.4 wt.% PPy was 250 F/g at a potential scan rate 10 mV/s in 1.0 mol/L KCl and it decreased by only 15% to 211 F/g at 500 mV/s. 

The Ultra battery design [2] substitutes a carbon electrode for a portion of each negative lead electrode. The combination of the carbon negative and the lead-dioxide positive electrode provides a pseudo-capacitor in parallel with a normal lead-acid battery in the same cell. The pseudo-capacitor can operate at high currents for short periods of time to reduce the stress on the battery. Meanwhile, the battery can store chemical energy and supply electrical energy for a longer period of time at a more moderate rate. 

In general, two modes of energy storage are combined in electrochemical capacitors (1) the electrostatic attraction between the surface charges and the ions of opposite charge (electrical double layer) (2) a pseudo-capacitive contribution which is related with quick redox reactions between the electrolyte and the electrode [14,15]. Whereas the redox process occurs at almost constant potential in an accumulator, the electrode potential varies proportionally to the charge-exchanged dq m 2L pseudo-capacitor, what can be summarized by formula (Eq. 12.6) ... 

Protic Ionic Liquids as Electrolytes for Carbon-Based Pseudo-capacitors... 

Pseudo capacitor Redox reaction Faradaic Super capacitor... 

Hybrid capacitors use a combination of battery-type and capacitor-type electrodes. For example, the negative electrode is a battery-type electrode and the positive electrode is an electrical doublelayer capacitor. Comparing to pseudo capacitors, the potential of battery-type electrodes is constant during charging and discharging. 

Electrochemical double-layer capacitors with activated carbon electrodes are commercially available from several companies. In the case of hybrid capacitors, lithium-ion capacitors which consist of the anode of a lithium-ion battery and a cathode of activated carbon are commercially available, as mentioned above. These super capacitors show great promise as next generation power sources for electric devices and electric vehicles. More innovation is needed before pseudo capacitors are suitable for commercialization. 

Figure 4.4 (a] Typical pseudo-capacitor (EDLC)-like behavior is observed owing to below optimal pressure, (b) At 1 atm gas pressure, the same cell works as Li-air cell as expected. 

The activation phenomena are coupled with the electrochemical double layer phenomena, which are comparable to a capacitor in the electrostatic sense of the term. The phenomena of species transport are, by their very nature, dynamic in our approach, they will be assigned a dynamic via pseudo-capacitors. The Ohmic phenomena will be considered to have no perceptible dynamic. 

This formula can, a priori, enable us to estimate the value of the capacitor or pseudo-capacitor of the phenomenon involved, using the experimental impedance diagram. 

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