Exceptional performance of water splitting coupled with methane partial oxidation by oxygen-permeable membrane reactor

•Coupling reaction of water splitting and partial oxidation of methane is achieved even at below 800 °C.•Ruddlesden-popper oxide promotes water splitting despite phase decomposition.•Considerable hydrogen production through the coupling reaction is possible.•Methane is converted while maintaining the syngas ratio (H2/CO) close to 2.