Zinc-Air Cathode: 2D Oxygen Diffusion & Polarization Map

Cathode Conditions

Catalyst quality 50%

Discharge current density 10 mA/cm²

O₂ partial pressure 0.21 atm

Electrolyte temperature 25 °C

Live Readouts

Cell voltage--

Current delivered--

4e⁻ Faradaic efficiency--

Surface O₂ / bulk O₂--

O₂ concentration field (bright = bulk-rich)

Catalyst site row

4e⁻ pathway → OH⁻ (efficient)

2e⁻ pathway → HO₂⁻ (lossy)

How this 2D view works

Instead of a 3D flythrough of O2 molecules, this view solves a real 2D reaction-diffusion field: a grid of oxygen concentration cells diffuses down from a fixed bulk concentration (top, set by O2 partial pressure) toward a catalyst row (bottom) that consumes O2 at a rate set by the delivered current. Each column of the catalyst row has its own local quality noise, so the depletion boundary layer visibly bulges and thins across the cathode instead of being a flat 1D profile.

dc/dt = D * d^2c/dy^2   (Fick's second law, explicit finite-difference)
surface flux  = (i / i_lim) * D * c_bulk / L
c_surface / c_bulk -> 1 - i / i_lim   at steady state

That steady-state ratio is exactly the textbook relation behind the concentration (mass-transport) overpotential used in the polarization curve on the right: eta_conc = -(RT/4F) * ln(1 - i/i_lim). The right-hand graph sweeps current density through the same Butler-Volmer/Tafel cell-voltage formula as the 3D simulator and marks the current operating point, so you can watch the boundary layer starve exactly as the curve bends toward its knee.