TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The proton-conducting membrane is formed by hot pressing a mixture containing water-insoluble solid acid material that is capable of superprotonic transition at specific temperature, and a porous structural binder. The solid acid material has a general formula of MaHb(XOt)c or MaHb(XOt)c.nH2O (where M is lithium, beryllium, sodium, magnesium, potassium, calcium, rubidium, strontium, cesium, barium, thallium or ammonium (preferably cesium and ammonium); X is silicon, phosphorus, sulfur, arsenic, selenium or tellurium, (preferably silicon) and a, b, c, n and t are rational numbers (preferably t is 3 or 4)), preferably CsH2PO4, Cs5(HSO4)3(H2PO4)2, Cs2(HSO4)(H2PO4), Cs3(HSO4)2(H2PO4), Cs3(HSO4)2(H1.5(S0.5P0.5)O4), Cs5H3(SO4)4.xH2O, TlHSO4, CsHSeO4, Cs2(HSeO4)(H2PO4), Cs3H(SeO4)2, (NH4)3H(SO4)2, (NH4)2(HSO4)(H2PO4), Rb3H(SO4)2, Rb3H(SeO4)2, Cs1.5Li1.5H(SO4)2, Cs2Na(HSO4)3, TlH3(SeO3)2, CsH2AsO4(NH4)2(HSO4)(H2AsO4), TeO4 or CaNaHSiO4. The volume ratio of solid acid to polymer is about 50/50. The proton- and electron-conducting membrane is formed using the solid acid material having free valence electrons.Preferred Process: The electrochemical device is operated by providing a fuel to the proton-conducting membrane which includes a carbon monoxide material and carrying out electrochemical reaction without removing carbon monoxide material. The electrochemical device is preferably operated at 100 degreesC or more. The solid acid material is heated at a temperature at which it undergoes superprotonic transition, before using it.    TECHNOLOGY FOCUS - POLYMERS - Preferred Binder: The structural binder is a melt-processable polymer (such as polyvinylidine fluoride), in-situ polymerized polymer, ceramic, glass, electrically conducting material (such as metal mixed with a polymer), polyester binder or electrochemically unreactive material. EXAMPLE - Solid acid material such as Cs2(HSO4)(H2PO4) or (NH4)3H(SO4)2 was mixed with a monomer such as dicyclopentadiene. Polymerization catalyst was added to the obtained mixture so that a solid composite membrane comprising solid acid and poly(dicyclopentadiene) was formed. The in-situ polymerization of the polymer led to higher impermeability of fluid than the composite which was formed by melt-processing.