A concentration cell has identical electrodes but different electrolyte concentrations. E_standard = 0 (same electrode material). E_cell = -(0.0592/n)log(C_dilute/C_concentrated) = (0.0592/n)log(C_concentrated/C_dilute). The cell drives toward equalising concentrations: dilute side is the anode (metal dissolves to increase [M^n+]), concentrated side is the cathode (M^n+ deposits to decrease [M^n+]). For Ag|Ag+(0.001M)||Ag+(0.1M)|Ag: E = (0.0592/1)log(0.1/0.001) = 0.0592 * 2 = 0.1184 V. Concentration cells demonstrate that EMF depends on concentration ratios.