To increase energy efficiency and power density of the system, we further optimized the cell structure. The resistance of the three-chamber cell was first studied by varying the thickness of the center chamber (Fig. ). To achieve a sub-millimeter center chamber thickness, we kept the AEM and CEM separated by only 200 μm with a porous spacer in the electrically active region, while preserving good sealing by extending them peripherally along opposite sides of the centerchamber PDMS sheet (Fig. ). Ohmic resistance can be linearly decreased by a reduction in the center chamber thickness (Fig. ). Center-chamber NaCl concentration, temperature, and flow rate were also investigated and optimized (Fig. ). With these modifications to the center chamber and cycling conditions, the high-frequency ohmic resistance of the system was reduced to nearly the sum of two membrane resistances.