The electrochemical reaction was modeled with the Nernst-Planck equation including terms for advection, diffusion and electrochemical reactions with Butler-Volmer kinetics. The phenomenon of electromigration is ignored in this simulation. Complete simulations including electromigration on simpler reaction conditions demonstrated that including this term had a negligible effect of the results but it made the program significantly slower. For each reaction simulation, the corresponding incompressible fluid flow is taken as a given that does not change during the reaction. The boundary condition at the inlet is a flow of 20 mM AQDS at a nearly oxidized state of charge (approaching zero) because the incoming solution is equilibrated with air. The simulation was originally run at this higher AQDS concentration of 20 mM, and the results, which are linear in the total concentration, were subsequently adjusted to reflect a 10 mM total AQDS concentration after an earlier experimental protocol was revised. The boundary conditions for the solid / liquid interface are a constant applied voltage. Applied voltage was described against a hypothetical reference electrode of AQDS / H2AQDS at 0.5 SOC, so zero volts on this scale implies that at equilibrium the local SOC around the wire would be 0.5. The numerical simulation was performed with an MPI C++ code derived from . Reaction time steps were carried out until a criterion for small changes in concentration was reached. The same upsampling technique was used to accelerate convergence as in the flow simulation, with the entire electrode first simulated to steady state on the 5.0 µm grid before it was simulated on the refined grids. Reaction simulations were carried out at multiple voltages. Because the voltage offset to OCV is difficult to simulate, the voltage was set iteratively to match the experimentally determined utilization fraction, rounding the applied voltage to the nearest one millivolt.