Over the past two decades faradaic impedance has emerged as the basis for an important technique in a form of spectral analysis applicable to a wide variety of materials.  This technique depends on the capacitive component of faradaic impedance.  Whereas the resistive component is independent of frequency and can be measured with DC, the impedance of the capacitive component is infinite at DC (zero admittance) and decreases inversely with frequency of an applied AC signal.  Varying this frequency while monitoring the faradaic impedance provides a method of spectral analysis of the composition of the materials at the electrode-electrolyte interface, in particular their electric dipole moment in the role of dielectric of a capacitor.  The technique yields insights into battery design, the performance of novel fuel cell designs, biomolecular interactions, etc.