Chemical aspects of the water-splitting thermochemical cycle based on sodium manganese ferrite

Water thermolysis by means of the sodium manganese ferrite cycle for sustainable hydrogen production is reviewed, with particular focus on known elementary chemical processes taking place on solid substrates in the 600–800 °C temperature range. For the purpose, in-situ high temperature x-ray diffraction technique has been utilized to observe structural transformations produced by both temperature and reactive environment. The water-splitting reaction and the regeneration of initial reactants are described as multi-step reactions, in which the role of carbon dioxide, through carbonation and de-carbonation reactions is highlighted. A thermodynamic phase stability diagram is reported for the system MnFe2O4/Na2CO3/CO2.

► Chemistry of Na–Mn ferrite thermochemical cycle for hydrogen production is reviewed.
► H2 generation by reaction of H2O with MnFe2O4/Na2CO3 mixture is a multi-step process.
► Regeneration of initial ferrite/carbonate mixture is influenced by multiple equilibria.
► Carbonation and de-carbonation can occur independently from the oxide redox process.