Heterogeneity in the Mo doped La0.55Sr0.45FeO3 cathode for direct CO2 electrolysis

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• Mo-doping in La 0.55 Sr 0.45 FeO 3 prevents the production of SrCO 3 in CO 2 electrolysis. • Mo 6+ accelerates the adsorption/dissociation process of CO 2 /CO. • Heterogeneous regions were found to enhance the CO 2 electrolysis. • Initial performance dropping during CO 2 electrolysis is related to adsorption of CO. The large-scale integration of intermittent renewable energies into the power grid could reduce the CO 2 emission from the combustion of fossil fuel, but it requires energy storage techniques to balance the energy production and demand. The electrolysis of CO 2 that converting electricity into chemicals/fuels provides a sustainable way of energy storage and CO 2 reduction. Solid oxide electrolysis cell (SOEC) operating at around 800 °C was able to provide highly efficient transformation of CO 2 because the high temperature was able to decrease the energy demand and increase the activation of CO 2 than room temperature electrolysis. In this study, Mo-doped ferrite perovskite, La 0.55 Sr 0.45 Fe 0.85 Mo 0.15 O 3 , was studied as the cathode of an SOEC for the direct electrolysis of CO 2 at 800 °C. Cell with La 0.55 Sr 0.45 Fe 0.85 Mo 0.15 O 3 cathode showed a significantly higher current density during CO 2 electrolysis than the one with La 0.55 Sr 0.45 FeO 3 cathode. Compared with the parent La 0.55 Sr 0.45 FeO 3 cathode that will subject to a superficial decomposition into Fe 0 and SrO or SrCO 3 at an elongated cathodic bias of − 1.4 V, Mo-doping will induce the production of Ruddlesden-Popper phase ( e.g. (La,Sr) 2 (Mo,Fe)O 4 , Fe-Mo-O oxides and Fe 0 ). La 0.55 Sr 0.45 Fe 0.85 Mo 0.15 O 3 cathode was found to an unobvious current decrease at − 1.1 V, but a cell degradation was found under a high bias of − 1.4 V. During the 97 h’ aging under a cathodic bias (−1.4 V), the reduced molybdenum cation in La 0.55 Sr 0.45 Fe 0.85 Mo 0.15 O 3 was found to be less mobile than Fe 3+/2+ , La 3+ or Sr 2+ , and the perovskite with Fe-deficit region were also found to be important for the activation of CO 2 and dissociation of CO in the electrochemical process.