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Butler-Volmer: Single Electrode Kinetics

About This Visualization

This interactive tool demonstrates the Butler-Volmer equation for hydrogen reactions on a platinum catalyst. The same equation describes both hydrogen evolution (HER) and hydrogen oxidation (HOR):

i = i0 [exp(αanFη/RT) - exp(-αcnFη/RT)]

The reactions:

  • Hydrogen Evolution (η < 0): 2H⁺ + 2e⁻ → H₂ (reduction, cathodic)
  • Equilibrium (η = 0): No net current flow
  • Hydrogen Oxidation (η > 0): H₂ → 2H⁺ + 2e⁻ (oxidation, anodic)

Parameters: Platinum catalyst with i0 = 1×10⁻³ A/cm², αa = αc = 0.5, T = 298 K

Watch the graph and electrode schematic update in real-time as you adjust the overpotential!

Equilibrium (No Net Reaction)

-0.3 V +0.3 V

← Hydrogen Evolution (Electrolysis) | Equilibrium (center) | Hydrogen Oxidation (Fuel Cell) →

1×10⁻³ 1×10⁻¹

Higher i₀ means faster kinetics (better catalyst)

Current Density 0.000 A/cm²
H₂ Production Rate ≈ 0 μL/(s·cm²)
Application At Equilibrium

Real-World Applications

  • Water Electrolysis (Negative Overpotential): Production of green hydrogen for energy storage and fuel cells. Used in alkaline, PEM, and solid oxide electrolysers.
  • Hydrogen Fuel Cells (Positive Overpotential): Converting hydrogen back to electricity for vehicles, backup power, and portable electronics.
  • Catalyst Development: Understanding exchange current density (i₀) helps design better catalysts. Platinum has high i₀, but earth-abundant alternatives are being researched.