Influence of Electrode Gas Flow Rate and Solid Oxide Ratio in Electrolyte on the Seebeck Coefficient of Molten Carbonate Thermocell

Abstract

Thermocells represent a promising way to utilize heat as a power source. The aim of this work is to develop a thermocell with identical gas electrodes using molten carbonate-based electrolytes. The cell can generate power from waste heat, and can also utilize the CO 2 rich off-gas available in metal producing industries. The flow rate of the gas supply to the electrodes needs to be optimized. Its effect on the Seebeck coefficient was not studied systematically before. The addition of solid oxide to the molten carbonate melt alters also the system's Seebeck coefficient. We report measurements where we vary the content of solid oxide in the liquid eutectic electrolyte mixture as well as the electrode gas flow rate. The Seebeck coefficient is reported for various ratios of eutectic (Li,Na) 2 CO 3 molten carbonate and dispersed solid oxide MgO, and for varying gas (CO 2 |O 2 ) flow rates to the electrode interfaces.

Gas electrodes with nickel based current collectors for molten carbonate electrolyte thermo-electrochemical cells

“…Also, the potential at Soret equilibrium will differ from the initial state potential. A slight potential shift, observed with the stable gold current collector, may be due to onset of the Soret effect rather than of any interface reaction [11] . But the potential drifts are significant http://engine.scichina.com/doi/10.1016/j.jechem.2019.05.001 for the cells with NiO and Li 0.1 Ni 0.9 O current collectors.…”

“…The initial state Seebeck coefficients ( ϕ/ T ) determined from the potential ( ϕ) measured at short time after establishing the required temperature difference ( T ) between the electrodes are shown in Table 2 . These initial state Seebeck coefficients were measured as reported previously [9][10][11] . To avoid anomalous thermogalvanic corrosion effect, the electrodes were exposed to a limited set of temperature differences, typically ∼ T = 10, 0 and −10 °C.…”

“…Recently we have demonstrated a high temperature thermocell using molten carbonate electrolytes with gas electrodes [9][10][11][12] . The molten carbonates are comparatively inexpensive, non-toxic, and safe, and they are more stable at higher temperatures than semiconductor thermoelectric materials.…”

“…A chemical reaction between the MgO and CO 2 is possible to favor the MgCO 3 formation. But the large lithium content in the electrolyte and high operating temperature reduces the MgCO 3 formation and retains the MgO phase [9,11,12] . In previous experiments the effective electrolyte composition and gas composition of the electrodes were optimized for enhanced and stable cell operation [9,10,12] .…”

“…In previous experiments the effective electrolyte composition and gas composition of the electrodes were optimized for enhanced and stable cell operation [9,10,12] . Also the CO 2 |O 2 electrode gas flow rate at the three-phase (current collector-gaselectrolyte) interface was studied to establish a well-equilibrated condition for reliable potential reading [11] . Operating conditions were thus partially improved.…”