Energy Storage in Electrochemical Cells with Molten Sb Electrodes

Abstract

An energy-storage concept is proposed using molten Sb as the fuel in a reversible solid-oxide electrochemical cell (SOEC). Because both Sb and Sb 2 O 3 are liquids at typical SOEC operating temperatures, it is possible to flow Sb from an external tank and use it as the fuel under fuel-cell conditions and then electrolyze Sb 2 O 3 during recharging. This concept was tested using a button cell with a Sc-stabilized zirconia electrolyte at 973 K by measuring the impedances under fuel-cell and electrolyzer conditions for a range of stirred Sb-Sb 2 O 3 compositions. The Sb-Sb 2 O 3 electrode impedances were found to be on the order of 0.15 cm 2 for both fuel-cell and electrolyzer conditions, for compositions up to 30% Sb and 70% Sb 2 O 3 . The open circuit voltages (OCV) were 0.75 V, independent of oxygen composition. Some features of using molten Sb as an energy-storage medium are discussed. Renewable energy sources, such as wind or solar energy, could help decrease our dependence on fossil fuels; but they produce intermittent power that may not be available when energy demand is highest. To take full advantage of these energy sources, as well as provide buffering for the electrical grid as a whole, the ability to store electrical energy at times when demand is low for later use when demand is high would be very desirable. Conventional ways to store energy are based primarily on compressed air or elevated water.1 With compressed air, off-peak power is used to run a compressor. At times of high demand, the compressed air can then be used to drive a turbine. In hydroelectric power plants, energy is stored by pumping water back to higher elevations. Unfortunately, both of these approaches require special geographic conditions, making them infeasible in many cases.One alternative for energy storage involves electrochemical devices, such as static Li-ion batteries, 2 metal-air batteries, 3 and flow batteries. [4][5][6] With these devices, energy is stored in the form of chemical energy and electricity is generated later by reversing the chemical reaction. An intrinsic advantage of electrochemical energy storage is the direct conversion of chemical energy into electricity with few moving parts. Among the various types of flow batteries, those based on zinc or vanadium redox cycles have received the most attention. 4,5 Reversible fuel cells are also a type of flow battery. In the conventional use of reversible fuel cells, surplus electricity would be sent to the cell to electrolyze water to produce H 2 ; electricity would be generated later by flowing the H 2 back to the cell, which would then be operated in the fuel cell mode.7 The low density of gaseous H 2 makes its storage challenging and typically requires that a significant amount of energy be used in compressing the H 2 . Several variations on the idea of reversible fuels cells have been proposed to reduce this storage problem. Because H 2 O and CO 2 can be electrolyzed with equal efficiency in solid oxide fuel cells (SOFC), [8][9][10][11][12][13][14] Zhan, et al. 14...

The stability of direct carbon fuel cells with molten Sb and Sb–Bi alloy anodes

“…Both Sb (melting point 903 K) and Sb 2 O 3 (melting point 929 K) have melting points below the temperatures typically used for SOFC operation, 973–1073 K, which precludes the formation of a solid oxide film at the electrolyte–anode interface as in the case of Sn. Based on previous experiments in our laboratory, the impedance of molten Sb electrodes are very low, less than 0.1 Ω cm 2 at 973 K, and reasonably independent of the Sb:Sb 2 O 3 ratio . Although the Nernst potential for Sb oxidation is lower compared to that for C oxidation, 0.75 V vs. ∼1 V at 973 K, this difference in oxidation potentials makes the reduction of Sb 2 O 3 by the solid carbonaceous fuels thermodynamically spontaneous.…”

“…The experimental apparatus is shown schematically in Figure and was similar to that used in an earlier study of electrochemical energy storage, where mixing of the molten Sb/Sb 2 O 3 mixture was critical . The fuel cell was attached to the end of an alumina tube with the cathode side exposed, using a ceramic adhesive (Aremco Ceramabond 552).…”

Molten silver as a direct carbon fuel cell anode

“…Based on our previous measurements with molten Sb, we expect that rate process 1), O 2À transfer from the electrolyte to the molten metal, is likely to be facile so long as there is a potential driving force [8,9,29]. Of course, the driving force could be low if there is a significant amount of oxygen in the Ag, as the experiments with pure Ag have already indicated.…”

A review of liquid metal anode solid oxide fuel cells

“…Being ion-conductive, bismuth oxide may solve the problem with oxide transport blockage through YSZ-anode media [26]. However, operating at lower power densities, liquid bismuth SOFCs require in-depth investigation and are not considered to be a feasible alternative to SOFCs with a tin anode [21,22] .…”