In this work, hausmannite (Mn3O4) is used as the key component of a modified Na-Mn thermochemical cycle for hydrogen production. Although this cycle has a lower theoretical thermodynamic efficiency compared with that using MnO (54% instead of 76%), the reduction of Mn2O3 to Mn3O4 occurs at temperatures of around 850 degrees C (about 550 degrees C lower than for MnO), and these less stringent operation conditions can be advantageous for increasing the durability of materials and reactors. The present study is mainly focused on determining how some relevant physicochemical properties affect the solid reactivity and, consequently, to the efficiency of hydrogen production. For this purpose, Mn3O4 samples with different morphological and textural characteristics were prepared by changing the conditions of the thermal treatment. These materials were characterized by XRD, SEM and temperature programmed reduction (TPR). The obtained results indicate that the surface area of Mn3O4 is the main factor affecting the hydrogen production yield, while the crystalline domain size has minor influence on the efficiency of the process. In order to explore the viability of the thermochemical cycle, the Mn3O4 sample that exhibited the highest hydrogen production was submitted firstly to hydrolysis and subsequently to a thermal reduction to recover the initial oxide. This study reveals that, although the removal of Na is not complete in the low temperature stage, reducibility of the solid does not appear to be significantly modified by the presence of these impurities. Overall, these results suggest that the Mn3O4 NaOH can be a viable alternative for the production of solar hydrogen. (C) Copyright 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.