We presented a novel method for grand-canonical first-principles MD simulations that uses the fluctuation-dissipation theorem to adjust the system's charge and potential around a specified electrode potential. This approach, termed FDT-SJM, maintains constant average charge and electrode potential. We applied this method to the study of Au(111) solvated interfaces with pure water, LiOH, KOH, Li, and K across an applied potential range from -0.84 V to 0.76 V vs SHE. The results for the EDL capacitance and PZC of each system show as in experiments that the EDL capacitance is dependent on the solvent (K > Li) and the capacitances are comparable to experiments. For the Au(111)/LiOH interface, the PZC was 0.54 ± 0.07 V with an EDL capacitance of 14.41 ± 1.19 µF/cm 2 . For the Au(111)/water + KOH interface, the PZC was 0.21±0.06 V, and the EDL capacitance was 20.87±2.15 µF/cm 2 .