The influence of side reactions on the performance of electrochemical double-layer capacitors
- Lawrence Berkeley National Lab., CA (United States). Energy and Environment Div.
A constant-concentration, constant-capacitance, macrohomogeneous porous-electrode model is used to investigate the effects of side reactions on the charging and cycling of electrochemical double-layer capacitors. A porous carbon capacitor with sulfuric acid electrolyte is a typical system, and corresponding physical properties are used to illustrate the effects. Oxygen and hydrogen evolution are considered the dominant side reactions, and a Tafel form for the kinetic expressions is assumed. It is shown that keeping the cell potential within the thermodynamic stability window of the solvent does not guarantee negligible losses, even if the kinetics are not particularly facile. Losses are substantial at early cycles and decrease to a constant value at later cycles; this value can be significant. The dependences of coulombic and energy losses on the maximum cell potential, electrode thickness, and discharge rate are discussed. In a poorly designed cell, the energy lost to side reactions can be as large or larger than the ohmic loss; hence consideration of side reactions is essential for good design. Electrochemical double-layer capacitors are of interest as moderate energy and power density devices that may find application as peak-power sources for electric vehicles.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 276635
- Journal Information:
- Journal of the Electrochemical Society, Vol. 143, Issue 6; Other Information: PBD: Jun 1996
- Country of Publication:
- United States
- Language:
- English
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