Electrowetting of Molten Carbonate Electrolytes

Abstract

The wetting characteristics of various molten carbonate electrolytes were experimentally measured and the dependence of the contact angle on polarisation was thoroughly examined for various temperatures and gas atmospheres. At open circuit under an atmosphere of CO2 and/or oxidant gases, addition of alkaline earth carbonates decreases the wettability of the electrolyte. Addition of alkaline earth carbonates also tends to decrease the temperature dependence of the contact angle. Upon polarisation, the contact angle shows a complex behaviour. In an oxidising atmosphere its dependence on potential is roughly symmetric (like an electrocapillary curve) but in a reducing atmosphere this is not the case. Generally, the contact angle increases upon cathodic polarisation but decreases in the anodic direction. These changes in contact angle are interpreted in terms of interfacial tensions. The complex dependence of contact angle on polarisation can be interpreted in terms of a superimposed electrocapillary and transport effects. As such, it may be affected by specifically adsorbed species at the electrode surface (especially complex oxides), by the basicity (oxide ion activity) of the melt, and by the potential‐induced segregation of the cationic species in the carbonate melt.

Wetting Kinetics of Molten Carbonate on Carbon

“…The wettability between a liquid media and a solid substrate is ubiquitous in nature − and used in industrial applications such as electrochemical devices, − chemical reactors, , and metallurgical furnaces. , For example, the wettability of electrolyte on electrode and internal cell component materials is the key factor to improve the power density and lifetime of molten carbonate fuel cells (MCFCs); thus, it is widely investigated in the last 10 years. , As a typical type of MCFCs using carbon as fuel, direct carbon fuel cells (DCFCs) can efficiently convert carbon energy into electricity without the efficiency limitation of the Carnot cycle. − The DCFCs involve the wetting between the liquid molten carbonate electrolyte and the solid carbon electrode. − In a typical DCFC, the carbon anode is in contact with the molten carbonate and oxidized at the carbon/molten carbonate (C/MC) interface . The wettability of molten carbonate on the carbon electrode defines the C/MC interface that allows the mass transfer between the anodic product and electrolyte. , Thus, a good wettability between the molten carbonate and the carbon anode ensures good electrochemical performances in terms of power density and efficiency. ,, The wettability of a liquid medium on a solid substrate is defined by the contact angle and the rate of the wetting process .…”

“…However, during the measuring process, the salt melting process and wetting process of salts on the substrate take place simultaneously; therefore, it is difficult to determine the effect of temperature on the wetting kinetics. For the vertical-plate method (Figure b), , it is difficult to measure the contact angle of molten carbonate on carbon directly due to the reactive trend between them, as well as the wetting kinetics. Chen et al , and Peng et al employed the vertical-plate method to reveal that the wetting of Li 2 CO 3 –K 2 CO 3 on the graphite surface was a dynamic process.…”

“…10,11 For example, the wettability of electrolyte on electrode and internal cell component materials is the key factor to improve the power density and lifetime of molten carbonate fuel cells (MCFCs); thus, it is widely investigated in the last 10 years. 6,12 As a typical type of MCFCs using carbon as fuel, direct carbon fuel cells (DCFCs) can efficiently convert carbon energy into electricity without the efficiency limitation of the Carnot cycle. 13−16 The DCFCs involve the wetting between the liquid molten carbonate electrolyte and the solid carbon electrode.…”

Wetting of polarized materials by molten carbonate

“…Wetting angle (contact angle) of molten carbonate of various eutectic compositions and LieNa eutectic with alkaline earth additives at a gold electrode in open circuit, under various gas atmospheres, at 650 C. From Hsieh and Selman[13].…”

“…Right, bottom: Schematic of cation distribution at OCV and change of this distribution due to electric field (arrow) under current load. From Hsieh and Selman[13].…”