Catalytic effect of MnFe2O4 on dehydrogenation kinetics of NaAlH4–MgH2

Abstract

The hydrogen desorption properties and decomposition processes of MnFe₂O₄-doped NaAlH₄–MgH₂ composites are investigated. The onset temperatures of three dehydrogenation steps of MnFe₂O₄-doped NaAlH₄–MgH₂ composites are 92, 116 and 115 °C lower than those of as-milled NaAlH₄–MgH₂. Furthermore, NaAlH₄–MgH₂ + 3 mol% MnFe₂O₄ displays good cycling stability at 300 °C and only a slight capacity loss after four cycles. The apparent activation energies estimated from the Kissinger analysis for NaAlH₄- and MgH₂-relevant decomposition are found to be 51.29 and 105.34 kJ mol⁻¹, respectively. XRD and XPS results show that NaFeO₂, Mg₂MnO₄ and the amorphous Mn/MnO_x species as well as iron oxides contribute to enhancing the dehydrogenation performance of NaAlH₄–MgH₂.