Supercapacitor Flashcards
Why is energy storage important?
Mobile storage for energy supply and utilization, stationary storage for load-leveling of power grids
Mobile storage includes applications like electric vehicles and electronic devices. Stationary storage aids in stabilizing power grids and effectively commercializing renewable energy resources.
What are the goals for energy storage systems?
- Higher power density
- Higher energy density
- Longer lifetime
- Lower cost
- Safer
- Less heat generation
These goals aim to improve the efficiency and usability of energy storage technologies.
What does the Ragone plot illustrate?
The performances of specific power vs. specific energy for different electrical energy-storage technologies
It helps in comparing the energy and power density of various energy storage systems.
What are the models of the electric double layer?
- Helmholtz model: Simplest, not accurate
- Gouy−Chapman model: Ions are not rigidly attached to the electrode
- Stern model: Specifically adsorbed ions and non-specifically adsorbed counter-ions
These models represent the structure of the electric double layer in electrochemical systems.
What is the effective thickness of the electric double layer (EDL) called?
Debye length
It is inversely proportional to the square root of ion concentration.
What are the criteria for electrode selection in supercapacitors?
- High conductivity
- High surface area
- Excellent corrosion resistance
- High thermal stability
- Controlled pore size distribution
These criteria ensure optimal performance and longevity of supercapacitors.
What is Murray’s Law in the context of energy systems?
- Constant mass flow for laminar flow in plant stems and leaf veins
- Mass diffusion or ionic/electronic transfer for insect spiracles
It describes principles of flow and transfer in biological and electrochemical systems.
What types of electrolytes are used in electrochemical supercapacitors?
- Aqueous: low-cost, safe, highly conductive
- Organic: higher cell voltage, sensitive to water and oxygen
- Ionic liquid: stable, high voltage, low volatility
- Solid-state: flexible, low capacitance
Each type of electrolyte has different properties affecting the performance of supercapacitors.
What is a pseudocapacitor?
A device that uses Faradic redox reactions by electrosorption or intercalation processes at the surface or near-surface region
It involves charge transfer without chemical bond formation, allowing for fast and reversible reactions.
What is the electrochemical stability range of water?
It varies depending on the potential windows for different pseudocapacitor materials in an aqueous electrolyte
Understanding this range is crucial for optimizing the performance of pseudocapacitors.
What are common reference electrodes used in electrochemical performance?
- Mercury/mercury oxide (Hg/HgO)
- Silver/silver chloride (Ag/AgCl)
- Saturated calomel electrode (SCE)
These electrodes are used to measure potentials in electrochemical cells.
What does cyclic voltammetry (CV) measure?
The current response as a function of applied voltage during a constant voltage scan rate
It is used to characterize electrochemical systems.
The current ( i ) at a given potential ( V ) in a CV curve is a sum of which contributions?
- Capacitive contribution
- Solid-state-dominated ion diffusion process (intercalation)
This reflects the combined effects of charge storage mechanisms in electrochemical systems.
What is the equation for potential point V in terms of charge-storage contributions?
𝑉 = 𝑘₁𝑣 + 𝑘₂𝑣¹/₂
Where v is the voltage scan rate.
What do Qₒ and Qᵢ represent in total charge storage?
Qₒ is related to the charge stored at the surface, while Qᵢ depends on the diffusion within the electrode
Qᵢ corresponds to the less accessible region.
What is the significance of a high Qₒ/Qᵢ ratio in electrodes?
Electrodes with a large Qₒ/Qᵢ ratio exhibit a high rate capability.
What does the Galvanostatic charge discharge (GCD) curve represent?
It represents constant current (I) during charge and discharge.
What is Coulombic efficiency?
The ratio of discharge capacity to charge capacity.
What are the two types of supercapacitors based on electrode symmetry?
- Symmetric (same electrodes)
- Asymmetric (different electrodes)
Define the term ‘redox reaction’ in electrochemical processes.
A redox reaction involves oxidation and reduction during discharge.
What is the function of the positive electrode in a supercapacitor?
It has a higher potential and is involved in reduction.
What is the function of the negative electrode in a supercapacitor?
It has a lower potential and is involved in oxidation.
What are the key parameters for hybrid supercapacitors?
- Rate capability matching
- Redox potentials to widen the operating voltage window
- Capacitance balance via active mass tuning
What materials are typically used for electrodes in EDLC?
Activated carbon (AC) as both positive and negative electrodes.
