An iron-base oxygen-evolution electrode for high-temperature electrolyzers

Abstract

High-temperature molten-salt electrolyzers play a central role in metals, materials and chemicals production for their merit of favorable kinetics. However, a low-cost, long-lasting, and efficient high-temperature oxygen evolution reaction (HT-OER) electrode remains a big challenge. Here we report an iron-base electrode with an in situ formed lithium ferrite scale that provides enhanced stability and catalytic activity in both high-temperature molten carbonate and chloride salts. The finding is stemmed from a discovery of the ionic potential-stability relationship and a basicity modulation principle of oxide films in molten salt. Using the iron-base electrode, we build a kiloampere-scale molten carbonate electrolyzer to efficiently convert CO2 to carbon and oxygen. More broadly, the design principles lay the foundations for exploring cheap, Earth-abundant, and long-lasting HT-OER electrodes for electrochemical devices with molten carbonate and chloride electrolytes.

Highly Durable and Efficient Seawater Electrolysis Enabled by Defective Graphene-Confined Nanoreactor

“…As shown in Figure d, resulting from the charge transfer at the interface of NiFeOOH-O v and the defective graphene layer, a built-in electric field (−1.34 V Å –1 ) is formed in NiFe@DG, which can repel the Cl – on its surface. Further, the energy barrier of Cl – from the graphene shell to O v in NiFeOOH-O v for NiFe@DG was calculated to be 0.91 eV (Figure e), higher than that (0.58 eV) for NiFe/G, suggesting that the graphene-confined structure plays a crucial role in preventing Cl – penetration . Combining theoretical and experimental results, it is deduced that NiFe@DG has greatly improved structural and (electro)­chemical durability as a result of the confinement effects of the core–shell nanoreactor.…”

“…Further, the energy barrier of Cl − from the graphene shell to O v in NiFeOOH-O v for NiFe@DG was calculated to be 0.91 eV (Figure 4e), higher than that (0.58 eV) for NiFe/G, suggesting that the graphene-confined structure plays a crucial role in preventing Cl − penetration. 43 Combining theoretical and experimental results, it is deduced that NiFe@DG has greatly improved structural and (electro)chemical durability as a result of the confinement effects of the core−shell nanoreactor. Such a structure prevents the corrosive chloride species in the electrolyte from accessing the encapsulated metals through the formed built-in electric field without blocking the passage of OH − , which can be ascribed to the fact that OH − is a hard base and therefore could strongly bind to the hard acid species of the catalytically active Ni 3+ based on the classical hard and soft acid−base theory.…”

Pure and Metal‐confining Carbon Nanotubes through Electrochemical Reduction of Carbon Dioxide in Ca‐based Molten Salts

“…A thermodynamically spontaneous dissolution/ absorption of CO 2 into molten carbonate in Li 2 O-containing molten salts (Figure S1, Supporting Information) is the keyenabling factor to achieve high current efficiency (CE). [10][11][12][13] Based on industrial maturation of molten salt electrolysis and promising functionality of CO 2 -derived materials, solardriven molten salt electrochemical CO 2 reduction is an attractive artificial photosynthesis. [14][15][16] Such a protocol, however, is hampered by the surging lithium resource price along with the booming lithium-ion battery industry.…”

“…Using excess capacity of electrolytic aluminum industry to electrolyze industrial CO 2 emission can not only reduce carbon emission but also relieve the pressure of production regulations. A thermodynamically spontaneous dissolution/absorption of CO 2 into molten carbonate in Li 2 O‐containing molten salts (Figure S1, Supporting Information) is the key‐enabling factor to achieve high current efficiency ( CE ) [10–13] . Based on industrial maturation of molten salt electrolysis and promising functionality of CO 2 ‐derived materials, solar‐driven molten salt electrochemical CO 2 reduction is an attractive artificial photosynthesis [14–16] .…”

Liquid Metal–CO2 Battery Bridged Intermittent Energy Conversion and O2 Production in the Martian Atmosphere

“…Molten salt CO 2 electroreduction provides another option for producing O 2 and CO or carbon materials on Mars without using water. − CO 2 can be directly reduced to CO in molten salt without the use of expensive catalysts or complex electrode designs, and, at the same time, released O 2 through an inert anode. − Fortunately, the application potential of molten salt electrolytes as a form of energy storage has been demonstrated. − Liquid metal batteries have been constructed by storing active metals such as lithium, sodium, and magnesium . This is a simple and efficient way of storing energy in molten salt electrolytes.…”