Thermochemical hydrogen production using manganese cobalt spinels as redox materials

Mn and Co spinels (Mn3-xCoxO4) were thermally reduced and subsequently oxidized showing successful hydrogen production from water splitting by a three-step thermochemical cycle involving sodium hydroxide (NaOH). The spinel materials overcome the main limitation of the Mn2O3/MnO redox cycle, reducing the required temperatures from 1300-1400 °C to 850-1050 °C. Additionally, the reduction process takes place through a single step reaction, avoiding the formation of intermediate species that makes much more complex the chemistry of the Mn2O3 redox cycle. On the other hand, the subsequent reaction with NaOH allows a hydrogen production of 52.5 cm3 STP/gmaterial·cycle, which is comparable to the obtained with other spinel-oxide cycles at similar temperature. The cyclability and stability of the hydrogen production with these materials after operation of several cycles have been assessed in a high temperature tubular furnace.