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Butler-Volmer: Dual Electrode Kinetics

About This Visualization

This interactive tool shows how Butler-Volmer kinetics at two electrodes determine battery performance. The Battery Operation and Electrode Reactions panels (above the graph) are key - they translate the abstract curves into real battery behavior. Watch how the voltage changes as you adjust current and kinetics!

Nickel-Metal Hydride (NiMH) Battery Example:

  • Positive Electrode: Ni(OH)₂/NiOOH at E₀ = +0.49 V (typically i₀ ~ 10 mA/cm²)
  • Negative Electrode: Metal Hydride (MH) at E₀ = -0.83 V (typically i₀ ~ 1 mA/cm², often rate-limiting)
  • Open Circuit Voltage: 0.49 - (-0.83) = 1.32 V (when no current flows)

Try This: Start with default values and increase the current slider. Watch the Battery Operation panel show voltage dropping (discharge) or rising (charge). The Electrode Reactions panel shows which reactions occur at each electrode!

Key Concept: As current flows, each electrode moves away from its equilibrium potential. The cell voltage is always the difference between the two electrode potentials. Better kinetics (higher exchange current density) means smaller deviations!

Select Mode:

Battery Operation

IDLE
No current flowing
OCV = 1.32 V
Both electrodes at equilibrium

Electrode Reactions

Positive (+)
Reduction
Negative (−)
Oxidation
0 100 A/cm²
Slow Fast
Slow Fast
Cell Voltage 1.32 V
Current Density 0 A/cm²
Power Density 0.0 W/cm²

What You're Seeing

  • Battery Operation Panel (above graph): Shows current battery state - voltage delivered (discharge), voltage required (charge), or open circuit voltage (idle)
  • Electrode Reactions Panel (above graph): Shows which reactions occur at each electrode based on charge/discharge mode
  • Two Butler-Volmer curves: Each electrode has its own curve showing current vs. potential relationship
  • Operating points (dots): Show where each electrode operates at the chosen current density
  • Vertical dotted lines: Drop from operating points to x-axis, showing actual electrode potentials (E+ and E−)
  • Red line on x-axis: Shows the voltage difference (Vcell = E+ − E−) - this is what the battery delivers or requires!

Key Learning Points

  • Discharge: As current increases, battery voltage drops below OCV (1.32 V) due to kinetic losses
  • Charge: As current increases, required voltage rises above OCV to overcome kinetic barriers
  • Slow kinetics = bigger losses: The electrode with slower kinetics (lower i₀) deviates more from its E₀
  • Watch the panels update: They show exactly how Butler-Volmer kinetics translate to real battery performance!
  • Rate-limiting electrode: In NiMH, the negative electrode (MH) typically has slower kinetics and limits performance