An inspectable 1D electrochemical teaching model, not a calibrated predictor for a material, redox couple or instrument. Review status appears below; AI review is not certification by an electrochemistry expert.
1. Physical system and units
A reversible one-electron reaction O + e⁻ ⇌ R at a planar macroelectrode. Both species have the same diffusivity D. Initially cₒ = C* and cᵣ = 0 in bulk. Excess supporting electrolyte permits neglect of migration; the solution is quiescent and convection is omitted. Electron transfer is fast enough to maintain Nernst equilibrium at the surface. Adjustable Butler–Volmer rate constants and transfer coefficients are not implemented.
The solver uses SI: D in m²/s, distance m, time s, area m², concentration mol/m³, current A and temperature K. UI input 1 mM equals 1 mol/m³; cm² is converted to m². Potentials refer to one ideal reference, with adjustable formal potential E⁰′.
2. Equations and current sign
∂cₒ/∂t = D ∂²cₒ/∂x² ; cᵣ = C* − cₒ
cₒ(0,t) = C* / {1 + exp[−F(E − E⁰′)/(RT)]}
cₒ(L,t) = C* ; cₒ(x,0) = C*
i = −FA D (∂cₒ/∂x)₀
E: E⁰′ + 0.350 → E⁰′ − 0.350 → E⁰′ + 0.350 V
tmax = 1.400 / ν ; L = 8√(D tmax)
F = 96485.33212 C/mol ; R = 8.314462618 J/(mol K)
x 轴从工作电极指向电解液。还原消耗 O,因此正浓度梯度对应负电流;氧化电流为正。初始高电位使表面 O 近似为 C*,但求解器仍施加精确 Nernst 边界。总浓度恒定来自相同 D、互补反应通量及相同初始/体相总浓度,不能无条件扩展到不同扩散系数。
The positive x direction points from the working electrode into electrolyte. Reduction consumes O, so a positive concentration gradient corresponds to negative current; oxidation current is positive. At the initial high potential surface O is nearly C*, but the exact Nernst boundary is applied. Constant total concentration follows from equal diffusivities, complementary reaction fluxes and equal initial/bulk totals; it must not be generalized to unequal diffusivities.
3. Numerical solution and display
Conservative finite volumes with implicit backward Euler, 700 uniform cells and 2800 time steps. Unknowns are cell-centred; each Dirichlet boundary lies half a cell away, giving boundary flux 2D(cboundary−cfirst)/Δx. Thomas elimination solves the tridiagonal system. Profiles display only 0–0.38L near the electrode; the computational domain is 0–L. Every step checks total inventory change against both integrated boundary fluxes.
A complete physical cycle is precomputed and replayed with synchronized plots, readouts and 3D composition. Playback speed changes viewing duration only. Marker colours sample local normal concentrations; counts and trajectories do not represent real molecules. The normal section has a separate magnified scale and hardware is generic. Camera motion does not alter the model.
4. Validation and review
Automated tests check Nernst sign and midpoint, zero flux at uniform equilibrium, fully discrete mass conservation, bounded concentrations, reduction/oxidation signs, peak separation and the Randles–Ševčík peak current, plus C*, √D and √ν scaling. The benchmark uses T = 298.15 K, D = 10⁻⁹ m²/s, ν = 0.1 V/s, A = 1 cm² and C* = 1 mM. Numerical peak tolerance is 3.5% and peak separation must lie within 52–69 mV. A finite grid and backward Euler introduce numerical error.
Independent AI cross-review re-derived finite-volume boundary signs, Thomas elimination and current direction. Spatial/time grids 350/1400, 700/2800 and 1000/5600 gave cathodic peaks −268.63765, −268.64344 and −268.64483 µA, separations 58, 57.5 and 57.5 mV, and one-step mass residuals below 3.89×10⁻¹⁹ mol/m². No material scientific blocker was identified. This is not human electrochemistry expert certification.
5. Limits
Migration, convection, ohmic drop, double-layer charging, finite electron-transfer kinetics, adsorption, coupled chemical reactions and electrode-edge effects are excluded. Domain length is reset for each scan and is not a real cell-vessel dimension. It exceeds the main diffusion scale over the finite cycle but remains a finite-domain approximation to semi-infinite diffusion. No experimental data import or fitting is performed.