Influence of the Nature of the Alkali Metal Cations on the Electrical Double-Layer Capacitance of Model Pt(111) and Au(111) Electrodes.

Understanding the properties of the electrical double layer (EDL) is one of the interdisciplinary topics that plays a key role in the investigation of numerous natural and artificial systems. We present experimental evidence about the influence of the nature of the alkali metal cations on the EDL capacitance for two model electrodes, Pt(111) and Au(111), in 0.05 M AMClO4 ( AM: Li+, Na+, K+, Rb+, Cs+) electrolytes using impedance spectroscopy measurements. Our data show that counterintuitively the differential EDL capacitance of both electrodes measured close to their potentials of zero charge increased linearly in the presence of alkali metal cations as Li+ < Na+ < K+ < Rb+ < Cs+. We also estimated the effective concentrations of these cations at the EDL, which appeared ∼80 times higher than their bulk concentrations. We believe that these findings should be of importance for theoretical modeling of the EDL and better understanding and faster design of new functional systems for numerous applications.