A method for fabricating an electrochemical sensor material includes positioning sheets of molded graphene nanoplatelets on each side of a proton exchange membrane and integrating graphene nanoplatelets into regions of the proton exchange membrane adjacent its surfaces by applying heat to increase the temperature of the proton exchange membrane to its glass transition temperature and applying compressive pressure to press a portion of each sheet of molded graphene nanoplatelets into the softened polymeric material of the proton exchange membrane. Following application of heat and pressure, the proton exchange membrane is cooled and excess graphene material is exfoliated. Electrochemical sensor components are cut from the material and electrochemical devices and systems are constructed therefrom.