Center chambers for three-chamber cells in this work were prepared using polydimethylsiloxane (PDMS) molding (Fig. ). An exploded view of the three-chamber cell including a PDMS center chamber is shown in Fig. . The center chamber thickness was adjusted to study the effect on cell resistance, as illustrated in Fig. . We measured the high frequency resistance of the cell using potentiostatic electrochemical impedance spectroscopy (PEIS) (Fig. ). PEIS measurements were conducted near OCV with a perturbation of 10 mV and frequencies ranging from 1 to 100,000 Hz. The x-intercept of the plot gives the high frequency resistance. LSV with a scan rate of 10 mV s -1 was applied near OCV to test the area specific resistance (ASR) from DC polarization of the cell (Fig. ). The slope of the polarization curve around OCV was calculated to approximate the resistance. The measured resistance values are shown in Fig. . The cell resistance drops linearly as the center chamber is made to be thinner. The cell with the thinnest center chamber we were able to achieve (0.2 mm) gives the resistance close to the sum of AEM and CEM, meaning the resistance of the center chamber itself becomes negligible. Effect of center chamber solution concentration (Fig. )