Next, the parameters for each reaction were fitted one reaction at a time in order to separate the ((2𝑘 × 2𝑘) + 1) dimensional optimization problem (where 𝑘 is the number of competing reactions and the + 1 is due to fitting 𝐿 () ) into (𝑘 -1) 2-dimensional optimizations and a single 3-dimensional optimization (in which the thickness of the boundary layer is fit). This procedure makes the problem more tractable and avoids the so-called "curse of dimensionality" in optimizations. It is also important to note that fitting the boundary layer was necessary to provide the best fit for the CO data, as the boundary-layer thickness dictates the mass-transportlimiting plateau (see Figure ), and is seldom measured or reported for CO2R current densities measured using a flow cell. We note that the fitted mass-transport boundary-layer thicknesses generally agree in terms of order of magnitude with values reported in previous flow cell studies;