Nickel oxide redox processes with oxide ion conductor-supported nickel oxide in dry and humidified methane: Effect of oxide ion conductors on induction period in nickel oxide reduction and subsequent hydrogen production

► Oxide ion conductors were investigated as oxygen carrier supports in a chemical looping process. ► Induction period in NiO reduction by dry and humidified methane was observed. ► A longer induction period was observed under a humid condition than under a dry condition. ► The induction period was decreased when the oxide ion conductors were used as supports. ► The performance of NiO redox cycle strongly depends on support materials of oxide ion conductors.