Electrochemical property of proton-conductive manganese dioxide for sensoring hydrogen gas concentration

► We developed a hydrogen gas sensor made of a ramsdellite-crystal type MnO2 (RMO). ► Our sensor enables in-situ measurements over a range of the 0.1-99.9% concentration. ► The RMO showed the electrical conductivity under 85 % relative humidity conditions. ► The wet RMO takes a protonic condition at room temperature.