A well-documented classical model is the Gouy-Chapman-Stern (GCS) model, which describes the double layer as a series combination of an inner layer and a diffuse layer. The GCS model has many variants, with more detailed treatments of the diffuse layer and the inner layer. A well-known hallmark of GCS-like models is the appearance of a minimum in the differential double-layer capacitance (𝐶 dl ) curve, named the Gouy-Chapman minimum, at a particular electrode potential, named the potential of zero charge (pzc), in low concentration electrolyte solutions. Deviating away from the pzc in cathodic and anodic directions, C dl grows and then decreases, resulting in a camel-shaped C dl profile with two peaks and one valley. The two peaks usually signify overcrowding of counterions near the metal surface, which are usually asymmetric due to different sizes of cations and anions. The two peaks move closer and eventually converge into a single peak as the electrolyte solution gets more and more concentrated. The aptness of the GCS model has been corroborated on mercury-like electrodes, firstly by Gouy in the 1910s and then by Grahame in the 1940s, see Parsons's review. In the presence of specific adsorption of anions, Grahame discriminated an inner Helmholtz plane (IHP) and an outer Helmholtz plane (OHP) in the inner layer. More than just a modification of the Stern model, Grahame's contributions sowed the seeds of ensuing developments considering field-dependent orientation of water molecules, discreteness of adsorbed ions, and quantum effects of metal electrons, as discussed in a recent tutorial. Valette and Hamelin and coworkers have demonstrated that the GCS model is valid also for silver single crystals in nonspecifically adsorbing electrolytes. The Gouy-Chapman minimum is absent in the study of Pajkossy and Kolb where 𝐶 dl of Pt(111) in a KClO4 and HClO4 mixture electrolyte with a concentration down to 1 mM was measured. Instead, their data show a C dl peak near the pzc in the anodic direction. Contrarily, Xue et al. observed Gouy-Chapman minimums for Pt(111) in 0.05 M MeClO4 electrolytes (Me=Li, Na, K, Rb, Cs), however, at potentials ~0.2 V below the pzc. More recently, Ojha et al. observed the Gouy-Chapman minimum for Pt(111) in 0.1 mM HClO4. In addition, they found that the Gouy-Chapman minimum turns into a maximum near the pzc when increasing the electrolyte solution above 1 mM, qualitatively consistent with previous observations of Pajkossy and Kolb.