  We study the electrode polarization behaviour of different
Na-Ca-phosphosilicate glasses by measuring the differential capacitance between
blocking Pt electrodes. At low applied dc bias voltages, we detect a linear
capacitance regime with interfacial capacitance values considerably larger than
expected from double layer theories and also considerably larger than found for
ionic liquids with similar ion concentrations. With increasing bias voltages,
the differential capacitance of interfacial layer exhibits a maximum around 1 V
and a strong drop at higher voltages. We suggest that these features are caused
by pseudocapacitive processes, namely by the adsorption of mobile Na+ ions at
the electrodes followed by electronic charge transfer. While pseudocapacitive
processes are well known in liquid electrochemistry, more detailed studies on
solid electrolytes should offer perspectives for improved energy storage in
solid-state supercapacitors
