The oxygen-releasing step in the water splitting cycle by MnFe2O4–Na2CO3 system

Investigation of the feasibility of the thermochemical two-step water splitting cycle based on MnFe2O4/Na2CO3 system is reported. Influence of temperature and carbon dioxide pressure on the oxygen-releasing step was investigated. XRD analysis was applied to obtain phase identification of reacted powders at investigated experimental conditions. Different sodium sub-stoichiometric Na1−δ(Mn1/3Fe2/3)O2−δ/2 compounds were observed and their structure determined by using Rietveld analysis. Selected experimental conditions permitted to define a T/pCO2T/pCO2 phase diagram, showing different solid phases coexistence regions. Experimental conditions that permit complete regeneration of the initial MnFe2O4/Na2CO3 mixture were identified (field I in the reported diagram), demonstrating the possibility of full chemical cyclical operation of the system.