Abstract
Due to their low melting point and high conductivity molten hydroxides are interesting electrolytes, or additive to other molten electrolytes for high-temperature electrochemical devices. There is nowadays a revival of such reactive media, first of all for their significant role in the electrode mechanisms in molten carbonate fuel cells (MCFCs) and the reverse co-electrolysis of water and carbon dioxide process, but also in different applications, among which direct carbon fuel cells (DCFCs), hybrid carbonate/oxide fuel cells. This overview shows the properties and interest of molten hydroxides and their use in relevant energy devices, pointing out their direct use as electrolytic media or as key species in complex kinetic processes. A thorough understanding of their behavior should allow improving and optimizing significantly fuel cells, electrolyzers, and probably also CO2 capture and valorization.
Highlights
Molten salts are of great interest in electrochemistry, in the field of fuel cells and electrolyzers
Due to the properties of molten carbonates and the high CO2 solubility in this medium (Meléndez-Ceballos et al, 2020), molten carbonate fuel cells (MCFCs) can be used for carbon capture and storage (CCS) applications, such as CO2 concentration and separation (Intergovernmental Panel on Climate Change, 2005; Wade et al, 2007; Cassir et al, 2012; McPhail et al, 2015; Fuel Cell Energy, 2017, 2019)
This review will focus on the role of molten hydroxides in several fuel cell systems and the MCFC, stressing out the promising applications related to such media, as pure phases or additives
Summary
Molten salts are of great interest in electrochemistry, in the field of fuel cells and electrolyzers. Due to the properties of molten carbonates and the high CO2 solubility in this medium (Meléndez-Ceballos et al, 2020), MCFCs can be used for carbon capture and storage (CCS) applications, such as CO2 concentration and separation (Intergovernmental Panel on Climate Change, 2005; Wade et al, 2007; Cassir et al, 2012; McPhail et al, 2015; Fuel Cell Energy, 2017, 2019). This device can be operated reversibly, as a molten carbonate electrolysis cell or MCEC (Hu et al, 2014; Perez-Trujillo et al, 2018; Meskine et al, 2020). They are subject to a similar auto-dissociation equilibrium, where H2O is the conjugated oxoacid: 2OH− ↔ O2− + H2O (1)
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