CO2 Capture Characteristics of Electrochemically Generated Li2O in Molten Eutectic LiNO3–KNO3 at Moderate Temperature

Metal oxides (MO) have emerged as attractive candidates for carbon dioxide (CO 2 ) capture due to their excellent thermal stability and high theoretical CO 2 uptake capacity, with particular emphasis on magnesium oxide (MgO) or calcium oxide (CaO) that requires high operating temperatures (300–900 °C). Here, we present CO 2 capture characteristics of a MO system of growing interest: lithium oxide (Li 2 O) in molten eutectic lithium nitrate (LiNO 3 ) and potassium nitrate (KNO 3 ), which is attractive due to its high theoretical capacities and a moderate operating temperature of only 150 °C. Our results reveal that CO 2 capture kinetics and capacities are markedly improved when Li 2 O is blended with the eutectic molten salt. Especially at low Li 2 O concentrations (<0.7 wt %, below the solubility limit of lithium carbonate (Li 2 CO 3 ) in the salt), a complete conversion to Li 2 CO 3 was achieved within 40 h. Next, we generated Li 2 O electrochemically in the same medium and applied it for CO 2 capture, finding that maintaining Li 2 O content below its solubility limit offers kinetic advantages, achieving complete conversion of produced Li 2 O to Li 2 CO 3 within 10 h. Clear evidence of reactivity of nitrite ions (NO 2 – ) with CO 2 was also observed. Although NO 2 – was previously described as functioning as a CO 2 uptake promoter for MgO in molten salts, X-ray diffraction and gas sensing analysis herein revealed an irreversible side reaction between NO 2 – and CO 2 in Li 2 O systems, resulting in undesired NO x formation. These findings strongly caution against the specific use of salts producing nitrite ions in CO 2 capture applications, yet underscore the potential for developing improved salts that circumvent this issue and enable electrochemical reversibility in future work.