Bubble-driven anodic gas in molten salt electrolytes

Herein online mass spectrometry is used to record real-time concentration curves of anodic gases released during the electrochemical oxidation of graphite anodes in molten CaCl2. The shape of these curves suggests that electrochemical oxidation is rate limited by the mass transport of oxidant ions to the anode surface. Anodic gas bubbles are formed and released from nucleation sites at this surface. Although the applied voltage is less than the decomposition voltage, an unexpectedly high release of Cl-2 gas indicates continuous decomposition of molten CaCl2. The origin of experimentally observed anodic gas bubbling is explained using phase-field simulations of a rising gas bubble in molten CaCl2.