Enhanced hydrogen production reversibility in the MnFe₂O₄-Na₂CO₃ thermochemical cycle via synergistic effect of liquid carbonate and CeO₂ nanoparticles

This study investigates the addition of 3 wt% of TiO₂, SiO₂, and CeO₂ nanoparticles as an anti-sintering strategy to enhance the reversibility of sodium manganese ferrite for hydrogen production. After preliminary tests, TiO₂ NPs were discarded due to cross-reactivity leading to pronounced sintering. SiO₂ NPs hindered the sintering due to the in-situ formation of NaFeO 2 ,SiO 2 solid solution but ultimately resulted in irreversible H₂ production. In contrast, CeO₂ NPs demonstrated high stability and chemical compatibility, stabilizing H₂ production at approximately 50 μmol/g, while the reference mixture monotonically lost reversibility in 5 cycles. Notably, combining CeO₂ NPs with a eutectoid (Na 0.93 Li 0.07 ) 2 CO 3 mixture enhanced H₂ production to 0.18/0.19 mmol/g. As a result, the H 2 produced during the 5th cycle was nearly twenty times that of the reference mixture. This improvement was attributed to a synergistic effect between the formation of liquid carbonate and the anti-sintering and oxygen gateway effect of the CeO 2 NPs. • The addition of NPs is proposed to improve the hydrogen production reversibility. • SiO 2 NPs reduce the sintering but result in no H 2 production reversibility. • CeO 2 NPs reduce the sintering and improve the H 2 production by 5 times. • Combining CeO 2 with eutectoid carbonate boosts increase by 1 order of magnitude. • A synergistic mechanism is proposed to explain the results.