With this information, the asymmetric CV seen in 9MA facilitated proton-transfer (Figure ), is consistent with 9MA existing primarily as its conjugate acid form (9MAH + ) in the acidic aqueous phase before the experiment is started. With the application of more positive potential, 9MAH + is driven into the pipette from the outer aqueous phase on the forward sweep, and then expelled from the inner organic phase on the reverse sweep, leading to steady-state and peak-shaped current profiles, respectively, on the different sweep directions. Switching the positions of the two phases (inside pipette versus outside, Figure ) produced a CV with peak-shaped current on the forward sweep and a steady-state current on the reverse sweep, again consistent with the model that 9MAH + is initially present in the acidic aqueous and transferred to the organic phase. This type of reasoning has been used previously to infer pathways of facilitated ion transfer. contact with the outer electrolyte containing 0.5 mM DPP and DPPH + . For simplicity, migration is not included in the model and transport through the cell was by diffusion only. Convection is also not expected to play a major role in these experiments. At the tip of the pipette, where the liquid-liquid interface is modeled to be, a square-scheme mechanism for facilitated ion transfer is considered (Figure ). The top edge of the square scheme represents the interfacial-direct mechanism, where aqueous protons react directly with DPP at the position of the simulated liquid-liquid interface. The other 3 legs of the square scheme make up the interfacial-sequential mechanism, which has two preceding chemical steps and a final electrochemical step. Specifically, a chemical step consisting of a heterogeneous organic-to-aqueous phasetransfer of DPP with equilibrium constant equal to the partition coefficient P, a chemical step consisting of a homogeneous acid-base reaction on the aqueous side of the interface with equilibrium constant Ka, and finally the electrochemically driven transfer of DPPH + (aq) to DPPH + (org). For the chemical steps of the square scheme, the forward and backward rate constants are related by the aforementioned equilibrium constants, and the rate constants for each electrochemical step are given a Butler-Volmer form depending exponentially on Δ 𝑜𝑜 𝑤𝑤 𝜙𝜙. Given that the stoichiometry of the interfacial-direct and interfacial-sequential electrochemical steps are different, the standard rate constants 𝑘𝑘 0 have correspondingly different units. To compare the kinetics of either step, an exchange current density 𝑗𝑗 0 was used to calculate 𝑘𝑘 0 along with the bulk concentration of all species (S8). Accordingly, the following simulations use 𝑗𝑗 0,𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 and 𝑗𝑗 0,𝑠𝑠𝑑𝑑𝑠𝑠𝑠𝑠𝑑𝑑𝑠𝑠𝑑𝑑𝑑𝑑𝑠𝑠𝑠𝑠 for comparison.